You are here

After playing around with a few transformers....

Customising, building or repairing your own gear? Need help with acoustic treatment or soundproofing? Ask away…

After playing around with a few transformers....

Postby Pangloss » Fri Feb 25, 2011 9:10 pm

Well...

I have spent a couple of weeks playing around with a few different transformer models with a view to making some much needed isolation between my recorder I/Fs and my (unbalanced desk) and here are a few useful conclusions I have drawn which I thought I might share with you.

Firstly, the xformers I tried were:

Behringer Hum destroyer with very small, cheap transformer (600:600)
Jensen JT-11 output style transformer (600:600)
Oxford Electronics A218 mini input style transformer (600:600)
Oxford A262 input style transformer (600:600 or 600:2400)
A straight piece of coax wire

I recorded the same track (with a variety of sources) through each and normalized the results, which I compared.

Now then, my plan was to situate the isolation boxes at the patch bay, rather than at the desk input. The advice I have read (e.g. on the Jensen website) is that in this case the best transformer type is an output type transformer. This is because capacitance of any downstream cable can destroy the top end of the signal if an input transformer is used. You will notice that only one of the transformers I had to try was an output transformer.

The first thing I realized was that the input type transformers weren't (in my case) any worse than the output type transformers in this role. In fact, at low signal levels (so as not to cause saturation) the Jensen, OEP262 and straight wire did not sound different enough to make a difference (I did not null, simply listened).

Secondly, remarkably, at consumer signal levels the Behringer was not half bad. If I was hooking up bits of unbalanced -10dB kit I wouldn’t have any concerns about using them, providing the levels were not too hot.

Saturating the transformers, obviously produced different results. In many cases there was no outright “best”sound as this depended entirely upon the instrument being recorded.

The Behringer obviously saturated easier. In addition to compressing the signal it also played with the top end a bit, making the signal wooly on some sources. HOWEVER – it had a great effect on kick drum, snare and toms. To the extent that I actually used it as an insert on some drum channels on the last mix I did.

The OEP A218 seemed to produce the same level of biggening on hot sources but WITHOUT harming the frequencies in the same way (not even compared to the straight wire). In fact, it sounded GREAT on vocals. I used it as an insert on lead vocals on the same track mentioned above and it was an instant Neve-a-sizer when the (balanced level) signal was nice and hot. I am going to mount one of these in a box for exactly this purpose. I recommend it as a very cheap way to get chubby but clear vocal sounds.

Lastly, the Jensen and OEP262 were both very good and the A262 was pretty much impossible to saturate. I was surprised at how similar they sounded, given their completely different constructions.

I have had a lot of fun with this and can see that a collection of transformers can actually be a great creative toolkit.

Fun fun fun.

Alec
Pangloss
Regular
Posts: 268
Joined: Tue Jul 10, 2001 11:00 pm

'These are my principles and if you don't like them...well, I have others' (Groucho Marx) www.ownlittleworld.net/tunes.html


Re: After playing around with a few transformers....

Postby grab » Fri Feb 25, 2011 10:59 pm

Cool - sounds fun! How much were those transformers each?
grab
Frequent Poster
Posts: 2373
Joined: Sat Jul 07, 2007 11:00 pm
Location: Cambridge, UK

 


Re: After playing around with a few transformers....

Postby Pangloss » Fri Feb 25, 2011 11:38 pm

Hi there,

I got the A218 from RS for about 11 quid plus VAT. I mounted mine in a mild steel box and got away without mu metal cans but if you are using an aluminium box or just want to be safe the can is about 7 quid. I think I will get cans for all of mine.

It works out about the same price for two of those as for a Behringer 2 channel box.

I got the Jensens off the bay second hand in a lot of 12.

I don't know if OEP still sell the A218 minis but you can get them on RS. OEP were recommended to me by a forumee here and I can second that they are very helpful indeed if you contact them direct.
Pangloss
Regular
Posts: 268
Joined: Tue Jul 10, 2001 11:00 pm

'These are my principles and if you don't like them...well, I have others' (Groucho Marx) www.ownlittleworld.net/tunes.html


Re: After playing around with a few transformers....

Postby ef37a » Sat Feb 26, 2011 12:01 am

These;

http://www.maplin.co.uk/ground-loop-isolator-33172 are actually pretty good in a neg tennish situation and can actually be found for 1/2 that price on the web.

I would be intersted to see how they stack up against your other collection Pan'
Dave.
ef37a
Jedi Poster
Posts: 7200
Joined: Sun May 28, 2006 11:00 pm
Location: northampton uk

#They did not listen, they are not listening still...Perhaps they never will?#


Re: After playing around with a few transformers....

Postby Pangloss » Sat Feb 26, 2011 12:21 am

I'm camping outside Maplin now.

Thanks for the OEP pointer BTW. Very nice people.
Pangloss
Regular
Posts: 268
Joined: Tue Jul 10, 2001 11:00 pm

'These are my principles and if you don't like them...well, I have others' (Groucho Marx) www.ownlittleworld.net/tunes.html


Re: After playing around with a few transformers....

Postby nathanscribe » Sat Feb 26, 2011 9:26 pm

So are we talking about just a transormer in a box, with a jack at either side? No other omponents?

What were you actually plugging into these? I'm prrsuming a line level output with fairly typical impedance..?

What inputs were these going into on your mixer - again, I'm presuming unbalanced line?
User avatar
nathanscribe
Frequent Poster
Posts: 860
Joined: Fri Jan 19, 2007 12:00 am
Location: Wakefield, for my sins.

I have no idea what I'm doing.


Re: After playing around with a few transformers....

Postby Pangloss » Sat Feb 26, 2011 10:52 pm

Hi - a couple of different situations actually.

The intended use for these iso boxes (which I used after my testing for one mix) is placed between my (balanced) Soundscape DA interfaces (output impedance about 50ohms, I think) and my (unbalanced) Soundcraft Series 2400 desk which has line input impedance of about 10kohms and runs at +4dBu levels.

However, the simple test I ran went from my Soundscape DA interface, through the transformers and back (recorded) into Soundscape via the balanced 25kohm inputs. Again the interfaces run at +4dBu levels.

As you say, they were simply trannies in a box. If I find the time I might try a few more models.
Pangloss
Regular
Posts: 268
Joined: Tue Jul 10, 2001 11:00 pm

'These are my principles and if you don't like them...well, I have others' (Groucho Marx) www.ownlittleworld.net/tunes.html


Re: After playing around with a few transformers....

Postby nathanscribe » Sun Feb 27, 2011 4:39 pm

Righto, cheers for that. Something to look into I think!
User avatar
nathanscribe
Frequent Poster
Posts: 860
Joined: Fri Jan 19, 2007 12:00 am
Location: Wakefield, for my sins.

I have no idea what I'm doing.


Re: After playing around with a few transformers....

Postby Martin Walker » Mon Feb 28, 2011 2:19 pm

Pangloss wrote:Saturating the transformers, obviously produced different results. In many cases there was no outright “best”sound as this depended entirely upon the instrument being recorded.

The Behringer obviously saturated easier. In addition to compressing the signal it also played with the top end a bit, making the signal wooly on some sources. HOWEVER – it had a great effect on kick drum, snare and toms. To the extent that I actually used it as an insert on some drum channels on the last mix I did.

The OEP A218 seemed to produce the same level of biggening on hot sources but WITHOUT harming the frequencies in the same way (not even compared to the straight wire). In fact, it sounded GREAT on vocals. I used it as an insert on lead vocals on the same track mentioned above and it was an instant Neve-a-sizer when the (balanced level) signal was nice and hot. I am going to mount one of these in a box for exactly this purpose. I recommend it as a very cheap way to get chubby but clear vocal sounds.

Lastly, the Jensen and OEP262 were both very good and the A262 was pretty much impossible to saturate. I was surprised at how similar they sounded, given their completely different constructions.

Hi Alec!

We most definitely need audio examples




Martin
User avatar
Martin Walker
Moderator
Posts: 9844
Joined: Wed Jan 13, 2010 8:44 am
Location: Cornwall, UK

Steampunk & Synth News | Mad Scientist Mode


Re: After playing around with a few transformers....

Postby ef37a » Mon Feb 28, 2011 4:25 pm

Martin Walker wrote:
Pangloss wrote:Saturating the transformers, obviously produced different results. In many cases there was no outright “best”sound as this depended entirely upon the instrument being recorded.

The Behringer obviously saturated easier. In addition to compressing the signal it also played with the top end a bit, making the signal wooly on some sources. HOWEVER – it had a great effect on kick drum, snare and toms. To the extent that I actually used it as an insert on some drum channels on the last mix I did.

The OEP A218 seemed to produce the same level of biggening on hot sources but WITHOUT harming the frequencies in the same way (not even compared to the straight wire). In fact, it sounded GREAT on vocals. I used it as an insert on lead vocals on the same track mentioned above and it was an instant Neve-a-sizer when the (balanced level) signal was nice and hot. I am going to mount one of these in a box for exactly this purpose. I recommend it as a very cheap way to get chubby but clear vocal sounds.

Lastly, the Jensen and OEP262 were both very good and the A262 was pretty much impossible to saturate. I was surprised at how similar they sounded, given their completely different constructions.

Hi Alec!

We most definitely need audio examples




Martin

.wavs mind you, none of this MP3 *hit!
And two more traffs are on their way mate.
Dave.
ef37a
Jedi Poster
Posts: 7200
Joined: Sun May 28, 2006 11:00 pm
Location: northampton uk

#They did not listen, they are not listening still...Perhaps they never will?#


Re: After playing around with a few transformers....

Postby Pangloss » Mon Feb 28, 2011 9:45 pm

Martin, Dave,

I may have some time on Thursday morning to create a few wavs using some of my own material.
Pangloss
Regular
Posts: 268
Joined: Tue Jul 10, 2001 11:00 pm

'These are my principles and if you don't like them...well, I have others' (Groucho Marx) www.ownlittleworld.net/tunes.html


Re: After playing around with a few transformers....

Postby Pangloss » Mon Feb 28, 2011 9:48 pm

Dave, you are a very kind man. I owe you a pint if you find yourself in London.
Pangloss
Regular
Posts: 268
Joined: Tue Jul 10, 2001 11:00 pm

'These are my principles and if you don't like them...well, I have others' (Groucho Marx) www.ownlittleworld.net/tunes.html


Re: After playing around with a few transformers....

Postby Martin Walker » Tue Mar 01, 2011 4:42 pm

Make sure you don’t get him saturated, or you might need a new transformer

(I’m only winding you up )


Martin
User avatar
Martin Walker
Moderator
Posts: 9844
Joined: Wed Jan 13, 2010 8:44 am
Location: Cornwall, UK

Steampunk & Synth News | Mad Scientist Mode


Re: After playing around with a few transformers....

Postby Folderol » Tue Mar 01, 2011 6:03 pm

Gah!
I respond with great reluctance having thought we used all these up in that 'other' thread
User avatar
Folderol
Jedi Poster
Posts: 4694
Joined: Sat Nov 15, 2008 12:00 am
Location: Rochester, UK

Save paradise, Pull up a parking lot!


Re: After playing around with a few transformers....

Postby nathanscribe » Mon Apr 25, 2011 4:57 pm

I'm resurrecting this to ask a quick question:

If I was to DIY an isolator for hum removal what would be the practical difference between a 600:600 and a 10k:10k transformer? I've seen isolators with both specs, and not a good explanation of why.

My sources are synths and similar, I run them to patchbays, and they're connected to my mixer, which is then routed back to patchbays and then to a firewire interface. I'm not yet sure exactly where the best place for isolation would be, but I suspect the nearer the mixer the better.

My first guess would be 10k:10k, but please correct me if I'm wrong.
User avatar
nathanscribe
Frequent Poster
Posts: 860
Joined: Fri Jan 19, 2007 12:00 am
Location: Wakefield, for my sins.

I have no idea what I'm doing.


Re: After playing around with a few transformers....

Postby ef37a » Mon Apr 25, 2011 8:20 pm

Yup!
Wrong!
For a general purpose isolator box you need "600" Ohm types.

10+10k transformers are usually used at inputs to unbalance a balanced line and they have a high winding resistance of around 2-3k total. This hardly matters at an input which should have an Zin greater than 10k (but there will of course be some loss, always is power loss with traffs). The transformer will also present much the same impedance to the line as the input alone and thus not load it unduly but put such a transformer at the SOURCE of a signal and you greatly worsen the output Z of the line probably causing HF loss with any reasonable length of cable.

600R traffs have winding resistances of typically 30Ohms and thus add very little loss in the line. They also tend to be somewhat cheaper to make and thus sell for any given level of performance. They are not however suitable for input duty.

So, put 600R 1:1 jobs on outputs to balance the signals and if you are feeding balanced inputs fine. If the inputs are not balanced this often does not cause much trouble for short runs, less than 15mtrs say, but where a problem does arise buy the best 10k "bridging" transformers you can afford and keep the unbalanced "higher Z" feed from the traff as short as possible.

And horses for courses. Traffs for electric guitars, synths,tape signals, FX pedals and other sources of less than splendid fidelity or at neg 10 levels probably won't benefit from 100quid Lundahls!

Dave.
ef37a
Jedi Poster
Posts: 7200
Joined: Sun May 28, 2006 11:00 pm
Location: northampton uk

#They did not listen, they are not listening still...Perhaps they never will?#


Re: After playing around with a few transformers....

Postby nathanscribe » Mon Apr 25, 2011 9:52 pm

Thanks Dave. The sources will almost entirely be unbalanced, and the patchbay routed to the interface and mixer is balanced (but currently patched with unbalanced cabling... which I intend to remedy when I can as I'm getting a touch of hum when patching into the mixer from there). So at the moment I'm not sure whether I'll be using isolation nearer the inputs or outputs. My reason for guesstimating a bridging type was because of that uncertainty. However, sticking a 600 Ohm box at the output of a synth that is causing ground loops makes sense and is something I'll take on board.

I've just grabbed a cheap ART cleanbox ii, which I've seen various recommendations for - and I believe that's a 10k 1:1. Better using that on the inputs, I take it?

Also, Canford seem to be doing a deal on some OEP Z300 at the moment. I fancied grabbing a couple and seeing what I could do.
User avatar
nathanscribe
Frequent Poster
Posts: 860
Joined: Fri Jan 19, 2007 12:00 am
Location: Wakefield, for my sins.

I have no idea what I'm doing.


Re: After playing around with a few transformers....

Postby ef37a » Tue Apr 26, 2011 5:47 am

Yup.
You're right!

From the specification the Art CB ll must use 10+10k transformers since they quote an insertion loss of 5.5dB when loaded with 10k. That would imply a 3dB roll off starting at about 20kHz for 1000pf of cable and typical balanced mic cable is about 100pf/mtr(that's a back of the e'lope guess!) so it would be wise to put the box close to the input not the source and not to exceed 5mtrs or so of cable.

Having a mixture of balanced and unbalanced sources in a system can be a nightmare but since virtually all mixers, even the very cheapest Berry types have balanced line ins it is very cheap and easy to "balance" sources such as synths, soundcard outs etc by wiring in a 120Ohm resistor in the earth side and making such sources impedance balanced. The downside is no earth loop break but the advantage is no signal degradation which must obtain with all but perhaps the very best transformers.

Of course you don't need to impedance balance if you use a 600R traff.

Dave.
ef37a
Jedi Poster
Posts: 7200
Joined: Sun May 28, 2006 11:00 pm
Location: northampton uk

#They did not listen, they are not listening still...Perhaps they never will?#


Re: After playing around with a few transformers....

Postby Hugh Robjohns » Tue Apr 26, 2011 9:41 am

If all your inputs are balanced (mixer and interface), and you want to run the patchbay balanced, then there is an easier and cheaper solution which I would strongly recommend: make up some new cables for your synths to operate as 'pseudo balanced'.

This approach almost always negates any problems with ground loop hums, doesn't degrade the sound as transformers can, is cheaper than buying a box load of transformers, and only requires a little light-duty cable construction and a few cheap electrical components.

The idea is to make use of the differential aspect of a balanced input to detect the unbalanced source signal without referencing it to the local ground -- and hence avoid ground loops.

All you need to do is wire up a TRS-TS jack lead using balanced cable. The TRS end (which connects to the balanced patch bay) is wired up in the usual way (but leave the screen off for the moment). The TS end connects to the unbalanced synth, and this is wired up with the hot wire to the tip and the cold wire to the sleeve. The cable screen connects to the sleeve, too.

In the balanced connector, you have two three choices. You could just trim back the screen, insulate it and leave it disconnected. This avoids re-connecting the ground loop and works perfectly well in 95% of cases.

However, in theory at least, the screen now acts as an aerial to dump nasty RF stuff into the source's ground! A better solution is to connect it to the balanced connector's ground pin via a 100 ohm resistor. This will present a high enough impedance to render any ground loop currents ineffectual but maintain the screen integreity reasonably well.

The best solution is to wire a 0.1uF capacitor across the resistor to provide a very low impedance path for Radio frquencies, and thus optimise the RF screening.

This arrangement is not an impedance balanced system -- so the normal ability of a true balanced circuit to reject electromagnetic interference doesn't apply here, despite using a 'balanced input'. But with near-line level signals that's rarely an issue anyway. The important thing is that this configuration does benefit from ground loop hum immunity because of the differential input's freedom from ground referencing, and that's usually the greater evil when working with ubalanced synths and the like.

The other advantage of this configuration is that you can now patch your unbalanced synths (or other outboard) without causing grounding problems across the entire system, and all the hums that go with it!

You can find suitable resistors and capacitors at Maplins in the UK (or any electronic supply outlet), and typical Maplins components would be the M100R resistor and N43CJ 0.1uF ceramic disc capacitor. These are small enough to be built into the TS plug given a little care. Make sure the cable screen is sufficiently insulated to prevent accidental contact with the sleeve or plug body. Some heatshrink insulation works well.

Hope that helps

hugh
User avatar
Hugh Robjohns
Moderator
Posts: 17098
Joined: Thu Jul 24, 2003 11:00 pm
Location: Worcestershire, UK

Technical Editor, Sound On Sound


Re: After playing around with a few transformers....

Postby nathanscribe » Tue Apr 26, 2011 11:25 am

Thanks again chaps.

Hugh Robjohns wrote:Hope that helps


It does indeed - in fact you recommended this to me in another thread about ground loops. It's on my list of things to try, I just need to wait for pay day to get some TRS jacks and a reel of cable..!

I'm presuming that to take advantage of this method I'd still need to run my patchbay-mixer connections balanced.
User avatar
nathanscribe
Frequent Poster
Posts: 860
Joined: Fri Jan 19, 2007 12:00 am
Location: Wakefield, for my sins.

I have no idea what I'm doing.


Re: After playing around with a few transformers....

Postby zenguitar » Tue Apr 26, 2011 1:16 pm

Hugh Robjohns wrote:If all your inputs are balanced (mixer and interface), and you want to run the patchbay balanced, then there is an easier and cheaper solution which I would strongly recommend: make up some new cables for your synths to operate as 'pseudo balanced'.

This approach almost always negates any problems with ground loop hums, doesn't degrade the sound as transformers can, is cheaper than buying a box load of transformers, and only requires a little light-duty cable construction and a few cheap electrical components.

The idea is to make use of the differential aspect of a balanced input to detect the unbalanced source signal without referencing it to the local ground -- and hence avoid ground loops.

All you need to do is wire up a TRS-TS jack lead using balanced cable. The TRS end (which connects to the balanced patch bay) is wired up in the usual way. The TS end connects to the unbalanced synth, and this is wired up with the hot wire to the tip and the cold wire to the sleeve.

The cable screen connects to the sleeve, but via a 100 ohm resistor, wired with a 0.1uF capacitor across it in parallel.

The 100 ohm resistor is there to raise the impedance of the screen connection for audio frequencies, minimising the chances of suffering ground loop hums, while the capcitor maintains a very low impedance for RF frequencies to maintain good RF screening protection.

This arrangement is not an impedance balanced system -- so the normal ability of a true balanced circuit to reject electromagnetic interference doesn't apply here, despite using a 'balanced input'. But with near-line level signals that's rarely an issue anyway. The important thing is that this configuration does benefit from ground loop hum immunity because of the differential input's freedom from ground referencing, and that's usually the greater evil when working with ubalanced synths and the like.

The other advantage of this configuration is that you can now patch your unbalanced synths (or other outboard) without causing grounding problems across the entire system, and all the hums that go with it!

You can find suitable resistors and capacitors at Maplins in the UK (or any electronic supply outlet), and typical Maplins components would be the M100R resistor and N43CJ 0.1uF ceramic disc capacitor. These are small enough to be built into the TS plug given a little care. Make sure the cable screen is sufficiently insulated to prevent accidental contact with the sleeve or plug body. Some heatshrink insulation works well.

Hope that helps

hugh

That might make a useful piece for the Q&A pages in the magazine, with a nice diagram and picture too.

Andy
User avatar
zenguitar
Moderator
Posts: 7430
Joined: Thu Dec 05, 2002 12:00 am
Location: Devon

Largely, but not entirely, dysfunctional.


Re: After playing around with a few transformers....

Postby ef37a » Tue Apr 26, 2011 1:25 pm

Nice one Hugh!

You could of course put a shedload of such gizmos in a tin as jack-jack "problem solvers".

Dave.
ef37a
Jedi Poster
Posts: 7200
Joined: Sun May 28, 2006 11:00 pm
Location: northampton uk

#They did not listen, they are not listening still...Perhaps they never will?#


Re: After playing around with a few transformers....

Postby Hugh Robjohns » Tue Apr 26, 2011 1:31 pm

nathanscribe wrote:I'm presuming that to take advantage of this method I'd still need to run my patchbay-mixer connections balanced.

Yes, it only works with balanced inputs, and any cabling or routing between your source and the balanced inputs have to be balanced too.

Hugh
User avatar
Hugh Robjohns
Moderator
Posts: 17098
Joined: Thu Jul 24, 2003 11:00 pm
Location: Worcestershire, UK

Technical Editor, Sound On Sound


Re: After playing around with a few transformers....

Postby Martin Walker » Wed Apr 27, 2011 6:44 pm

Soldering up some pseudo-balanced cables for all my keyboards made a HUGE difference to my background noise levels a few years ago

Highly recommended if you’ve got synths/keyboards with unbalanced outputs and a mixing desk with balanced inputs


Martin
User avatar
Martin Walker
Moderator
Posts: 9844
Joined: Wed Jan 13, 2010 8:44 am
Location: Cornwall, UK

Steampunk & Synth News | Mad Scientist Mode


Re: After playing around with a few transformers....

Postby ketracel » Fri Jun 20, 2014 11:46 pm

Fantastic thread for resolving the interference side of things.

What are the variations in addressing the issue of level?

Consider unbalanced synth outputs are usually -10dBv running into mixer inputs which are balanced +4dBu. In this case there is a massive 12dB loss of signal. Sure, significant amounts of gain can be applied on the mixer, also with additional noise mind you is there a cleaner, efficient or optimal solution, can transformers also help here?
ketracel
Poster
Posts: 19
Joined: Sat Oct 13, 2007 11:00 pm

Re: After playing around with a few transformers....

Postby ef37a » Sat Jun 21, 2014 8:10 am

ketracel wrote:Fantastic thread for resolving the interference side of things.

What are the variations in addressing the issue of level?

Consider unbalanced synth outputs are usually -10dBv running into mixer inputs which are balanced +4dBu. In this case there is a massive 12dB loss of signal. Sure, significant amounts of gain can be applied on the mixer, also with additional noise mind you is there a cleaner, efficient or optimal solution, can transformers also help here?

I would not consider 12dB to be a "massive" loss nor making it up "significant"! The line inputs on even a cheap mixer should be capable of this without adding noticeable noise. Indeed, any noise that does intrude is likely to come from the synth!

Yes, decent transformers might be a good idea to balance the signal and give galvanic, possibly earth free operation but unless you go for a step up ratio you will always incur a small voltage loss. But be wary of a step up past 1:2 (~ +6dB) because just this ratio, with a 10k line input Z, will load the synth by 2.5k any lower and the output amplifiers might start to protest. The TL07 series are very poor at driving loads much below this for example.

Note I said "good" transformers? The products from OEP/Walter at about £10 each (600R:600R) are actually a bit too good for synths! I would not go for exotics.

Dave.
ef37a
Jedi Poster
Posts: 7200
Joined: Sun May 28, 2006 11:00 pm
Location: northampton uk

#They did not listen, they are not listening still...Perhaps they never will?#


Re: After playing around with a few transformers....

Postby nathanscribe » Sat Jun 21, 2014 9:20 am

FWIW, I have an Orchid Electronics isolator that was an absolute bargain at 35 quid shipped - absolutely no trouble at all with the sound quality, there's plenty of bottom end coming through (which is something I've had problems with from the ART Cleanbox), and a peek inside revealed transformers of about that calibre. That's no criticism, I'm very happy with it.

The only thing I've got against these budget units is they all distort from my 909 clone and Moog LP outputs. I'm guessing those chaps are just a little hotter than most

By way of pondering, would it be possible to rig up a box with a switchable step up/down/1:1 operation..?
User avatar
nathanscribe
Frequent Poster
Posts: 860
Joined: Fri Jan 19, 2007 12:00 am
Location: Wakefield, for my sins.

I have no idea what I'm doing.


Re: After playing around with a few transformers....

Postby ef37a » Sat Jun 21, 2014 11:05 am

nathanscribe wrote:FWIW, I have an Orchid Electronics isolator that was an absolute bargain at 35 quid shipped - absolutely no trouble at all with the sound quality, there's plenty of bottom end coming through (which is something I've had problems with from the ART Cleanbox), and a peek inside revealed transformers of about that calibre. That's no criticism, I'm very happy with it.

The only thing I've got against these budget units is they all distort from my 909 clone and Moog LP outputs. I'm guessing those chaps are just a little hotter than most

By way of pondering, would it be possible to rig up a box with a switchable step up/down/1:1 operation..?

I can't find a proper specc' for the Orchid box (shame Orchid!) but the Cleanbox 2 is rated for 0.05%thd at +24dBu at 100Hz and that is pretty good and I doubt the Orchid is any less? In any event the Orchid is available with XLR connectors? Be a bit daft to fit "pro" connectors to a device that cannot handle pro levels? And, AFAIK Orchid lekks are NOT daft!
I suspect the distorting devices are to blame in some way.

Re switchable ratios? By the time you have bought a suitable switch (head hurts! Can you do it with a bog-s DPDT?) and faffed about you might as well make two boxes IMHO! In any case there would always be the danger of a 6dB hike in level. At the worst possible moment of course!

A MUCH more flexible arrangement would be to go active and use an LM4562 or similar.

Dave.
ef37a
Jedi Poster
Posts: 7200
Joined: Sun May 28, 2006 11:00 pm
Location: northampton uk

#They did not listen, they are not listening still...Perhaps they never will?#


Re: After playing around with a few transformers....

Postby Folderol » Sat Jun 21, 2014 5:11 pm

Another wrinkle to this.

A few weeks ago, I was browsing Canford Audio (as you do) and noticed they were selling off OEP 10k input transformers at £7 each as stock clearance, so at that price I decided to grab a pair for experimenting (today they still have two left).

OEP kindly provide reference schematics for using these in current mode as an active unit with a TL071. I tried out a slight variation and was astonished at the performance! In fact I thought I must have made a mistake in the wiring, and double and triple checked that I was indeed getting total isolation from my sig gen.

For instance, after the usual sine wave checks, I tried bunging in a 100Hz square wave at +20dBu, and my jaw hit the floor as I saw a near perfect square wave on the 'scope

A lower amplitude square wave at 10kHz (I didn't want to be too unkind to the unit) showed just a bit of ringing, but increasing the neg. feedback cap killed that, with only a moderate (quite acceptable) rounding of the front edge.

I haven't had the chance to do any serious distortion checks, but simple A/B listening doesn't reveal anything.
User avatar
Folderol
Jedi Poster
Posts: 4694
Joined: Sat Nov 15, 2008 12:00 am
Location: Rochester, UK

Save paradise, Pull up a parking lot!


Re: After playing around with a few transformers....

Postby nathanscribe » Sun Jun 22, 2014 9:24 am

ef37a wrote:I can't find a proper specc' for the Orchid box (shame Orchid!) but the Cleanbox 2 is rated for 0.05%thd at +24dBu at 100Hz and that is pretty good and I doubt the Orchid is any less? In any event the Orchid is available with XLR connectors? Be a bit daft to fit "pro" connectors to a device that cannot handle pro levels? And, AFAIK Orchid lekks are NOT daft!
I suspect the distorting devices are to blame in some way.

The Orchid uses a VTX 101-1604, which is 600:600 - haven't seen distortion specs to compare though. Like I say, it's noticeably better than the ART, whatever the quoted figures. I also know that the Moog and 909 kick put out enough welly in the sub-100Hz range to cause nastiness - even the Radial JDI I had could be tickled into nervousness around the edges by certain bass patches - I don't know why, or even what kind of distortion exactly was happening, but my ears tell me 'tis the case


you might as well make two boxes IMHO!

Fair enough! Just pondering.
User avatar
nathanscribe
Frequent Poster
Posts: 860
Joined: Fri Jan 19, 2007 12:00 am
Location: Wakefield, for my sins.

I have no idea what I'm doing.


Next

Who is online

Users browsing this forum: No registered users and 1 guest