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Any resistor in series with the signal followed by another resistor to ground forms a voltage divider, however small. In this particular case you cut roughly 10% of the signal that comes out of IC2B, in addition to providing a slightly different taper to the left half of the gain pot, which also...

Funny that you should use gyrators for the EQ - I have been working on a similar arrangement (volume on inverting opamp + gyrator mid control) on a JMP1-based dirtbox, after being disappointed by the bax tonestack in that setting. Indeed the Friedman similarity is apparent, to the point of...

Using original schem refdes: - You don't really need R26, R27 and C23. - I would keep R14 as it forms a voltage divider with R12. - You could probably skip the last opamp and take the signal out after the vol pot. That last stage is just mixing channels and its corner freq is practically...

It is considered good practice to have first and last stages on separate dual opamps, especially when huge gain increases are present (or so I have read in multiple sources). In my very limited experience, I have only had issues if/when overgained signal is entering the last section, or if that...

2sk117 are used as buffers, so absolutely nothing special about them :) I tossed in j201 in my Baja builds back then because that's all I had. Use any small signal jfet, or even replace them with opamp buffers, it won't make a difference at all sound-wise.

Leg 2 of LoCut should go to VREF and not to ground. Although I suspect that this is only part of the issue, your Vref voltage is too high to be caused by this accidental ground connection. Double check that you have 1/2 V+ between R16 and R17, and track from there.

I'd be tempted to adscribe to Cybercow's answer, however, I kinda feel there's a catch somewhere in the question. IME it is possible to get a JFet to exhibit the same gain as a BJT just by adjusting the components values around it, but the downside is loss of headroom. Haven't tinkered enough...

Since the mid frequencies rely heavily on the corner frequencies of both bass and treble circuits (at least for the "cut"), there is no *easy* way to implement a mid shift on the Beta. It would quickly become a nightmare of switches and dual pots for it to be somewhat effective. An alternative...

Creo que todos hemos pasado por esto ;) I have piled up hundreds of bookmarks related to circuit design, reverse engineering, electronic & audio theory and so forth over the years. Every time I revisit once I stumble upon some info that I hadn't understood or that had gone over my head when I...

Muamp and SRPP are "self-biased", so jfet variation or spread of parameters matters much, much less. Think of the upper jfet as a trimmer that has already done the work for you :)

I find the Peavey Bandit transtube preamp unbeatable when it comes to SS "pedal platforms". No pcb for it (as far as I know) but not too complicated to do either. There is a nice simplified version of it here.

The Catalinbread Sabbra Caddabra was designed specifically to ape the Supergroup + Rangemaster thing. Otherwise, you can tweak the EAE Model Fet to Supergroup specs. IIRC the Iommi setup on the early albums was: Modified Rangemaster (almost full freq boost as opposed to treble) -> Bass channel...

So f*n cool, mate! Nice to hear it played by someone else than me :) I also tend to get whining from the breadboard withthis kind of circuits, I usually rejig some of the gain stages further apart til it stops. the resistor + cap after the Hi cut control is there to counter the treble bump from...

Sure, temol ;) At drain of last gain stage: After hi cut control: Nothing too outrageous, kinda standard-ish JCM but with more gain. Trying to ape 90's King Diamond type of tone, a bit more modern than 90's standard HM, but not quite modern sounding by today's standards, not scooped nor...

I did some sims just to compare side to side, here's some observations. We have those three circuits, left to right: - First one is a fairly standard jfet gain stage, with "cathode follower". - Second one is the same, but with a follower nicked from AMT L2 pedals (those that have it, e.g. S2...

Do you mean the whole bootstrapped follower thing? I have never seen it in any pedal design, personally. There is an old thread on DIYSB about a similar idea using bjt, but I don't recall seeing it in any "complete" circuit. I've ltspiced it with fets, it does increase gain and it does exhibit a...

I'm not knowledgeable enough on mosfets, but the ubiquitous RG Keen certainly is: http://www.geofex.com/article_folders/mosboost/mosboost.htm

Cool design!! This amp has an intereating topology. Kinda like the non-interactiveness of the treble control, although the mids don't seem to do heaps. I wonder which stage clips first, 6AN8, cathodyne PI or power stage, and which one is responsible for the sound characteristics?

I tend to use jfets with tight specs (SMD J201, 2N5484, J113, 2SK208R, and the dmos LND150), and rarely bother checking their Vp or IDSS. By simulating on Ltspice, you can start with drain and source values that are in the ballpark, then check with the multimeter and do some small adjustments to...

Personally, for jfet stages, I focus on 3 things: - Bias point (asymmetry) - Clipping point (gain) - Source capacitor if present (freq response) When converting from 9 to 18v (or more), leaving all source components the same and just changing the drain resistor to bias the jfet will get you in...