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Which charge pump does it have in it?

Here are my measured Fv on a bunch of Russian diodes from my stash:

D9B: ~.27
D9V: ~.27
D9E: ~.27 (seeing a pattern?)
D9J: ~.32 (woops)
D9K: ~.32 (oh, ok)
D2i (I think? smaller grey-body diode from the 80s): .32V
D2V: .2V, but these aren't practical for pedals anyway
D312A: ~.25V
KD522B (silicon): .55V (lower than 1N914)

I think I might have more ... Anyway, almost all the Russian detector diodes are indistinguishable for our purposes. Most of them didn't even measure different resistances across them. You can just get whatever's cheapest, but none are an actual substitute for a 1N34A if you really need the slightly higher forward voltage.

Very useful info. Thanks!

I finally got a chance to put this on the breadboard and test it out. I had simulated it in LTSpice to do some quick testing and get an idea of how far it could be pushed first, and the bread board results are pretty consistent with the simulation.

The first thing to note is that if you are using 1n4148 type diodes for the clippers, then whatever version of the Big Muff circuit you are using is close to irrelevant for this test because the clippers alone pretty much set the level going into the final amplifier stage. If you were to do different diodes, then you could end up overdriving the output stage depending on what you did use. Given that, I put what's close to a Violet Ram's Head version on the breadboard. I had a slightly modded first gain stage but not by a whole lot.  I used BC550C transistors for this test. With the VRH values in the final amplifier (resistors of 100k, 390k, 2.7k, and 10k) at 9V I get about a 2V peak-to-peak swing on the output of the amplifier (before the volume pot). If I move that to 18V with the same values for the resistors, it'll move up to about 2.2V peak-to-peak on the output swing. There is a slight change in tone probably from increased headroom in the initial amplifier stage.

I then changed the output amplifier to use 68k, 680k, 2.2k, and 30k resistors. This should be a big increase in the output level. At 9V, the output level is about a 4V peak-to-peak swing with maybe a touch of distortion added in the output amplifier. With the same resistors at 18V, it gets a bit more than a 6V peak-to-peak swing on the output with no added distortion in the output wave shape.

If you were to move the collector resistor down to 27k from the 30k, you could probably do it at 9V without much change in the tone of the pedal and still get a good boost in volume. If that's not enough, pushing it to 18V with the 30k and the 2.2k does give a pretty good increase in output level

I've got some D9B diodes that I've been using and they sound good to me as clippers. I've used them for hard clipping and for inline crossover distortion and they worked well in both settings. I can't compare them against any of the other D9x types though since I don't have any others yet.

Tayda 1n34a diodes come with a warning. Many here have had dud batches of them from there. I've had batches where about 5% of them were bad. They do also seem fairly fragile to me compared to other Ge diodes I've got. Those I have that work and measure within spec sound fine though.

I missed the pin counting too. Those readings do make more sense now.

The 1n5817 is for polarity protection. Get a measurement of the voltage drop across the 1n5817 and across R12.

The JRC4558 latching up in the circuit got me intrigued, so I set up my breadboard with one op-amp of the dual with the input at half supply using two 10k resistors and the other half with the input connected to ground. I grabbed a handful of op amps out of the bag popped in there and took the measurements of the output voltages and the total current draw. I then moved the grounded input to half supply using two 100k resistors and took the current measurement again. The table below shows the results.

The NE5532 really doesn't like its input at ground in a single-supply setting. It oscillates and draws a bunch of extra current. The OPA2134 and OPA2604 are either oscillating or on the verge of it. The TLE2072, TL072, LM833, TL062, NJM4558, MC33078, NJM2082, and NJM4580 all latch up, but they don't seem to draw any extra current because of it. The LM1458 is weird sitting at about 2.0V and maybe oscillating but it still draws on the low end of the current. The LM358 handles the voltage really well and has a low current draw, but it might sound like crap. The TLV2372 is similar but it's optimized for really low voltage power rails and not really aimed at audio at this power supply voltages. It could sound good here though. The TS912 and TS922 look good as they always do and might be a good choice. The TLC272 and TLC2272 both did really well and would be good to look at if you were set on using a FET input op amp. The one that was kinda surprising to me was the NJM2904. It didn't latch up at all and used very little current. It'd probably sound pretty good in there.

If I were going to build a new one, I'd try the TS912. They've sounded really good everywhere I've tried them and their performance in the latch up test here was perfect. Too bad they've EOLed the PTH versions.


OPA       GND(V)     Half(V) Current(mA) Current with both at half supply (mA)
LM358   0      4.5      0.6      0.5
LM358   0      4.5      0.6      0.6
LM1458   1.97      4.5      0.87      0.8
TLV2372   0      4.5      0.9      1.2
JRC2082   8.9      4.5      2.9      4.1
OPA2134   0.137   4.5      8.7      8.1
OPA2134   ~0.220   4.5      8.6      8.2
TL072   8.46      4.5      2.8      3.3
TL072   8.46      4.5      2.7      3.2
TS912   0.035   4.5      0.5      0.6
TS922   0.021   4.5      2.4      2.2
LM833   8.48      4.5      2.5      3.9
LM833   8.48      4.5      2.7      3.9
NE5532   ~ 1.135   4.5      ~ 18.0   6.3
NE5532   ~ 1.135   4.5      ~ 21.0   6.2
TLE2072   8.33      4.5      2.7      3.1
TLC272   0      4.5      0.8      1.4
TLC2272   0      4.5      1.6      2.2
MC33078   8.41      4.5      2.6      3.3
JRC4580   8.48      4.5      3.1      4.7
JRC4558D   8.5      4.5      2.4      3.5
JRC4558D   8.5      4.5      2.4      3.5
TL062   8.47      4.5      0.2      0.3
JRC2904   0      4.5      0.7      0.7
OPA2604   ~1.0      4.5      9.4      10.0

First thing to note is that mine is the older 2012 version so it doesn't have the power supply filtering resistor or extra cap and the polarity protection is the crowbar type. None of that should really matter and I stuck a 10Ω resistor in front of the power supply input to the PCB so I could check the current draw, so that's more the same now.

Here's my voltages:
Power Supply 9.05V
JRC4558
1  4.97V
2  4.97V
3  4.87V
4  Gnd
5  Gnd
6  8.48V
7  8.48V
8  9.02V

So, so much for my saying I hadn't seen the JRC4558 latch up this way. The one on my board is actually latched up. But given that, it is stable and not oscillating and the total current draw of the board is still only sitting at about 2.7mA. So, it isn't causing any issues. That could be different with other op amps though. For example, I've seen an NE5532 draw a ton of current on the breadboard when it latched up.

Your voltages are correct -- for a battery that's only putting out 5.93v. Use a fresh battery or a power supply and take voltages again.

Jon brings up a good point.  If you were using a battery when you blew through R12, you may have significantly depleted the battery before the resistor fried...although I'm not sure if a 9V battery would provide more current than a 1/4W resistor could handle.

Jon, would he see any voltage on pins 5-7?  That op amp is grounded and unused.  (Sure, I could breadboard it, but I'll bet good money you've built this one.  )

Pin 8 should be seeing close to the supply voltage and not 0V. Pins 6&7 could actually be at something other than ground even though pin 5 is at ground. Some types of op-amps will latch up in a single supply setting with the input at ground. For those op-amps, it's best to set the input pin of an unused section at half supply. I haven't seen it be a problem with a 4558 and I haven't tried it with an OPA2604, but if it did latch up, that could explain the high current draw. Put still, I'd think that pin 5 should still be at ground.

If you aren't using a battery, it could be that you've got a short or stray connection somewhere that's drawing a lot of current and causing your supply to sag.

I did some messing around with this circuit some time ago and to me, op-amps with bipolar inputs worked better than FET input op-amps. I didn't try an OPA2604 at the time, but I did test an OPA2134. In the end, I went with the 4558 and didn't even bother to socket it.

I'll pull out the board and take some voltage measurements.

That's basically the idea, although you can alter the gain of the amplifier stage by either raising the collector resistor or lowering the emitter resistor or both. You may need to alter the bias resistors depending on what happens with the other two resistors. You may not need to move to 18V at all. It depends on how much extra gain you need.

I don't have a Kingslayer or an Ultrastoner build of a Big Muff, so I can't compare directly. I can make a pretty good guess of where the volume level of the Ultrastoner should be based on the muffs I do have and comparing the output stage values.

Maybe we can figure out how much more gain you need from the final amplifier stage this way -- where do you set the volume level of the Kingslayer normally and how far do you have to turn it down to bring it down to the level of the Ultrastoner?

You could mod the thing to go off of 18V too. The final stage could then be made to have a ton of gain with no added distortion.

I would be interested in doing this, but wouldn't know how to go about doing it.
...

It wouldn't take much to do it. If the caps you have in there are rated at 25V or more, they'll all be OK. If you had any 16V caps in, especially in the power section, they'd need to be changed.

If the circuit you are using has a power filtering resistor in it, you need to make sure that it can handle the power across it, but the current draw is small enough that it shouldn't be a problem with any of the circuits I've seen.

The first gain stage is probably going to be a bit cleaner, but that shouldn't really be a problem. The middle two clipping stages aren't going to need any changes really since everything there is pretty much limited by the diodes. If you've got a mod in place to toggle out any of the diode sets, then it could get cleaner and louder here because the clipping from the transistor will be reduced.

The only real modification needed is in the output amplifier, and even here it'll work without any mods. But, you would want to mod this section because the whole point would be to allow this section to have more clean gain. The tone control section attenuates the volume quite a bit, so the final amplifier is where you get most of the volume. At 18V, you can get a bunch of gain out of this amplifier. The only changes needed are in the resistor values. What you want to use depends on how much gain you need. It isn't hard to figure out though.

I just put 18V on a couple of my Big Muff builds. It works fine. One of them has settings that can remove both sets of clipping diodes. This gets loud at 18V! I've been wanting to test a tone control mod, so I might have a go at putting this on the breadboard and take a look at what happens with the 18V mod while I'm at it. I'll let you know if I get a chance to do it any time soon.

The problem is not with gain or volume in the US. It is with matching its level with the high output level of my other pedals. I run into a SHO, then into a Kingslayer, which gives a high combined output signal (and sounds awesome). The US sounds best (to me) alone, but can't get close to the output of those two pedals combined. So, I'm wondering how to get the level of the US up to match the others, not to unity with my guitar signal. I use either my SHO/KS tone, or my US tone, but need the US tone boosted. The problem there is the US doesn't sound as good (to me) with a boost.
Does that make sense?
Is there a super transparent boost that might work with it?

Try modding the output amplifier resisters. The gain of the amp is pretty much given by -R_c/R_e. If you look at the charts with various Muff parts list, you'll see that there are other variants that have higher output gain. You can use one of these as a starting point. If that still doesn't get you enough volume, you can change the output to an even higher gain. The bias resistors on the base may also need to be changed. Look at the matching set in the parts list for the one you use.

You could mod the thing to go off of 18V too. The final stage could then be made to have a ton of gain with no added distortion.

You can increase the output boost level of the Muff circuit by changing the resistors in the final amplifier stage. These are R22 and R23 in the Mudbunny schematic. You also need to alter the bias resisters if you go very far from the values that are currently there for R22 and R23. The various other Muff circuits can give you some hints as to what will work. You could actually push for more boost than even any of the normal circuits have if you want to. You could move to 18V and really put some gain out of the final stage.

The Muff's do usually have quite a bit of gain though. I've got one where I use Ge diodes and it still has well past unity on the output and I use pretty hot pickups. So, check that everything is working as it should be before you look into altering the circuit.
 

They all look to be coupling caps to me. It looks like all the frequency critical stuff is handled by other caps. I'd try it with 4.7µF or 10µF caps in those locations.

I finally got to do the mods to my Harbinger. So these are the results.

Moving to 4.7k for R46 does seem to help to me. I think it helped in being able to dial the gain into a better setting.

I put R41 and R44 at 1k. I did this because I can use the CV control section to put the minimum resistance where I want it to be. But, I did try it with the normal 100kC pot in there first. 1K is too small. It gets too fast for the lamp to even respond and then going further CW just locks up the LFO. I'd guess that a 2.7k resistor for these two would be about as fast as you'd want it to go. With the CV controlled board in there, I have the smallest resistance at about 3.3k and that goes plenty fast for what I want.

The depth and strength of the vibe or chorus stayed good and strong up to the point where the lamp really couldn't respond fast enough, so it should be fine to reduce those two resistors to get a faster LFO going.

Congrats on getting it working! Now for the fun of playing with it.

I'm surprised the EHX power supply had that much hum even with all the filtering on the 18V filter board. That's pretty nuts really.