tone stack location?

[gsr]

Hello, I have been researching all I can as plan another amp build. I came across this schematic of a two knob Trainwreck which was further modified by Bruce Collins in '08. My question is, "has anyone done something like this, except placing the tone stack after the 2nd triode? The order would then be; input, v1a, gain pot, v1b, tone stack, first triode of phase inverter as gain recovery stage, master volume. Dumb idea?

[Steve Conner]

There's no wrong place to put the tone stack. The closer you put it to the end of the amp, the more it sounds like a Marshall.

[redelephant]

Not sure I get your question right, but...

You can pretty much place the tone stack where ever you wish. Placing it after the preamp allows the preamp to be seriously overdriven, while placing it between V1 and V2 will attenuate the siganls from V1 a bit, so V2 won't be as eaasily overdriven...and so forth. There are no rules, and nothing dumb about placement of the tonestack before or after the second, third, ..., gainstage. It all depends on what you're after.

The only thing you have to ensure is that the signal into the PI is large enough to drive the output to rated power, before the preamp is overdriven. That is when master is on max, the output must clip before the preamp.

Sorry if I got your question wrong...

[gsr]

Thanks Steve and Redelephant for your replies. My thinking is that placing the tonestack between v1 and v2 is a bit of a compromise position, but might make the amp pedal friendly while still breaking up naturally. I guess I was looking for versatility. I love my tweed builds and I love simplicity, but pedals are fun, too. I am considering this build with 6L6s or 5881s with 5U4 rectifier. Thus the appeal of the master volume.

[gsr]

Please elaborate on this. I have much to learn. My reasoning with the tone stack between v1 and v2 is we seem to be dumping some gain there anyway through the resistor to ground after the coupling cap, so the tone controls might be a little less lossy in that position.

The only thing you have to ensure is that the signal into the PI is large enough to drive the output to rated power, before the preamp is overdriven. That is when master is on max, the output must clip before the preamp.

[imaradiostar]

There's no wrong place to put the tone stack. The closer you put it to the end of the amp, the more it sounds like a Marshall.

hahaha! I like that.

I have been toying with an EL84 based design that would use a variable mid cut between the LTPI and the power tube grids. I figure EL84's are pretty tolerant of high driving impedances and it would be interesting to see the tone of an amp that's mid heavy throughout the preamp then scoop out those mids right at the end.

Jamie

[Chuck H]

+1
I've drawn up numerous schems with the same idea. Well, to elaborate... In the schems I've drawn I have the bass mid and treble controls located such as to allow the bass to be trimmed for OD tones, generate ample mid and upper harmonics and then trim mid later in the circuit. ie: across the PI outputs so that somewhat scooped tone can be achieved. The trouble is that if the power tubes are clipping hard it all sort of becomes moot IMHE. Steve's is the best blanket analogy. But in the end, if your clipping the power tubes, any tone controls are pretty much 'distortion character' controls and fail to offer much control of the final frequency balance. If you OD the power tubes even more than a little the final EQ is up to the power tubes, OT and speakers. And they ain't got no knobs. I am penciling an attenuator that controls individual frequencies. Weber has already tried this with limited success. My design may be a tad better but I don't think there's much application for it in the long haul.

[guitarmike2107]

Although this has already been said here's how I look at it.

With the tone stack early in the pre-amp, you cant get a scooped "metal" type tone. These are generally great on amp where the power section is used for distortion.
With the tone stack later in the pre amp you can create distortion before the tone stack and then control the distorted mids, which would allow you to get a scooped distorted sound.

The other factor is most often when the tone stack is later in the amp a cathode follower is used, this does add a smoothness to the tone.
I have just built an amp with a tone stack after V1 and then inserted a cathode follower later on just to see the tonal difference, I liked it.

I have also built an amp with the tone stack after the second gain stage, because there is little overdrive before the tone stack it acts more like a first stage driven tone stack.

I think you need to find out what makes an amp pedal friendly as this is your real concern, There are plenty of pedal friendly amps with the tone stack after V1

[Steve Conner]

Yes, as was said above the two basic flavours come down to "Tone stack before distortion" or "Tone stack after distortion".

I guess there are also amps with two tone stacks, one at the beginning of an overdrive preamp and one at the end. I've built such things myself. The hardest bit is what to call the first set of tone knobs. Mine were labelled "Fart" and "Sizzle".

If all the stages are distorting, like an 18 watt with its balls nailed to the wall, then it's anybody's guess what the tone controls will do. IMO it's hardly worth including tone controls in that case.

To me a pedal friendly amp is just one with a good, loud, well-balanced clean tone. A Fender Twin or whatever. The opposite of an 18 watt.

[guitarmike2107]

Even on the balls to the walls amps the tone controls do have a place, The advantage is if you use the guitar volume to turn down the drive, which brings in the effect of the tone controls more so. So at full drive you have thick harmonic distortion, Then with the guitar volume backed off to clean up the sound you can get a little scooping going on for a nice “easy on the ears” clean sound.

[redelephant]

Please elaborate on this. I have much to learn. My reasoning with the tone stack between v1 and v2 is we seem to be dumping some gain there anyway through the resistor to ground after the coupling cap, so the tone controls might be a little less lossy in that position.

Yeah, agree a tone stack is a more useful level dump than a resistor divider since u get more out of it.

What I mean about bringing in the issue of ensuring the output reaches max before preamp is that sometimes placing the tonestack last, after a high gain preamp, the signals are attenuated so much that the preamp crunches before the output. I've done that a few times, and ended up either removing a gain stage, or reducing their gain and also adding voltage dividing resistors between stages, which is a waste.

I think the tone stack can be the most brainthrashing part of guitaramp design. The type of tone stack, it's frequency response, and where to place it, can be a serious pain in the red eye. I spent some serious amounts of time, months, on trying to figure out my own stack, and in the end I've settled on a variation of the Baxandall type similar to the ones used by Ampeg. I usually place mine after the preamp, without a cathode follower.

[gsr]

I spent some serious amounts of time, months, on trying to figure out my own stack, and in the end I've settled on a variation of the Baxandall type similar to the ones used by Ampeg. I usually place mine after the preamp, without a cathode follower.

This is where I am at! I checked the Ampeg schems and they are eerily similar (mine would leave out the preamp switches). How did they know what I was up to? HAHA. Seriously, is this a good sounding circuit? Any suggestions for tweaks/improvements?

[gsr]

To me a pedal friendly amp is just one with a good, loud, well-balanced clean tone. A Fender Twin or whatever. The opposite of an 18 watt.

I guess I was looking for a bit of a compromize. The best of both worlds if that is possible. And of course all this in a simple, elegant circuit. Oh, to dream...

[mooreamps]

I like the way Bruce calls out a 12AY7 for the front end. I think he really nails it for tone on this one. By putting the T/S between V1 and V2 lends for a more of a clean channel layout ; where as putting the T/S at the end of the preamp is more of a setup for an overdrive channel... But of course if you want a preamp channel as an overdrive, you would set-up the bias as such as well.
Good luck with this one.. Sure looks like a winner to me.....


-g

[redelephant]

This is where I am at! I checked the Ampeg schems and they are eerily similar (mine would leave out the preamp switches). How did they know what I was up to? HAHA. Seriously, is this a good sounding circuit? Any suggestions for tweaks/improvements?

Hehe...I found out Ampeg used my tonestack about a year after it became my standard solution Proof that time machines actually do excist!

I moved the highs a little up and use 2.2n and 220p for the treble, I believe Ampeg usually used 4.7n and 470p in the treble. Bass I usually use 10n and 1n. Sometimes I vary those values a bit, either moving one or both frequency up or down, depending on the type of response I want. I really like the fact that this type of tone stack gives both boost and attenuation of mids, and even better that when adjusting one control it only affects that frequency without adding or subtracting from the other. (U can really tweak the bass up or down and the mids-treble isn't affected much at all, and vice versa).