Bugle & PS mystery voltage?

Folsom · « **on:** 3 Oct 2013, 04:30 am »

My bugle makes a bad sound now, hissy/fuzz. I'm not sure what it is, but it gets sent through the RCA jacks to amplifier.

It only happens when the Bugle is turned on. But it also can happen if the Bugle is turned off and line is connected to neutral instead. (essentially the PS doesn't have to be on for this to occur, I know this because someone wired a cord incorrectly that I found while starting trouble shooting) I'd think this means there is some form of a connection between line and earth ground being made in my equipment, but I can't figure that one out just yet. Perhaps there is something about the Bugle or PS I'm missing.

Any thoughts? It just randomly began today. No prior issues. Nothing else in my system experiences problems.

But my preamp is the only devices (atm) with earth ground. All RCA's and speaker terminals are isolated. There is no connection between earth ground and line anywhere in the power distribution for my system.

Folsom · « **Reply #1 on:** 3 Oct 2013, 07:45 pm »

My thought now is that an opamp or voltage regulator is broke so line is trying to ground through the amplifier. Would that be a decent assumption of Bugle topology?

hagtech · « **Reply #2 on:** 5 Oct 2013, 10:13 pm »

What do you mean "line is connected to ground"?

jh

Folsom · « **Reply #3 on:** 6 Oct 2013, 06:12 pm »

Sorry I meant neutral, that's on AC side.

Neutral and safety ground don't mix. Safety ground is connected to chassis and turntable. The turntable doesn't have to be plugged in for the new noise.

hagtech · « **Reply #4 on:** 9 Oct 2013, 04:45 am »

How loud is the noise?

jh

Folsom · « **Reply #5 on:** 9 Oct 2013, 05:15 am »

It's loud enough that you can not listen to music at all. It's almost as loud as my radio tuner's output.

It goes away a one or two seconds after turning off the psu.

It changes volume just like regular signal. It's pretty ground-hummish. No surprise since it is grounding through amp.

hagtech · « **Reply #6 on:** 11 Oct 2013, 04:06 am »

Did you try other interconnects? Is it a hum, as hiss, a buzz, or scratchiness?

jh

Folsom · « **Reply #7 on:** 11 Oct 2013, 09:20 pm »

Closer to a hum. I'd think the other devices would be bad if it was interconects.

That is in less it's turntable interconnects but music still plays and the noise is both channels.

Folsom · « **Reply #8 on:** 22 Oct 2013, 04:36 am »

New opamps no luck.

I'm going to double check the grounds for the PSU to Bugle. Caps... I dunno it's weird that it just started.

Folsom · « **Reply #9 on:** 23 Oct 2013, 03:20 am »

Hm

One channel has 80mv AC voltage, the other bout 130mv, at the output. That's with nothing attached

Positive and negative voltages are fine going to opamp.

One I it resistor wandered to 1.5k so I reset it to 1k

All diodes are correct about .28 forward bias each.

Folsom · « **Reply #10 on:** 23 Oct 2013, 04:39 am »

Folsom · « **Reply #11 on:** 23 Oct 2013, 05:12 am »

Not sure what's up. Capacitors seem ok *measure within range

hagtech · « **Reply #12 on:** 23 Oct 2013, 07:26 am »

Can you post a photo?

jh

Folsom · « **Reply #13 on:** 23 Oct 2013, 08:53 am »

Folsom · « **Reply #14 on:** 23 Oct 2013, 08:56 am »

Sorry my smart phone is well, stupid and it'd take me an hour to delete extras, I can barely type.

Folsom · « **Reply #15 on:** 23 Oct 2013, 09:07 am »

It sounds like a ground noise now.

I tried another volume control, nothing different. The one I us is 10k. Then directly into a classDaudio miniamp.

Folsom · « **Reply #16 on:** 23 Oct 2013, 08:27 pm »

Should I try connecting the grounds from RCA's coming in (turntuble) to the rest of the RCA's, and not to the Bugle, since the Bugle is connected post amplification? I was just looking at the schematic and trying to think of ways to reduce ground loop problems. But frankly I can't tell what could really be causing them.

I don't think at any point circuit ground connects to the case. I can't measure it anyhow.

Why my volume control can be sensitive to ground, even when the knob doesn't connect to the RCA's or any part of it, is beyond me. The volume control doesn't have any power going to it, just a box. But I'm worried why it acts that way is also part of the larger problem.

Disconnecting earth ground from the box the Bugle is in does nothing.

poty · « **Reply #17 on:** 24 Oct 2013, 06:38 pm »

Hello Salis,
I tried not to intervene with JH's help as I mostly can't clearly understand your problem.
It seems (looking at your photo) that you have modified input circuit by adding something. You've also added output switch (?). Could you present a schematic sketch of the changes?
I also noticed two wires: white and blue, going from the left battery connectors to the input area. What is it for?
I'm completely confused also when you mentioned a volume control and it's impact on the noise. Could you elaborate more?
Is it possible to check mains connector for correct connections? (Bugle side and mains side).
In my opinion you should follow clear procedure for checking beginning from the output RCA and gradually connecting the parts of circuit until you spot the source of the hum.

Folsom · « **Reply #18 on:** 24 Oct 2013, 09:20 pm »

The white and blue wires go to a pair of variable resistors, LDR. It's not possible for current to enter that way.

There is a selector switch for output from Bugle or 5 other RCA sets.

The mains are fine, but I can tell you that when the cord (not assembled by me) was reversed on line and common there was a noise from grounding through amplifier.

My volume is in another box, all connectins are floating, but if the input and output are switched (RCA's going to it) it works but then touching the knob increases a ground loop noise it gets in reverse.

It just occured to me that maybe the LDR is grounding through my new amp that may have much less impedence than the last one. If that is the case I got to think of something... But also it would seem the Bugle PSU would be trying to as well. But it puts out correct voltage.

Could something be causing an impedence rise in the PSU? Perhaps I should disconnect it and take measurement. Perhaps there are also no DC blocking caps on amplifier. (I think it does though)

Folsom · « **Reply #19 on:** 24 Oct 2013, 09:32 pm »

The signal carrying cap are attached to resistor legs that tracing an schematic show. ( the leads were to fat )

I too trust Jim. He is a much higher level than myself making simple AC products.