5E3 Input Options

[Shawnobi]

Hi, after some thoughts.

Ripping out an old 6V6 P2P build I did and I've built a 5E3 board to go in.
Now my chassis has 1 jack input and I don't have space for all 4 inputs due to the previous layout design.

Can probably squeeze two inputs, as I'm aware that the 5E3 is affected by both volumes interacting. Do I need all 4? I've considered keeping the 1 input and having a 4 way selector switch.

What are peoples views?

[Shawnobi]

I guess I could also 'Hard bridge' the 2 channels as seems popular.... Hmm

[DRH1958]

You could build the standard hi/lo two jack setup. Then instead of using the 820R/25uF common bias setup for both triodes, you could do 1.5k /10uF for each and put a mini toggle to switch the input to bridge the channels that way. I wouldn't worry about the two volumes, just keep them the way they are. Separately biasing each stage will ensure that the one channel is properly biased if you use only that triode. It wouldn't be if you used the common bias setup. Another way would to be to bias the second triode a little differently. One of the methods of thickening up tone is to parallel triodes with slightly different bias points, so you could use a 1.8k or 2.2 k to bias the second triode. If you don't like it, just put the 1.5k back in.

[mozz]

Put a stereo jack in. Then use a y splitter to access both inputs.

[Steve A.]

I would use the stock 5E3 circuit omitting the two Lo input jacks. (If you really needed to use a Lo input from time to time you could make up an in-line adaptor.) One advantage with this arrangement is that you could put the 33k grid stoppers right on the tube socket with shielded cable going to the jacks.

Steve Ahola

P.S. I do like the "hidden mode" on the stock 5E3 but if you are going to split the cathodes I would go for a thicker sound for the Normal channel.

[pdf64]

See http://music-electronics-forum.com/t30576/ for the arrangement I use.
Apologies to deci belle, I neglected to respond to his last query in that thread.

[Shawnobi]

Thanks for all of the suggestions. (pdf64 - will have a proper read of that later).

I was thinking that I could just leave the 2 inputs I wasn't using unwired. Hadn't considered this would inpact the circuit at all. Do the input jacks need to be the type that switch to ground when unplugged?

[pdf64]

Do the input jacks need to be the type that switch to ground when unplugged?

Each channel needs a switching jack socket, to avoid hum when nothing is plugged in.
My arrangement requires the 'B' channel to have a stereo switching socket.

[Shawnobi]

Each channel needs a switching jack socket, to avoid hum when nothing is plugged in.
My arrangement requires the 'B' channel to have a stereo switching socket.

You can tell I've wired more guitars and pedals than amps, hey?

[Steve A.]

[QUOTE=pdf64;418954]See http://music-electronics-forum.com/t30576/ for the arrangement I use.

I worked out an arrangement so that with 1 regular/mono and 1 stereo switching jack sockets, I could achieve all the above, such that -
Input A (Normal / Link) - plug into this ONLY to use both channels.
Input B (Lead) - plug into this to use 'Lead' channel; doing so disables the 'link' function, allowing the channels to be used independently.

Great idea for a 2 channel amp!

I... can't see any use for -6dB padded inputs (just turn the guitar tone down a little if additional loading on the pickup is desired).

I can't remember the last time I plugged my guitar into the Lo input jack (besides jamming with a friend using a single Champ amp back in 1970!) In any case it might come in handy with a line level instrument like a keyboard however it would be easy enough to wire up a dongle for applications like that.




Steve Ahola

[Shawnobi]

Just dredging up this thread of mine as I've finally built the amp and just finishing the input.

I've ended up with a single input jack. I've a switch that selects between input 1 on each channel. The other channel is grounded when not selected.

The other 2 inputs are unused and permanently grounded.

Can anyone see any glaring flaws in my design that I'm missing here?

[Dave H]

Can anyone see any glaring flaws in my design that I'm missing here?

The guitar will always be connected to a 'Lo' input. ie. loaded with 136k. Do you really want that?

[Shawnobi]

The guitar will always be connected to a 'Lo' input. ie. loaded with 136k. Do you really want that?

Dang. No!
Both supposed to be highs (Note that the 1M input resistor is still present at the input jack).

So my input resistance is 1M. But I should be seeing 34k from the grid stoppers for the 'Bright' input, yes? But poss' not with my design because one 68K stopper is grounded??
So I should be connecting the 'spare' 68K's back onto the input to get the 34K in parallel?

[Steve A.]

Dang. No!
Both supposed to be highs (Note that the 1M input resistor is still present at the input jack).

So my input resistance is 1M. But I should be seeing 34k from the grid stoppers for the 'Bright' input, yes? But poss' not with my design because one 68K stopper is grounded??
So I should be connecting the 'spare' 68K's back onto the input to get the 34K in parallel?

If following the original schematic you would leave the unused inputs ungrounded. If both channels have a common cathode you can access the "secret" mode by turning up the unused volume control.

For the Hi input you want a 1M grid load and 34K grid stopper (measure with a DMM if necessary.)

Steve Ahola

[mozz]

You're defeating one of the great uses of the 5e3, being able to jumper both channels.