Dist+ Booster...

[petemoore]

I have been debugging this Dist+ type thing all day.
 Suffice to say It got 'third degree' extensive debugging, more than twice...etc
 It boosts like alotsa. Inserting a diode pointing toward ground kills it.
 Inserting a diode the other way has no effect.
 I checked the PinV's: 1-7 are quite near Vref, Pin 8 is 8.90v [battery], pin 4 ground.
 So I'm using two 100k and two 100uf's as the divider...the schematics I have don't show this part.
 I have a 1meg fixed resistor for OA 1's feedback loop.
 I have a 100k resistor for OA2's feedback loop..oh I'm using the other side of a dual for gain recovery...this thing has alot of output.
 diodes across lugs 1and 3 of the volume pot have no effect either.
  This one's got me stumped. I never heard of such a thing!!!
 I'm sure it's a little error, but having been back and forth on It I'm hoping someone might offer a different approach or see a clue from these strange goings on.

[petemoore]

I find there's a power surge thing going on.
 It oscillates in volume over 15-30 second intervals of half third way boost almost off and off.
 As good as all the voltages 'look, and the way it sounds great with no distortion except the OA's, It surprizes me that I can't just connect diodes from signal to ground somewhere and get clipping///I don't know if it's impedance or boost but this is the first circuit that gets the amp to half volume with the volume all the way down....
 Like speaker popping output but no Clippo, the diode in the one direction still kills it and it takes a second to 'recharge' and work it's way back on, very similar to the 'power surge' terminology...definitely circuit induced volume swells and drops...doubtful its a bad connection...It went together very well [fine job I say, but I'm 'biased' lol], it is stable when wiggled 'n such, I've done many elimination processes on it.
 So I'm beginning to try thinkin power supply.
 Can I get Vref, 9v and ground from a 741...enough current and such to run the circuit?
 If not, is the divider I have [two 100k's, a 100uf across one and a 100uf across the rails 'good'? or what are good values for the divider?
 Both Oa's are gaining, I can cut the gain by tagging resistors across the feecback resistors.
 Hopefully I can get somewhere with this one, I need a good Dist+!!!

[Joep]

Hi Pete,

Check the project at Tonepad there is a schem and a PCB for the Dist+

Although you divider has different values it should work properly.

What opamp are you using? The Dist+ uses a 741 which is a single opamp. You are talking about Oa1 and Oa2.....  :?

Good luck,

Joep

[petemoore]

I tried TL082s 072 and a 4559.
 I'm using the first half [pins 1 2 3] for the Dist+ section, the second section is the schematic in the thread "Adding a Volume recover stage on a Dist+"...just down the page a bit

[Joep]

Hi Pete,

Yeah, In the mean time I figured out you are using the new circuit.

Try to build each opamp stage separate and see how they work.

Is the circuit still drawing so much current as you discribe in the other post? That is an indication that something is seriously wrong. This type of circuit don't draw that amout of current.

Bye,

Joep

[petemoore]

I 'forgot' to mention I found the draw problem in the 'add on' 33k's to the divider circuit.
 They had a llittle 'touchy' problem, they've been eliminated from the circuit.

[brett]

Probably not your problem, but one time I was building something similar I connected the +ve input directly to the junction of the Vref voltage divider, instead of using a 1M or thereabouts resistor.  This conducted all AC to ground, and things were very quiet  :oops: .  I only mention it because you described the voltage divider but not the resistor tying Vref to the input.

Also, you've got a small (0.1uF) isolating cap between the output and the diodes, right??  I only ask cos I know that I tend to get the complex stuff right but make the dumbest simple mistakes. :roll:

cheers

[petemoore]

There are three resistors from Vref, one to the OA 1 input via [1meg?] resistor, the other is a 100k to OA 2's input, the third is the 10k and looks to bleed some highs off via the 1 meg pot.
 I have caps between OA 1 output and OA 2 input, and all the other places they're marked on the schematic...A real baffler.
 connecting the diode facing ground clamps the voltage in the circuit ie no voltage reads with the diode in that way.
 Which led to the ongoing PS inspections...thing is the pin voltages look fine...one more day and it's new DIST+ board time I think.

[petemoore]

Upside down and back and forth...looks real good...sounds pretty good.
 Still bugged tho.
 Pin voltages without diodes:
 1   4.34
 2  4.40
 3  3.41
 4   G
 5  4.25
 6  4.42
 7  4.43
 8  8.81
 With any diode pointing at ground
 1  3.25
 2  3.24
 3  2.95
 4  G
 5  2.63
 6  3.07
 7  1.36
 8  8.82
 All + readings from ground, battery at 8.82v+
 The thing is 3-5x times louder than anything...can someone explain how a diode would fail to clip at such levels? ...diode put in the other 'non kill' way.
 I think the diode to ground circuit kill is a clue somehow...I'd think a gated blurt when string slamming would at least get through with all the fantastic output levels...oh the diodes still dont clip after the recovery stage which uses a 100k gain setting reesistor...
 I changed the Voltage divider...it tests good, it's on a little board.
 It's been about two days now with the circuit 'looking' good...the DMM's been ALL over it every which way that could possibly tell me anything...looks good sound good too...just kinda bugged it won't distort past OA OD.
 I'll wait for a time in case anyone can theorize something I could try before starting a DIST+...I've done like ten now...many of my OA have moved to vying for first string pedalboard positions since I got the GREAT CHIPS Ti sent me...probly got an old board around here but most of them were for 741's...
 The Muff FUZZ...quite the attacker sustainer Distortion unit...GOOD One, the SD-1 beautiful sounding harmonic content, my ears find them very pleasing to listen to for extended periods...REALLY getting to liking my OA Clipping devices these days !!!
 I used to buy these things alot, my testimony is they [Boss etc. ones 'I' had] rarely, if ever, sounded this good, with the exception of the Ochre  MXR Dist+.

[Joep]

Did you used this schem?


Did you include C6 and C7 in you one? Try replacing them, they look faulty to me.

Bye,

Joep

[petemoore]

Ok...replacemint the caps as you mentioned did allow diodes to ground, the out put is still very exremely high, but no clipping [go refigure!]...
 I use 1meg fixed for every 1m shown including the 1m reverse taper gain pot..perhaps if I diddle with the value there..seems it should be set at full gain tho.
   The 1meg reverse taper gain pot is a fixed 1meg. same for the feecback loop. I suppose this sets the gain at max.
  I'm sure it's some simple thing I looked at ten times...lol

[spongebob]

Sorry I didn't spot this earlier:

If you put a 1 Meg resistor in place of the 1 Meg pot you will set a fixed gain of about 2 on the first opamp! If you want full throttle distortion, omit the pot or replace it with a low value resistor.

The gain of an opamp with noninverting input is set by the ratio of the resistor in the feedback loop vs. the one going to ground. For example, without the 1 Meg pot the gain of the first OA would be 1 + (1000 / 4.7).

Hope this works...

[petemoore]

First thing tomorrow!!!
 There ya go, that makes sense...
 Sorry ... If I'd put a pot on there in the first place...But I didn't have one.
 Grueling study after a time, but by making mistakes on perf, you really learn some lessons...be it the hard way
 After going upside down and all over that circuit for a couple days, I could just about rattle off where each part is on the schematic and on the board...lol...gets me thinking about how the circuit works in new ways more than if I didn't go back and forth around it.

[petemoore]

I left some lead above the board, so I can get a smaller one tagged [paraleled] on it N/P

[Vincent Volta]

Hey,
this kind of weird mistakes and things going odd wont happen...
if you try every circuit on a breadboard first.
Better yet, build yourself a test module with included input/ output jacks, a 9v power supply and a volume pot along with a bypass switch. Good luck!

[petemoore]

The speed at which circuit parts can be changed with a breadboard is greater than with a perf.
 The speed at which circuit parts can be changed with perfboard far exceeds the speed at which diagnosis of Which Part should be changed occurs for a hardboard..an unbeatable learning tool for debugging hardboarded [PCB/Perf] circuits.
 Perhaps I soon build another with socketted all caps, measured resistors...etc.
 With all that, I wouuld have done well to have purchased a larger breadboard long ago...

[petemoore]

All socketted, measured, retested, debugged, good voltages
hideous sound
                       :oops:
:evil:
:twisted:
:?:
:?
 How importatn is the 1meg reverse taper?

[spongebob]

How important is the 1meg reverse taper?

You could try a 500K pot if you don't have a 1Meg at hand. The lower the resistance, the more gain you get.

[petemoore]

Lower the resistance the higher the gain.
 RIght now it's kinda werkin haff ok.
 I used a dual 500k wired to be `1meg pot.
 I found one out of 7 OA's tried [TL082] that doesn't sputter too bad.
 Putting the diodes and cap to ground in made a diifference and had an effect
 Ill try working with it more after a while, but I dunno, it didn't seem real stable, had a fair amount of 'cross'fire' goin on in there...