Silver Jubilee

[TIMBO]

Hi Guys, Done the last checks and all was good on the startup.Voltages seemed to be in range (i'll post later)  But with scratch builds there is always going to be a problem. The overall sound is great, but a hum/buzz is quite loud. The first thing i found was the .047 cap on the input jack was picking up interference from the wires to the LED, i removed the cap which helped greatly but when the wires are moved near the 1M resistor it increases the hum. The photo shows that the circuit for the relay is close to the input and gain pots.Could this be part of the buzz problem.

The next problem is the reverb is not very loud, when the tank is tapped the BOING comes through loud and clear.
The level pot when turned to max it produces a white noise.
The presence pot is a bit scratchy and adding to the buzz.

Any thoughts, Thanks

[TIMBO]

A few more pics.

[JayB]

I love your boards.

I'm not sure what to do with the reverb as it is designed. I know the grid off the reverb pot can be a pain and I usually shield that. With the way it's designed as it, it's going to be a fight matching the reverb with volume. Maybe switch the reverb OT primaries? Inject it into the other side of the PI?

The presence is always going to be noisy when turning the knob since it will have some DC on it. Honestly, I like that presence design.

I learned the hard way to keep any later grids or anything on later grids away from previous grids.


Did you put the leds on the faceplate? and how does the diode clipping sound?

[TIMBO]

Thanks for the reply JayB,The reverb is there, just not as loud as i thought it would be.I might look through the post to see if anything helps.

The leds are on the circuit board.
I have not been able to give the clipping circuit a good thrashing due to the bad buzz i am getting.
This leads me to the problem.
I always thought the buzz was coming from the wires of the indicator led.
Disconnected one wire of the 5v tap, Buzz still there.
Disconnected both wires, Buzz gone
The layout i used had the relay on the circuit board and the circuit on a separate board at the back of the chassis so i'll try that and see what happens. Thanks 




Update :- Removed 470u cap and rect diode from under input jack which helped greatly.
           Still has some hum, louder when switched to gain channel
           which is amplified through MV and tone stack.

Would a larger cap help. Thanks

[JayB]

If the 5v tap has a center tap, which I doubt it does, don't use it.

I use 470uf for simple switching of relays using the 5v tap and never have any problems. What I do know , is that the relay coil grounds and it's filter cap ground needs to be away from any preamp grounds. Preferably grounded by the power transformer. Any where near the input or right on the input ground like I did once, was hum from hell. All that filtering gets thrown into your preamp inputs.

I always end up using a long ground wire back to where the power transformer is since I like to keep my relays close to where they need to be in the circuit. Keeps from having long grid wires.

[TIMBO]

Thanks for that JayB,I am using the 5v tap which does not have a centre tap.I have relocated the cap and rect diode to the other end of the chassis. I still have some buzz so i'm going to use a DPDT switch in place of the relay to see if i still get the buzz.I'm Thinking it could be coming from the clipping circuits.Thanks