Help needed: improving the Marshall Guv'nor!

[Hardtailed]

Given this schematic: http://www.generalguitargadgets.com...s/guvnor_sc.gif

My original Guv'nor is getting old and I want to retire it from my pedalboard since it's somewhat of a vintage item by now. Since I use it 90% of the time and no other OD pedal as made me smile as much, I decided to clone it. But I would like to "improve" it a bit. I don't want to change it's tone, but I wish it would have a bit more output (it doesn't hit the front end of my Marshall as hard as I wish).

First thing, I won't be building it as a pedal, but rather as a rackmounted unit, with relay switched true-bypass. Thus it will be powered with a wall-wart. I'm thinking about going with 12V since it's easy to source. I guess I should be able to get a bit more headroom this way.

Not being a master in electronics, the only way I can think of to get more headroom, is to remove the clipping LEDs, but I'm afraid this might change the sound too much, or it might make the opamp run out of headroom and clip in a bad way. What about doubling the LEDs? Or using LEDs with a higher turn-on voltage? Any recommendation?

Any other parts I need to change to use 12V? Any advantage in going even higher than 12?

Thanks in advance!

[Roobin]

As far as 12v goes, it will mean that there will be a lower clipping threshold. Why not use 9v? It's standard in lots of things. If using 12v, make sure capacitors are rated for it (use 16/18v preferably).

If you remove the clipping LEDs, it won't clip. You could try replacing them with Si or Ge diodes to change the sound.

(it doesn't hit the front end of my Marshall as hard as I wish).

Do you eman that it doesn't have enough output level? If so, you could try placing a transistor buffer stage after, or an IC stage.

Hope all goes well!

[Hardtailed]

Well yeah, I mean the output level is not quite high enough. I remember reading about removing the clipping diodes in a Tubescreamer and running it on 18V (2 batteries) to use it as a "clean mid booster". Removing the diodes means the signal is not clipped so it passes through unaffected (technically) except for tone shaping. Of course, the Guv'nor doesn't use the diodes (LEDs in this case) in the same fashion (they shunt the signal to ground, instead of working on the feedback loop).

I don't need the actual clipping, I just want the signal boosting and tone shaping, but with my stock unit, the output level is not high enough so I have to raise the gain a bit to get enough overdrive. I'm guessing, if I remove the diodes, raising the gain will just send more "clean" signal and the additionnal clipping will happen inside the amp (with tubes instead of diodes). But since the circuit is so different from the Tubescreamer, I am unsure if this will work.

Maybe I should just build the damn thing and then experiment with and without the diodes

[Roobin]

Ok, with clipping, there are two main types:

Soft clipping.

This is where diodes are placed in the feedback loop of an op-amp. Cause the edge of a signal to clip, but not go flat (like hard clipping)

Hard clipping

The diodes are placed after an op-amp stage, going to ground. They clip the signal (literally) so its not a smooth sine wave anymore.

N.B. Could someone please explain it better. This is just a generalistion, and I'd appreciate a bit more depth.

So, if you don't have the LEDs, the thing wont clip. That's fine for your application. If you boost the clean ouput singal, it will overdrive the tubes, causing tube overdrive. Is this what you want? If theere is not enough ouput level, you could also try adjusting the resistors in the feeedback loop of an op-amp.

[Hardtailed]

Well, I guess I forgot to actually look at the schematic, the signal doesn't pass through the opamp or any gain stage after the clipping stage. So I guess removing the diodes wouldn't be that big of a deal . Or maybe I'll just put a switch so I can experiment, or even a pot!

BTW, how much of a difference does the tone stack makes? I usually leave everything at "noon" on my OEM Guv'nor. I'm tempted to remove the tone stack from the circuit. That would save some $$$ too 

[jrc4558]

Try running it at 24VDC. It wil be loud, more dynamic and verrrry gainy!

[Mike Burgundy]

Try it and see, just don't do anything you can't reverse.
Consider the fact that:
-tonestacks almost always change response (slightly) even when set flat
-a Guv'nor without the tonestack and without clipping is far from a Guv'nor. Its a clean booster with a hipass filter.
You might want to investigate the several clean boosters out there.

Signal levels will significantly go up if you remove the diodes (think about it - they need something larger than the clipped signal to actually clip, right?)
Increasing voltage will increase *headroom* (this only makes sense with removed diodes) but not the gain itself - voltage gain in opamps is set by the ratio between the feedback and input resisitor, not supply voltage. With higher supply, the opamp can supply more output voltage before it itself starts clipping, but it doesn't automatically do so.
Be advised that the TL072 family is rated for an absolute mazimum supply voltage of +/-18V so don't go overboard

[MartyMart]

You could build it "exact" as far as the LED's, then try doubling them ( 2x in series each way )
this will "clip" much later and give you a volume lift too.
12v with Vb at 6v will get you some "clean headroom" maybe "tripple" the LED's in this case ?

The tone stack is at the "end" of the circuit ( I have Mike's schematic ) so
perhaps just use a simple BMPI stack there ( one knob 2x caps 2x resistors )
Use a final extra TL071 ( single opamp ) as a buffer at the end, for slight gain
recovery after the Eq section .... BINGO, should sound great !

Be aware though, as Mike said, the tone stack at "12 o'clock" is still having an effect
due to all those components and "ground" taps ....

MM

[Hardtailed]

Try it and see, just don't do anything you can't reverse.
Consider the fact that:
-tonestacks almost always change response (slightly) even when set flat
-a Guv'nor without the tonestack and without clipping is far from a Guv'nor. Its a clean booster with a hipass filter.
You might want to investigate the several clean boosters out there.

Hey, you're the guy who drew the schematic I'm using

I tried a microamp with my setup (Les Paul + Marshall, what else?) and it sounded like sh*t. Too much bass before clipping, the tone was muddy as hell. I've experimented with various "mid-boosters" (really: ODs with gain at almost zero) and the only one that gives me what I want (the sound of my amp, but with more gain) is the original Guv'nor. It really sounds like adding a gain stage to my amp. But I'd still want the additionnal clipping to happen in the amp than the pedal (tube vs LEDs...).

However, I just realized that, removing the LEDs, although it would give me more output (by not shunting to ground everything above or beloe +/- 1.6V) would also remove some bite because clipping introduces additionnal harmonics. I would need to modify the tone stack to bleed off less high-frequency content. This is getting a bit out of the scope of this project since I'm not doing it for fun, but rather because I need this pedal and my original one is getting too old for stage use.

I think I'm gonna start by building the stock circuit, using GGG's printed board (already ordered). But I'm ordering various opamps to try out (including the expensive Burr Brown OPA2604) and I'll probably be using 25K pots for the tone pots (been doing some searching on this board and this seems to be a popular mod, I guess it gives more range to the controls). Once everything is working, I'll probably do some experimenting with the LEDs and tone stack.

Any thoughts?

OPA2604

Thanks a lot for the help so far!

[DuncanM]

Looking at the schematic, if you lose the clipping diodes you'll get more output but it probably won't sound like a Guv'nor anymore.
If you keep the diodes and up the supply voltage you won't improve things as the diodes will still limit the level before the tonestack to 2V peak to peak.
If you lose the tonestack you will get more output but the tonality might change somewhat but the Guv'nor character will remain.
Doubling up the LEDs is worth a try and might suit you - depending how much gain you normally dial in...

My choice would be to add an output stage after the tonestack to up the level - a single transistor/FET stage should do the job - or stick a clean booster pedal of your choice in the effects loop (Minibooster,Sparkle Boost, Mosfet booster etc.).

[syndromet]

I have a Danelectro Daddy-O, and from what I can tell it is pretty simular to the Guv'nor. I changed my IC to a lm358, and changed the clipping leds for a 1N34a and a 1N4148. That took away the fuzzy sound of my pedal and turned the pedal into a more bluesy pedal. I like it a lot more now.

Don't know if this will help you at all, but it's a very tweakable circuit.

[Bucksears]

Does everyone else have that issue with the Guv'nor that it doesn't have a low-gain clipping sound, it only clips when going into higher gain? Not a 'gated' sounding distortion, it's just a little dark until you crank the gain and it starts clipping; sounds great at that point, but I'd love to hear a lower gain sound out of it.

[Gus]

Over the years things like this come up

There is a lot going on that you need to think about for a mod like this

there is the gain range of the op amps before clipping then there is the output stage current sink source and recovery from clipping when the LEDs are conducting.  The LED current is limited by the 1K , 8V-1.7V lets make it 6V means about 3ma peak current in the leds,  Now the opamp is driving its feedback network and all of a sudden with a greater input to the gain stages the leds conduct the output stage then has to supply <= 3ma more current,  Depending on the opamp this might make a tone difference with the opamp and battery used

There is the way the LEDs clip.  I am not sure but I think new red LEDs could be a different semiconductor materal than the ones used when the petal was first made(R.G. etc?) and might have different voltage and clipping how "fast" the diode turns on. Think Ge with the soft curve and Si with the more rapid turn on
From a digikey cat #T051 page 1526 some panasonic LED numbers for VF(V)
            Red led GaP      2.03V to 2.6V
another Red led GaAlAs 1.72V to 2.5V
another Red led InGaAlP 1.92V to 2.5V
and there are more.

then there is the clean signal "headroom" before the diode starts to clip so it is not just "stacking" diodes for more turn on voltage for a higher clipping level the sound could change even if the vol are reset to match after the clipping stage

max output is set by the leds 1.7V is a good first guess for an older red led so a max of about 3.4V P to P after the LEDs and then the loss in the passive tone volume network

All that said and there is more

Two things about keeping the tone and increasing the drive

One you could place say a CLEAN X2 gain stage after it

Two read the section in GEOFEX about the TS output buffer you might want a low Z output or maybe even a higher Z output to drive or not drive the grid of the first tube positive if possable(dedends on the tube amp first stage circuit) This will dictate what type of gain stage you would want.  A standard X2 opamp circuit will most likely give you a low Z output, you can add a series R to the output
but you can design a BJT or FET gain stage to have an output Z that you might want if that is part of the sound.

R.G. Mark. John. GFR. Aron etc..... what do you think

[Hardtailed]

This ain't making my life easier... but I realize it's important to understand all these things! So all the input is greatly appreciated.

You did scare me a bit though, as I didn't realize the importance of the LEDs used. I ordered the part from Small Bear and just picked up whatever 3mm red LEDs they carried. Anyway, not a huge problem, LEDs are cheap so I can experiment easily.

I also ordered only film capacitors in place of ceramics (save for the one electrolytic 10uF one), wonder how that will change the tone. Again, ceramics can be obtained cheaply if I don't like it.

As for opamps, of course I ordered a TL072 since that's what was in the original (visual confirmation!), I also ordred a JRC4558 for kicks and a OPA2604, which I hope will be the best sounding since it is dramatically more expensive than the other ones.

I am very grateful for all the suggestions. Since I am using the PCB from GGG, I can't modify the basic layout much. However, the output buffer/booster idea could be implemented with some sort of a "piggy back" circuit. I ordered the "C-sized" enclosure so I could put the PCB vertically, that should allow more than enough room to add stuff to it if need be.

[Gus]

I did not mean to scare.  You posted you liked your Guv'nor!  I was just trying to make the point you might want to build the replacement as close to what you have at first.

  LEDS.  What I would do is measure the leds in your Guv'nor! with the diode function of a DMM, then measure what you have and pick close to what is in the stock one.   I would care more about turn on voltage that you read on the DMM.

Sometimes IMO it is the mix of parts and how they interact that sometimes gives an effect it sound.  Thats why I posted the stuff I did.

Jack and R.G. and other have posted about opamp recovery in the past.

To start I would use the stock opamp.  Then change and add things to get the volume up, maybe it won't sound the same maybe better maybe not.

Have Fun

[wampcat1]

Here is what I would do.
Buy a Daddy-o (danelectro), there are a few changes to make to make it nearly identical to the guv'nor.
Here is the image, I can send you a pic of the circuitboard after the changes if you'd like - it involves cutting a few traces.
http://aronnelson.com/gallery/Brian-Wampler-Indyguitarist/daddy_o_guvnor_mod?full=1


Thanks,
Brian

[javacody]

wampcat, I'd be interested in those photos, please.