Op-Amp Distortion clone (another one!) - couple of questions..

[newfish]

Hi All,

I've recently built an MXR D+ clone, based on the Tonepad schematic...

http://www.tonepad.com/getFile.asp?id=115

The only changes were to have R8 as a 1M pot (with 33K 'stop' resistor), with R6 as 1K, C4 as 0.1uF (from pin 2 to ground) for more 'gain'.

Clipping diodes are a 5mm red LED, and a 1N9149 silicon diode, and op-amp is a TL061.

I've added a switch to put a single Back-to-back diode pair either in the 'classic' Output-to-ground configuration, or to place them in the 'tubescreamer-style' feedback loop.

Both options work very well, but what's bothering me is that the 'classic' diode placement results in a muffled sound, compared to the feedback-loop placement.

Is this to be expected?

Components C6 and R9 are reversed on my board - the resistor coming first.  Will this make any difference at all?  My hunch would be 'no', but am open to ideas.

Thanks for reading.

Ian.

[Joe Hart]

I believe it is to be expected because diodes to ground clip the signal much harder and therefore cut the signal down much more. You could add a resistor to attenuate the signal when you switch to the feedback loop diodes to keep the signal in the same volume range. Hope this helps.
-Joe Hart

[newfish]

I believe it is to be expected because diodes to ground clip the signal much harder and therefore cut the signal down much more. You could add a resistor to attenuate the signal when you switch to the feedback loop diodes to keep the signal in the same volume range. Hope this helps.
-Joe Hart

Thought as much!
I already have a 10K on the output - and don't want to go lose any more 'clip' threshold.  
There's a *small* volume drop in 'Hard Clip' mode, but nothing I wasn't anticipating / can't live with.

Cheers!

*EDIT*

Bah!  Sometimes I'm far too blonde...

Why don't I put an R/C filter in the 'diode to ground' option?
I could leave the top-end where it is, and *still* have cheesy 80s hair-metal on the low / mids!
Yes!  Shall try this sometime over the weekend (Little Man's 4th Birthday Party takes precedence...)

Hooray for thinking out loud!

****

[petemoore]

 Another DOD250 / Dist+ experiment went well over the last week.
  ...At a Jammnight the D+ was commented on as 'what kind of Distortion box is that?'...the Amplifier [Deluxe Reverb, nice] owner [I thought] was commenting on what I guess what a jack/plug anomoly [weird noise, not horrendous in volume, was 'shaken loose'...only lasted a for few seconds of mild noise mayhem...who knows].
  Anyway, last weeks D+ comments were clarified this week, as in "Really, what was in there, I thought that one sounded great" [it did !].
   I used the 250, and it was much synthier sounding than the D+.
   Rather than attempt to recant accurately what the diode configurations are in those, the D+ has: 
   -Si-->lGe->l-- :
       --l<Si--
  ...for assymetrical clipping.
  A mornings project [hopefully goes well/fairly quickly] involves mods to the 250...
   Preference for opamp/diodes both contributing to the distortion sound involves finding a balance between the input strength and the diode threshold. The 741 with no diodes is 'raw', with Ge's it's what you said and low output [the diodes cut/clipping signal after the amplification...adding a booster of course will bring signal back up where  it's more fierce output, that's a different distortion box then...

[Quackzed]

i got a little opamp/diode blend sound from a resistor  between the diodes and ground. i believe i was using 4 si diodes (2 one way and 2 the other with a 5k resistor between them and ground, symmetrical with a 5k first, it was a bit off, too much i guess, sounded more like a somewhat loudish clean/od alongside a fizzy distortion... but with a 1k or lower it just kinda took the hard thunk of the low end distortion away, made it a little more open sounding...
something to try, but it sounds like you found a good setup,
i might try the si ge < si setup... as well... i have too many 'open' sounding overdrives as is, and the dist+/250 gets nice and compressed sounding without the added resistor...

[wavley]

Another DOD250 / Dist+ experiment went well over the last week.
  ...At a Jammnight the D+ was commented on as 'what kind of Distortion box is that?'...the Amplifier [Deluxe Reverb, nice] owner [I thought] was commenting on what I guess what a jack/plug anomoly [weird noise, not horrendous in volume, was 'shaken loose'...only lasted a for few seconds of mild noise mayhem...who knows].
  Anyway, last weeks D+ comments were clarified this week, as in "Really, what was in there, I thought that one sounded great" [it did !].
   I used the 250, and it was much synthier sounding than the D+.
   Rather than attempt to recant accurately what the diode configurations are in those, the D+ has: 
   -Si-->lGe->l-- :
       --l<Si--
  ...for assymetrical clipping.
  A mornings project [hopefully goes well/fairly quickly] involves mods to the 250...
   Preference for opamp/diodes both contributing to the distortion sound involves finding a balance between the input strength and the diode threshold. The 741 with no diodes is 'raw', with Ge's it's what you said and low output [the diodes cut/clipping signal after the amplification...adding a booster of course will bring signal back up where  it's more fierce output, that's a different distortion box then...

I have one that I do:
-GE-->|-LED-->|
|<--GE--|<--GE--

I like the way it sounds.

[blackcorvo]

you could try the connection of the diodes like in this schematic:


this seems to smooth the distortion a bit without reducing much of the clipping.