General Audio Research BA-2C build -- PT spec question

[Purplenoise]

I have built a p2p ba2c and the gar pcb version. They sound/behave very differently. For the p2p I have used lower ratio input transformer ( 1:7) and the sound is really nice and dynamic with a hint of tube compression even with high output mics and without engaging the 20db input pad.
The pcb version even with a 600/10k input sounds very compressed and saturated even with the 20db pad on…a bass through it is like going through a limiter. Cool sound nonetheless but not really a ba2c sound.

 

[HerbertR]

I have built a p2p ba2c and the gar pcb version. They sound/behave very differently. For the p2p I have used lower ratio input transformer ( 1:7) and the sound is really nice and dynamic with a hint of tube compression even with high output mics and without engaging the 20db input pad.
The pcb version even with a 600/10k input sounds very compressed and saturated even with the 20db pad on…a bass through it is like going through a limiter. Cool sound nonetheless but not really a ba2c sound.

It would be interesting to know with components - especially the Input TX are you using for both builds? I have used a Sowter 9610, 200/20K, as for the Output a Edcor XSM 10k/600.

 

[Purplenoise]

It would be interesting to know with components - especially the Input TX are you using for both builds? I have used a Sowter 9610, 200/20K, as for the Output a Edcor XSM 10k/600.

In the pcb version I have a tamura tpc-203 input (600/10k) and edcor wsm 15k/600 output.
In the p2p I tried a ea2622 with zobel network just to check the ratio behavior and it works really well. Currently I have a Jensen jt-115 which is really nice as I am waiting for two sowters. One with 200/47k and the other 200/10k. They said 90days wait haha.
The output is a gapped cinemag 27101

 

[craigmorris74]

Why would the transformer that's closer to the original ratio make this circuit sound less like the original?

 

[Purplenoise]

Why would the transformer that's closer to the original ratio make this circuit sound less like the original?

The pcb version is not an exact copy, the website is a little misleading on that. It’s based on the ba2c circuit. If you email them they recommend a 200/10k or even a 600/10k despite the fact that in their bom the say that 200/50k is recommended. Maybe if you only work with low output ribbon mics but with medium to high output condencers you will need a pad…even with the low ratio transformer. Then you will need to make up the level with a compressor or something.

 

[emrr]

The pcb version is not an exact copy, the website is a little misleading on that. It’s based on the ba2c circuit. If you email them they recommend a 200/10k or even a 600/10k despite the fact that in their bom the say that 200/50k is recommended. Maybe if you only work with low output ribbon mics but with medium to high output condencers you will need a pad…even with the low ratio transformer. Then you will need to make up the level with a compressor or something.

If you built one cap coupled (not a) BA-2 and one p2p direct feed, they will be very different. Headroom will be about half in the cap coupled, at best, maybe less.

An original old anything like this will almost always need an input pad with a condenser. My originals have plenty of output level for vocal use with a U67 into a 20dB pad into the amp. 250:50K in 50K:250 out. FWIW. 250:12K5 versus 250:50K should be 6dB, not enough to save you from using a pad in most cases.

 

[Purplenoise]

If you built one cap coupled (not a) BA-2 and one p2p direct feed, they will be very different. Headroom will be about half in the cap coupled, at best, maybe less.

An original old anything like this will almost always need an input pad with a condenser. My originals have plenty of output level for vocal use with a U67 into a 20dB pad into the amp. 250:50K in 50K:250 out. FWIW. 250:12K5 versus 250:50K should be 6dB, not enough to save you from using a pad in most cases.

Thank you emrr. Yes my p2p has tons more headroom and transformers are 150/17k for input ( till I get my order from Sowter) and output 30k/600.
Of course I have a 20db pad ( followed your advice from another thread) and the unit is very versatile.
The pcb version no matter how I pad it is almost like a compressor…a cool sound but very specific

 

[emrr]

The pcb version no matter how I pad it is almost like a compressor…a cool sound but very specific

It's probably in overload most of the time. A real one can show flatlined waveforms and not sound distorted. It may never sound similar, but may sound more similar set 10dB lower on the output.

 

[Purplenoise]

It's probably in overload most of the time. A real one can show flatlined waveforms and not sound distorted. It may never sound similar, but may sound more similar set 10dB lower on the output.

Yes exactly…a bass through the pcb version is “flatlined” even at very low gain settings so I guess the first stage is working a lot harder than the p2p. I believe the first tube runs at similar voltages to the second stage.
The p2p on bass is wide, open and dynamic at moderate levels.