Mockman build report

[msb69]

I built the Mockman pedal with the stock components, and without the optional LEDs.  The pedal seems overly bright, so I'm planning some mods.

First, I'm going to insert bigger caps in each of the feedback loops.

Second, I'm going to replace the two 470k feedback loop resistors with a dual-ganged 500k pot, so I can adjust them on the fly.

msb69

[WGTP]

http://aronnelson.com/gallery/WGTP/AlteredMuff?full=1

Here are some mods based on Gus Smalley's original mods and some other stuff that was floating around here, if you interested.  I like this design a lot.   

[Dr Ron]

I'm in the middle of a Mockman build and am waiting for 100pF caps.

I've thought about adding a tone control.
That would most likely involve adding a fet or transistor output stage, such as in the 808 or Rat.

[msb69]

Here are some more updates on mine.  After lots of tweaking, I've got the unit sounding just the way I want.  Here are the tweaks I did from the original specs:

1. Used a DPDT toggle switch to select between 2 different input caps -- .01 uF and .047 uF

2. Placed a 470 pf cap in feedback loop 1

3. Placed a 270 pf cap in feedback loop 2

4. Replaced the cap in between the gain stages with a DPDT on-off-on toggle switch.  In the "off" position, just a .01 uF cap is operating.  In one of the "on" positions, I have a .047 uF cap.  In the other I have a 0.1 uF cap.  Thus, I can select between .01 uF, .057 uF, and 0.11 uF -- the higher the cap value, the higher the gain in the pedal (and the more brightly the two clipping LEDs light!).

5. A unorthodox mod:  I placed a .022 uF cap between lugs 2 and 1 of the output volume knob.  This was the only way I could get rid of the excessive high end in the pedal.  (I tried increasing the .01 output cap, but that just added more bass without cutting treble.)  The only odd behavior I get with this mod is that, when the 0.11 uF cap is selected in between gain stages, you cannot max out the output volume -- it causes the sound to shut off completely.  It's not big deal, as I have no need to dime the output volume.  The pedal is already plenty loud.

I've named the pedal the "NASAL DRIVE".

msb69

[jmusser]

That's what I find when I built it, that it was way to bright, but I do like it's crunch very much. I'll eventually get in there and change the cap values to darken it up some. It's a good meaty distortion pedal.

[Dr Ron]

I just finished my build, and it is very bright.
I haven't tried any of the mods you suggest ... thanks btw!

This is frustrating - you'd think they'd have put up some usable schematics and Runoffgroove.
Next time I'll stick to something more finished - mb an 808 or the supa nova at GGG.

I was considering putting in a switch for the LEDs.
Do they make a big difference?

I'm also wondering if a tone control is really needed here.
Did your mods really tune a cool tone (i.e. so the tone control isn't necessary)?

The next issue is to find out why my on/off LED isn't working.
I used a 1N4148 Signal Diode with a 5.1K resistor. Perhaps a lower value resistor.

[msb69]

I was considering putting in a switch for the LEDs.
Do they make a big difference?

I'm also wondering if a tone control is really needed here.
Did your mods really tune a cool tone (i.e. so the tone control isn't necessary)?

The LEDs increase the clipping from the pedal, and give it more gusto.  It woould be cool if you could use a switch to go from LEDs to standard diodes.

For my tastes, the mods I have done have eliminated the need for a tone control.  However, I tend to use bright amps (Vox AC30), so my pedal is voiced a little dark.  The biggest influence I have found on the pedal's tone is the cap in between gain stages -- it's critical.

msb69

[WGTP]

There should be several ways to reduce the highs.  Increase the cap size in the feedback loop.  Try doubling or quadrupling it.

Also, look at the ROG amp simulations.  Several have a resistor, cap, resistor, cap at the end before the output pot.  That is another good way to roll off some highs.  My amp must be really dark, I don't have any high roll off on my distortion circuits.   

[B Tremblay]

I just finished my build, and it is very bright.
I haven't tried any of the mods you suggest ... thanks btw!

This is frustrating - you'd think they'd have put up some usable schematics and Runoffgroove.
Next time I'll stick to something more finished - mb an 808 or the supa nova at GGG.

I'm sorry to hear that you are so unhappy with the circuit's sound.  WGTP raises a good point - what amp are you using?  Would it be considered a bright amp?

[lovric]

the tone pot is ok, the treble cut sort. but it is really taken care of with msb69's cap on the vol pot. that's a one position treble-cut control.

runoff groove and its secret message is at the end of the record not in the beginning... 

[Dr Ron]

> I'm sorry to hear that you are so unhappy with the circuit's sound.  WGTP raises a good point - what amp are you using?  Would it be considered a bright amp?

I have a 70's Deluxe Reverb tube amp.
The Mockman didn't let some sounds go through, although it did seem to have a nice transparency to it.

I think it may have some issues with input and output impedance, besides being too bright.
The 10K input resistor may be the issue. It also sets the gain of the first stage.
It might also be that it has too much gain in one or both stages. There was some whistling.

One solution would be to add a transistor bufffer at the input and output (ala TS-808).
Another would be to put the LEDs in the first stage and use the second as a buffer.
Then it would be more like the Son of Screamer, but with hard clipping (and a different sound).

We could also put a pot before the 2nd stage input, which would lower the second stage gain and act as an RC filter.
With the .01 cap, I believe higher frequencies have infinite gain.

I didn't expect to have to modify the design right off the bat.
I suppose I could solder in some extra caps into the feedback loops and see how it sounds.

[WGTP]

The Mockman is similar in design to the Muff Fuzz.  It is unusual in that is uses 2 inverting op amp stages rather than the more typical non-inverting used in TS, DIST.+, etc.  The resistor (10K) at input sets the input impedance and the gain for the first stage.  10K is pretty low and is responsible for the rockmanish sound in that it rolls off highs and the cap rolls off lows.  The Muff Fuzz uses a 100K resistor at input and one of Gus Smalley's mods is to use a 220K resistor, which I prefer, giving the circuit a more amp like distortion tone.  With a 100K input resistor and 1M cap in the feedback loop of the first stage, the gain is only 10 and diodes in this loop won't clip much.

The cap and/or resistor before the 2nd stage in inportant in that i helps set the gain for the next stage.  Just using a cap with no resistor and a 470K resistor in the FBL provides a butt load of gain.  If you use a 1K resistor and a 470K resistor in the FBL the gain is 470.  That will get even LED's cooking.  I couldn't use just the .01 cap without oscillation.  Another Gus mod is to add a 10K resistor inbetween stages. 

Most of the distortions around here will need to be taylored to your rig if no tone control is included, that is the whole point of tweaking.   The PV in my lab is dark and I stuggle to get enough treble with some circuits. 

[B Tremblay]

I didn't expect to have to modify the design right off the bat.

Well, that's why breadboarding a circuit is the best approach.  With the circuit on the breadboard, you can determine whether it will meed your needs in its stock form, or if it will need to be altered to match your rig.  After reading the list of mods you suggested, it seems that re-designing it to your taste will be no challenge for you.

[jmusser]

The circuit is pretty bright sounding but I like it a lot. it's definitely one of the cruchiest pedals I've built. My tube amp is horribly bright to start with, so it's not a good choice for me to play this circuit through. I can darken it through my SS amp, and the added brightness of the circuit I feel gives it a nice bite.

[msb69]

Wow -- I sure feel lucky that I found some combinations of mods that work for me.  It seems like there are a million things one could try! 

For those of you looking to reduce the brightness, I highly recommend all the mods I did.  I had taken my earlier (mostly stock) version of this pedal to a local shop to get some opinions on the tone.  Generally folks thought it was pretty cool.  But when I brought my current version in for a listen, it was clear I had done something right!

msb69

[Dr Ron]

I think that I'd like to add a tone control, rather than tuning it specifically for my amp.
(Actually, this is meant to be a gift for a friend, and I don't know what amp he has).
I've reviewed several effects, and it doesn't look as though an output buffer is necessary.

I was thinking of a Big Muff Pi circuit.
The components are: 100K pot, 100K and 39K resistors, .01 and .004 uF caps.
I'd love some comments before building it.

Brian, sorry for complaining about your design. Although I do have a ton of EE knowledge,
I have to order almost every part.

On the other hand, I've learned a lot about designing and modifying effects!

[WGTP]

http://www.generalguitargadgets.com/diagrams/gus_muff_mod2.jpg

There you go.  Just change the part values to the stock BMP, or whatever you like.

[Dr Ron]

I installed the optional LEDs and the pedal is now usable.
I think they are necessary, perhaps because the of the high gain.