Volume control not working on express clone.

[amiga]

Hi there.

Some time ago I built an express clone ( Ceriatone ) and have had it working very well for the last couple of years however I had some problems with an unstable input jack so I decided that it might be a good idea to change out all of them with the vintage Switchcraft type.


After putting it back together the volume control does nothing, the amp appears to be on full volume. I replaced the volume pot and that did nothing. I checked the ground connection from the 1st pin of the pot ( looking from the back with the pins up ) to the bus bar and chassis and that seems O.K. The E.Q controls respond O.K but the amp is too loud of course. I have had a good look around and I'm stumped, was wondering if anybody had any ideas of where to look ?

The only other thing I did was replace the 500pf treble cap with a 630v film capacitor of the same value.

Thanks.

[guitarsnguns04]

Post a picture or two and we will figure it out for you

[marcoloco961]

Normally when a volume knob is not functioning properly and is stuck "wide open" the pot has lost it's ground reference. Even though it looks good do a continuity check or just redo the solder joints. I'm betting that is all it is.

[Firestorm]

Check the bright switch wiring, too. A short there can bypass the volume pot.

[amiga]

I'll get some pictures later on today.

Thanks for all the suggestions. I checked the ground with a MM and it seems O.K.

Not sure about the behavior of how the volume works in a wreck circuit but
the volume pot measures little or no resistance ( it's fully open at 7 o clock and on full ) when I go through all of the ranges ( using a DMM ). If I remove the wire that goes from the volume pot to the centre post of the treble pot then the volume pot starts working correctly. The other pots measure within spec and work correctly.

I'll check the bright switch circuitry again later on today but it looks like nothing is wrong there.

[Firestorm]

If I remove the wire that goes from the volume pot to the centre post of the treble pot then the volume pot starts working correctly.

When you do that, it should not work at all. Something is wired crooked.

[amiga]

Sorry if I wasn't very clear with my previous post. This is with the amplifier turned off actually.

If I disconnect the wire from the volume pot to the treble pot, then I am reading just over 1M on the DMM with the volume on 0. I was just trying to trouble shoot the pot by isolating it from the rest of the circuit.

With the wire from the treble pot connected as it should be, the DMM is reading almost zero ohms in both directions and slightly increasing in resistance around 12 oclock.

I just want to confirm with anyone if this would be the correct behaviour so I can get a clearer idea of where to go from here.

Anyway here are some shots.

[Firestorm]

With the amp off and the connection from the treble pot to the volume pot in place, turn volume pot and all tone pots up full and measure resistance from the volume pot wiper to ground. It should be about 670K. If you turn either the treble pot or the bass pot all the way down, this resistance should drop to about 500K. If you turn all tone pots all the way down, the resistance to ground should drop to zero. Does all this happen?

When you say the volume control has no effect, does that mean that the amp is fully on even with the volume pot all the way down?

You are using an audio taper pot for the volume, right?

[amiga]

With the amp off and the connection from the treble pot to the volume pot in place, turn volume pot and all tone pots up full and measure resistance from the volume pot wiper to ground. It should be about 670K.

With the volume , and three tone settings up on full I am reading 670K on my DMM

If you turn either the treble pot or the bass pot all the way down, this resistance should drop to about 500K.


530K with the treble pot turned down and about 520K with the bass pot turned down.


If you turn all tone pots all the way down, the resistance to ground should drop to zero. Does all this happen?

Yes, resistance is zero with all three tone pots down. Volume still up on full btw.

When you say the volume control has no effect, does that mean that the amp is fully on even with the volume pot all the way down?

Yes that's correct. I noticed it right away as I powered up the amp, I had all the controls on zero and the hiss was noticeably quite loud once I switched the standby to on. In fact with all amp dials on zero, I could play guitar and I could still hear it coming through the speaker.

Normally, I am able to play it at comfortable bedroom levels with a nice crisp and clean tone on about 1 if I have to.

You are using an audio taper pot for the volume, right?

Yes that is correct. It's a 1MA pot.

I haven't powered the amp up since I had this problem out of fear of damaging the amp, so at this point I've made a few changes, cleaned things up a little here and there. Will power up again when I feel confident enough and see if there is any improvement.

Thanks for your help.

[Tillydog]

Check the bright switch wiring, too. A short there can bypass the volume pot.

+1

Make sure the centre lug on the volume pot hasn't punched through the insulation on the red wire going from the bright caps to the RH lug (per your pictures) on the volume pot.

0.02p

Andy

[Structo]

Is that bright cap combo touching the ground buss?

[Firestorm]

I haven't powered the amp up since I had this problem out of fear of damaging the amp, so at this point I've made a few changes, cleaned things up a little here and there. Will power up again when I feel confident enough and see if there is any improvement.

Based on your DMM readings, you should be able to confidently power up with the three tone controls set all the way down. This should ground out the signal and you can experiment from there. (If that doesn't happen, it tells you something, too.)

[don280z]

You said you also replaced one of the Bright Caps?
Have you tried operating the Bright Switch?...If one of the caps is shorted it would bypass the volume control giving you full volume.....

[amiga]

I will fire it up today and see what I can accomplish.

I have checked the wiring on the bright switch and it is fine. I have one of the cap leads to the bright switched heat shrinked as well, hard to see from those angles.

You said you also replaced one of the Bright Caps?

The only cap I replaced was the 500pf treble cap ( 1st picture ).

[amplifiednation]

I had a similar problem with a build a few months ago and realized after a lot of troubleshooting I had a wire reversed at the 2nd triode. Take some pics we will help you figure it out

Edit: sorry I wasn't logged in, couldn't see the pics. I'd like to see more though!!