Philip_BlueFX

Trying to get rid of in-out trafos on a G9. Noise Issue?
« on: December 27, 2020, 05:07:27 PM »
I have just build the G9 -single channel- core circuit on point-to-point fashion. I was curious if I can get rid of the input and output transformers for an electronically balanced circuit and so I did using a dual-opamp circuit.

Some issues emerged in the process though that I am not sure are related to this circuitry or not.
I have just ordered the lundahl transformers to make the comparison (that was the whole point actually).

Now what's my issue? Noise of course.
I get pink noise (from the looks of it) out of the SRPP Tube as shown in my spectrum analyzer (through Studio One). I poked around with my oscilloscope and I believe that this noise starts at the SRPP output (pins 1/7/8 of V2) and is not present earlier. I tried to switch the valves with one another with the same results. The noise is affected by the volume pot only, not the gain. Also, the noise is present at the same volume with or without the output balanced circuit.

Studying on the SRPP theory, it seems that the source impedance should be matched for the SRPP stage, meaning the resistors at play. This made me wonder if the impedance (~6,5KOhms) is way off. .

What would the impedance be that the SRPP "sees" with an LL5402 output?
Any ideas what could cause this noise to emerge?

Attached are my spectrum analysis and the output circuitry.
- You're always gonna suck before you rock.


squarewave

Re: Trying to get rid of in-out trafos on a G9. Noise Issue?
« Reply #1 on: December 27, 2020, 07:41:43 PM »
Now what's my issue? Noise of course.
...
The noise is affected by the volume pot only, not the gain. Also, the noise is present at the same volume with or without the output balanced circuit.
If the noise is affected by the volume pot, that would suggest that it's origin is upstream.

Try grounding the upstream side of C31 (assuming there's no DC there). If that eliminates the noise, then post more of the upstream circuit.


 

Related Topics

  Subject / Started by Replies Last post
4 Replies
1792 Views
Last post March 27, 2010, 09:18:05 AM
by JanusRec
30 Replies
5549 Views
Last post July 16, 2010, 06:34:15 PM
by PRR
12 Replies
4963 Views
Last post January 24, 2011, 09:14:55 AM
by ruffrecords
10 Replies
2159 Views
Last post April 26, 2011, 09:57:03 PM
by sodderboy