[sdiy] TR-909 undersized DC blocking caps

[Stewart Pye]

Hi Richie,

I simulated this in LTSpice and got the same results as you. I was 
obviously wrong. Please accept my apologies for doubting you. At least 
I've learnt something, and it's interesting to know. I've always put a 
separate coupling cap on the input end of each summing resistor so have 
never had to calculate or test such a circuit.

Regards,
Stewart.



Richie Burnett wrote:
>> Again, I disagree...
>>
>> Are you saying that if you do a sim of a summing op amp with Rf of 
>> 20k (I cant read the value on the schematic), a common 1uF coupling 
>> cap, a 13k input resistor going to your signal source and 9 other 13k 
>> resistors going to ground that you get a HPF cutoff of 120Hz?
>
> Yes!  PSpice simulation shows this, as does the actual TR-909 I tested,
>
> -Richie,
>