4007 Chopper-Trem (who needs another trem design?)

[anotherjim]

Putting Duck's Rowdy deviant version together on the breadboard.

First, got the PSO running first strike. Getting 2.6 to 8 Hz range. Hot-diggity-dog! Yeeeehaaaaaa!
Paul can feel smug about the lower supply making it possible.

Next, the pre-amp. Looks clean on scope.

Next, next -  I haven't done the next yet. TBC...

[duck_arse]

what brand 4007 is that, how old is it, and how many volts percolation at the fast end? your f range matches one of my maxx mojo aged stock motorolas.

rowdy deviant?

[anotherjim]

4v p-p low end. 3.6v top end.
Probably Phillips HEF, but I'll check later.
Got an ancient National somewhere.

[anotherjim]

The ancient one is dead.

Rest I got are middle-aged Philips. 2002 if I read it right.

I don't have any C antilog for the speed, so I'll see if there's a linear with resistor alternative - maybe 1M pot with 270k on the wiper. Otherwise all the faster speed range is at one end of travel.

Circuit now complete less LED's. It's all good to me. I'm not hearing any nasty distortion.

Deviant  - as in it deviates from the original design.

[PRR]

> I don't have any C antilog for the speed

Wire log/audio pot backward and turn it backward. Same as reverse log after you train your fingers to go the wrong way. Get-by until your next pot order.

There is no resistor hack for most speed-pot applications.

[anotherjim]

Yes, I can probably only make a log with the hack. I'm ok with backward - was thinking if I can get a better response than a backward stock log  without a special order. Should have been clearer - sorry.

[duck_arse]

you don't think I've actually got C250k pots here, do you?

3V6 at the fast end suggests you might go an E24 lower. I was having 2V5 as the no-faster voltage on the new TI chips, but the old MOT's were 3V5 then stopped w/ next E12, so good enough for me.

[edit :] and no distortion? any of that fade-in trem I mentioned?

[anotherjim]

I haven't tried anything hot in the front end. My bench tester these days is a fairly good Chinee telecaster so I don't suppose I'm pushing it.

[anotherjim]

OK, I see/hear it now. With a DS1 in front going strong I get the trem coming in on the delay. On the scope I see flat top to the wave with some dipping on the bottom.
I think this is due to the channel pin 5 to 4 signal voltage rising near to the gate threshold on the pos swing & bringing the channel toward cut off.
I like the effect actually, its kind of addictive, and I'm sure I've heard it on some recordings. Can't think of any in particular though. It's very like toggling the pickup selector to a lower volume pickup.
I'm not worried about it.
It's good!

Oh I can't get a speed pot hack combo that's good. If I get it near 6Hz at half way, it's raised the minimum speed to 4Hz. Need an odd pot size like 330k to get better & I've got nothing between 220K and 470k. Mind you, 4 to 8Hz isn't too shabby is it?
BTW, I've got a 10k limit resistor in the speed, not 12k. Tried 8k2 and it dies.

[duck_arse]

I was looking at pin 5 today - it sits at ~620mV w/ no trem or sig, and then shifts as much as 600mV with signal. so I shifted the bias voltage, retrimmed, does the same thing at the higher bias as well. good - so I don't need to un-rowdy the name.

I've found the 4 cap pso (at least the transistor version) will have a lowest speed, such that if the pot is disconnected, it will still oscillate at that low speed. so 500k pot would prolly still perc, but with a very long slow end. and if you change two of the 220nF's one way or the other, you can shift the range easy.

also, the layout dia has been corrected - Q1 now faces the right way. oops.

[duck_arse]

an update - I haven't forgotten, am actually soldering this currently.

my C taper is only 200k - we'll say no more bad about that. I now have (after much plugging, scribble) 2.6~8.5Hz, in two ranges. I moved the pot to the centre of the string-of-four caps, and switch the two fixed legs - 33k always, short/open 68k each leg.

the caps - I found a slight difference in measures depending on which sized cap was where, but am going with (pin 6) - 220nF - 470 - 220 - 470. and because the output level of one range is slightly different to the other, and the wave shape/distortion changes slightly, I'm going to be claiming that as a feature. don't try and stop me!

[anotherjim]

It occurs to me that you could have a BJT PSO, ditch the 5v reg & go back to 9v and use spare inverter/n-channel for mill' bypass. So much choice.
I was trying to cut down my consumption of 4007's (got to be a Bond catch in that number?) but now have added to bass amp sim' to the roster. More of that soon after some live testing.

[duck_arse]

no, no! no bjt's ! I've been fooling wit der 2N7008, just cause it was there on the bb, it does a real nice job of waggle. even got f ranges and resistor values written down. yuge output at 9V, no reg needed.

[pinkjimiphoton]

> I don't have any C antilog for the speed

Wire log/audio pot backward and turn it backward. Same as reverse log after you train your fingers to go the wrong way. Get-by until your next pot order.

There is no resistor hack for most speed-pot applications.

the only hack that works is to turn it around as paul suggested.

that said, you CAN mess with the lower part of the sweep with a trim pot used as a tapering resistor.
wire the trimmer as a variable resistor, and put it between the wiper and low speed side of the pot... leave the pot connections intact, but splice in the trimmer in parallel.

then you can eliminate the "frozen" part of it... the first 70% or so of the sweep is mainly useless, but with this hack you can dial up the speed to get a useful range out of the first half of the pot's travel.