No..

Quote from: zbt on Yesterday at 12:24:14 PMHas anyone tried to make a discrete TA7136?

The easy way out is to look at the schematic for the Boss WAZA craft DS1w.   They use a discrete opamp.  It has some specific design features which look sort of like what the TA7136 has.

As far as emulating the TA7136 it's got a lot of parts.   There would be some motivation to simplify it.

I put together a spice model for the TA7136 but the original schematic in the datasheet doesn't have the values so you have to guess the values.   I know someone on one of the audio groups did a similar thing.   The guessed values in that thread are somewhat different to mine.   I at least tried to match the open loop response and equivalent input noise.  I also tried to set the bias current to be in keeping with the use of Widlar current sources being for low current.  I didn't compare the two models since the other model seemed like it had too much bias current on the first stage.

As with many IC designs the current sources can do funny things when the opamp overloads because the current sources share a common reference voltage.  While the Boss WAZA Craft design definitely does not try to copy the internal schematic of the TA7136, it does seem to have specific design features to emulate how the TA7136 clips on the negative rail.  The Boss WAZA Craft design is quite complex so I assumed they needed to add those design features in.  I didn't model the WAZA craft circuit in spice.

I did design a much simplified circuit in spice and tried to broadly match it to my TA7136 spice model.  One design hurdle was to squeeze more gain out of the simplified circuit.   For small signals it seemed to match the TA7136 spice model.   As part of simplifications I removed a lot of current sources.  When I compared the clipped waveforms of the TA7136 spice model and the simplified circuit I could see significant differences.    I played with it a bit but it seemed like some of the current sources need to be put back.    That's going to blow out the idea of having a simplified circuit.

At the time I left it at that.    I didn't build it to see if I could hear the difference between the simplified circuit and the TA7136 or Boss WAZA Craft circuit.

I might have left out some details but that's the general idea.   At the end of the day a solution exists in the Boss WAZA Craft circuit.

I've been curious about how different op amps can change the sound of the DS-1 circuit. The design I'm working on is different enough that it should be obvious that I'm not trying to copy the sound of any particular iteration of the DS-1. Josh Scott has said that the old DS-1 sounds identical to the newer DS-1A, but I've never played a vintage unit to compare myself. What influence does the TA7136 have on the tone? How is it different from a recent DS-1?

I've been fascinated with the DS-1 circuit, mainly because of the different ways the distortion is produced with this circuit - the combination of a hot BJT boost, distorting an op amp, and clipping diodes at the end. I tried to keep those aspects of the design while taking care of some things I thought were problematic about the sound, mainly the output volume. I did use a socket for the op amp, so I'm looking forward to experimenting with different chips. I guess I'm trying, ultimately, to not lose too much of the essence of the DS-1 sound.