EH Doctor Q voltages?

[LucifersTrip]

Does anyone have some good working voltages for this thing, especially for the transistor


It's supposedly from this schematic, but the diodes are different and the left one is a red led.


I built it with no substitutions. With a LM4558 or TL072 it doesn't work. There's no quack... The trimmer basically does what a wah pedal would do. It starts bassy and then trebly as turned cw.

LM4558/TL072 voltages (9.68 supply):
1: 8.77
2: 7.15
3: 0
4: 0
5: 4.83
6: 4.84
7: 4.82
8: 9.52

Q1
e: 0
b: .54
c: .006

It "works" with a LM1458, but not up to snuff.  Firstly, I don't get any quack for the first 50% of the sensitivity and it seems a bit muddy.  After 50%, it's cool especially with the 3rd to 6th strings, very much like the demos I've heard, but the 1st and 2nd (high e, b) are dull. The high E actually doesn't sound unless the sensitivity is in the final 25%.

LM1458 voltages (9.68 supply):
1: 2.30
2: 1.99
3: 0
4: 0
5: 4.82
6: 4.84
7: 4.88
8: 9.56

Q1
e: 0
b: .04
c: .005 - .006 when strumming, otherwise 0

The above is with the switch thru the .01uF. It sounds worse with the switch thru the 47K. It's boomier with a volume drop, but high e and b are sharper. The trimmer only gives me a quack in a very small range.

I actually couldn't find any voltages on a bunch of quick searches, so any would be cool. The transistor voltages can't be right. I'll experiment more in the meantime.

thanx

[drolo]

I have never has any luck with getting the original DR Q schematic to work correctly.
I much prefer the biasing trick on the Doctor Quack as it seems to make for a more stable unit and allows other op-amps to be used.

Does it work any better if you stick a booster in front of it? If so, the Quack's buffer might help too.

Sorry, can't really comment over the voltages. Someone cleverderer surely will ;-)

[Mark Hammer]

I like the clarity of Jack's buffered input, but I've never had problems getting a Q to work.  The 1458 IS critical, though, if one is not going to use Jack Orman's biasing tricks.  You can sort of get some sweep with a 358, but the 1458 works best.

Four things to consider:

1) The rectifying diode does a better job if it is germanium or Schottky.  A lower forward voltage subtracts less envelope output going to the transistor.

2) How big a feedback resistance are you using in the gain stage feeding the diode?  Maybe you need a little more gain.

3) What's the taper of the sensitivity pot?  Maybe the problem is because you've bunched all the usable settings at one end of the rotation.

4) The 100R resistor that sets the attack time also eats up drive current to the transistor.  reducing it to, say, 68R  or even 47R will produce a faster attack and also derive more sweep from the same sensitivity setting.

[LucifersTrip]

hey David/Mark,

I will definitely try that fet stage at the input...

Mark, thanx much for the suggestions, though I'm not going to tweak anything until I know I'm close to working voltages.
I used a pretty small, tight vero (above).

Regarding the feedback resistance & sensitivity pot, it's the same as the layout above, except for that red led. I have the Dr Quack minus the fet stage and 10K/second red led to ground


btw, have you had different luck with different 1458's? This was actually my last one so no experimentation yet.

thanx

[Mark Hammer]

I sat down once and plugged in an assortment of different dual op-amps into the socket. The results are somewhere here in the archives, though I'll be damned if I know where.

But I tried NE5532, TL072, CA3240, LM4558, LM358, LM/MC1458, and a couple others, I think.  I didn't try multiple versions of each type, but quite honestly, I don't see how that would matter.  The resulting sweep was a function of the general architecture of the chip, not unit-to-unit variations.  Some (and I forget which) swept SO wide that it was unusable.  Others would generate precious little sweep.

It is quite conceivable they could be persuaded to yield a decent sweep with some circuit changes, but if you want plug and play, a 1458 will take you there immediately.  Same goes for the Bass Balls envelope follower section.

[LucifersTrip]

The fet stage at the front did indeed make an improvement.

Now, instead of around unity volume, it's much louder and there's more treble & clarity, but unfortunately the same problem with the high strings. The high e barely sounds at all if playing single notes and the b is very low. The low e,a,d are a little dull, the g is very loud and trebly and contributes the most of the sound when strumming. Only if I hit the high e and b very hard do I get anything....

There was an improvement in the sensitivity control. Instead of no quack for the first 50%, now only the first 20-25% is quackless.

With a fuzz in front of it (also with fet stage up front), all the strings are around equal in volume. The sensitivity is good for the first 20%. Any further and it would be like pushing a wah thru the floor and adding 10 times the treble.

No one with working voltages?  What should I see on that transistor...and pin 1 & 2?

[PRR]

> What should I see on that transistor...

About what you got. E is hard-grounded. C has no DC source, so we might think zero or we might know that if B is high then C can show a few milliVolts. B varies with signal and pot, really should be zero when NO-signal or whan pot is down, will never rise above ~~0.6V.

> and pin 1 & 2?

With no signal the OUT and -In should follow the +In, if they can.

+In is a red LED, 1.6V. (So why do you have zero??)

A LOT of opamps won't work with inputs closer than 2V to either rail. Some will flip-out and slam the opposite of what you expect (maybe your 8.77V?).

The LED bias at IC1a +In is clearly missing.

[drolo]

expect (maybe your 8.77V?).

The LED bias at IC1a +In is clearly missing.

+1 that really made a difference in my builds

Are you testing with the normal or bass position?
I found that the normal position was never producing any interresting results and always leave it hardwired in bass position. Works great with bass and guitar. Tweaking the 2 filter caps helps to get the range wanted.

Your description of the issue makes me wonder whether the problem is not in the filter area, not so much the detector. Maybe something misconnected or shorted ?

[LucifersTrip]

> What should I see on that transistor...

C has no DC source, so we might think zero or we might know that if B is high then C can show a few milliVolts.

thanx alot! I wasn't expecting that since I'm used to distortions. I won't worry about it now.

+In is a red LED, 1.6V. (So why do you have zero??)

I used the original schematic above where 3 & 4 are grounded. It looks like the scheme is gone (no direct linking) so I re-added it
http://www.luciferstrip.com/fuzz/doctorq-schematic.gif

The LED bias at IC1a +In is clearly missing.

I added the led/10K and now pin 3 is 1.81V. Unfortunately little or no change to sound.


>(drolo): Are you testing with the normal or bass position?
Thru the .01uF, since it sounds far better, but thru the 47K, there are no dull strings sound. On the 47K side, the trim is only good in a very small range. I get much lower volume, a less fuller quack and a swell after the quack if I stop strumming.

I'll start looking for other errors.

edit:
...and it now works with a 4558 and sounds the same

[deadastronaut]

hi lucifer: just a heads up, i tried many EF's while doing the zodiac fuzz+envelope... none of them responded well to B+E strings/notes..

but the Q-tripper does,...i had it on breadboard and tweaked it for ages and stripped it  down to its bare 'good' essentials.

rare Q tripper clip ,  it had a mix control on it, you hear this when the sound goes thinner, i removed that. 

as you can hear the top strings are fine...
https://dl.dropbox.com/u/7464107/qtripper.mp3

https://dl.dropbox.com/u/7464107/Q-Tripermodded.jpg

it needs a 2sk30a for Q2..definately, i tried other fets, no joy....just my 2p

[Mark Hammer]

That sounds very good, Rob.  Nice and responsive, without being over-the top.  Kudos.