TG1 Balanced In & Out Without Using Trafos?

My question is about the configuration Igor calls, "Poorman's Variant Without Transformers At All With Balanced Input Without Elma Output Switch". Title mentions that there's a "Balanced Input" but gives no indication about the output. Am I to assume that the output is balanced as well? My guess is yes, but I'd feel a lot better getting some confirmation.
And about the Elma output switch... Why can't it be used in a transformer-less variant? Was that Igor's idea to make this particular option more affordable?
Basically, I'd like to have balanced ins & outs (without transformers) as well as the Elma on the output if it's feasible. If someone could chime in with some info regarding this stuff that would be fantastic.
-John

The idea to replace the elma with an output potentiometer is another money-saving idea, unrelated to the transformer-or-not choice.

AFAI understand, the output is not balanced, if neither a transformer nor the optional additional OPA604 based output stage are used. However, this is not likely to be a problem due to the fairly beefy output from the transistor output stage.

I am currently considering building the additional OPA604 output, but I would only do this to match the higher output of my transformer (bypass-switch set to 'iron') setup. This is due to the Carnhill output transformer I am using, which at a 1:1.7 ratio leaves me with an additional +4dB gain. The OPA604 can be set up to provide additional gain for the clean (non-transformer) output, so that there isn't a level jump when switching between clean and iron modes.

Before adding the transformers I used my TG with the opamp-balanced input stage and no additional output stage, the classic 'poor man's variant' which also works and sounds great!

Thanks brio. Glad to know that the "Poorman's" variant sounds great. Can the additional OPA604 be used to make the output balanced? I'm curious; why bother with a balanced input and not have a balanced output? I've never come across any gear (DIY or otherwise) that had this kind of combination.

briomusic said:

The idea to replace the elma with an output potentiometer is another money-saving idea, unrelated to the transformer-or-not choice.

AFAI understand, the output is not balanced, if neither a transformer nor the optional additional OPA604 based output stage are used. However, this is not likely to be a problem due to the fairly beefy output from the transistor output stage.

I am currently considering building the additional OPA604 output, but I would only do this to match the higher output of my transformer (bypass-switch set to 'iron') setup. This is due to the Carnhill output transformer I am using, which at a 1:1.7 ratio leaves me with an additional +4dB gain. The OPA604 can be set up to provide additional gain for the clean (non-transformer) output, so that there isn't a level jump when switching between clean and iron modes.

Before adding the transformers I used my TG with the opamp-balanced input stage and no additional output stage, the classic 'poor man's variant' which also works and sounds great!

Click to expand...

sine_wave said:

Thanks brio. Glad to know that the "Poorman's" variant sounds great. Can the additional OPA604 be used to make the output balanced? I'm curious; why bother with a balanced input and not have a balanced output? I've never come across any gear (DIY or otherwise) that had this kind of combination.

Click to expand...

The output being unbalanced (if so then preferably making things 'impedance-balanced') is the best thing to do here in my opinion. The typical reasons to make a balanced out other than being earth free (which needs a transformer anyway afaik) would be the possibility for higher undistorted output levels - which is not an issue here with the very high supply voltage of the TG - or being able to feed symmetrical inputs while achieving good noise rejection from it - which can be easily achieved by feeding the unsymmetrical out to the inphase output and gnd plus a resistor to match the output impedance as outphase output. Anyway, noise rejection will most likely not be an issue in nearly all realworld cases because of the high output level and low out impedance of the TG. On the other hand it is more or less problematic if an electronically balanced output would be fed into an unbalanced input at some point, this might lead to unwanted distortions, depending on the topology. So - why make an effort to gain nothing and cause potential problems? My TGs are totally fine with the original output.

You might have come across this topology unknowingly, it is often used in large console channel inserts (SSL 4/6k if I remember right) and the GML stuff for example. If George uses it in his boxes (which are clearly no cost-saving considerations) I'm cool with it too  8) 8)

Michael

Sorry fo a stupid question...
there are in-out ready-made PCB?
Can work on DAOC?
Thanks

ilfungo said:

Sorry fo a stupid question...
there are in-out ready-made PCB?
Can work on DAOC?
Thanks

Click to expand...

There is a small pcb from the SLL9000 layout using a That chip. It's simple enough you should be able to use a small board and build it.

http://www.mentol.dk/diy/tegning/DIY_9k_preamp.pdf

I found the PDF link in a Chinese DIY forum BTW.

Thanks kazper 
works for input and output ?
thanks