My S3X

[Tom-s]

Wanted to share my experience with the Single Ended eXperimenters kit. Hope to inspire others.
Purpose build for use with Klipsch Heresy III speakers (and AKG K340 headphones from time to time).

It was build stock first. After some time i installed the C4S upgrade.
Then i build the Mainline type volume control into S3X.
After that i changed the caps for 1.9uf MBGO-2 output and FT-3 0.1uf interstage Ruskies.
That's how it is for now (not in pictures). Planning on some powersupply "upgrades" in the future. And some alternations to the input/output wiring.

Relevant topics that got me this far:
Volume control/powersupply: https://bottlehead.com/smf/index.php?topic=10991.0
Input impedance: https://bottlehead.com/smf/index.php?topic=10985.0
Powersupply: https://bottlehead.com/smf/index.php?topic=11134.0
Balanced speakers for S3X: https://bottlehead.com/smf/index.php?topic=11053.0
Klipsch Heresy III and S.E.X.: https://bottlehead.com/smf/index.php?topic=98.msg101551

Pictures:
Stock: https://ep1.pinkbike.org/p5pb16498301/p5pb16498301.jpg
Finisched top plate: https://ep1.pinkbike.org/p5pb16519340/p5pb16519340.jpg
Overview bottom side: https://ep1.pinkbike.org/p5pb16519341/p5pb16519341.jpg
Close-up volume control: https://ep1.pinkbike.org/p5pb16519343/p5pb16519343.jpg

Will post more later on.

Edit: The pictures with MBGO-2 parafeed coupling and FT-3 interstage coupling caps:
https://ep1.pinkbike.org/p5pb16521276/p5pb16521276.jpg
https://ep1.pinkbike.org/p5pb16521277/p5pb16521277.jpg

[sammyk]

Thanks for posting this reference Tom, found a lot of useful stuff here that for some reason I couldn't find with forum search. Looking forward to your updates.

[lyons238]

any updates to this build?

I'm considering a few upgrades myself:
- Ugraded power cord (have)
- C4S Upgrade (have)
- PEC Carbon POT (have)
- Cardas RCA Jacks (have)
- Vintage pilot light (have)
- Upgraded output caps (want)
- Upgraded interstage caps (want)
- Power supply bypass caps (want)

Still not sure of exactly which caps I want or the exact specs I should get.

[Tom-s]

No updates, don't have the time for now. Will try to finish the powersupply upgrades this spring.

For output / parafeed caps 1-3.3 uf 450V caps good film, vintage PIO, modern oil or something "audiophile" will work (i used cheap Russian caps).
For interstage coupling best for the money is Russian FT-3 teflon 600V 0.1uf pair (10-20$ shipped).


For the powersupply it's probably best to put a big cap in the last 100uf position. I'm considering some 800-1000uf electrolytic caps myself with a big film bypass cap. If you can manage to fit a pair of chokes, this will also be worth it. See mcandmars thread.

[Paul Birkeland]

For output / parafeed caps 1-3.3 uf 450V caps

At least a 600V rating is preferred for the parallel feed cap. 

[lyons238]

Thanks for the info. I’m going to build and stick with stock for a while but I’m planning to try some upgrades caps so I’m just doing some research now and making some considerations before I spend the money on some good caps. I’ve also heard bigger values in output could have more extension while a lower uf may have more quantity but less extension. Is this accurate? If so I may stick somewhere around the stock values but upgraded film caps with a higher V rating. I’ve also been looking at heat ratings. The Mumforfs have like a 50C rating I think? Would 75C be more appropriate I’d imagine?

[Paul Joppa]

By my calculations, 1.25uF is the compromise value, and gives measured bass that is 3dB down at 27Hz.

The trade-off is bass small-signal extension vs. bass distortion. A larger capacitance will get you deeper extension, but at the lowest working frequencies the impedance presented to the tube is less than the design target, so the bass power capability is reduced.

It's been my opinion (based on modeling) for some time that the range of half to twice the compromise is reasonable, giving small signal response to 40-20Hz respectively.

Remember, if the load (speaker or headphones) has significant impedance variations they will also impact deep bass performance in ways that are difficult to predict. Use your ears! In fact, I sometimes suggest that you acquire some inexpensive caps to experiment with first, and save to cost of boutique caps until you are confident you know what value you want in your system.

[lyons238]

By my calculations, 1.25uF is the compromise value, and gives measured bass that is 3dB down at 27Hz.

The trade-off is bass small-signal extension vs. bass distortion. A larger capacitance will get you deeper extension, but at the lowest working frequencies the impedance presented to the tube is less than the design target, so the bass power capability is reduced.

It's been my opinion (based on modeling) for some time that the range of half to twice the compromise is reasonable, giving small signal response to 40-20Hz respectively.

Remember, if the load (speaker or headphones) has significant impedance variations they will also impact deep bass performance in ways that are difficult to predict. Use your ears! In fact, I sometimes suggest that you acquire some inexpensive caps to experiment with first, and save to cost of boutique caps until you are confident you know what value you want in your system.

good advice. ill also be using both LCD-2C's and HD650's with quite different impedances but relatively close overall sensitivity. so ill have to find a middle ground. i may try and compare a smaller value cap to a larger value to the stock and see which works best with both headphones. thanks!