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AMP (Fanless) Suggestions for Auratones AND Reftones?

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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby ef37a » Sun May 17, 2020 7:09 pm

"The problem with a digital volume co trol is that the more you turn it down, the worse the signal-to-noise ratio becomes. This doesn't happen with a passive analogue volume control.

So if you end up having to run your digital gain control at, say, 60% in order to have a sensible level fom the amps, your interface converters are effectively then only working as 14bit rather than 24bit! Probably not what you wanted! "

Did not know that Hugh! Anyway, never liked 'em.

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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby iasomph » Sun May 17, 2020 7:29 pm

Hugh Robjohns wrote:
iasomph wrote:Anyway I'm quite a bit shocked that not all the amps come with at least some kind of very simple attenuators (at least a switch with 3-4 sensitivity settings...

Professional studio/PA amps all do.

Hi-fi amps generally don't.

Cheap amps definitely don't.


Hugh, you're the best! I bet you spent the whole afternoon replying to my posts, lol! Thanks :D

The Drawmer APM-90 seems quite a professional tool but it doesn't have it!

The Amphion 100 mono seems also a professional tool and it doesn't have it (at least, I suppose! Since on its case I cannot see any sensitive switch / rotary knob)!

Also the Auratone A2-30 amp doesn't seem to have it, and it's not so cheap, considering the modest power output that it handles!

True pity that these little boxes (which would be a great choice due to their form factor in a home studio desk) don't have this feature! :o
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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby iasomph » Sun May 17, 2020 7:31 pm

James Perrett wrote:
Hugh Robjohns wrote:
iasomph wrote:Anyway I'm quite a bit shocked that not all the amps come with at least some kind of very simple attenuators (at least a switch with 3-4 sensitivity settings...

Professional studio/PA amps all do.

Hi-fi amps generally don't.

Cheap amps definitely don't.

Power amps without volume controls are intended to be used as part of a system where something else includes a volume control. In the case of a Hi-fi amp the volume control will be in the accompanying preamp while, in the case of the Drawmer amps that the OP mentions, they will be intended to be used with Drawmer's own range of monitor controllers.

Thanks! Yes I've read it was intended to be use in conjunction with their old monitor controller...but it's a pity that they need to be bounded. A gain control feature would have made this compact amp a very interesting one for my purposes!
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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby iasomph » Sun May 17, 2020 7:35 pm

Hugh Robjohns wrote:
iasomph wrote:The KH-120A were connected directly to my sound card via balanced connection. So, I may be wrong, but shouldn't balanced inputs/outputs be immune from hisses?

You're quite right: you're absolutely wrong! ;-) Balanced connections are able to reject some forms of external interference, but they cant do a ything about signal noise. And the audible hiss you're complaining of comes from the inherent signal noise from electronic amplification. That noise might be generated within the power amp circuitry itself, or it might be coming from the circuitry in the preceding devices. If it reduces when you attenuate the amplifier input, then it's probably mostly noise from the preceding equipment.

Also, adding another device (like a volume pot) in the path it's something I want to avoid. I had a previous experience with a "cheap" volume pot and it screwed up stereo balance.

Yes, cheap ones will do that, especially if you haven't optimised the gain structure to ensure they operate in the most accurate part of their range. But there are more advantages than disadvantages to having an analogue volume control, and good quality ones aren't that expensive. Switched attenuator types are the best and readily available for DIY constructions.

So, adding a passive volume pot just for adjusting the amp sensitivity and risking to make worst the stereo balance or degrading the sound would be a pity...

In that situation, two mono trimmers (ideally added to the amplifiers themselves) would actually make a lot more sense, and could be calibrated accurately then left alone.




Can you please recommend me the two mono trimmers you are speaking about? So I can check what kind of product it is and how it would need to be integrated.

Also, any recommendation about a good volume pot? In my case, it should be placed between the amp and the speakers, or between the sound card and the amp?
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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby iasomph » Sun May 17, 2020 7:41 pm

Hugh Robjohns wrote:
iasomph wrote:Would the digital volume control of the Babyface Pro be enough...

The problem with a digital volume co trol is that the more you turn it down, the worse the signal-to-noise ratio becomes. This doesn't happen with a passive analogue volume co trol.

So if you end up having to run your digital gain control at, say, 60% in order to have a sensible level fom the amps, your interface converters are effectively then only working as 14bit rather than 24bit! Probably not what you wanted!

PS: I just checked, and the "switches" on the back of KH120A are for the output level: 114, 108, 100 or 94 db (db SPL at 1m). /quote]

They set the maximum output level that can be generatd for a given nominal input signal level. They are input signal attenuators, serving as a coarse level adjustment alongside the fine level adjustment of the sensitivity trim control.

I didn't know that! Actually I thought it was completely the opposite. So, ideally, the digital control volume of the sound card should be left set at 0 db?

If this is the case, why people keep saying that it's much better to connect the Genelec The Ones (8341) monitors digitally to the sound cards via AES/EBU connection, instead of using the standard XLR connections? They say the sound improve a lot. But wouldn't this mean to control the speakers just digitally (also in their volume)?
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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby Hugh Robjohns » Sun May 17, 2020 10:52 pm

ef37a wrote:Did not know that Hugh! Anyway, never liked 'em.

I may have exaggerated the wordlength reduction slightly for effect ;-) but the point is certainly valid.

For every 6dB reduction in level by a digital volume control, the converter uses one less bit. And if the signal starts out with a large headroom margin (as we recommend) it's not hard with a dodgy gain structure in the monitor chain to end up with only 14 bits carrying audio, with the correspondingly reduced signal-noise ratio! So the apparent signal-noise ratio varies with the volume setting.

On the other hand, an analogue (passive) volume control attenuates both the signal and the noise floor equally, so the signal-noise ratio is essentially maintained regardless of the volume setting.
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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby Hugh Robjohns » Sun May 17, 2020 11:01 pm

iasomph wrote:The Drawmer APM-90 seems quite a professional tool but it doesn't have it! ... The Amphion 100 mono seems also a professional tool and it doesn't have it ... Also the Auratone A2-30 amp doesn't seem to have it, and it's not so cheap...

Shocking what some manufacturers think counts as professional, huh? Really disappointed that the Drawmer doesn't have an input sensitivity control. Those guys are normally very good about things like that -- although to be fair they do include level trimmers for each output on their excellent monitor controllers which would do the same job.
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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby ef37a » Mon May 18, 2020 6:50 am

iasomph wrote:
Hugh Robjohns wrote:
iasomph wrote:The KH-120A were connected directly to my sound card via balanced connection. So, I may be wrong, but shouldn't balanced inputs/outputs be immune from hisses?

You're quite right: you're absolutely wrong! ;-) Balanced connections are able to reject some forms of external interference, but they cant do a ything about signal noise. And the audible hiss you're complaining of comes from the inherent signal noise from electronic amplification. That noise might be generated within the power amp circuitry itself, or it might be coming from the circuitry in the preceding devices. If it reduces when you attenuate the amplifier input, then it's probably mostly noise from the preceding equipment.

Also, adding another device (like a volume pot) in the path it's something I want to avoid. I had a previous experience with a "cheap" volume pot and it screwed up stereo balance.

Yes, cheap ones will do that, especially if you haven't optimised the gain structure to ensure they operate in the most accurate part of their range. But there are more advantages than disadvantages to having an analogue volume control, and good quality ones aren't that expensive. Switched attenuator types are the best and readily available for DIY constructions.

So, adding a passive volume pot just for adjusting the amp sensitivity and risking to make worst the stereo balance or degrading the sound would be a pity...

In that situation, two mono trimmers (ideally added to the amplifiers themselves) would actually make a lot more sense, and could be calibrated accurately then left alone.




Can you please recommend me the two mono trimmers you are speaking about? So I can check what kind of product it is and how it would need to be integrated.

Also, any recommendation about a good volume pot? In my case, it should be placed between the amp and the speakers, or between the sound card and the amp?

There might be a 'trimmer box' on the market but I have never come across one.
However, such a box is pretty simple to build. You could use two 10k Ohm log potentiometers but if this is a 'fit & forget' setting, cheaper and easier to use two multiturn pre set pots.

You will need a small. 50x50mm piece of stripboard (commercial name "Veroboard") and soldering kit. The benefit of the M'turn pots is that you can set the levels with great precision and they cannot get knocked out of kilter.

Not done any electronics DIY? This is a good project to start with and once up and running you will never be stuck over a wet weekend by a broken cable ever again!

If you fancy having a bash, PM me.

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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby James Perrett » Mon May 18, 2020 12:28 pm

The problem is that we are probably dealing with balanced connections here so you'll either need a dual gang precision matched pot (which is expensive) or you'll need to delve inside the amp and modify it after the balanced line receiver.

Personally I'd go for a fixed attenuator to set the desired maximum level and then continue to use the level control on the Babyface which will then be working at a more appropriate setting.
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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby Hugh Robjohns » Mon May 18, 2020 12:53 pm

Yes, in this situation that would be the best and easiest solution.

Work out how much attenuation is required by looking at the amount of attenuation dialled in on the interface, and then build suitable U-type balanced attenuators to replicate that.

And it's easy to build the required three resistors into the XLR plugs to each amp.

There's a good explanation and calculator here on how to build U-type balanced attenuators:

http://www.uneeda-audio.com/pads/
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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby iasomph » Mon May 18, 2020 4:34 pm

James Perrett wrote:The problem is that we are probably dealing with balanced connections here so you'll either need a dual gang precision matched pot (which is expensive) or you'll need to delve inside the amp and modify it after the balanced line receiver.

Personally I'd go for a fixed attenuator to set the desired maximum level and then continue to use the level control on the Babyface which will then be working at a more appropriate setting.

Don't they sell these products as finished - ready to buy? I have really zero experiences about DIY and soldering....
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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby James Perrett » Mon May 18, 2020 4:54 pm

iasomph wrote:Don't they sell these products as finished - ready to buy? I have really zero experiences about DIY and soldering....

Yes - if you are talking about the variable attenuator then they're called monitor controllers. A simple passive balanced monitor controller does pretty much the same thing.

If you want a fixed attenuator then XLR attenuators are available but you need something designed for higher impedances than the standard microphone attenuators. The first ones that I found that claimed to be for this use are the ones at

https://rothwellaudio.16.ekm.shop/balan ... rs-3-p.asp

but I'm sure that there are others.
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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby ef37a » Mon May 18, 2020 5:05 pm

I am always amazed James by the number of widgets you CAN buy and the really useful ones you don't seem able to! (would that I were ten years younger and/or a bit fitter. I reckon I could clean up!)

I can recommend the Mackie Big Knob Passive controller in the sense that it does its job well. Personally I could have done with some status LEDs.

@OP if you are relatively young and intend to keep an interest in music and the attendant electronics I strongly suggest you get some basic soldering kit and have a go. Learning how to test out cables and measure some basic electrical quantities, e.g phantom power, batteries, will save you much frustration and downtime for years to come. And maybe a little money to boot!

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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby iasomph » Mon May 18, 2020 5:06 pm

James Perrett wrote:
iasomph wrote:Don't they sell these products as finished - ready to buy? I have really zero experiences about DIY and soldering....

Yes - if you are talking about the variable attenuator then they're called monitor controllers. A simple passive balanced monitor controller does pretty much the same thing.

If you want a fixed attenuator then XLR attenuators are available but you need something designed for higher impedances than the standard microphone attenuators. The first ones that I found that claimed to be for this use are the ones at

https://rothwellaudio.16.ekm.shop/balan ... rs-3-p.asp

but I'm sure that there are others.

Thanks James! I will take these in account when making the final choice of the amp for the Auratone. For me would be much better to buy them instead of building them myself.

I also just discovered that the new Babyface Pro FS got this nice upgrade: +19 / +4 dBu switch on the bottom adds a direct way to reduce the output level, thus improves SNR for sensitive active monitors, avoids distortion / overload, and helps to keep TotalMix FX faders near 0 dB instead of high attenuations.

So I can also consider selling my Babyface Pro (still 3 year warranty in mint condition) at a good price and find a good deal on the new FS model, this could be an even simpler way to go, since these fixed attenuators don't come cheap!

Anyway, the most important thing is to understand if I need a monitor controller for the new monitoring setup I have in mind (I opened another thread about it). The best choice about the amp / attenuators, etc....I think it will also depend on the best way to control the whole monitoring solution I'm evaluating....that's a sort of hybrid digital-analog solution.
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Re: AMP (Fanless) Suggestions for Auratones AND Reftones?

Postby Hugh Robjohns » Mon May 18, 2020 5:18 pm

ef37a wrote: I reckon I could clean up!

Sadly, I don't think you would! As we discovered with our superbly engineered and unique (as a commercial product) pseudo-balanced cables for ground-loop busting on synths etc, the market for such things is actually uneconomically small, and trade is extraordinarily lumpy!
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