Grid Stopper Question

[guitarmike2107]

I don’t see the point of sticking a 0.022 cap after the tone stack, this is needed when connected to a PI input to stop the controls scratching but it’s not needed here? And as far as I can see is not doing anything here as it’s pretty much a short circuit for the full guitar frequency range.
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What else have you done to tame the bass early on other than the 0.001uf coupling cap after the first stage,
If the amp is going into good higher gain territory you probably would want to tame the bass a bit more or boost the highs a bit more.

If you look at a cascaded JCM800 there is a reason why they cut the bass at the first cathode and then use treble peaking caps before the first volume control, too much bass sounds rubbish distorted along with the rest of the signal.

One way that I have used to help tame the bass as the volume is turned up past 3 o’clock is to strap a resistor from the volume control wiper down to ground, this mostly effects the bass in the last ¼ of volume control rotation.

If you have a 1Meg volume pot and a 1M resistor strapped as above you can easily work out where the bass will roll off at different volume/gain level settings.

[surfsup]

One way that I have used to help tame the bass as the volume is turned up past 3 o’clock is to strap a resistor from the volume control wiper down to ground, this mostly effects the bass in the last ¼ of volume control rotation.

Interesting. I strapped a 1M from pin1 to one side of the pushpull and a jumper from the other to the other pin3, to effectively make it a 500k pot instead of 1M. That didn't do anything. I'll try this idea of yours and report back.

I don't have a smaller 600V cap for the coupling unfortunately at this time is why I went down to 1n0 and no lower. Was going to order one on my next order. I can series two but that's a lot of work with no turret to solder to.

FYI, the cap and 33k make a difference. Its quite apparent. I assumed the caps in the TS would function the same way. I measured DC voltage on the T/B pots and was reading 0 if memory serves so I didn't think the cap would really block any DC to the grid of stage three - but now we're getting into "I have no idea what I'm talking about" territory.

[guitarmike2107]

FYI, the cap and 33k make a difference. Its quite apparent. I assumed the caps in the TS would function the same way. I measured DC voltage on the T/B pots and was reading 0 if memory serves so I didn't think the cap would really block any DC to the grid of stage three - but now we're getting into "I have no idea what I'm talking about" territory.

Interesting, the 33k will affect high end roll off a bit and overall you have raised the grid leak value to 56k +33k = 89k. so that’s two important changes, I wonder if you would notice any difference if you removed the cap but left the resistor in place?

The way I suggested setting up the volume pot/resistor would vary the resistance from 1M(volume turned down) to 500k (full volume)

I find these online tools useful for getting a quick estimate as to how the caps will change low frequency roll off.
http://ampbooks.com/home/amplifier-calc ... capacitor/

[surfsup]

I wonder if you would notice any difference if you removed the cap but left the resistor in place

I had a 220k instead of the cap before and a 3k3 instead of a 33k

This was more blatty sounding. The cap seemed to help. I initially put the cap as a bypass on the 220k but there was no change sonically to my ears. Once I removed the 220k, voila. Big difference and I was able to use a 12ax7 instead of a 12at7 for V1

I use the f=1/(6.3*RC) for figuring the freq. I have it tattooed on my brain.

I'll try your mod. One other thing about this tonestack is I notice as I crank up the bass, the duncan software shows a midscoop to zero at about 97% rotation, which seems to be similar to what I hear. I was thinking about putting a 10k resistor between the bass and treb pot so it can never really go to zero. This would eliminate that funky effect with bass cranked.

How does one "edit" the schematic in the duncan TS software? I can't figure out how to build your own schematic. the duncan PS software allows it. Maybe it is not allowed in the TS software?