Would this practice amp setup work?

[ggedamed]

[...]Would one be sufficient, or are there better alternatives?[...]

One 2N5457 Fetzer Valve stage should give you around 1.5Vpp 3Vpp input headroom and x2 gain. So it will be squeaky clean.
I understand that you only want clean as in Hi-Fi clean. Then you can use almost anything - JFET, BJT, opamp.
Then again, using the same JFETs as input stages will give you a single set of input parameters for both channels.

[sajy_ho]

sajy_ho,

Any reason you chose two fetzer valves in series? vs say one?

Just for a little more gain and no other reason! I'm using two MPF102s with Vp less than 2.5V and have not experienced any clipping even with active pickups.

[pappasmurfsharem]

OK So what about this.

I added a fetzer valve for the clean channel however I'm not really sure how to control the gain in that.

I think I have the buffer pre-tone stack setup correctly and the "recovery stage" should have a gain of 4.3x <--- not sure here.

Any recommendations?


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[sajy_ho]

OK, well done buddy! Here is some suggestions:
1. Eliminate the JFET buffer in front of Ruby and change the value of C19 to 100-220n for more Bass. You already have a nice buffer for increasing signal's current, so the second buffer will be unnecessary. otherwise you may experience some noise.
2. Lower the value of C24; 220n will be enough.
3. Measure Vp and IDss of that 2n5457 in the Fetzer valve and use the calculator at the end of its own page for calculating the value of R33. Be aware that those values will differ from one JFET to another even with the same numbers! Then tweak Trim2 for closest possible Vd . After that You can also exchange the trimpot with equivalent resistor for less noise.
4. Increase the value of C10 if you're using a wall wart. 220u will be good.
5. Use a kind of speaker jack that disconnects headphone's out when speaker is connected, something like this: http://www.marshallup.com/images/source/07_Parts/CliffOneQuarterInchS2BNBCL1160AExternalThreadJackSocketa.gif
6. Use a 47u cap between Headphone jack's sleeve and ring pins. Negative goes to sleeve, positive to ring and tip; otherwise you will hear a HUM trough headphones!
7. Do not pay attention to my terrible English

[ggedamed]

Observation at points
5. You want to wire the jack so it disconnects the speaker when you connect the headphones kinda like here. Scrap that. LM386 IS a headphones amp. Why do you need a second jack?
6. I don't think the 386 will too happy about it.

Here's a nice schematic I did before I remembered there's no need for it . The values are from Rod Elliott's page linked above.

[sajy_ho]

Observation at points
5. You want to wire the jack so it disconnects the speaker when you connect the headphones kinda like here. Scrap that. LM386 IS a headphones amp. Why do you need a second jack?
6. I don't think the 386 will too happy about it.

Here's a nice schematic I did before I remembered there's no need for it . The values are from Rod Elliott's page linked above.

I built a Ruby and there was a hum trough headphones, then I found this:http://3.bp.blogspot.com/-qowGTZwyg4g/T47SLp4qqkI/AAAAAAAABQA/zhTu46i4LuM/s1600/Noisy%2BCricket%2BMkII%2Bwith%2Bheadphone%2Bout.png
That 47u cap completely filtered the noise. That jack is necessary whan you are using that cap, otherwise there is no reason to use that!

[pappasmurfsharem]

Scrap that. LM386 IS a headphones amp. Why do you need a second jack?
6. I don't think the 386 will too happy about it.

Convenience, intention is for a 3.5" headphone jack, and a mono 1/4" for use with a cab. I always seem to misplace my 3.5"1/4" adapters.
I can make the jack switched, but it wont be particularly necessary since I will be unplugging whichever is not being used.

OK, well done buddy! Here is some suggestions:
1. Eliminate the JFET buffer in front of Ruby and change the value of C19 to 100-220n for more Bass. You already have a nice buffer for increasing signal's current, so the second buffer will be unnecessary. otherwise you may experience some noise.
2. Lower the value of C24; 220n will be enough.
3. Measure Vp and IDss of that 2n5457 in the Fetzer valve and use the calculator at the end of its own page for calculating the value of R33. Be aware that those values will differ from one JFET to another even with the same numbers! Then tweak Trim2 for closest possible Vd . After that You can also exchange the trimpot with equivalent resistor for less noise.
4. Increase the value of C10 if you're using a wall wart. 220u will be good.
5. Use a kind of speaker jack that disconnects headphone's out when speaker is connected, something like this: http://www.marshallup.com/images/source/07_Parts/CliffOneQuarterInchS2BNBCL1160AExternalThreadJackSocketa.gif
6. Use a 47u cap between Headphone jack's sleeve and ring pins. Negative goes to sleeve, positive to ring and tip; otherwise you will hear a HUM trough headphones!
7. Do not pay attention to my terrible English

1. Sounds good, how would I vary the gain of the fetzer valve? and do you think the recovery stage is good enough with 4.3x gain? Do you think I should change R35 to a 10k+a 50ktrim so I can adjust from unity gain to 6x gain?

The bsiab doesn't really need the recovery as when I've tested with 3 bands before it has massive output. Not sure on the fetzer though.

3. yeah I put a question mark on the R33 (2k?)to remind myself to figure out the proper value.

[sajy_ho]

Yes, that gain is already too much for driving a 386 chip. You don't want to overdrive the 386 because of its nasty sound distortion, so 4.3x will be enough.(Otherwise you like 386's distortion, just like some of my friends)
For the best results you need to use suggested resistor values from ROG for the Fetzer valve, and gain will not be variable. Av (V/V) in that calculator will tell you the amount of gain(x). If you want more gain just use a Jfet with lower Vp.
As for the headphone out, I meant if you experienced any HUM through headphones, connect that 47u cap; and then you will need to separate headphone out from speaker out.

[pappasmurfsharem]

Yes, that gain is already too much for driving a 386 chip. You don't want to overdrive the 386 because of its nasty sound distortion, so 4.3x will be enough.(Otherwise you like 386's distortion, just like some of my friends)
For the best results you need to use suggested resistor values from ROG for the Fetzer valve, and gain will not be variable. Av (V/V) in that calculator will tell you the amount of gain(x). If you want more gain just use a Jfet with lower Vp.
As for the headphone out, I meant if you experienced any HUM through headphones, connect that 47u cap; and then you will need to separate headphone out from speaker out.

I can lower the gain if necessary using maybe a 15-20k instead of 33k

The BSIAB doesn't need the volume boost to overcome the 3 band TS. The fetzer however might be another story

[sajy_ho]

Now everything is OK, I can't wait to hear about its sound, good luck buddy 

[pappasmurfsharem]

This is what its supposed to end up like if I order it.
I would normally try to get the offboard wiring to be at the board edge for everything to be neat, but that would end up making the board a bit larger plus wasted space

In its current state its ~$27 for 3 boards. I also used SMD J201s since thats what I have, making the adapter board is such a pain. although I suppose I could order a ton from OSH park.

[sajy_ho]

Ohhhh! I forgot to tell you, that C10 must be as close as possible to the 386; otherwise you will hear a crackle noise from oscillation. Also if you experienced that kind of noise even after mounting C10 near the chip, you should increase its value to 220u or 470u.
Good luck. 

[pappasmurfsharem]

glad I didn't order any yet.

Sadly I'm going to have to redesign everything.

Oh well.