Wierd issue diagnostic help

[greiswig]

I've been tinkering a bit with the slope resistor and the bass in my D'Lite-ish build. All is well, but suddenly there is something odd happening that I'm hoping someone might point me to a solution for.

If the amp has been off for awhile, when you first turn it on and switch from clean to overdrive or vice versa, there's a big POP. This is a switch (or footswitch) that operates a relay, and the relay has a diode across the coil already.

Here's the oddest part: If you toggle the switch back and forth 6-8 times, the loudness of the pop goes down after every toggle. Now you're okay, and you can make the switch without the pop happening. Turn the amp off or on standby for a long time, and you're back to square one, with the loud POP.

Seems like a cap is getting and holding a charge somewhere, but I don't have any idea where. I've poked around with a voltmeter a bit, looking for odd voltages that shouldn't be on the one side of a cap, but haven't found anything that really screams "leaky cap."

Any suggestions? Many thanks in advance...

[Mark]

Dear Greiswig

I am experiencing a similar problem, but I find that the noise occurs when I operate the switches. I then found the noise occurred when I tapped the chassis. I haven't had time to look at the amp again, by I suspect the problem is a bad earth, possibly the negative bias point going to earth. I'll let you know what fixes the problem when I get time to look at the amp.

[tubedogsmith]

Have you got a .01 cap on the switches? I don't put one in the amp but I've got them in the footswitch. I never had a problem with the amp switches until the last couple weeks. It's gotten cold and dry here in florida and I guess static electricity is building up. I went ahead and put a couple caps on the switches in the amp and it stopped the pop.

[Mark]

The reason I suspected the output tubing is the guy who owns the amp complained that it stopped working. We found the the earth measured okay when we were probing it, but in operation it didn't work.

It worked like a gem once the earth was tightened.

[Structo]

Greiswig,
Do you have the 10M resistor from the entrance to the OD to ground?

I'm thinking that is what that is for, to prevent popping.

I haven't experienced any popping on my amp.

I pretty much have my amp as shown in the Tweaked layout now.

[greiswig]

Thanks for the suggestions, folks. I'll report back if/when I figure out what it was.

[Mark]

I worked on the D'Lite today. I touched up any joints that looked as if they could be dry, and I relocated the earth for the output tubes so it was making direct contact with the chassis.

I thankfully no longer have a problem.

[greiswig]

Checked my grounds, and nothing changed. But I think the .02uF cap attached to the OD relay is leaking, judging from some odd voltage readings from it. I'll switch it out and report back.

[Funkalicousgroove]

Greiswig,
Do you have the 10M resistor from the entrance to the OD to ground?

I'm thinking that is what that is for, to prevent popping.

I haven't experienced any popping on my amp.

I pretty much have my amp as shown in the Tweaked layout now.

That resistor is totally superfluous unless you have a small cap preceeding the OD input, otherwise the OD input network(220K/100K pot) serves as enough reference to ground to prevent popping.

the issue sounds like a Tube or a bad ground. Make sure the nuts are tight on your switches as well-

[talbany]

Try using a 9v battery to run the switches..isolate your relay power supply
If it stops you know it's in your supply..Thats my suspect
Are you using a regulated supply?
Too high a voltage on the relays will sometimes cause them to pop/snap...





Tony VVT

[greiswig]

Try using a 9v battery to run the switches..isolate your relay power supply
If it stops you know it's in your supply..Thats my suspect
Are you using a regulated supply?
Too high a voltage on the relays will sometimes cause them to pop/snap...

Tony VVT

Good suggestion, Tony. Would undervoltage cause problems? I've got 4 relays in this build, and one of the things that I noticed is that the 14V supply voltage drops to around 8V when all 4 relays are engaged. I'm asking too much of this power supply, evidently.

[talbany]

That does not sound like the case here since the pop starts on power up... and drops out when start switching them.. (Voltage Drops pop goes away) 14 volts is not unusually high at least not enough to cause the issues you describe.. Do all the relays pop or just the OD.. Does it pop with the footswitch unplugged?..With that many relays I would regulate it might help with the DC offset

Tony VVT

[Funkalicousgroove]

I'm going to agree with Tony, perhaps use 5v relays and regulate your 14v to 5v, use plenty of filtering as well, 1000-3300uf. If your supply is dropping to 8v you are putting too much strain on your transformer, regulating this at 12v will be straining both the transformer and the regulator-

[Structo]

I went with a 8v regulated supply and used the ultra sensitive 5v relays.

I am only using two relays at this point so it doesn't strain it too much anyway.

[greiswig]

I'm going to agree with Tony, perhaps use 5v relays and regulate your 14v to 5v, use plenty of filtering as well, 1000-3300uf. If your supply is dropping to 8v you are putting too much strain on your transformer, regulating this at 12v will be straining both the transformer and the regulator-

I'm surprised that the otherwise unused 5V tap isn't able to supply enough current to run 4 of these little relays plus the LED's that are in series with 2 of the coils. But yeah, it sounds like I am taxing it. Thanks.