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The schematic for the mf104 is floating around online. It's something like 12 pages long. You could probably DIY it but it would be a lot of work.

Only the first 2 pages are relevant, it doesn't look too bad really.

That gutshot earlier in the thread is for the 105 or 108.

(mod edit) link since it's not loading: http://www.analoguediehard.com/studio/effects/moog_moogerfoogers/moog_mf-gutz.jpg

Unfortunately the MF Drive schematic isn't on that page. I haven't had any luck finding that one, but would be very interested in checking it out.

I haven't verified this yet but I started a thread @ FSB that has the boards and the traces outlined.  Here is the schematic I came up with and the link to the thread.

https://www.freestompboxes.org/viewtopic.php?t=31250

Oh sweet, I was curious what was kicking around in that line, nice piece of design work for the price.

Nicely done

I thought you were going to break in to a musical number.

Aentons has already given you the answer, Delay time range "3.2 - 8.5mS", 1024 stages / 2 x clock frequency = 160-60kHz.

Got Pfizered about 90 minutes ago, can't really lift my arm, my back aches and I feel a little out of it and I couldn't be happier.

I got the 'derna, and had the same thing with the arm. It felt super heavy for half a day. Then a little malaise and all good.

It wasn't heavy as such (apart from maybe the first six hours when I was still a bit dazed) just any movement 'the wrong way' felt like tearing every muscle in it, nearly back to normal this morning though... unless I poke it.

A day and a half with only one arm working and sleeping on my right side was worth a little avoiding a potentially horrible death.

I did get some further effects (although as forum age goes, I'm on the lower end which seems to impact reaction severity) the Saturday gave me a very bad 2 hour dizzy spell and some minor heart fluttering through Monday and then a 103/72 blood pressure drop on the one week anniversary, which took it out of me for a couple of days, but totally back to normal now and I've just done several days strenuous work.

A friend of my mum's, son, apparently had heart fluttering too and was understandably quite panicked so a potential side effect to be aware of, although I feel I should say, be sure to follow up with your medical practitioner.

I may not be active here any more but I do still lurk and this one is bugging me.

R9 and R48 can't just be trimmed, they're part of the de-emphasis network and set the cut off of that low pass filter with the 33n, they counteract the pre-emphasis set by the input op amp and are part of the filtering.

If you want to increase the output level, you need to either equally reduce the value of R6,7,8 & 33. Simulation tells me the frequency response isn't flat in this, but you can try about 6k8. Technically you may need to increase C3 to about 1.5uF and C27 to 470nF to keep bass the same doing that but... probably not that noticeable.

Or, make R48 - 33k, R9 - 6k2 and C4 - 18n, not exactly identical cut-offs but close enough, you'd need to tweak the aforementioned resistors up or down to tweak it further, or there's a hair of extra gain to be had by reducing R10 to 470R.

And with that, I'll leave you all to it.

Got Pfizered about 90 minutes ago, can't really lift my arm, my back aches and I feel a little out of it and I couldn't be happier.

I got the 'derna, and had the same thing with the arm. It felt super heavy for half a day. Then a little malaise and all good.

It wasn't heavy as such (apart from maybe the first six hours when I was still a bit dazed) just any movement 'the wrong way' felt like tearing every muscle in it, nearly back to normal this morning though... unless I poke it.

A day and a half with only one arm working and sleeping on my right side was worth a little avoiding a potentially horrible death.

Got Pfizered about 90 minutes ago, can't really lift my arm, my back aches and I feel a little out of it and I couldn't be happier.

Here are approximate voltages from Haberdashers build;
IC1
1 4.5v
2 4.5v
3 4.5v
4 0
5 4.5v
6 4.5v
7 5v
8 8.5v

IC2
1 4.5v
2 4.5v
3 4.5v
4 0
5 4.5v
6 4.5v
7 5v
8 8.5v

IC3
1 4.5v
2 4.5v
3 4.5v
4 0
5 4.5v
6 4.5v
7 4.5v
8 8.5v

IC4
1 4.5v
2 4.5v
3 4.5v
4 0
5 4.5v
6 4.5v
7 4.5v
8 8.5v

IC5
1 6v
2 4.6v
3 6v
4 4.5v
5 6v
6 4.5v
7 6v
8 4.5v
9 6v
10 4.5v
11 6v
12 4.5v
13 0
14 6v
15 4.5v
16 6v

IC6 - This chip is LFO so voltages will be shifting around a lot, but you should be getting around 8.5v on pin 4 and pin 11 will be ground.
1 3.3v
2 4.4v
3 4.9v
4 8.5v
5 4.2v
6 4.2v
7 5v
8 4v
9 4.4v
10 4.4v
11 0v
12 4.7v
13 4.2v
14 7.2v

In relative terms, I can't see anything amiss with yours... the fact it did work then didn't says to me either a bad solder joint or the 4009 must have blown so I guess, re-flow the board and if that doesn't work, swap the chip out.

Can you post your voltages?

The 4009 is static sensitive, possible it got a zap and then crapped out.

...

The signal always passes through a pre/de-emphasis network, while they're supposed to be neutral, they pretty much always audibly impact tone, so that could be what you're hearing?

The signal has to pass through IC2 pin 7 to reach the BBD's and the output of the BBD's is pin 7&8, if your audio probe is definitely working and there's not something weird going on, you can't possibly have any modulation.

Could a bad cap on the compander be the cause? Possibly... I mentioned Tayda tantalum capacitors because last time I tried to use one for digital power filtering it ended up injecting noise rather than removing it and I've avoided them since, I've also heard of their electro's simply being shorts.

Signal comes from IC1 pin 7, goes in to the companders input at pin 6, comes out at pin 7.

If you don't have a scope, just audio probe pin 7 & 8 of each BBD while adjusting its bias.

I don't have a scope but I think I've got it dialed in real close.

However, what does it mean when I get zero sound out of pins 7 and 8 of the BBD's, IC's 3 & 9?

That they're not passing signal and you have no effect... when working, you should hear clean undistorted vibrato on each chip there.

Pin 4 & R3.

I assume you want a split supply for more headroom?

The J-FET is biased off centre through that divider to get more signal swing @9V, but if you're feeding it a split supply, it's probably unnecessary and the 3M3 can indeed just go to ground.