Blackface Tone stack box for Champ

[asilker]

So I've got an idea, wondering if anyone would like to chime in. I've got a Supro Super 1x6v6 amp with an 8" Jensen. It's very similar to a 5F1 champ. I love it, and I find myself using an eq pedal to scoop the kids a bit and then I click it OFF for dirt. The amp breaks up REAL easy so mostly I'm looking for something to give me a small cut and give me some blackface scoop.

I'm thinking something like this:


Would a passive assembly cut way too much out of the signal?

If I need a gain stage, I think I'll go op amp. Would I put that before or after the tone stack?

[Vitrolin]

gain stage before tonestack (10-20dB), and probaly also a recovery gainstage post tonestack with no that much gain.

if you only have a gainstage after tonestack you will be amplifying a lot of noise

I love it, and I find myself using an eq pedal to scoop the kids a bit and then I click it OFF for dirt.

hihi scooped kids 

[asilker]

I love it, and I find myself using an eq pedal to scoop the kids a bit and then I click it OFF for dirt.

hihi scooped kids 

DOH!

But ok cool. I've got a stereo op amp around here somewhere. That'd probably be the thing to use.

[PRR]

> Blackface Tone stack box for Champ

The AA-model Champ is Blackface tonestack plus Blackface era NFB around the power stage.

Steal the whole plan. It works.

If you need a MID control, replace the bottom resistor (6.8K in big amps but 15K in Champ for a little more gain and a little less dip) with a 50K or 100K Audio taper. Wire so "5" gives about 10K. Then 6.8K or 15K are either side of "5". And "10", 50K-100K, takes most of the dip out for screaming mids again.

[asilker]

I'll give it a look! And I might even use a trimpot for the mid control and only keep the treble and bass top mounted. I really value simplicity, plus my main amp for a long time was a bandmaster so for its sake I have a preference

I'll have to brush up on basic op amp powering and all of that. Maybe I'll be able to draw up a schematic plan before the end of the week and post so someone can tell me if something needs tweaking!

I'm excited about this project. IMO the best ideas are often the simplest. Maybe I'll wire a mini switch in to bypass the tone stack and only go through 1 op amp stage like the micro amp. 2 pedals in 1 for not much more labor

[B Tremblay]

The Tonemender may be of interest to you.

[asilker]

Oh very cool. The work is already done for me...

[Mark Hammer]

In a perfect world, you mic up the Supro, feed it a sweep signal generator, and plot the frequency response, given the specific speaker and cab properties.  Then, armed with that frequency plot, and some serious cogitation about how you play and what you like, you load up the Duncan tonestack calculator and work out the values of the relevant components to achieve the degree of tonal control at those points where you need to have the most intervention or control capability.

[asilker]

After a wide round of projects, I'm back to this one...

I'll be going for the tonemender design. It seems someone on Reddit fabricated pcb's for this design a while ago. Does anyone know if there's a source where I can buy a tonemender pcb?


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[Phoenix]

You're putting this in front of your amp right? Not in an effects loop? It may or may not give you the response you're looking for depending where it's located in the signal chain, particularly with overdriven tones, so keep that in mind.
Anyway, you'll definitely want some amplification/buffering, otherwise you'll lose about half your signal voltage. I've got two circuits here, one amplified/buffered, the other a passive arrangement to illustrate the amplitude differences. But the circuit on the left hand side should give you what you're after. It's got a ~1Meg input impedance, 100ohm output impedance, and should give the impression of approximately unity gain - but you may need to tweak the value of R9 to taste. Or, if you wanted an adjustable boost, you could replace R9 with a suitably-valued pot for gain control.
Hope this helps.

[asilker]

You're putting this in front of your amp right? Not in an effects loop? It may or may not give you the response you're looking for depending where it's located in the signal chain, particularly with overdriven tones, so keep that in mind.
Anyway, you'll definitely want some amplification/buffering, otherwise you'll lose about half your signal voltage. I've got two circuits here, one amplified/buffered, the other a passive arrangement to illustrate the amplitude differences. But the circuit on the left hand side should give you what you're after. It's got a ~1Meg input impedance, 100ohm output impedance, and should give the impression of approximately unity gain - but you may need to tweak the value of R9 to taste. Or, if you wanted an adjustable boost, you could replace R9 with a suitably-valued pot for gain control.
Hope this helps.

Thanks Pheonix! The Tonemender (link above) features a dual op amp for stages before and after the tone stack.

I'm sure your designs are quality, but my skills aren't up to free form building...

[Phoenix]

Thanks Pheonix! The Tonemender (link above) features a dual op amp for stages before and after the tone stack.

I'm sure your designs are quality, but my skills aren't up to free form building...

Haha! I just took a look at the Tonemender, and other than some added features in that design, mine is grossly similar.
Not sure If you'll find a PCB, but they do have a perf layout which shouldn't be too tricky.

[thermionix]

If you remove the V1a cathode bypass cap from a 5F1 Champ (accidentally omitted on the official Fender schematic), the sound gets very dull and boring, almost exactly like a blackface Champ.

[davent]

After a wide round of projects, I'm back to this one...

I'll be going for the tonemender design. It seems someone on Reddit fabricated pcb's for this design a while ago. Does anyone know if there's a source where I can buy a tonemender pcb?


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ROG does have the pcb art so you could make a go of it yourself or... there are people around that etch up boards for others, sell their services, so maybe a request in the For Sale/Trade thread will turn up an etcher that can help you out.

http://www.runoffgroove.com/tonemender-pcb.pdf

http://www.diystompboxes.com/smfforum/index.php?board=7.0

dave