Paul_C's 2019 builds (having fun!)

[Paul_C]

Yes, I was aware of that - 2N2907 is what was listed on the schematic - I was just seeing what would happen, being very new to doing more than just putting a kit together.

I will return to the OK one day, hopefully with a little more knowledge from helpful people like yourself

I've ordered a breadboard along with the tester so I can tinker without soldering, and I'll add those suggestions of yours to any future experimenting.

My feeling is that learning what doesn't work is still useful to me at this stage and having my mistakes pointed out is good too, so don't be afraid to let me know

[Paul_C]

I spent a little time tinkering with my Random Number Generator this evening.

First I removed the transistors and attached sockets, then tried a few different swaps.

Swapped a 2N4401 first for a 2N5088 (more noise, fizz and mayhem) and then a 2N3904 (not as much fun as the 5088 but not awful).

I'm waiting on a few other transistors coming from China, including some low gain varieties, which I'll try too when they arrive.

I also swapped the 100K Lin vol. pot for a 10K which gives much more usable range.

[Paul_C]

I think the bug has definitely bitten - I've just sold a Count To 5 to raise funds for more builds, despite having enough parts for three pedals off my wishlist already in my pedal building box

[BetterOffShred]

Yeah dude it's lots of fun. Stockpile those parts

[Paul_C]

My build list has now jumped to six, once I've totted up what extra parts I need.

First thing I want to do though is have another go at sorting out the OK, this time on a breadboard, and I don't need to order anything for that.

[Paul_C]

I was wrong (I think) - I've put the OK back together and got it to make a noise, but not completely successfully, so it looks like I will need to order something or wait for an order which is on the way.

With a guitar plugged in and strummed, the output is at best intermittent, but mostly it's quiet and then loud and distorted (but not in a nice way, more an "I'd better not do that too often or it might break the amp" sort of way).

I swapped over various transistors with no improvement, but this may point to the source of the problem, in that the only transistor (or any component) still present from my previous attempts is one PNP 2N2907 as I'm waiting on an order from China, so I wasn't able to swap it.

I'm going to assume for now that the sensible thing to do is wait, so I can put it to one side and make a start on something new, which I think will be Parasit Studio's Parallel Universe layout.

[Dowi]

Hey Paul, just dropping here to say that lately i'm keeping an eye open on your build threads.
I've started to study (again) electronics in my free time since a month or so and next week i'm gonna receive the components to start traying some builds on breadboard, and i'm definitely gonna give a try to the first ones you approached.

[Paul_C]

Nice one !

I'm pleased I chose to start the other build thread now if it gets other people interested, especially as I'm only at the beginning of learning myself !

You've reminded me that I got a big bag of 2N2907s from China this morning so I need to try one in the OK MKIII to see if it helps

Beware though, it gets addictive pretty quickly

[BetterOffShred]

I just have one thread for all my builds

[Jero]

You've reminded me that I got a big bag of 2N2907s from China this morning so I need to try one in the OK MKIII to see if it helps

Metal can or to-92?

[Paul_C]

You've reminded me that I got a big bag of 2N2907s from China this morning so I need to try one in the OK MKIII to see if it helps

Metal can or to-92?

The first ones I bought, which may or may not have been problematic, were metal cans, the new ones are TO-92

[Paul_C]

Right, help needed

I've fitted a new 2N2907 and it's better than it was, but still not right.

The issue appears to be that, for a reason I don't yet understand (being new to this), it needs a hot signal going in to get sound to come out.

This is with the Control pot maxed out (B100k), if I turn it anti-clockwise then it's not long before it goes quiet. If I play single notes or use a lower output pickup I have to play harder or it won't make a sound. I've tried rotating the transistors out of curiosity and while the output changes it doesn't improve things.

So I'm assuming something is either not boosting the signal when it should, or strangling it when it shouldn't.

I've not got a switch in the circuit yet, just input and output jacks, and I checked the battery was ok - 9.4v

Any suggestions gratefully received.

[Paul_C]

Curiouser and curiouser - I've spent the last half an hour or so swapping transistors and got at least one surprising (and IMHO) cool result

There are three transistors in the OK layout - Q1 and Q2 are listed as MPSA18 and Q3 as 2N2907.

I started off swapping Q1 for pretty much every different transistor I had and it sounded fairly similar with a lot of them, and I still had the problem that it only really worked at all with the input control (B100k sweeping between a 100nF and a 10nF capacitor) all the way up (100nF). This was also true when the socket was empty . . .

So next up I swapped Q2 - none I tried were of any use until I stuck in an MPSA13 - BINGO!

It still doesn't work as it should but it does work as a sort of fuzzy square wave tremolo which starts off quite quickly and slows down as the note decays - I like it !

The input control also seems to have an effect across its whole sweep, which is the first time that's happened

One thing which seems to be helping it do it is a rogue MPSA18 which has an hFE of around 650 compared to all the others I have which are around 430, I tried a different MPSA18 and the effect was much less pronounced.

So I still don't have a working OK, but I do have a working circuit which is making interesting noises, so I'm going to consider that done and I'll put it in an enclosure when the Parallel Universe is finished. I've not yet decided on a name, but OK-ISH seems appropriate.

[BetterOffShred]

Mpsa13 is a Darlington.. probably like 40k hfe
I never built the OK.. wish I could help.. if it only works swept one way on the cap blend you may have a bad cap. Maybe pull them both and install new

[Paul_C]

ah - so the ridiculous jump in gain explains the unexpected result

as this is my 3rd attempt the capacitors are both new and tested before they went in - the pot works with the MPSA13 in too, so if there's a list somewhere which will point out a transistor with an hFE somewhere between the MPSA18 and 13 I could try that (I have done a quick search but found no such list as yet).

I turned my other OK board into an LP layout so I can either turn it back or do some more transistor swapping and see what noises it makes

I'm also tempted to return to my RNG and see what else is possible from it - it does the fuzz and some extra notes but mostly just octaves, so it's worth experimenting with.

I'm not totally bothered about getting a working OK as what I've got is fun too, in its own way