TS10 - that extra 220R

[Mark Hammer]

Perhaps they are incorrect, but the only schematics I have ever seen of the Ibanez TS10 show a circuit that is identical to the TS9 with the exception of a 220R resistor between the input buffer and the noninverting pin of the op-amp.

I've read some posts of people who prefer the 10 to the 9, and I can't imagine such a small resistance would have any audible effect.  Any experience with this, or any reason to expect, on the basis of theory, that the circuit would exhibit audible differences?

Or is it:
a) a mistake or omission in the posted schematics, and there's more to it than the 220R resistor;
b) a case of people trying out a single example of the 9 and 10 and mistaking their respective component tolerances for something "special" in the design?

[FiveseveN]

I'd wager everything I own on (b).

[Rob Strand]

It's real, you can see it on the PCB.

R6 220 ohm

The 10k I'm not sure if it's R8 or R11 due to the ambiguous PCB markings.

Click for hires shot:


While not a TS9/TS10, as a backup you can see the same resistor on the factory schematic of the Ibanez MF5 (Modern Fusion Potato/Bug casing from 1990/1992).

[Dormammu]

After some issues with noise and hiss, I often insert similar resistors into the inputs of op-amps. For the most part, even with increased resistance of 2-10k.

[Rob Strand]

I've read some posts of people who prefer the 10 to the 9, and I can't imagine such a small resistance would have any audible effect.  Any experience with this, or any reason to expect, on the basis of theory, that the circuit would exhibit audible differences?

I seriously doubt it would affect tone.

Small values will help prevent RF breakthrough.   They also help minimize damage due to ESD.

In some cases resistors are used instead of links!  Not always small in value either, sometimes quite nominal.

Interestingly the input buffer on the TS10 is biased for more swing.

[antonis]

Interestingly the input buffer on the TS10 is biased for more swing.

It was time..!! 
(20 years after, they might decide to also fix output buffer bias..)

[Rob Strand]

It was time..!! 
(20 years after, they might decide to also fix output buffer bias..)

Off hand, Ibanez don't always use the highest hFE grade parts (2SC1815-GR hfE = 200 to 400, VBE ~ 0.6V), so that trick helps.

When I take a look at that pic I'm sure I can see a 2SB1815-BL, the high grade part ? (the transistor near the thumb/finger).  That's not common.

[antonis]

Off hand, Ibanez don't always use the highest hFE grade parts (2SC1815-GR hfE = 200 to 400, VBE ~ 0.6V), so that trick helps.

I can't believe Ibanez engineers didn't know that by using a humble cap for bootstrapping could result in much lower than 510k bias resistor, hence less voltage drop across it..

[Rob Strand]

I can't believe Ibanez engineers didn't know that by using a humble cap for bootstrapping could result in much lower than 510k bias resistor, hence less voltage drop across it..

It's the design culture of pedals 500k input impedance is OK and the circuit is cheap.  With the extra bias ckt it does complicate things.