Quote Matt Houghton:

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Quote Goddard:

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What interests me is the input impedance adjustability.

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Yes, I know what you mean. In my own experience, some dynamics seem to be more audibly affected by this than others. The SM57 for example. If you're not aware of it, the <a href="/sos/jan12/articles/magneto-variohm.htm" target="_blank">Magneto Labs VariOhm</a> might be of interest.

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Matt, thanks, yes I'd seen Hugh's review already and had appreciated his pointing out there that the typical condenser mic-oriented fixed input impedances of many preamps and interfaces makes them less than optimal for the dynamic and ribbon mics many of us also may wish to use, a point I wish all the mfrs would appreciate inasmuch as implementing a basic input impedance adjustment functionality in their products would not really be that difficult nor costly at even lower price points and could even be a big selling point as some mfrs like ART seem to have grasped.

As it stands now, the choices available are to accept less than optimal dynamic mic performance with many pre's and interfaces, purchase a higher-priced pre with adjustable input impedance, purchase an add-on impedance adjuster, or DIY. In this last regard, you and Hugh might be interested in an article by Paul Stamler which appeared some time back in another publication (which I won't mention or link to here but which can easily be located online by searching for "SM57 impedance gizmo").

http://cpc.farnell.com/pro-signal/psg01351/adaptor-phase-reverse/dp/AV1451 9?in_merch=Featured Products&MER=e-bb45-00001001

Buy a couple of the above and remove the phase wires and use the switch to load the mic with two different resistors.

Dave.

Thanks to the SOS team for doing this test. I am interested in how the recordings were rated and the scoring methods. Whilst the overall conclusion seems to be that the differences between these pre-amps in a listening test are very small; the scoring would suggest the opposite.

The ART pre-amp attains the highest score (7.5) when used with the Brauner mics. It attains the highest score (7.4) with the Sennheisers and a joint 4th place (5.6) with the Royer. I think this is a fantastic result. The Mackie achieves 2nd place with the Brauner (6.8), a very good 3rd place with the Sennheisers (5.6) and 6th place with the Royers (3.8). Again, a good result with two out of three mics. However, in the Brauner test the ART scores 7.5 and the API only manages 2.9. In the Sennheiser test the ART has 7.4 and the Maselec only 3.5. The differences between first place and last seem fairly wide using this scoring method. Yet it is supposed to be difficult to tell them apart. Shouldn't the scores have been a bit closer?

Dave.

Quote Goddard:

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...implementing a basic input impedance adjustment functionality in their products would not really be that difficult nor costly at even lower price points and could even be a big selling point as some mfrs like ART seem to have grasped.

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It's a marketing gimmick with little practical benefit in my view, and isn't a very intelligent engineering solution. Okay, so there are sound technical reasons for using a very high input impedance with ribbons, and since some old-school dynamics were designed to work optimally with the even older-school 600-ohm input Z of some ancient console mic preamps, loading them properly allows them to perform as the designer intended.

What we're talking about here, basically, is taming unwanted reasonances in the mic to preamp interface resulting from old-school design assumptions that are no longer relevant.

But within reason, variable input impedance makes no difference whatsoever to any electronically driven mic (ie. pretty much all modern capacitor mics and all active ribbons and dynamics), and is not appropriate for more modern dynamic mics designed with typical modern day mic preamp interfaces in mind. Added to which, it potentially compromises preamp noise performance.

Rupert Neve had the right idea when he adopted something around 5k Ohms as a standard input Z on a lot of his later designs...

In many ways it's the mic preamp comparison all over again. While messing with mic impedance will produce subtle tonal differences with some specific types of mic, it's still less than changing or moving the mics -- and the tonal changes are even less predictable than swapping mic preamps!

Most modern mic preamps usually have an input Z of between 1.2 and 1.5k, while a few are a little higher (up to about 2.5k ohms). Rather than add in complex and potentially performance-robbing variable impedance facilities just to cope with the odd ancient mic designed for a different world, wouldn't it actually be better to modify the ancient mic to work with the modern world?

So stick your 600 ohm resistor across the back of the XLR connector inside the Sm57 and be done with it! Ancient mic design instantly adapted to work in the modern world. Moving on...

hugh

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Technical Editor, Sound On Sound

Quote Goddard:

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As it stands now, the choices available are to accept less than optimal dynamic mic performance with many pre's and interfaces,

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I wouldn't call it less than optimal as a 2k ohm input impedance has been standard for many years and most mic designers will have designed and optimised their mics with this in mind. Think of the variable input impedance as another eq control - a way to alter the sound to your taste.

James.

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JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

Quote Dave Anderson:

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I am interested in how the recordings were rated and the scoring methods.

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As I think Sam explained in his conclusions, the scoring isn't in any way scientific or statistically meaningful. I did it just as a way of trying to see if there were any significant trends. The problem was that the number of people who offered opinions at all was very low, and those that did offer opinions did so incompletely -- often only mentioning and 'rating' two or there mics in each set anyway.

Of course, we had far more results posted for the Brauner set than either of the others, which make the statistics for that mic a little more relevant, but it's still only a very vague indication of trend.

As to the process, where people voiced opinions of each mic I allocated a corresponding score from 1-8. 8 meaning they picked it as first (or equal first) choice, down to 1 where they rated is least liked, or failed to say antyhing about it at all. Intermediate numbers were allocated on a subjective basis according to the subjective descriptive terms. I then divided the total by the number of contributions to arrive at an averaged 'rating'. I also totted up the number of times each mic was rated first choice as a backup means of identifying trends.

It was really just as a 'bit of fun' -- there is no statistically meaningful data there. If only one person voted first place for one mic, it would have scored 8!

Quote:

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Whilst the overall conclusion seems to be that the differences between these pre-amps in a listening test are very small; the scoring would suggest the opposite.

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Not really, if you look at how many people contributed views, and how the trends developed in time as previous listeners revealed their scores and influenced the decisions of others.

It's actually a lot more interesting and relevant to read the subjective comments from people. Where some said a mic was smooth, rich and full, others described it as shrill and bright. Where one person picked a high end preamp as 1st choice, they often picked a low-end one as second choice (and vice versa). There was no consistency in identifying any of the preamps, either within an individual's choices, or across the group as a whole.

The ART did seem to get picked more often than the others, which was a surprise... but when people publish their preferences on line, as they did here, that will inherently influence the decisions of others, and I think that's what we're seeing.

H

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Technical Editor, Sound On Sound

Quote Exalted Wombat:

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Really, this preamp test (along with the "you don't really need a seperate master clock" one) are the most encouraging reports I've seen in any gear mag for a long time.

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+1 And I bet a similar test could be done for A/D converters above a certain price point.

But I think amidst all this debunking that saves us money it's worth remembering that a good room and nice instruments are crucial and cost money. So if we want to make better recordings it's still an expensive hobby/profession, we just need to sacrifice some of our gearlust and be prepared to pay for a decent live room or concert hall. That being said, unexpected gems can be found for free e.g. schools on the weekend.

Quote Hugh Robjohns:

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Quote Goddard:

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...implementing a basic input impedance adjustment functionality in their products would not really be that difficult nor costly at even lower price points and could even be a big selling point as some mfrs like ART seem to have grasped.

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It's a marketing gimmick with little practical benefit in my view, and isn't a very intelligent engineering solution. Okay, so there are sound technical reasons for using a very high input impedance with ribbons, and since some old-school dynamics were designed to work optimally with the even older-school 600-ohm input Z of some ancient console mic preamps, loading them properly allows them to perform as the designer intended.

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Your "marketing gimmick with little practical benefit" statement seems a bit at odds with what I took away from your recent VariOhm review.

Quote Hugh Robjohns:

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What we're talking about here, basically, is taming unwanted reasonances in the mic to preamp interface resulting from old-school design assumptions that are no longer relevant.

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Don't know how many people using ribbons are plugging them directly into audio interfaces rather than into a better spec pre first, but there still seem to be quite a few pro/semi-pro dynamics being offered with 150, 200 or 600 Ohm outputs. As for taming unwanted resonances, I take it you mean those which cause the response characteristics to be altered when loaded by a different impedance than designed for?

Quote Hugh Robjohns:

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But within reason, variable input impedance makes no difference whatsoever to any electronically driven mic (ie. pretty much all modern capacitor mics and all active ribbons and dynamics), and is not appropriate for more modern dynamic mics designed with typical modern day mic preamp interfaces in mind. Added to which, it potentially compromises preamp noise performance.

Rupert Neve had the right idea when he adopted something around 5k Ohms as a standard input Z on a lot of his later designs...

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True enough, and there are folks upgrading old relics, like by changing transformers on some older mic's what began to sound like duds, to modernize. But then, there are still 50 Ohm ribbons in a lot of places too.

And while I concur in that regard (appropriately designed "modern" mic) that Neve's 5K inputs might have seemed the right idea at the time, it also created a demand for these:

http://www.sowter.co.uk/specs/3678.htm

Quote Hugh Robjohns:

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In many ways it's the mic preamp comparison all over again. While messing with mic impedance will produce subtle tonal differences with some specific types of mic, it's still less than changing or moving the mics -- and the tonal changes are even less predictable than swapping mic preamps!

Most modern mic preamps usually have an input Z of between 1.2 and 1.5k, while a few are a little higher (up to about 2.5k ohms). Rather than add in complex and potentially performance-robbing variable impedance facilities just to cope with the odd ancient mic designed for a different world, wouldn't it actually be better to modify the ancient mic to work with the modern world?

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No argument about the effects of mic placement, although I don't see mic impedance in the same way.

Even some modern repro's of classic pre's (some UA's come to mind) offer switchable tapped mic input transformers (some even on Hi-Z inputs although that seems rather a rarity rather than the rule even at the higher end), so I'm not so sure "performance robbing" (insertion loss?) is that problematic if the input stage is designed properly and a quality tranformer (which can solve a few other problems in addition to impedance matching) is employed.

Perhaps where the cost of an input transformer couldn't be justified and a transformerless equivalent were attempted instead there might be consequences in case of some mics, but hopefully such an impedance adjustment could be switched out and bypassed completely when not desired.

Quote Hugh Robjohns:

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So stick your 600 ohm resistor across the back of the XLR connector inside the Sm57 and be done with it! Ancient mic design instantly adapted to work in the modern world. Moving on...

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By "stick your..." I take it you're referring to Stamler's "gizmo".

Heheh. I'd only mentioned that article as I thought it might possibly be of interest in regard to how the evaluation was done there and with what results, in view of the present SoS preamp comparison. Hope I didn't rub some fur the wrong way.

Although I have actually tried an SM57 gizmo and it does offer a different sound, I would much prefer a transformer-based approach like the VariOhm and was actually looking forward to trying it out, but am now having second thoughts that I might just be buying into a marketing gimmick.

Quote Goddard:

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Your "marketing gimmick with little practical benefit" statement seems a bit at odds with what I took away from your recent VariOhm review.

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I think I said in my conclusion something along the lines of it was "an interesting and unusual box"... what's that if not gimmicky?

Quote:

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... but there still seem to be quite a few pro/semi-pro dynamics being offered with 150, 200 or 600 Ohm outputs.

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The modern standards for microphone output impedance are 150 ohms (European) and 200 ohms (American), and since the notion of voltage matching (instead of impedance matching) was adopted as standard over fourty years ago all mics designed competently since then have been designed to work into an input impedance of around 1.5kohms or more. Any mic with an output impedance of 600 ohms (or 30 ohms) was designed in a different era to work with a different type of interface!

Quote:

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As for taming unwanted resonances, I take it you mean those which cause the response characteristics to be altered when loaded by a different impedance than designed for?

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Yes. Transformers (and directly connected moving coils can be lumped in with this generalisation) are often quite sensitive to the way they are loaded, with quite significant response variations if not loaded as intended.

Quote:

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And while I concur in that regard (appropriately designed "modern" mic) that Neve's 5K inputs might have seemed the right idea at the time, it also created a demand for these

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...er that's just a normal mic input transformer intended for macthing with typical modern preamp electronics. Neve's tendency towards 5k input impedanaces was simply about optimising the voltage matching interface for modern electronic-output mics.

Quote:

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No argument about the effects of mic placement, although I don't see mic impedance in the same way.

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Fair enough. It is another of those 'I really don't understand it so I'll pretend it's art' aspects of sound recording!

Quote:

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I'm not so sure "performance robbing" (insertion loss?) is that problematic if the input stage is designed properly and a quality tranformer (which can solve a few other problems in addition to impedance matching) is employed.

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Very few preamps with variable impedance options achieve it with switched transformer windings -- although that would be the optimal way to do it and it is how the Variohm works. The performance aspect I mentioned is more to do with varying noise performance as the input Z is changed in the simpler preamp designs, than anything.

Quote:

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By "stick your..." I take it you're referring to Stamler's "gizmo".

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Calling a simple shunt resistor a 'gizmo' does rather highlight the lack of understanding of basic electronics and audio engineering, doesn't it?

Quote:

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Although I have actually tried an SM57 gizmo and it does offer a different sound, I would much prefer a transformer-based approach like the VariOhm and was actually looking forward to trying it out, but am now having second thoughts that I might just be buying into a marketing gimmick.

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As I said, the VariOhm is well designed and does what you'd expect with ancient dynamic mics designed for use with old-school impedance matched and low-impedance preamps. It is of little use with most modern ribbons because the impedance options are all far too low, but would be okay with some vintage designs that want to see 50 or 600 ohms.

I have a Focusrite ISA428 pre-pack with variable input impedance, and I can't remember the last time I moved the switches. They stay at the highest setting almost permanently. But then I rarely use my SM57s...

hugh

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Technical Editor, Sound On Sound

Quote Hugh Robjohns:

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The ART did seem to get picked more often than the others, which was a surprise...

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Maybe more people own an ART than any of the others, and they were voting for the sound they were used to?

But then we'd have to assume there WAS a difference in sound... :-)

Have any distributors complained yet? "If you're going to say all preamps are the same, why should we advertise?"

Quote Exalted Wombat:

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Have any distributors complained yet? "If you're going to say all preamps are the same, why should we advertise?"

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The devil is in the detail that you take such a devilsh delight in completely ignoring. At no point have we ever suggested that 'all preamps are the same' and, to be honest, your continued gnoring of this particular bone is beginning to make you look a bit daft...

What we have demonstrated is that there was very little noticeable difference in sound character between these eight preamps when the preamps were used to provide clean gain and operated well within their design parameters. That is a very specific situation -- and one which is representative of the way most people use their preamps most of the time -- but it is far from the only way preamps are employed.

As we have already discussed, and hope to follow up in a future issue, if the preamps are used in more challenging ways and circumstances than those of our test here, their differences will also be a lot more obvious, with some rising to the challenge magnificantly, and others not.

And of course, there are many other aspects of each preamp that are very different, again as we have already discussed.

H

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Technical Editor, Sound On Sound

Hugh, I won't quote your latest response, as I don't disagree with anything you've said (although I may have misheard due to listening through some 600 Ohm cans, I think we actually agree (mostly) and just have (slightly) different viewpoints).

Just wanted to thank you for your further exposition on the topic and for your taking the time to do so. One of the reasons I choose to read SoS is for your technically well-grounded views, and always find your viewpoint refreshing (your recent editorial on "boutiques" comes to mind).

Regarding resonance and noise, I believe I understand now to what you were referring, which I think ties in with this lifted from Jensen's site? (because I'd rather not go digging through my library):

"TRANSFORMER SELECTION

To determine the proper ratio transformer for your application, you will need to know the Voltage Noise and Current Noise of the active amplifier device to which the secondary of the transformer will be connected. If you divide the Voltage Noise by the Current Noise of the device you will get a value in Ohms. This value is the Optimum Source Impedance for best noise performance using that particular amplifier device. Select the transformer whose secondary impedance most closely matches the calculated value.

Example: An AD797 has an input Noise Voltage of 1.2nV per root Hertz Max. @ 1kHz and an input Current Noise of 2.0pA per root Hertz. This gives an Optimum Source Impedance of 600 Ohms."

How I think this all boils down is that mics and preamps tend (hopefully) to work optimally when seeing the respective load and source impedances for which they were designed, and as those design parameters have shifted over the years, this can now result in those impedance expectations no longer coinciding so that sometimes a mic input trannie becomes useful to re-align the respective impedance expectations.

Are we on the same page? (albeit perhaps peering at it through different spectacles)

My curiosity was in regard to what input Z setting was used for the ART MPA II (assume this is specified in the article, but the issue hadn't yet arrived at the bookstore here where I buy SoS on my last visit there, so I was curious...)

In any case, I trust you will keeping calling 'em as you hears 'em regarding "marketing gimmicks" and "vintage modern" hype (e.g. your AT4047 review), and very much approve of accompanying audio samples (so long as recording parameters are specified).

Quote Goddard:

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How I think this all boils down is that mics and preamps tend (hopefully) to work optimally when seeing the respective load and source impedances for which they were designed

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Yes.

Quote:

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... and as those design parameters have shifted over the years, this can now result in those impedance expectations no longer coinciding...

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Yes.

Quote:

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... so that sometimes a mic input trannie becomes useful to re-align the respective impedance expectations.

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Yes... but not all preamps that offer variable impednaces achieve that variation using transformers. Some just shunt the input with different resistors along similar lines as the 'gizmo' idea. This is likely to have a deleterious affect on the preamp noise peformance.

Quote:

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My curiosity was in regard to what input Z setting was used for the ART MPA II (assume this is specified in the article, but the issue hadn't yet arrived at the bookstore here where I buy SoS on my last visit there, so I was curious...)

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I believe it was set to the highest impedance option since that would be most appropriate for the modern capacitor mics and ribbons we were using.

Thanks for the kind words of support -- SOS is unusual in having very supportive owners and publishers who value integrity and honesty far above profits, and are very willing to publish justified warts'n'all reviews and features as a genuine service to our loyal readers.

H

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Technical Editor, Sound On Sound

may not be a fair to comment yet but by just listening on my laptop computer speaker on the Brauner mic: C, E, and H seem to have the richest fullest sound. and yes, when you start stacking tracks is when the quality really matters. I will have to comment again when I have a chance to listen on some better speakers.

Seriously, I thought they all sounded very usable and not nearly as different as expected them to be. Very surprised for as wide a range of pre's as they were.

--------------------
Jeff Ling
www.RECW.com

One thing in this still confuses me slightly.

Amid all the discussion of the various rights and wrongs of attempting to match impedances between mics and pres, are the experts now saying that I wasted my time and money buying my ONE pre-amp that actually has this feature?

Whilst I am deaf as a post in one ear, the other one works well enough for me to hear a discernible difference when I tweak the preamp impedance to allow my vintage grampian DP4 to do its admittedly feeble best..

Over to you, techies...

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Me? But I`m such a loveable old bugger!

If you like what happens when you flip the switch, it's not wasted money, is it?

Modern mics require voltage matching, not impedance matching, and for that the higher the input impedance the better. But some mics of elderly design do often give of their best when terminated with 600 ohms (or lower, sometimes).

Hugh

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Technical Editor, Sound On Sound

Wow!! Sam followed up in the magazine. Excellent guys! Its about time that publications started exploiting their web presence more. Our opinions have been shared with the general public. I feel that this is a positive step and wish to encourage our trusted media outlets to travel further down this road. In Canada/America, our media has very little interest in what we think. They view us as numbers to impress their stock holders and that's all. We all know how that is helping the economy don't we Maybe we'll see more of this in the future.
Thanks!

PS. And for the naysayers: Yes - I do understand that our opinions were used to justify an agenda but... they were USED. Credit where credit is due I say

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Just a fan of music...

We have no stock holders, and we do value our readers' opinions very much.

H

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Technical Editor, Sound On Sound

I am looking into buying one of these preamps, maybe the ART, and have come across several options. I have a few questions for SOS.
1) Which version of the ART PRO MPA-II preamp did you test, the standard ART PRO MPA-II or the ART PRO MPA-II Reference Series?
2) Did you use the normal tube plate voltage setting or the high plate voltage setting for your tests?

After reading the manual, I have deleted my question about Celsius vs Fahrenheit, decibel scales, and the "Tube Warmth" meter.

Quote Jorge:

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1) Which version of the ART PRO MPA-II preamp did you test, the standard ART PRO MPA-II or the ART PRO MPA-II Reference Series?

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Standard

Quote:

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2) Did you use the normal tube plate voltage setting or the high plate voltage setting for your tests?

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High

hugh

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Technical Editor, Sound On Sound

Thanks,Hugh. The articles were a little confusing because the first one showed a picture of the ART PRO MPA-II Reference Series (with the R on the far right side of the faceplate), the second article showed a picture of the ART PRO VLA-II, and the text of both articles simply said ART PRO MPA-II.

nice content really

--------------------
jason

Sorry -- my mistake. It was an R model we used. The picture in the first article in October last year, with the preamps piled up, was of the actual models used.

Sorry for any confusion.

H

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Technical Editor, Sound On Sound

Thanks Hugh. The ART PRO MPA II Reference Series is apparently similar to the standard series, except with upgraded and matched 12AX7 tubes, gold contacts and some aesthetic design changes. Unfortunately, the Reference Series seems to have been a limited edition and is sold out everywhere I have looked (in the U.S.). Many people comment on poor sound from the stock Chinese tubes in the standard MPA II and audible improvements after replacing the stock 12AX7 tubes with various new or new old stock tubes. Words like warm, harsh, phenomenal and awesome characterize some of the testimonies. Also, most 12AX7 tubes seem to be marketed based on character of tone for guitars with little discussion of use for vocals. "Matching" of pairs of tubes seems to be an occult art as well. Since the $750-per-tube Telefunken made in the 60's gold standard tubes seem to be sold out, it becomes a totally subjective trial and error audiophile-like game to choose the "best sounding" 12AX7 replacement tubes. Back to square one.
Maybe I will drag out my old Mackie 1202VLZ3 or the M-Audio DMP3, or just buy a new interface with integrated preamps and forget about the ART. I did kind of like the M/S feature of the ART though.

Jorge, the 12AX7 (ECC83) has never been the best valve choice for a microphone pre amp. It is a high mu, high slope valve where you really want high gm and low anode impedance.

The E88CC/6DJ8 seems the valve of choice for this application but you, or someone else qualified would have the change the cathode bias resistors and the anode (plate) loads to the appropriate values.

A very common and good value alternative (because those pesky gitamp boys use them!) is the 12AU7/ECC82.

Dave.

Thanks Dave. Given that I don't know what mu or gm are referring to or what slope you mean, and I don't have a clue what would be appropriate cathode bias resistor values, I think it would be best for me not to plan to do those modifications on a preamp I haven't even bought yet! If the 12AU7 were a direct drop-in substitution for the 12AX7, I might consider it but from what I am reading on the internet it has about 20% of the gain of the 12AX7 and I can't imagine the conversion would be entirely effortless. I haven't had a 12AX7 in my hand for at least 40 years, although I do remember them from my junior high school days.

Hugh, is there any chance someone at SOS could share with us which tubes (number and brand) ART used to upgrade the 12AX7s in the Reference Series preamp? Those RS preamps seem to be completely out of production now and not available in the retail market, but the standard ART PRO MPA II preamps are still readily available.

Well, acting purely as a listener, and without much tech stuff making me go cross eyed, I would agree that (1) The mics make a difference (I liked the Royers best but I have some Royer mics so may be prejudiced) (2) the cheapest mic pres sounded as good as the ones costing 10-20 times more, well certainly to my ears the Art Pro MPA II at about £300 was as good as those costing 10 times more such as the Prism Sound Orpheus.

So my conclusion for what it's worth (not much I hear you say) is that the Royer mics with most of the pre's that I heard sounded great. The cheap pre's and the Mackie even sounded pretty good, and as far as I'm concerned the expensive pre's added nothing significant. But then I'm only a cloth earded musician. (I use Royer 101's with a DAV BG1 and there's nothing wrong with the sound I get on classical instruments).

Sorry Jorge.
Well at least we now know where both of us are coming from! My point was that the X7 is not a good valve to make a mic preamp with, they are not particularly low in distortion and (for technical reasons) will be noisier than a lower resistance valve. They are found in hi fi power amps as the front end and phase inverter but then all is enclosed in a distortion reducing feedback loop.

It is entirely possible that your quest for an "audiophile" 12AX7 is a futile one.

It may seem paradoxical to you since I am a V old "valve man" but IMHO the things have had their day (and getting reliable samples is getting ever harder and ever more expensive) pre amps with far less noise and distortion can be made using solid state devices and at a fraction of the cost and size...And yes! I know all about the "valve sound" and that is fine for them as wants it but even here, modelling is biting valves very closely on the bum!

Dave.

Dave, I am not locked into getting a tube preamp, and don't know enough to judge your statement that the 12AX7 is in general a poor tube / valve to use for a mic preamp. It does seem a bit of a generalization as over the years many companies have produced good sounding mic preamps using that tube model. And I most certainly am not an "audiophile". I am just trying to get a good sounding mic preamp for a couple vocal recording channels, and was responding to the results of the SOS blinded testing. The problem is that the ART PRO MPA II Reference Series that was used in the testing is no longer available and I am not sure how the standard model compares with the Reference Series model. Hence my question to SOS about which tubes ART used in the Reference Series to upgrade the 12AX7s that are in the standard series.

Hi Jorge,
The devil is as ever in the detail or in this case, the level. The 12AX7 will give very low distortion, as will almost any other triode, if the signal volts are low enough. Triode distortion is almost perfectly proportional to output and valves can easily put out 100+volts peak to peak so if you run one at around 0dBu it is going to be very clean. IIRC none of the pre amps in the test were run at anything near "dirt" point?

As to other 12AX7 mic amps I could not say, my Morgan Jones "bible" is out on loan atmo' but I am sure he found that selecting valves could find you samples with distortions an order apart? Then other designs might put the triodes in a negative feedback loop? I do not have schematics for the ART but I suspect this is not the case there.

But then if one thing came out of the tests it was that there seems to be no such thing as a "gooder" sounding pre amp, all seem good!

Dave.(were you UK I would gladly send you 10, nicely burned in, ECC83s and you could pick two or three best and return the rest!)

Edited by ef37a (22/01/13 07:56 AM)

Quote ef37a:

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IIRC none of the pre amps in the test were run at anything near "dirt" point?

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You are correct. It was a deliberate and carefully maintained condition of the test -- for which we have been criticised, unjustly in my view. Our thinking was that for the vast majority of people in the vast majority of recording situations, the requirement of the preamp is to provide clean gain for the microphone signal. Most 'colour' is actually introduced through the choice of microphone, its position, and the mix processing.

All preamps will colour the signal when deliberately overdriven, but the characteristics then become so complex and variable (depending on circuit technology and topology, gain settings, microphone sensitivity and more) that there is no meaningful, comparable or representative test that can sensibly be performed... in my view.

Quote:

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But then if one thing came out of the tests it was that there seems to be no such thing as a "gooder" sounding pre amp, all seem good!

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Certainly they were all capable of providing more than adequate 'clean gain'. Their ergonomics, build quality and facilities varied greatly, and I've no doubt some produced nicer noises when deliberately overdriven than others, but for the purpose of amplifying a mic signal without bending it in any significant way, modern preamps across the budget range are all capable of doing a decent job. Even a budget preamp is unlikely to be the weak link in anyone's recording chain -- which was the point of the exercise.

H

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Technical Editor, Sound On Sound

I've been doing some tests on the effects of a buffer on a guitar pedal board vs straight-through cabling recently, and whilst I was "in the zone" I dug out my own collection of not very esoteric preamps and did a quick and dirty version of the SOS test with clean electric guitar. Using a Line 6 Back Track as source the difference between my pres was truly tiny (in fairness not much gain was needed). After I finished the tests I restrung my Strat and ran a couple of recordings whilst I played them in. Now obvously this was a totally different "performance" so I couldn't do my null tests, but the subjective difference was an order of magnitude greater than that from the different pres - you'd have identified the new string recordings 10 out of 10 (irrespective of whether you preferred them) in a blind test. All for under a tenner!

Pedal Board Buffer Test here if anyone's interested in the method.

Good article in the mag, and I'd love to hear the "pushed" versions sometime.

A.

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Andi, www.thedustbowl.net Mixing, Mastering, Audio Editing at The Dustbowl Audio

Not at all surprised at the new-string comparison, and glad that your version of the 'clean preamp' test matched our own findings. We will do the 'pushed preamp' test at some point, but we haven't resolved the matching difficulties yet...

H

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Technical Editor, Sound On Sound

Quote Hugh Robjohns:

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..... but we haven't resolved the matching difficulties yet...

H

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Reamp?

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Andi, www.thedustbowl.net Mixing, Mastering, Audio Editing at The Dustbowl Audio

It's more about working out how to ensure a consistent amount of 'push' on each compared preamp....

H

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Technical Editor, Sound On Sound

Ah, never thought of that. I guess any standard you decide on ends up being a bit arbitary and wrong for as many reasons as it is right, in which case why not make it truly subjective and push each pre to the point where the panel decides it sounds at its best for the application and go with that and also a "bit" more to make the distinctive sound more obvious?? I'll lend you my Auteur if you fancy a change of flavour at some point.

All the best.

A.

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Andi, www.thedustbowl.net Mixing, Mastering, Audio Editing at The Dustbowl Audio