Overdrive input treble peaking capacitor

[aab0mb]

So i've seen the Gil input mod for low end roll off which is 4.7M paralleled with a 47pf which seem like a super low cutoff to me as far as cutting bass flub. Isn't that like 7.2hz?

And then I saw Xtian mention trying the Marshall 470k+470pf (720hz?) which he said worked well and makes sense to me in terms of less flubby bass response, mids and highs leveling out a bit in terms of clipping response and making for less of the bass clipping buzz and rattle. It seems to actually help icepick highs by allowing them to be compressed as they hit the ceiling sooner. Someone correct me if this is incorrect.

Instead of Gil's resistor and cap in parallel method before the tradition OD network of 220k and 100k trimmer, I've added a .001 uf cap in parallel with the 220k resistor which is connected directly to the trimmer. This should give me the same 720hz rolloff that Xtian applied.

Is there a reason NOT to do this? Has anyone tried it? I just tacked the .001 cap on there and it acted as expected. Really helped lessen the bass fizz and put a little articulation on the string when playing low notes.

As far as I understand, most gain-y amps cut bass before clipping to keep things smooth and then cut highs after clipping to take out the fizz. The Technology of The Tubescreamer is where i remember first reading about that concept and the SLO or JCM800 are also good examples of this. Why was HAD letting tons of bass into the front of the OD section and cutting bass after? It seems backwards but maybe there's a method to the madness? Harmonic content created by clipping the full signal without bass attenuation and then filtering off the fundamental so only higher harmonics on the lower octave of the guitar are coming through?

[ayan]

So i've seen the Gil input mod for low end roll off which is 4.7M paralleled with a 47pf which seem like a super low cutoff to me as far as cutting bass flub. Isn't that like 7.2hz?

And then I saw Xtian mention trying the Marshall 470k+470pf (720hz?) which he said worked well and makes sense to me in terms of less flubby bass response, mids and highs leveling out a bit in terms of clipping response and making for less of the bass clipping buzz and rattle. It seems to actually help icepick highs by allowing them to be compressed as they hit the ceiling sooner. Someone correct me if this is incorrect.

Instead of the additional resistor and cap in parallel before the tradition OD network of 200k and 100k trimmer, I've added a .001 uf cap in parallel with the 220k resistor which that is connected to the trimmer. This should give me the same 720hz rolloff that Xtian applied.

Is there a reason NOT to do this? Has anyone tried it? I just tacked the .001 cap on there and it acted as expected. Really helped lessen the bass fizz and put a little articulation on the string when playing low notes.

As far as I understand most gainy amps cut bass before clipping to keep things smooth and then cut highs after clipping to take out the fizz. The Technology of The Tubescreamer is where i remember first reading about that concept and the SLO or JCM800 are also good examples of this. Why was HAD letting tons of bass into the front of the OD section and cutting bass after? It seems backwards but maybe there's a method to the madness? Harmonic content creating by clipping the full signal without bass attenuation?

To clarify, the network I used to use was comprised of a 4.7Meg resistor in parallel with a .0047uF cap, so 4,700pF, not 47pF. In any case, that doesn't happen in vacuum because that network is in series with the V1B output cap, which is .047uF, in series with the V1B plate output impedance and in series with the 220K + 100 K trimmer input to V2A's grid. If you want to do the math, you need to take all of that into consideration. I definitely consider this a bass reduction network, as opposed to a treble peaking one.

Cheers,
G.

[aab0mb]

So i've seen the Gil input mod for low end roll off which is 4.7M paralleled with a 47pf which seem like a super low cutoff to me as far as cutting bass flub. Isn't that like 7.2hz?

And then I saw Xtian mention trying the Marshall 470k+470pf (720hz?) which he said worked well and makes sense to me in terms of less flubby bass response, mids and highs leveling out a bit in terms of clipping response and making for less of the bass clipping buzz and rattle. It seems to actually help icepick highs by allowing them to be compressed as they hit the ceiling sooner. Someone correct me if this is incorrect.

Instead of the additional resistor and cap in parallel before the tradition OD network of 200k and 100k trimmer, I've added a .001 uf cap in parallel with the 220k resistor which that is connected to the trimmer. This should give me the same 720hz rolloff that Xtian applied.

Is there a reason NOT to do this? Has anyone tried it? I just tacked the .001 cap on there and it acted as expected. Really helped lessen the bass fizz and put a little articulation on the string when playing low notes.

As far as I understand most gainy amps cut bass before clipping to keep things smooth and then cut highs after clipping to take out the fizz. The Technology of The Tubescreamer is where i remember first reading about that concept and the SLO or JCM800 are also good examples of this. Why was HAD letting tons of bass into the front of the OD section and cutting bass after? It seems backwards but maybe there's a method to the madness? Harmonic content creating by clipping the full signal without bass attenuation?

To clarify, the network I used to use was comprised of a 4.7Meg resistor in parallel with a .0047uF cap, so 4,700pF, not 47pF. In any case, that doesn't happen in vacuum because that network is in series with the V1B output cap, which is .047uF, in series with the V1B plate output impedance and in series with the 220K + 100 K trimmer input to V2A's grid. If you want to do the math, you need to take all of that into consideration. I definitely consider this a bass reduction network, as opposed to a treble peaking one.

Cheers,
G.

My mistake on the cap value. Ok got it, it's shaving the value of the coupling cap down and the 4.7M is for pop reduction. I see both yours and Xtian's tweaks being useful.

In my case, I have a plexi-ish clean section being fed into the D-style drive network. So the EQ falls right before the drive network. Not sure how to do the math on that one but the treble peaking cap across the OD input 220k seems to work better than a coupling cap approach before the OD input network. Would I be better off inserting a treble peaking network before the 220k on OD input?

[ayan]

My mistake on the cap value. Ok got it, it's shaving the value of the coupling cap down and the 4.7M is for pop reduction. I see both yours and Xtian's tweaks being useful.

In my case, I have a plexi-ish clean section being fed into the D-style drive network. So the EQ falls right before the drive network. Not sure how to do the math on that one but the treble peaking cap across the OD input 220k seems to work better than a coupling cap approach before the OD input network. Would I be better off inserting a treble peaking network before the 220k on OD input?

If I understand you correctly, you have the EQ before the OD without a "recovery" stage in between -- which would be the V1B stage in a regular ODS topology? If so, I wonder how much gain you can get out of that, since the tone stack attenuates the signal quite a bit. Irrespective of that, it's fairly straight forward to try different things such as either bypassing the 220K resistor with different value caps, or add a treble peaking network before the 220K resistor. Personally, I think I never liked the sound of a treble peaking network anywhere in a ODS. Even if you do it early on, by engaging the bright switch for example, the overdrive doesn't sound as good to me. If you do it later, like bypassing the master with a brightness cap, the overdrive sounds terrible in my opinion. Making the cap very small can work, but by the time the effect is virtually negligible on the OD, it is definitely negligible on the clean channel -- referring to a single master topology here. And if that is the case, one could wonder why bother using the brightness cap at all.

G.

[aab0mb]

My mistake on the cap value. Ok got it, it's shaving the value of the coupling cap down and the 4.7M is for pop reduction. I see both yours and Xtian's tweaks being useful.

In my case, I have a plexi-ish clean section being fed into the D-style drive network. So the EQ falls right before the drive network. Not sure how to do the math on that one but the treble peaking cap across the OD input 220k seems to work better than a coupling cap approach before the OD input network. Would I be better off inserting a treble peaking network before the 220k on OD input?

If I understand you correctly, you have the EQ before the OD without a "recovery" stage in between -- which would be the V1B stage in a regular ODS topology? If so, I wonder how much gain you can get out of that, since the tone stack attenuates the signal quite a bit. Irrespective of that, it's fairly straight forward to try different things such as either bypassing the 220K resistor with different value caps, or add a treble peaking network before the 220K resistor. Personally, I think I never liked the sound of a treble peaking network anywhere in a ODS. Even if you do it early on, by engaging the bright switch for example, the overdrive doesn't sound as good to me. If you do it later, like bypassing the master with a brightness cap, the overdrive sounds terrible in my opinion. Making the cap very small can work, but by the time the effect is virtually negligible on the OD, it is definitely negligible on the clean channel -- referring to a single master topology here. And if that is the case, one could wonder why bother using the brightness cap at all.

G.

I have v1a, vol, v1b, CF, TMB like in a bassman or plexi. I should have written that more clearly. However, your inquiry is still valid in terms of, "how is this driving the OD section differently than the blackface style?"

I think you're right about the bright caps. I was testing at pretty low volume which isn't great for fine tuning frequency response. I removed all the treble peaking caps. I will test the amp at proper volume for a duration before tweaking again.

I'm hyper sensitive to over bass-ing things due to studio mixing and being aware of how bass eats headroom as well as making for flubby/fizzy distortion. It feels like I've been over most of the tweaks for flub and icepick in the non HRM type overdrive circuit. I may have to live with the fact that this amps voice is a bit lower in the low mids than I'm accustomed to.

I knocked this up because I had the clean section built already and had an extra tube to play with. If the proper volume tests don't pan out in terms of clean/od tone, I'll look forward to converting it to a proper d-style thing with a blackface clean section.