Octave up problem with TS-like FX

[Phorhas]

Hi
I built a TS-like OD and made the gain 500k(pot) in the FB / 1k(->.22uf) to Vref.

when I set it to high gain, I get an octave up effect on the 1st E string from aroung the 15th fret and up...

Why is that?
How is it delt with?

[aron]

We need to see the schematic. Is it the complete TS schematic? If so, maybe  something is misbiased after the first op amp?

[cd]

Let me guess, you used assymetrical clipping, right?  If so, the octave up effect is normal.

[Phorhas]

Thanx for answering guys

We need to see the schematic. Is it the complete TS schematic? If so, maybe something is misbiased after the first op amp?

Ok, basically it's a TS with a few changes. it uses the basic gain stage and tone sections and the 808 sections

Voltages on the OA:
8 - 8.46v
4 - 0
1,2,3,6,7 - 4.25
5 (input of first stgae) 4.18v

Q1 (fet buffer):
D:8.50  G:3.78(1M bias res. to Vref)  S:4.13 (3k9)

Q2
C: 8.44  B:3.40  E:2.95

Let me guess, you used assymetrical clipping, right? If so, the octave up effect is normal.

Yes I did. and in my real TS as well (1n4148/1n4001) and it does that too...

is that the price for asym clipping?

[cd]

Let me guess, you used assymetrical clipping, right? If so, the octave up effect is normal.

Yes I did. and in my real TS as well (1n4148/1n4001) and it does that too...

is that the price for asym clipping?

Yup.  Clip the signal unevenly, more even harmonics = noticeable octave effect at some places on the neck.

[Phorhas]

I never noticed an octave up in my tube amp

[aron]

darn, good call, I forgot about asymmetrical clipping, but I how asymmetrical? What is the diode string like?

[Fret Wire]

The 1N4148/1N400x diode combo does sound nice. Awhile back, I measured 25 of each diode to see how much difference there was between similar types.

The variation of each lot was about +/- .010 of the average.
1N4148 - .604
1N4001 - .565
1N4005 - .558
1N4007 - .566
1N270  -  .260
1N34A -  .272
1N60 black case - .264
1N270 black case - .252

Of course, buy another lot of the same types, and the averages will change. The proportional differences will be the same. I haven't done this in large numbers with LED's yet. I'll have to try some standard 3mm & 5mm red, yellow and green types.

Your ears are the final judge, but I wonder how much of a measured voltage difference between diodes you need before you start getting asymmetrical clipping? You can hear the .040 difference between 4148's and 4001's. I doubt you could hear less than that difference. Probably wouldn't be hard to see on a scope or simulation program.

[aron]

I tried an LED and Ge and that had was asymmetric, but I got way more octave, misbiased etc... by simply misbiasing the transistor in my Shaka HV.

[cd]

Don't forget that different diodes clip differently (hard/soft) so even if you match the voltge drop, you're bound to hear a difference compared to two of the same diode.

[Fret Wire]

True

[Phorhas]

what about the pin voltages... they semm ok... are they?

[cd]

All the pin voltages are OK.

[Phorhas]

I changed the clipping diode to symmrtric pair. it still has an octave up.

shouldn't the voltages on the Gate of Q1 and Base of Q2 be closer to exactly 1/2v ?

[shtgoosephour20]

i know that Ibanez uses symmetric clipping in such pedals as the TS808 and TS9. I know that Boss has a patent on asymmetric clipping which they use in the SD-1 Super Overdrive. So what the differnece? which rocks more? IM goign to mod my SD1 so it has all the TS808 org specs but i might want to keep the asymmetric clipping. just looking for any knowledge about the subject and preference among artists. i play classic rock through a Semi Hollow Body wiht PRS Satana III PUs into a HOt Rod Deville.