Balancing output of a consumer EQ

Help Support GroupDIY:

john12ax7

Well-known member
Joined
Oct 15, 2010
Messages
2,103
Location
California, US
ruffrecords said:
Bottom line the simplest solution not to lose 6dB is to add a transformer to the EQ input.

I agree.  No need to overcomplicate things.  Edcor is one choice for decent inexpensive transformers.
 

Bo Deadly

Well-known member
Joined
Dec 22, 2015
Messages
2,958
Location
New Jersey, USA
moamps said:
You described it in your reply 33.
What's exactly "Tascam problem"?This schematic is part of a Rane product, I used it only to illustrate how it was done in principle in UA2192.
I suppose it does imply that's what's happening but it might be a bit of a leap to assume it's like that Rane circuit. The "Tascam problem" is when a circuit like that Rane one is used and the cold output is grounded at the receiving end such that the op amp is driving a 100 ohm load and it causes enough supply stress on the chip that the other op amp (driving the + output) exhibits some distortion. But there could be something about the UA circuit that avoids the distortion and then it's not really a "problem". For example, if the supply has enough headroom, there could be another buildout resistor inside the feedback loop and thus maintain the same output level but limit current in the event the output is shorted. Or it's using some other kind of current limiting arrangement.

That is a weird piece of gear though. It's a high-end converter that uses the old crappy Urei construction? It sounds like the marketing department did a focus group while the engineers were out to lunch.
 

JohnRoberts

Well-known member
Staff member
GDIY Supporter
Moderator
Joined
Nov 30, 2006
Messages
23,259
Location
Hickory, MS
squarewave said:
I suppose it does imply that's what's happening but it might be a bit of a leap to assume it's like that Rane circuit. The "Tascam problem" is when a circuit like that Rane one is used and the cold output is grounded at the receiving end such that the op amp is driving a 100 ohm load and it causes enough supply stress on the chip that the other op amp (driving the + output) exhibits some distortion. But there could be something about the UA circuit that avoids the distortion and then it's not really a "problem". For example, if the supply has enough headroom, there could be another buildout resistor inside the feedback loop and thus maintain the same output level but limit current in the event the output is shorted. Or it's using some other kind of current limiting arrangement.

That is a weird piece of gear though. It's a high-end converter that uses the old crappy Urei construction? It sounds like the marketing department did a focus group while the engineers were out to lunch.
It is bad practice to drive an active output short circuit into ground. Besides the obvious stress to the ic (which is why less than professional gear often have high output impedances).

That current will find it's way back to the PS, if lucky it will only cause a little extra crosstalk.  ::)

JR 
 

Newmarket

Well-known member
Joined
Oct 10, 2016
Messages
1,160
Location
Brighton Sussex UK
JohnRoberts said:
It is bad practice to drive an active output short circuit into ground. Besides the obvious stress to the ic (which is why less than professional gear often have high output impedances).

That current will find it's way back to the PS, if lucky it will only cause a little extra crosstalk.  ::)

Indeed. Damage Limitation. I've trained myself not to be surprised when an FX pedal etc states an output impedance of, say , 1K0.
Possibly because a TR or TRS jack will be at least momentarily shorted to 'Ground' when plugging / unplugging...
 

abbey road d enfer

Well-known member
Staff member
GDIY Supporter
Moderator
Joined
Jan 22, 2008
Messages
14,486
Location
Marcelland
moamps said:
EQ circuitry can be overloaded that way. IMO, better solution is using an unbal/bal output driver.
I don't see how adding a THAT 1240at the input of an unbalanced circuit can overload it, and how balancing the output of said unbalanced circuit could help it. significantly driving a balanced input.
The issue that seems to be recognised is that the converter has an output scheme with non-floating legs, which prevents using the full differenetial voltage for driving the subsequent gear, hence the 6dB loss. OTOH, the unbalanced output has no loss when driving a balanced or differential input.
I hope we're all talking about the same...
 

moamps

Well-known member
Joined
Sep 24, 2005
Messages
2,234
Location
Croatia, HR
abbey road d enfer said:
I don't see how adding a THAT 1240at the input of an unbalanced circuit can overload it, and how balancing the output of said unbalanced circuit could help it. significantly driving a balanced input.....I hope we're all talking about the same...

Nominal input level of consumer gear is smaller than in pro (in range -10 to 0dBu) so if you rise input level at the input of it for 6dB to +4dBu  as nominal, the headroom of the EQ decreases. If you place balanced driver to the output, this will not happen.
 

john12ax7

Well-known member
Joined
Oct 15, 2010
Messages
2,103
Location
California, US
I also interpreted it as prefering the approach of step down input with step up output like 1246 / 1646  combo as you gain 6 dB internal headroom. As opposed to 1240 with unity gain output.
 

ruffrecords

Well-known member
Joined
Nov 10, 2006
Messages
14,549
Location
Norfolk - UK
moamps said:
EQ circuitry can be overloaded that way. IMO, better solution is using an unbal/bal output driver.
The schematic  for this device show a power rail of over 40V so I expect overload will be unlikely.

Cheers

Ian
 

craigmorris74

Well-known member
Joined
Sep 9, 2005
Messages
800
Location
benton, ky
FWIW, the EQ in question hasn't been overloaded by any of the signal that I've sent through it.  Also,  I have 10 other channels of pretty good lineage,most of it built from projects that originated on this forum, and this device sounds as good or better than several of these units when boosting, even at extreme settings.

I have a couple of Edcor 10K:10K on order, so I'll be reporting back with how that approach works soon.
 

Dualflip

Electronic monk
Joined
Nov 15, 2008
Messages
1,552
Location
Mexico City, MX
I agree with abbey, an electronic balanced solution is best in most cases, but considering that this EQ is far from hi-end, a cheapy trafo like an Edcore is the easiest solution, I wouldn't use anything much better than that since the price of a good transformer is probably more than the price of the EQ itself. Only problem with Edcor trannies is the long lead times, and during COVID times they may be even longer... Any transformer is more expensive than the 1246/1646 solution.
 

abbey road d enfer

Well-known member
Staff member
GDIY Supporter
Moderator
Joined
Jan 22, 2008
Messages
14,486
Location
Marcelland
Dualflip said:
Any transformer is more expensive than the 1246/1646 solution.
Maybe not...  ;)
https://www.amazon.com/PAC-SNI-1-Noise-Isolator/dp/B000K50HJE/ref=sr_1_14?dchild=1&keywords=hum+killer&qid=1597906845&sr=8-14
 

Dualflip

Electronic monk
Joined
Nov 15, 2008
Messages
1,552
Location
Mexico City, MX
abbey road d enfer said:
Maybe not...  ;)
https://www.amazon.com/PAC-SNI-1-Noise-Isolator/dp/B000K50HJE/ref=sr_1_14?dchild=1&keywords=hum+killer&qid=1597906845&sr=8-14

I stand corrected, what about 2 for $0.41 USD ? https://www.aliexpress.com/item/4000456180096.html?spm=a2g0s.9042311.0.0.58fa4c4dlNBBa2

I've used tons of those to kill hum in conference rooms with small PA's, laptop A/V connections, projectors, etc... Don't even bother measuring THD or freq. response, its better not to know.....
 

abbey road d enfer

Well-known member
Staff member
GDIY Supporter
Moderator
Joined
Jan 22, 2008
Messages
14,486
Location
Marcelland
Dualflip said:
I stand corrected, what about 2 for $0.41 USD ? https://www.aliexpress.com/item/4000456180096.html?spm=a2g0s.9042311.0.0.58fa4c4dlNBBa2

I've used tons of those to kill hum in conference rooms with small PA's, laptop A/V connections, projectors, etc... Don't even bother measuring THD or freq. response, its better not to know.....
With 0.29H inductance and 135r DCR, they are not really adequate for inputs, just barely acceptable for outputs, provided the stage that drives them has enough oomph and the load is not too hard. It's thetype of fix that should never be left permanent IMO.
 

Newmarket

Well-known member
Joined
Oct 10, 2016
Messages
1,160
Location
Brighton Sussex UK
ruffrecords said:
I agree. I do not know why I thought it was impedance balanced.

Well tbh it's so easy to mix up the terminology around this topic - balanced / impedance balanced / differential / floating / ground cancelling etc etc - schematics much more use  :) Cheers.
 

Dualflip

Electronic monk
Joined
Nov 15, 2008
Messages
1,552
Location
Mexico City, MX
Today I got some of those cheap Chinese 1:1 600:600 transformers in the mail. All I can say is: they looked bigger in the pictures. Just for fun I'll measure the Inductance, THD and Freq. Response. They sure look like +27dBu line output transformers, huh?

Thumb.png


 

Dualflip

Electronic monk
Joined
Nov 15, 2008
Messages
1,552
Location
Mexico City, MX
volker said:
That's the EI14 sized one right? The number gives the long side of the lamination in millimeters.

I missed that one!, Are these usable in any way or are they just saturation machines? CJ? I've used a mixed feedback driver to lower the distortion on output trannies and the "Zero Field" technique to lower distortion in small input trannies, however they were at least OEPs nothing like these cheap things.

I've used slightly bigger chinese ones for conference rooms, actually one of those conference rooms used to belong to one of the 3 big record labels, i'll let you guess which one, they had huge hum noises in their PA system which they used to listen to their artists new albums, they also had a virtual conference system and hum was a problem everytime they connected a laptop to the projector and audio at the same time, I ended up using tons of cheap Chinese trafos, try explaining to a label executive that they need to spend 2K on Jensen transformers, they did not find that offer attractive so I ended up using the cheapest thing I could find, even Edcore was out of the question .

Some label manager listened to his artist's new album in the PA after I fixed it and told the A&R that it was one of the best sounding PA conference room systems he ever heard, so the transformers can't be that bad, to be fair I also measured the room, repositioned and EQ'ed the system, however the trafos were at least 3-4 times bigger than these EI14. That was 8 years ago, time flies
 

Latest posts

Top