# Questions about Traynor YBA-3 CS tone stack



## Patrice Brousseau (Aug 12, 2020)

Hello all,

Quite puzzled by the controls?

Usually, it’s well known that Traynor used a passive tone stack. On my YBA-1, low-range expander is mid and high range, presence.

Not sure about this one. The bass and treble expanders looks to be some kind of active James controls but I link the schematic for some experts to confirm.

So, bass and treble are obvious but the bass and treble expanders are cryptic to me. Bass boost looks to be some kind of « loudness » control to my ears. Treble boost is obvious though… Presence adds a little sparkle.

Also wondering however about a little more hum when cranking the bass expander. Maybe it’s time to re-visit the grounding on the pots or even, a couple of substitutions with new parts.

My YBA-1 doesn’t exhibit any more hum if I crank the low range expander but it’s obviously less powerful.

Thanks,

**BTW, I know some use it as a guitar amp but it’s wonderful as a bass amp!

Patrice


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## Paul Running (Apr 12, 2020)

Just to confirm Patrice, is this the version of tone control for your amp?


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## Patrice Brousseau (Aug 12, 2020)

Paul Running said:


> Just to confirm Patrice, is this the version of tone control for your amp?
> View attachment 364487


Yes, that is. In fact, I think they are all the same but I could be wrong…


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## Patrice Brousseau (Aug 12, 2020)

In fact, this schematic is more like mine (68-69 with choke and no master):


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## Paul Running (Apr 12, 2020)

Patrice Brousseau said:


> a little more hum when cranking the bass expander


I believe that would be typical...enhancing 120Hz (FW fundamental), when the bass expander is full.


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## Patrice Brousseau (Aug 12, 2020)

So, what would be the mid control? Treble expander? Are bass and treble expanders active?

Thanks,

Patrice


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## Paul Running (Apr 12, 2020)

The Bass Expander/ Presence would be considered an active circuit; note how part of the signal if fedback from V2B plate, through a tone network, back to V2B grid...similar to an active tone circuit, using op-amps.
Note the operational condition of V2B, 22KΩ plate load with 150Ω cathode resistor and 190VDC plate.


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## Paul Running (Apr 12, 2020)

Same deal with the treble side, active control. A complex system of tone management with the feedback. A good project to run on a simulator.


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## Patrice Brousseau (Aug 12, 2020)

Ok, to resume, the CS is almost completely active EQ if I follow you correctly, right? A different approach than the YBA-1 my little head (non-techie) tells me…

I’ve managed to make it sound almost identical to my V4 by tweaking the different pots.

Thanks for your knowledge Paul!

Patrice


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