Hello!
I've built a PT-80 delay but i'm fighting hiss on the input buffer. I read all topics about it but got no answer..
This is what i've done:
-Removed all other ICs
-Tried different power supplies
-Replaced TL072, and tried other OPAMPs
-Replaced components
All resistors are metal-film. I also simulated the freq response of the input buffer and it shows 18db gain on higher freqencies, so i raised 470pF capacitor to lower the gain in the 10-20Khz range. Some beneficts, but still lot of hiss.
Any idea about? Reference schematic is the one of GGG
Thanks
Hissing is often caused by bad contacts or by RF oscillation.
Is your circuit showing RF oscillation?
If you don't have a scope to tell, how well is your power supply bypassed?
Thank you for the reply RG!
Yes i do have a scope, i did a check and everything seems ok, i only get the switching spikes of my PSU, but well above audio range.. I use separate supply for digital and analogue supply, and both are 100uF + 100pF bypassed. Same thing for Vdd/2 reference.
Tried with RC4558, AD712 but nothing changes..
I plug my delay on the HI input of my jtm45 so the hiss comes out a lot. Component values are ok, i also tried to raise the 1K feedback to 10K but i loose top and doesn't solve the problem.
I don't get this behaviour...
I solved, lowered the gain at input and compensated at output buff to not color the dry signal