Modified Pharaoh

[traktop]

No problem. I was just about rewiring it, but I will start with the input first.
In the mean time, I started my first 1590a build, (naga viper).
Thank you so much.

[rocket88]

Think I found the issue. Since the effect is a big muff, right now there is NO fixed resistor at the input setting the impedance going into the first stage. So, what we need to do is add one and change the nature of the pregain pot, because right now it's wired so that it varies the input resistor, not acting as a pregain control.

What I want you to do is attach a 39k resistor to the spot where the pregain is attached to the board, and attach the input to the other end. This is the value in the russian muffs, and may fix the issues. I'm looking over everything else now too and see what other issues there could be. If this fixes it all, we can easily add the pregain pot, but I want to make sure we get this up and running first without it.

I reached out to the guy that built it and verified if, but he hasn't gotten back to me yet. I want to know of he made any changes to get it to work, since all he did was send me an email saying verified.....

[traktop]

I ommited the pregain pot, but it had the same issue, so tomorrow will try it.
Ok, so you want me to add a 39k resistor to the wiper, which goes to the board input, and the "to effect" lead coming fron the 3dpt switch to lug 3, don´t you? I´m asking you this because your layout do exactly the opposite wiring, (lug 3 to board input and lug 3 to the stomp switch).
Or maybe just omit the pot, and wire "to effect" lead to a 39k resistor and then to the board...
Cheers, Gilberto.

[rocket88]

omit the pot for now completely. you'll take your input wire that went to the pot and connect a 39k resistor to the wire, and connect the other end of the resistor to the board that has the wire that went to the pregain pot.

[traktop]

Ok, I will let you now my results
Cheers.

[traktop]

I finally ommited the switch and tried with the 39k resistor, but it behaves the same as if 500k pot was almost at minimum.
I think there must be something wrong on the path before the clipping stage, since the effect with no clipping is quite a mess, (very low volume and sounds like if someone threw a thick carpet over the cabinet). The clipped signal is stronger and clearer, but it sounds like if it lacks something.
The oscillation is gone when plugged into my pedal board. It happened the same with my new nagaviper built, (oscillation when plugged straight with no buffered pedal in front or after, but no oscillation into my pedal board, don´t know why...)
Since the clipping stage is quite at the end of the circuit, I´m going to measure all the components before. What do you think about the transistor measures I did with the multimeter?
Cheers, Gilberto.

[rocket88]

ok, i looked over the board and it looks fine, the voltages look good too, that leaves that the problem is with the switch wiring for the clipping diodes. something has to be a miss. i'm taking another look at it and going to figure out what the issue is, because once we get this ironed out, it should be fine for anyone to build.

oddly enough the guy that said he verified it hasn't gotten back to me, so it's down to you and me figuring this out, and we will.

[traktop]

I used a dp6t lorlin switch. I threw a lead from linked 1&2 high pot lugs to 1 switch pole, then connected each daughterboard row lead to their respectives switch terminals. Finally I connected the upper daughterboard row to what it seemed to be Db1¿ D61¿, (anyway, what was called Sw2 in the old pharaoh layout).
May be I should just disconnect the lorlin and try a simple configuration with a couple of diodes wired to a dpdt switch, (on-on), to see how the clipping section behaves with and without diodes.
There are two more 1n914 diodes involved, (d13-d14). May be I should check them too...

[rocket88]

hmmm, i'm not sure about that company's switch as i made the layout for the alpha 6 position 2 pole rotary switch. when you look at the bottom it should basically be like this.



but there's a little difference between the vero and in the diagram above. we are using the daughterboard to hold our switches rather then putting them directly on the switch. so, with that in mind we are making the connection to the board and all the diodes with the top row of the daughterboard (DB1), and each diode set is connected to the switch at its own row to 1-6(SW1-SW6) on the switch. the second connection to the board is made directly to highs 1 & 2 through pole A on the switch.

[traktop]

The switch Im using is exactly the same like your drawing, using just one pole and the 6 lugs that connect with it on each of the 6 clicks, (the other pole and the rest of the lugs remained unused).  I wired it like you. I just connected the pole used on the switch, (upper blue arrow on your drawing), straight to 1&2 lugs of the high pot, (not straight to the board). There is also a lead coming from the apropiatre point on the main board, (from Q3 collector), to 1&2 high pot lugs of course, (so the switch pole would remain connected through that lead to the board as well...)

I just did what I told you one post above, but simpler: omit any kind of switch and just connect a lead from lugs 1&2 of the high pot to the main board point where Db1 should be connected, (the point that goes straight to the 470n cap). That way I could hear the pedal sound with no clipping at all, (it would be like if I would be using diodes 11 and 12, which are just jumpers). So the result is that the unclipped sound remains being quite low in volume and without  any kind of treble. I dont know, but something tells me that  maybe there is something wrong with the tone or the highs pot, (not the pots wiring, since I checked it and they are properly  connected).

[traktop]

Wait, there is something wrong with 250k tone pot. I took it out and measured it with a multimeter while giving a run to the pot. It stops reading on one portion near to the end, but it comes back before finishing the run. Strange, because I get plenty of highs and volume with the diodes, not with unclipped signal though...
I think Ive got a 100k B and 2 x 500 A/B pots, but not 250k resistors, (just 390ohms and 2.2m), but I do have plenty of caps of different values.
 Should I play with the 22/470 nf caps to get something similar to the 250k pot with a 500k pot¿
Cheers, Gilberto.

[rocket88]

that's odd. for shits and giggles swap the pot with something else, even if it's not the right value and see what happens.

[traktop]

No luck my friend. The tone pot started doing weird things yesterday, so I tried with a 500k, but the main problem is still there. I measured the other pots and they were fine. Ive got to get the main circuit going on first , so Im going to take the board apart and check component by component. I will drop a line when I got something.
Cheers, Gilberto.

[traktop]

Well, I disconnected the main board and checked all components one by one. Only the 10uf input cap measured 7.4uf, so I replaced for a 9.8 one. Replaced all transistors, (just in case), checked pots again, solders, jumpers and daughterboard...
Exactly the same... I tried excluding the clipping board, (jumper from highs 1&2 to main board Db1), with same results.
I think that you could tag it as verified, since the problem relays on the already verified pharaoh main board.
You did a similar thing like I did to my turborat, (clipping daughterboard, but this one ended full of switches  on the chassis...), so it should work.
I think the initial feedback problem wasnt because of the missing 39k resistor at the beggining, since I had the same problem with my new nagaviper build, but all problems faded away into my pedalboard.
If I feel not so depressed tomorrow night, I will give it another try...
Just out of curiosity:
How much both transistors should measure¿ (mpsa18/2n5089)

[traktop]

I mean, hfe gain.

[rocket88]

gain shouldn't matter that much. should follow the same rules as the big muff. bellow 500 increase in bass, above 500 increase in treble.

i've got another stupid idea. what if you take and make a direct connection to one of the diode sets. if it works then, we've got a switch or switching problem. i have a real pharaoh and with the jumpers it's super loud and doesn't clip as much.

[traktop]

Not a stupid idea at all, in fact I tried it, but forgot to post it, (last night was intense...). Tried going straight, (skipping the switch), and with a jumper, but no luck.
I remember my rat raising up in volume quite much with no diodes as well.
The unclipped signal had some less gain as expected, but much lower in volume and no treble at all.
I think I forgot to say that I used 2 x 2.2M pulldown resistors on the switch, but those just go to ground when switched off the effect.

[rocket88]

You shouldn't need any more pull down resistors. There's already a 1M pull down at the input if I'm not mistaken. The two 2.2M pulldowns could be the issue.

[traktop]

The notes under the layout says "2m pulldown resistor on input", and the layout has no input pulldown resistor, that´s why I soldered it on the switch. Anyway, I´m going to omit them and see what happens

[traktop]

Pull-down resistors out, but same thing. The only difference is that now it don´t oscillate without buffers after or before, so those resistors were messing with impedances too much for sure...