12ax7 with Transformer Pre-amp : Booster/OD guitar pedal

[Printer2]

We do! Nowadays we call them distortion pedals, overdrive pedals, fuzz-boxes, dirt pedals, et cetera, and they are everywhere - just about everyone who plays electric guitar has at least one, and many have several. Their function is exactly what Randy Bachman intended - to go between guitar and amp, and add distortion and sustain to the guitar sound, beyond what the guitar amp itself can create.

Today's Herzog's are usually solid-state, which is much cheaper and more convenient for the manufacturer, but there have been quite a few valve-based ones too, from the Chandler Tube Driver to the Effectrode Blackbird.

None of the hundreds and hundreds of solid-state Herzogs - at least none that I've ever heard - have produced the long, smooth, sustain of the original, which is remarkable for its complete lack of harshness. Instead, many of us have trained our ears to tolerate, maybe even enjoy, the harsh buzz of clipping semiconductor diodes.


-Gnobuddy

Sorry for the delay, too busy to follow too many threads. No the overdrives are not Herzogs, very few out there with a 6V6 and an output transformer. On the OT, all amps did not have enough iron to pass the cranked amp's output. Whether they sounded better that way or not is up to individual taste. You get people upgrading Champs, Princetons, 5E3's and some like with many happy at the 'improvement'. But then again it all depends on how you use the amp.


For the OP, I have schemed different ideas to color the sound, some tube based. It all depends on the footprint you want the device to occupy. To get high voltages for preamp tubes to run at there is the transformer option, voltage multipliers, small switching supplies built with the 555 IC, or off the shelf switching modules from China. Then there is the actual circuit and what you want it to sound like. There is no reason not to have an OT, there are the sub-mini tubes or even miniature power tubes that put out a watt that can be used. It all depends on what you are looking for and how big it will be along with what you want to spend.

 

[Gnobuddy]

No the overdrives are not Herzogs, very few out there with a 6V6 and an output transformer.

By that definition, I agree, there are no Herzog's except the original Bachman / Gillies ones. And if I were a rich collector of antique guitar electronics, that's the definition I'd use, adding that it also had to be made by Gar Gillies himself.

But if we're not antique guitar electronics collectors, but rather musicians and DIY electronics engineers, then a functional definition (rather than a literal one) might be more appropriate, and Randy Bachman's own words tell us what his engineering design goal was:

"Growing up playing violin, I loved the sustain, especially of a viola or cello. So early on in the mid ’60’s, I found out that by plugging a small amplifier into a bigger amplifier, I could get this sound. Now I was taking the power out, which normally would go to the speaker and plugging it into the input of another amp. The result, for a few short minutes was a cool, great new sustained sound.

So it seems to me that any guitar pedal designed to produce a smoothly distorted, sustained, sound, is doing exactly the job that Bachman envisaged.

Musical tastes changed along the way, and the slow, swelling notes that Bachman used to set the world on fire in the mid 1960s wouldn't get much attention today. Perhaps that's why today's crop of (functionally) Herzog-alikes don't sound much like the original, real Herzog + Gillies amp?

That's another thing: I see nothing in the circuit of the original Herzog to produce that smooth, sustained sound. In fact, the Herzog is nothing more than a Champ with a dummy load, and we all know Champ's sound pretty harsh and ratty when overdriven heavily (a la ever guitar tone on Derek & The Dominos, for example.)


So from the moment I first saw the Herzog schematic, I have been wondering why Bachman's lead tone was so smooth, rather than Champ-harsh.

Just a few days ago, I found a quotation attributed to Randy Bachman himself, ( "Gar" Gillies' Herzog® - All Tube Guitar Effect - garnetamps.com - Home of the Garnet™ Amplifier Company ) where he said that the Herzog plugged into Bachman's big Fender amp didn't sound right; so "Gar" Gillies built him a new guitar amp, and it was the Herzog + Gillies amp that produced the "American Woman" smooth, singing, sustained tone:

...Gar proceeded to build me a tube pre-amp, which when put into another amp, got me the desired sound. But not really, the sound was a little weird in a Fender amp which was all that was around, so Gar decided to get parts from Heathkit and build an amplifier to go with the unit.
<snip>
...till the wee hours of the morning, making the most incredible Moose and Ox bellowing, distortion/blotto screeching sounds that would make us laugh. But once it was smoothed out, it was smooooth.

So the custom one-of-a-kind guitar amp that Gillies designed and built for Bachman with Heathkit parts, in combination with the Herzog, is the missing piece in the "American Woman" sound.

I have never turned up any more information than that, no schematics, no description. I have no idea what Gillies built with his Heathkit parts, or exactly how it was tweaked to remove the Herzog's harsh overdrive, replacing it with that smooth singing cello-like sustain Bachman became known for.


-Gnobuddy

 

[mozz]

Based on the valvecaster.

 

[JMFahey]

How would it be more complicated than making a tube mic pre?

You are comparing very different things.
A Mic Pre, tube or oherwise , is expected and designed to ve very flat and very clean: a Guitar preamp quite the opposite
So we are already starting with different feet.

I’m sure a power amp section would be unnecessary; it only needs to bring the level near line-level?

Quite the opposite, a tube preamp and a tube power amp, specifically a pentode driving an transformer which in due time drives a significant load, no matter how low powered, clips VERY different from a an overdriven *triode* driving a *resistor*
Here, you have not one different variable but two.

So wouldn’t a tube mic pre, with individual gain and level controls achieve the same thing?

No.

I can’t see how it should be too difficult to modify a well known tube mic pre and fit inside a guitar pedal.

*Again*, a mic pre is NOT a guitar pre.

 

[thoglette]

There is an audible difference, but it is not what I expected from all the claims I read: when you turn up the power on the SCXD, the bass starts to diminish, with no audible change in timbre. The PRRI doesn't exhibit this effect.

Agreed - matches my observations. Current amp in use has a "too small" OT to get rid of some bass.

There I have seen a small guitar amp OT generate enormous amounts of distortion on my 'scope - but only at very low frequencies around 20 Hz, far below the guitar bandwidth.

There might be a point a which useful IMD might arise (much like mains IMD from PS sag) but I'll leave that for later
Likewise in guitar HF mismatch from side to side is not going to be an issue.

 

[Printer2]

If I only had the time. I have plants that need attending, lighting, timer, ventilation and such, otherwise I would throw something like this together. Don't take the values as given being suggested as I just did a quick copy and paste to give the general configuration as a jumping off point. It uses a high voltage supply that goes for about $8 online from a 12V wallwart that does the heater and SS supply. The HV module fits in the 4X4 box, can use standoffs for mounting, if needed a interference shield of sheet steel (another 4X4 lid) can be mounted in part with the ground screw. A bracket for the tube socket, the fiddly bits on the box lid, maybe even a stomp switch. Not elegant but only a few bucks for a prototype enclosure.

 

[Gnobuddy]

Is there any pcb/layouts/schematic for a 12ax7 pre amp with transformer to make a booster/OD pedal for guitar?

Amazingly enough, I stumbled across one last night. Here you go, the Fuzznikator: FuzzniKator Push-Pull Tube Distortion/Preamp Box

I have no idea if this thing sounds good or bad, so this post is not a recommendation for the Fuzznikator. But this is the first (and so far, only) circuit I've run across that more or less fits your original request, so I thought you might be interested.

-Gnobuddy