Preamp Pedal

[stutter]

I was wondering if someone could help me.Im going to build an SEL preamp in a pedal.http://annex.ax84.com/cliffc/amps/AX84/SEL/06.07.25/AX84%20SEL%20Schematic.pdf From this schematic.I was wondering how i would wire up a 3dpt switch with this,and where i would wire an output socket.

Cheers

[QSQCaito]

Well, that's an amp. If you said you're going to build the peramp of it, I believe you're going to build it upto the Master Volume control. After it you have the power valve. 2 12AX7, that will probably be quite powerful.

If I'm not wrong you could put an output jack from the Master volume wiper, which is leg 2. And ground obviously, which is leg 3 of the master volume pot.


What remains unclear to me is why the 12AX7 are labelled V5 and V4, the power stage V2. Where are valves 1 and 3?}


You don't need the complete power section, you don't need to power up the power valve.

SW1 DPDT gives power to the amp. The Stand by switch is also needed. Don't use it until a couple min. You need valves to heat up. And well, if all switchs are ON it would be working. You could most probably put a DPDT as you regularly do in a stompbox, with it's led. You'll have a DPDT to turn it on, a pilot lamp and a spst. And a stomp switch to bypass it or not.

I doubt that you can do it in a stompbox, it would fit(in a bigg stompbox) but you'll probably have noise issues, as HUM. I would build in a big box, seperate. And use a relay to bypass it. I wouldn't have my tubes in the floor, moving around.. having to take care of it being stepped.

Hope it helps.

DAC

[sfx1999]

Have you ever worked with tubes before? The SEL and the similar HO are difficult to get working. If you don't know what you are doing, you will get hum, buzz, squealing, etc.

[stutter]

Yeah i have worked with tubes before but this is the first time i have used them in a pedal.Sorry should have made myself clearer i willl only be building the preamp tonestack and rectifier board in that schematic.I think if i lay it out properly and compact i should be able to fit it in a medium sized hammond box.The biggest thing is the PT but i will be using a toroidal one so thats more space saved.

[sfx1999]

Well this is much more feasible now. You would take the output right after the master volume to your switch. The LED will be a problem, though. You will use the heater supply for it. It would be much easier to use a bulb. The thing is, if you run the heaters to your switch, they may induce hum in your output.

Here is the problem, though. Your B+ will be much higher than on the schematic because you don't have a power stage. You might be better off using the HO as a base.

One thing to note, you can get away with not having a standby switch.

[Pushtone]

Well, that's an amp.

What remains unclear to me is why the 12AX7 are labeled V5 and V4, the power stage V2. Where are valves 1 and 3?}

I'm glad this came up. I was going to post about the new(ish) organization of projects over at ax84.com

Chris at ax84.com has gone modular! with his new CORE projects.
All the familiar projects, the P1, Firefly, Hi-octane are now labeled as LEGACY projects.

The new CORE projects are modular in the sense that you can combine any preamp with any power amp.

NICE!

So those missing valves are part of one of three different preamps. One preamp even omitts a valve.
It threw me for a loop when examining the power supply schem. I was like" what the heck are all these B+ for?!?"

When it became clear to me it was a wonderful picture and design discipline.
I'm 100% behind the CORE projects. The 50 watter is soooo tempting but I'll built the 20watt PP first.
And the LEAD PREAMP makes for a full featured DIY amp.

Check out the board layouts and see how Chris has gone modular with the pre, power, and recto boards.
Opened my eyes to tube amp construction on several important areas I could not see in a schem of the whole amp.

Cheers to Chris and ax84.com for the brilliant site and projects.
It's a shame that diystompboxes gets kinda a bad rep over in their forum.

[stutter]

Yeah i dont use standby switches when building amps anyway.Could i just use a couple of Zeners to drop the B+ a bit? The toriodal transformer im using is 200v and 6.3v im not sure what that would come out as after being rectified though.

[sfx1999]

Actually, looking at that, you may not have to. But yeah, you can reverse bias zeners in series with the B+ to drop the voltage. You will want to use a string of smaller zeners to do it. You have to be careful that they don't short; that's why you would use small ones. They need an adequate power rating, too. 1W 10V should work.

[QSQCaito]

Well, that's an amp.

What remains unclear to me is why the 12AX7 are labeled V5 and V4, the power stage V2. Where are valves 1 and 3?}

I'm glad this came up. I was going to post about the new(ish) organization of projects over at ax84.com

Chris at ax84.com has gone modular! with his new CORE projects.
All the familiar projects, the P1, Firefly, Hi-octane are now labeled as LEGACY projects.

The new CORE projects are modular in the sense that you can combine any preamp with any power amp.

NICE!

So those missing valves are part of one of three different preamps. One preamp even omitts a valve.
It threw me for a loop when examining the power supply schem. I was like" what the heck are all these B+ for?!?"

When it became clear to me it was a wonderful picture and design discipline.
I'm 100% behind the CORE projects. The 50 watter is soooo tempting but I'll built the 20watt PP first.
And the LEAD PREAMP makes for a full featured DIY amp.

Check out the board layouts and see how Chris has gone modular with the pre, power, and recto boards.
Opened my eyes to tube amp construction on several important areas I could not see in a schem of the whole amp.

Cheers to Chris and ax84.com for the brilliant site and projects.
It's a shame that diystompboxes gets kinda a bad rep over in their forum.

That's very clever!! You can build your favorite preamp, with the power stage you like the most. cool and very clever.

Yeah i dont use standby switches when building amps anyway.Could i just use a couple of Zeners to drop the B+ a bit? The toriodal transformer im using is 200v and 6.3v im not sure what that would come out as after being rectified though.

Well, rectified voltage should lower a bit.

Anyway, I'd rather use voltage regulator than zener. But if it's just for a led a zener should be more thank Ok

[stutter]

Right so now i know how to wire up the output....Where would i wire up the *circuit input and output* that is needed when wiring up the 3DPT switch?.Im not changing anything of the preamp except a cold bias stage like the Soldano maybe 39k cathode resistor at the third stage.Then turn the cathode follower into another Gainstage.  More metal than i will ever need.

[sfx1999]

I wouldn't recommend having your last tube be a gain stage. You would have to change the tonestack and such.

Anyway, you might want to look into the Supercharger GTO.

[stutter]

Yeah but id just connect the tonestack to the anode on the last gainstage.Nice and simple.

[sfx1999]

I know that, what I am saying is the original cathode follower has a lower impedance than your gain stage would, requiring you to use different values for the tone stack.

[stutter]

hmmm didnt know that.Well ill just leave it as a cathode follower then...if i ever need more gain add another tube and use both triodes for a cascode boost etc

Cheers