RFSiesta
Well-known member
Hi, We own a very custom 80 that includes 24 TSM equalizers, to be used through switchable inserts, over patchbay connections (channel 1-24 are already normalized through them).
I always found them to be a little bit too "tubby" and saturated sounding to get used often. We now got a couple of replacement modules from the bay and I like the sound of them much better than mine - it's more open, more information depth as it seems. A bit more grainy as well, which is good.
There are only some differences between them, one is different filter types in different modules. I decided to ignore this, as all the six replacements sound great, no matter what caps.
Second difference: my TSMs have TL071, three of the "old" ones have 7814s and the other three house 8004s, iIrc. Both types are almost impossible to track, and changing a couple of 071 for OPA134 has not made a big difference in sound.
I don’t think they are responsible for any magic here
Next difference is a 1k series resistor following C18. This, in combination with the peak LED circuit, should lead to some audio clipping - but when we removed it and also bypassed the clipper, it also did not make the difference we were looking for.
So: What we now make responsible for the difference is the missing output stage:
In the schems you see a class A/B output stage following the last TL071. In our case, those have been replaced by only 5534 and a wire bridge, leaving the whole AB block empty. Should be powerful enough to drive the insert return stage with Z=10k? But maybe the sound is different.
We plan now to populate the AB output stage. We could not track BD517/518 or BD519/520s pairs - there’s people who used BD135/136 here in the Trident 80. The 80 circuit has similar output stages, with one big difference: If R72 of the TSM schem was moved directly to TR2 base it would not affect the collector current of TR2, so the 80 circuit is completely symmetrical.
I have two questions now:
- How does the TSM output stage work? It's not symmetric, R72 is 12k - so current through TR2 is heavily limited, as soon as the output hits any regular - or even lower - input Z, a mic input for example. TR1 has full current available. I don't get the point of this configuration :-X
- And: anyone knows replacements for TR1/TR2? Should we try BD135/136? Voltage is rated lower - 48V, but this is well inside the limits. Pinout could be different, of course. I would order more than a couple if they work as a replacement. Any other ideas?
Thank you!
I always found them to be a little bit too "tubby" and saturated sounding to get used often. We now got a couple of replacement modules from the bay and I like the sound of them much better than mine - it's more open, more information depth as it seems. A bit more grainy as well, which is good.
There are only some differences between them, one is different filter types in different modules. I decided to ignore this, as all the six replacements sound great, no matter what caps.
Second difference: my TSMs have TL071, three of the "old" ones have 7814s and the other three house 8004s, iIrc. Both types are almost impossible to track, and changing a couple of 071 for OPA134 has not made a big difference in sound.
I don’t think they are responsible for any magic here
Next difference is a 1k series resistor following C18. This, in combination with the peak LED circuit, should lead to some audio clipping - but when we removed it and also bypassed the clipper, it also did not make the difference we were looking for.
So: What we now make responsible for the difference is the missing output stage:
In the schems you see a class A/B output stage following the last TL071. In our case, those have been replaced by only 5534 and a wire bridge, leaving the whole AB block empty. Should be powerful enough to drive the insert return stage with Z=10k? But maybe the sound is different.
We plan now to populate the AB output stage. We could not track BD517/518 or BD519/520s pairs - there’s people who used BD135/136 here in the Trident 80. The 80 circuit has similar output stages, with one big difference: If R72 of the TSM schem was moved directly to TR2 base it would not affect the collector current of TR2, so the 80 circuit is completely symmetrical.
I have two questions now:
- How does the TSM output stage work? It's not symmetric, R72 is 12k - so current through TR2 is heavily limited, as soon as the output hits any regular - or even lower - input Z, a mic input for example. TR1 has full current available. I don't get the point of this configuration :-X
- And: anyone knows replacements for TR1/TR2? Should we try BD135/136? Voltage is rated lower - 48V, but this is well inside the limits. Pinout could be different, of course. I would order more than a couple if they work as a replacement. Any other ideas?
Thank you!
