Death By Audio Robot Question

[goldenmonkeycolor]

I built the death by audio robot according to this schematic...

http://3.bp.blogspot.com/-btNLPGu6jQc/TxgVV4J9DcI/AAAAAAAAAoY/tUf_kvzgw2k/s1600/Robot+schematic1.JPG

and the vero layout from John Kallas!  Thanks John!

I feel the tone of this schematic is too muffled and bassy compared to the real deal.  SHould I mess with the 330nf input cap?  or should I try to mess with the 470pf cap in between pins 6 and 7 of the TL072?

maybe something else?

Thanks much for help with my newbness!

[GibsonGM]

Well, don't know the circuit, but provided you built it correctly - yes, the input and output caps have a lot to do with controlling bass frequencies, as well as that 470p cap.  Plus the 'middle' .33u coupling cap.    Feel free to mod to your heart's content!! 

Might try making the 470p >> 100pF, or even lower if you feel like it.   That should make things a little brighter, I'd think.   Being in the feedback loop, the highs that are fed back actually make the opamp amplify highs LESS.   The smaller that cap, the less this effect (the onset of decreased gain will shift higher).  It's good for when something is TOO bright...

If neither approach does much, then I dunno what more to do, not being familiar with the HT8950.    Let us know if this does anything good...won't hurt a thing to try it.

[goldenmonkeycolor]

Well, don't know the circuit, but provided you built it correctly - yes, the input and output caps have a lot to do with controlling bass frequencies, as well as that 470p cap.  Plus the 'middle' .33u coupling cap.    Feel free to mod to your heart's content!! 

Might try making the 470p >> 100pF, or even lower if you feel like it.   That should make things a little brighter, I'd think.   Being in the feedback loop, the highs that are fed back actually make the opamp amplify highs LESS.   The smaller that cap, the less this effect (the onset of decreased gain will shift higher).  It's good for when something is TOO bright...

If neither approach does much, then I dunno what more to do, not being familiar with the HT8950.    Let us know if this does anything good...won't hurt a thing to try it.

im thinking thats it, because I've built it before and it didnt have this problem- think i may have used a 47pf by mistake... and i think that might actually be the correct value and the schematic may be incorrect!  i'll report back with my findings.

thanks so much for the help!

[Mark Hammer]

A friend brought me his Robot pedal to "smooth out" for him.  The schematic you show is incomplete, and does not allow for the switching of modes (or whatever you want to call what the rotary switch does).

It was about a year ago or so, but I seem to recall changing the 470pf feedback cap shown for a higher value.  Although the calculated rolloff is roughly 780hz with the values shown, it is only a 1-pole lowpass filter, applied to an 8-bit A/D, sampling at 8khz, so a fair amount of nasty aliasing still gets through.  I think we raised it to 680pf or something near that, and it yielded something that was not too dull, but more usable, more "musical", and less of a pure noise effect.

[goldenmonkeycolor]

A friend brought me his Robot pedal to "smooth out" for him.  The schematic you show is incomplete, and does not allow for the switching of modes (or whatever you want to call what the rotary switch does).

It was about a year ago or so, but I seem to recall changing the 470pf feedback cap shown for a higher value.  Although the calculated rolloff is roughly 780hz with the values shown, it is only a 1-pole lowpass filter, applied to an 8-bit A/D, sampling at 8khz, so a fair amount of nasty aliasing still gets through.  I think we raised it to 680pf or something near that, and it yielded something that was not too dull, but more usable, more "musical", and less of a pure noise effect.

Sorry guys I had a lot of stuff come up and never got back to this one.  I recently built one up again and Yeh I have the switching working and in place- I thought the pedal was working fine for a while, but i guess i just did not notice this crazy volume pot action.

I am getting this HUGE jump somewhere around the middle of the pots rotation.  I cannot figure it out for the life of me.  Maybe its the output of the ht8950?  or maybe I'm not wiring the pot correctly?  I have the input going into pin 2 (weird, but thats what vero layout and schematic says) output from 3 and ground to pin 1. 

Ive changed pots, tried different wirings, tried removing the pot (though Im not sure i did that correctly- i was thinking why not just remove the pot and put a simple attenuator at the end of the circuit?)  Ahhh! Its driving me absolutely nuts!  Checked all resistors though i dont have a way to to measure caps in circuit.

Any ideas would be greatly appreciated!  been trying to get some help for a while to no avail

[peterg]

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