Treble reduction on OD channel

[greiswig]

I'm trying to figure out the best way to reduce the unwanted portion of the treble from the OD channel on a non-HRM. Bypassing the V2a plate resistor works, but I understand that this may cause some interactions with the Miller capacitance? Should I just be looking to increase the value of the snubbers on that tube?

[ampgeek]

G,
I jumped directly from 270 pf up to 470 pf and observed a tremendous reduction of treble in the OD tone. Backed them off to 330 pf and I like what I am hearing.

The bottom line is you will definitely hear the effect of tweaking the value of these snubbers.

Dave O.

[Structo]

Have you increased the treble cap on the board to 330pf?

[butwhatif]

One cure is to put an .01 cap or other value of choice from OD2 plate and take it to ground (a/la an hrm mid control) with a resistor to signal ground. It works pretty well, but adjust to taste, as it can work too well.

[greiswig]

Have you increased the treble cap on the board to 330pf?

I tried it for a bit, but went back to the stock value mostly because of the OD tone. If I can tame the highs on the OD channel (if I can ever get rid of the fizz enough to concentrate on the voicing!), I'll see about putting that 330p treble cap back in.

[dave g]

A .01 is far too big for this type of thing IMO. Try Gil's high frequency taper. Use a .001 in series with a trim pot wired as a variable resistor to ground. Gil uses 250k, Dogears likes 500k, I like 1M...try them each and see what floats your boat.

[greiswig]

A .01 is far too big for this type of thing IMO. Try Gil's high frequency taper. Use a .001 in series with a trim pot wired as a variable resistor to ground. Gil uses 250k, Dogears likes 500k, I like 1M...try them each and see what floats your boat.

I presume that V2a is the plate to tap for this?

[dave g]

Whoops, forgot that part

Actually, I take it off the top of the OD Level/Ratio pot (after the 150k). I wouldn't put it on V2a.

[heisthl]

I'm trying to figure out the best way to reduce the unwanted portion of the treble from the OD channel on a non-HRM. Bypassing the V2a plate resistor works, but I understand that this may cause some interactions with the Miller capacitance? Should I just be looking to increase the value of the snubbers on that tube?

You could try using cheaper coax or tacking in a 30pf to ground at one or more entrance or exit points.

[greiswig]

I'm trying to figure out the best way to reduce the unwanted portion of the treble from the OD channel on a non-HRM. Bypassing the V2a plate resistor works, but I understand that this may cause some interactions with the Miller capacitance? Should I just be looking to increase the value of the snubbers on that tube?

You could try using cheaper coax or tacking in a 30pf to ground at one or more entrance or exit points.

Hmmm...I guess this is sort of the question behind my original question. There are a number of ways that this can be done. Which is least likely to cause other issues? As I said, O'Connor suggests splitting the plate resistor, and bypassing half with a cap to bleed some off. Seems to me that you want to roll off the treble before even the first stage of that tube, so that you're not wasting energy trying to amplify a signal you don't even want to use?

[butwhatif]

OD2 plate is where you want to do it, after all the clipping. Although HAD used to do it before OD1 also--

[heisthl]

OD2 plate is where you want to do it, after all the clipping. Although HAD used to do it before OD1 also--

Ouch! that makes my head hurt just looking at it - If you've worked it out tell me what is there. Thanks

[Fischerman]

My amp is HRM and has no snubbers on the V2 socket...so this might be different but...increasing that 150k grid stopper on V2a's grid will reduce top end at the expense of a little bit of gain.

As far the treble bleed, I tried it but never found values that I liked as much as a 1000pF cap across the OD2 plate resistor. Right now my amp just has the 1000pF cap across OD2's plate resistor and a 200k grid stopper on OD2. I still keep my HRM treble control pretty low though (like between 1/4 and 1/3 of the way up).

[dogears]

All this discussion is interesting.... I have had no need to do any of this stuff on my HRM. Every time I tried, I was disappointed with the tone. For me, the original way seems best and yields the most familiar tones. Turning the HRM treble control too low dulls and compresses the tone. It also effects the mids and bass. The biggest I ever put the OD2 grid is 180K. The real HRM Dumble I got inside had a 150K and the treble trimmer set up about 2/3!! It was super creamy and not harsh or bright. No snubbers either.

If the amp is too bright and requires such radical treble bleeding, I'd be looking elsewhere for some issue.

[mlp-mx6]

+1. My HRM has no snubbers either. I can't imagine the muffled tone I would have if I snubbered (g) that amp.

I did use the "treble bleed" on my non-HRM. I also put switchable snubbers on it, just because I could and I wanted to experiment. DPDT center-off switch, 270pF and 390pF, IIRC. I stay with the 270pF, pretty much. I only use the higher value with a Strat, but I don't mess around with the Strat much with that amp. I haven't found a good way to dial that amp in for the Strat.