Traynor Midrange control?



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Traynor Midrange control?

Postby qersty » Sat Jan 12, 2019 9:56 am

So I was reading the schematic for the Traynor TS-50B to try find out what the tone controls do. I have kinda always been confused looking at them but today I realized the bass and treble were quite simple to run by themselves in the tone stack calculator with a Marshall stack if you get creative and well:
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That's a Traynor if I've ever heard one! The trouble is the mids, however...
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I just cant wrap my head around it. My first thought was either some notch filter or BMP-tone but a quick check on AMZ confirmed it is not. I looked at some schematics of RC-bandpass filters and I kinda can see the semblance but I am not really sure. What i do understand is that the pot "switches order" of the high and low-pass sections but I have no idea how this would graph. That is if I'm even right at all, I have extremely limited knowledge of electronics but I would like to learn a bit more. Any ideas? i would love if someone who knows about this kinda thing could help out. These traynors sound awesome and it would be super cool to know a bit more about why they do.
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Re: Traynor Midrange control?

Postby DRodriguez » Sat Jan 12, 2019 10:59 am

It's a variation on the Twin-T style filter.

You can play around with it here Use the resistance slider on the right side to sweep the pot.
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Re: Traynor Midrange control?

Postby qersty » Sat Jan 12, 2019 12:11 pm

DRodriguez wrote:It's a variation on the Twin-T style filter.

You can play around with it here Use the resistance slider on the right side to sweep the pot.

Thank you very much! very interesting filter
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Re: Traynor Midrange control?

Postby eatyourguitar » Sun Jan 13, 2019 2:13 am

I used LTspice and I got the same result. I wanted to see if the phase was rotating 360. it actually goes through a 180 phase rotation depending on input frequency. the phase also changes direction twice from input to output.
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if we measure after the first high pass filter, you can see what is going on with the phase before we put it all together at the output.
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Re: Traynor Midrange control?

Postby qersty » Tue Feb 12, 2019 4:32 am

I found another circuit like this but more sophisticated in the Bass JCM 800, very different topology than other Marshalls with a baxandall tone stack instead of the typical FMV. The controls are very interactive but are misleadingly labeled as if it was a semi-parametric EQ. Also worth noting is the placement of the mid control in relation to the EQ.
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