Bright on Clean Without Additional Relays - non HRM

[ayan]

You guys know I have been thinking about this for a long time now, but never felt like drilling my amps to add another relay. At the end of the day, this is analogous to what I used to do at the OD network entrance years ago. The brightness network can probably be something like a 220k//500pF or thereabouts and can be added right at the existing channel switching relay, replacing what normally is a straight wire in non HRM amps. It can be defeated with an optional panel switch, or the Bright front panel switch can be replaced with a DPDT center off to keep the original Dumble options stock and add this one. I haven't had the time to put this into my gigging amp yet, but it looks like a winner on paper and I like the fact that it works independently of any pot settings... maybe I'll be able to lose the horrible master bright caps!

To those brave enough to try it, I'd be curious to know what kind of a resistor and cap pair you end up with.

Cheers,

Gil

[vibratoking]

Sounds like a clever idea. It seems you'll also have to cut a trace on the relay board to make it work?

[ayan]

Sounds like a clever idea. It seems you'll also have to cut a trace on the relay board to make it work?

No, no cutting of anything is required. The relay board, in a non HRM amp, should have the NC of one pole jumped with a wire to the NO of the other. Rather than using a straight wire to jump those two points, there would be this cap//resistor pair instead, as shown on the schematic.

Gil

[vibratoking]

No, no cutting of anything is required. The relay board, in a non HRM amp, should have the NC of one pole jumped with a wire to the NO of the other. Rather than using a straight wire to jump those two points, there would be this cap//resistor pair instead, as shown on the schematic.

Gil

Quite a few of us have PCB versions of the relay board where the NC to NO connection is made via trace. That trace would have to be cut to have the RC on clean only. You can see an example in this rev 5 layout. http://ampgarage.com/forum/viewtopic.php?t=12873

Cutting the trace is OK with me and I'll try it when I get some time...I like the idea.

[ayan]

If you're not a true copycat like me, I guess you'd have to X-Acto blade the trace, just as if you wanted to use your relay board for an HRM amp.

G.

No, no cutting of anything is required. The relay board, in a non HRM amp, should have the NC of one pole jumped with a wire to the NO of the other. Rather than using a straight wire to jump those two points, there would be this cap//resistor pair instead, as shown on the schematic.

Gil

Quite a few of us have PCB versions of the relay board where the NC to NO connection is made via trace.

[Structo]

One of the best mods in my opinion.

This is how I did it.

I believe I have a 120pf cap on it.

This layout is with the AGB relay boards.

[norburybrook]

If you're not a true copycat like me, I guess you'd have to X-Acto blade the trace, just as if you wanted to use your relay board for an HRM amp.

G.

No, no cutting of anything is required. The relay board, in a non HRM amp, should have the NC of one pole jumped with a wire to the NO of the other. Rather than using a straight wire to jump those two points, there would be this cap//resistor pair instead, as shown on the schematic.

Gil

Quite a few of us have PCB versions of the relay board where the NC to NO connection is made via trace.

That's exactly what I did for my BM

Marcus

[JD0x0]

subscribed. I'll have to try this soon. Thanks for the diagrams, everyone!
I think this is exactly what my amp needs.

[norburybrook]

My simpler solution is to turn down the tone a little on my guitar before hitting the OD switch



Marcus

[ayan]

I am not saying this is not "electrically sound," but in one case you end up grounding the extra relay at the ground buss for the audio signal. Dumble went through the hassle of routing the relay grounds from the voltage regulator at the front of the amp all the way to the diametrically opposed end, on the back of the amp, for what I can only assume is a valid reason: noise control. You may want to consider running a wire from the front panel switch to the original relay ground in the back of the amp instead, so as to leave the audio ground alone.

Gil

One of the best mods in my opinion.

This is how I did it.

I believe I have a 120pf cap on it.

[Structo]

Thanks Gil.

I'll look into that.
Do you mean the wire from the top of the switch to the bus wire?

Didn't you discover that either #124 or #102, did not have the rear switches grounded?

I just realized that layout I posted shows the right hand lug of the Volume pot to ground, that is an error.

I'll fix it.

[ayan]

Yes, I am referring to mixing audio and relay grounds.

124 and at least one other amp here in L.A. didn't have the PAB switch grounded. Both amps have an ON-OFF-ON jazz/rock switch, so you could achieve "true PAB" that way. However, the owner of the amp that is not 124 could hear a difference between the J/R middle position and the PAB via footswitch (which has the 22 Meg resistors VS an open circuit in PAB). He called Dumble and asked him about that, and the response was "I'm surprised you can hear the difference."

Gil

Thanks Gil.

I'll look into that.
Do you mean the wire from the top of the switch to the bus wire?

Didn't you discover that either #124 or #102, did not have the rear switches grounded?

I just realized that layout I posted shows the right hand lug of the Volume pot to ground, that is an error.

I'll fix it.

[Structo]

OK
Thanks for the recollection, now I recall it.

[jcsifu]

One of the best mods in my opinion.

This is how I did it.

I believe I have a 120pf cap on it.

This layout is with the AGB relay boards.

I was excited to read the title of this post as this mod is exactly what I have been trying to figure out for a while now. I really can use this mod. I have been trying to figure out how your switching works but I can't get my head around it, maybe because I have different boards than you do(ceriatone relay boards). Do you by any chance have a schematic version of your mod? Or any bit of info to point me in the right direction to understanding the switch function? Sorry to beg but I have no shame...

[Smitty]

...

To those brave enough to try it, I'd be curious to know what kind of a resistor and cap pair you end up with.

Cheers,

Gil

I've been fiddling with this for about six months. Try a 470 with a 47pf. I've had success with that combo for a strat. Perhaps 100pf for a 335. It'll be different for each player though. It depends how high you want to run your Volume and Master.

IMO, this is the fix for these types of amps.