Not sure why ??

[HOTTUBES]

I put together this circuit as shown in the above pic , i wanted to try different clipping diodes to see what i liked the best ....
But it seems that what ever diode i install makes no difference in the sound at all , no gain increase , no tonal changes what
so ever etc .....

just wondering what the cause might be ....




Thanks for any help  !!

[PRR]

Is there a proper schematic?

AFAICT, D1 isn't doing anything; D2 D3 make a unipolar 1.2V diode which will have very slight effect.

But that's as far as I will go without a circuit layout (opposed to a parts-layout).

[LucifersTrip]

Did you just try various silicon diodes or try ge's, schottky & led's?  Did you try various arrangements (3 one way, 2 another, etc) or just make direct subs...

[sault]

Those two serial diodes... did you put them both in the same direction? (hey, I've done it!)

[teemuk]

It seems this thread is totally devoid of information of what diodes you used. Unless there are drastic differences in the forward voltages of the diodes they will all sound about the same.

[seedlings]

Does the volume increase significantly when you turn up the gain?  If not, you may not have the series capacitor and resistor from pin 2 to Vref (or ground) and then you don't get any gain at all. Looking at the layout, coming off of pin 2 you have R6, C4, R2 and R1 all in series to Vref.  This shouldn't be... not sure if the schematic and layout match up much at all.

Off of pin 2 you should have a 1k resistor in series with a .22uF cap to Vref, and without this you get no gain.

CHAD

*edit: I was thinking Vref was +9v, but it is 4.5V off the 10k/10k divider, so yes, the layout is correct, but still check connections to R6 and C4.  If R6 is accidentally a 100k or even 10k you won't get much gain.

[Mark Hammer]

The big clue for me was "no change in gain".  Possible that the ,22uf/1k network from pin 6 is not actually going to Vref?  If that's the case, then you certainly wouldn't have enough signal boost to clip under any circumstance other than some schottkys with the lowest conceivable forward voltage.

[sundgist]

This looks like a corrected layout. Havn't checked myself just noticed there was a difference.
The diodes look correct here.




edit: C7 looks the wrong way round compared to the schem. Also the two halves of the opamp have been swapped. At a quick glance over this looks ok.
edit: I meant, looks ok other than C7 being reversed.
edit: Sorry, moved the file, refresh if you don't see it

[HOTTUBES]

Sorry for the late reply :

i have tryed the fallowing diodes ..

1n34a
Leds
4001
4148
914

I have tryed them all in both directions thinking maybe i had something in the wrong way , but still no change in any case .....
the real funny thing is that i can remove all the diodes and still have a decent amount of gain on tap etc etc ...

i had a very close look at my work , and i believe i have it all built correct according to the top diagram i posted ...




thanks again for any help !!

[sundgist]

i had a very close look at my work , and i believe i have it all built correct according to the top diagram i posted ...

Thats where the problem is...

The position of the diodes in that layout are wrong. If you've built it part for part to that layout then just move the diodes (observing polarity of course).
I would also turn C7 around.

[HOTTUBES]

OK , great !
I will change them out & report back with my findings !!


Thanks !!

[HOTTUBES]

Well i changed the position of the diodes as shown in the new pic etc etc , and there was a marked improvement in the level of gain , and overall response , so were getting closer .....this may turn out to be a nice sounding OD !!!!

The end goal is to add a switch that will allow me to switch from 1N34A germs , to 3mm LEDs for clippers ...
Any location that would work the best to sub out ....D1 , D2 , D3 , or will it matter




A noob just trying to learn .......


Thanks for your helps guys !!

[HOTTUBES]

MERRY CHRISTMAS       !!!!

[PRR]

> Any location that would work the best to sub out ....D1 , D2 , D3 , or will it matter

Remove ALL the diodes. Bring short wires out from pins 6 and 7. Tack-solder your various diodes here. When you find a good combination, make a note. When you have several good combinations, buy a switch and wire the combos to it.

[sundgist]

> Any location that would work the best to sub out ....D1 , D2 , D3 , or will it matter

Remove ALL the diodes. Bring short wires out from pins 6 and 7. Tack-solder your various diodes here. When you find a good combination, make a note. When you have several good combinations, buy a switch and wire the combos to it.

That would equate to pin 1 and 2 on the layout above which i've updated to show the position for your wires (refresh if you don't see it). These would go to the two centre pins on a dpdt switch.

If you wanted 3 options ie. LED, Silicon, Germ use a dpdt on/off/on switch and leave the combination with the highest forward voltage on the board. Most likely this will be your LEDs. Remove the diodes as Paul mentioned replace D1 with one LED and put the second next to it in the opposite direction. If you want to save some space you can now remove row 1 as it is no longer needed.

[HOTTUBES]

Interesting tip !!
Why do you want to leave the diode with the highest forward voltage on the board ?

[sundgist]

Interesting tip !!
Why do you want to leave the diode with the highest forward voltage on the board ?

Lets say you have the board built as above and you want 3 flavours of diode clipping, LED, silicon and germanium.

You could replace the diodes on the board with LEDs and wire the centre pins of your dpdt (on/off/on) switch to the points marked on the layout.
Wire your silicon combination across the top pins and your germaniums across the bottom pins.

When the switch is in the centre (off) position the silicon and germ diodes are out of the circuit so clipping is taken care of by the LEDs on the board which will conduct at 1.2v or more depending on type.
Switching to silicon which conducts at a lower .7v means the signal is clipped at this voltage so cannot rise above this, effectively taking the LEDs out of the circuit. Same goes for germanium which conducts at .3v.

[HOTTUBES]

I'm only going to use two different types !
Led & Germanium on a SPDT switch ....

How would you recommend i wire that up etc ....?

What diodes will i need to go on the board ?
What diodes need to go on the switch ?




Thanks for your Help !!!

[sundgist]

Pin 2 of the spdt to the marked point on row 3 on the layout.
Led combo from row 2 to spdt pin 1.
Germ combo from row 2 to spdt pin 3.