E.W.S Tri-Logic II Bass Preamp [traced]

[george giblet]

Actually I'm using an older Firefox.

The more I think about the EWS Tri-logic III the more I think the tone control is like the Xotic Bass RC,
https://aionelectronics.com/blog/tracin ... c-booster/#

The Tri-logic II uses a single opamp 3-band EQ but the Tri-logic III is going to use a single opamp 2-band EQ with a separate parametric for the mids.

When you design a 3-band EQ there's a lot of trade-offs and you end-up with low resistor values. The boost frequency-response tends to have a lump in the mids as a result of the smaller resistor values. If you take a 3-band and cut-out the 2-band you end-up with that type of response as well. BTW, when you cut the mid circuit off a 3-band the bass and treble of the remaining 2-band version this doesn't work the exactly the same as the bass and treble in the 3-band. That's the type of control in JohnK's schematic. So maybe JohnK's circuit isn't representative of the real unit.

If you were to start the 2-band design from scratch not use resistor values from the 3-band. If you look at the boost/cut profiles of the EWS tri-logic II 3-band they have some similarity to the Bass-RC boost/cut profiles. So that makes me think the Tri-logic III may very well have a similar circuit to the xotic Bass-RC circuit.

The Tri-logic III has switchable bass (40Hz/80Hz) and treble frequencies (4kHz/8kHz). If we take the Bass RC circuit as a reference we might expect the bass caps to be 33n+33n for 80Hz and perhaps another set of 33n caps switched in for 40Hz. The treble we might expect 2x10n caps for 8kHz based on the fact the Bass RC specs are 8kHz. That would imply another 2x10n switch in parallel with those for 4kHz. However, I have my doubts in the accuracy of how companies give tone control specs. It could well be the treble caps for 8kHz are 2x4n7 and then another 2x4n7 to get 4kHz. FWIW, the guitar treble control uses 2x4n7's. What I'm saying here is you can't trust the published specs to determine the frequencies/caps as they rarely match up.

As an over-riding caveat there's no facts behind what I've said here. It's entirely technical speculation. However, if down the track someone gets some gut-shots the resistor values might help decide if there's any truth in these speculations.

If we work out the circuit it wouldn't be hard to work out the cap values by AB comparison against the real unit. Comparing the tone-controls of a Bass RC vs a Trilog III would help too. Obviously a hard-core de-gooper can measure the caps.

[Paul_5]

I wouldn't mind finding out how to change the lows to 40, highs to 4k.

That would make it very ‘Ampeg’ like, wouldn’t it...?

[jeepe]

hi, happy new year!

I'd like to ask what you think of John K's parametric trilogic?

In terms of how good idea you think it is to build it? (after building the original version II presented by you:) )

I mean, the functionality looks cool, parametric with frequency and goodness control...
I'd like to build it...
is it a medium bad idea, or medium good, or perhaps a pretty good idea?

EDIT: your previous post just gives a thorough answer