5E3 Volume control question

[gtrplr2]

I recently completed my 5E3 kit and I am trying to figure out where I went wrong, it has Alpha 1M pots. On both channels the volume knob responds from 0 to 2 normally, then from 2 to 8 there is no volume change, then at 8 the volume picks up again. I have rechecked the wiring and component values 3 times without anything being evidently wrong.

[Dave H]

It's OK. That's one of the design 'features' of the 5E3

[gtrplr2]

It's OK. That's one of the design 'features' of the 5E3

It actually was not OK. I had the output jacks wired wrong. Once I got that straightened out, the volume control works like it should through the full rotation of the volume control.

gtrplr2

[Dave H]

Good work in finding the fault. I thought it was OK because your first post was a perfect description of how I remember the volume pot working on the first 5E3 I made. It’s normal for this circuit as it has the connections to the wiper and CW terminals reversed compared to the usual way of wiring a volume pot.

Dave H

[gtrplr2]

Thanks Dave H,

I had it wired for a MM OT, and not the one I have. It became obvious after an email from Bruce at Mission Amps about the OT.

gtrplr2

[Gee]

Thanks Dave H,

I had it wired for a MM OT, and not the one I have. It became obvious after an email from Bruce at Mission Amps about the OT.

gtrplr2

Out of interest, what was wrong with the way the OT was wired?

[gtrplr2]

From Bruce,

On the MM OT the two tip lugs "ARE" connected to each other because the jacks need to be in parallel, why?, there is only one 8 ohm tap in the MM OT. The MM OT uses one mono jack and one switching jack. You do not have the switching jack. Two mono jacks are needed so that either the 4 or 8 ohm jack can be used with the matching speaker load. You can not have a switching jack because if there is nothing plugged in, it will ground out the unused jack and wreck the impedance of the OT or worse, just kill most of the audio.


So when I originally hooked it up I was looking at a diagram for the output jacks for the MM OT, (mine is not a MM). So I hooked the tip lugs together, and it gave me the weird situation I was having with the volume control. When I rewired the jacks with nothing hooked together and then switched around the wires to the jacks, (yellow to the 8 ohm jack tip, green to the 4 ohm jack tip and the ground wire to the barrel of the 8 ohm jack-with no ground wire to the 4 ohm jack) it works great, plenty of volume evenly all the way through the rotation of the pots.

gtrplr2

[Gee]

gtrplr2 - Thanks for the explanation. I can see how that would have changed the behavior of the amp. It's interesting that the volume behaved in such a way when wired like this.

[gtrplr2]

No problem Gee.