Yet Another Duplex Drive- with improvements!

[warriorpoet]

Man, it's so good to see all these Duplex drives being finished; it's a great circuit!

So, my goal on this was to build it to sound as close to the YouTube clips as possible. Every G2ish I've built to this point has been DARK. There are all sorts of mods and suggestions from across the Internet, but I think this fix finally nails the issue once and for all. It comes down to one single cap: C5.

Here are the vitals, then I'll get into the build itself:

G2 darkness fix- looks like there might be an error in the original circuit trace, based on what I'm hearing.

C5: 100pF (internet schematics, build docs say 1nF)

Kit Rae mod:
R10: 18k (build doc says 15k)
R11: 100R (build doc says 680R)

I found with the cap switched, any germanium diode under ~.3fV sounds great, and the darkness problem is GONE!

IMPORTANT: The higher the fV, the darker the G2 side sounds. Low threshold germaniums (under .3fV) are ESSENTIAL to achieving the correct harmonic "signature".

Here's what I settled on:

D1, 2, 5, 6 (G2 diodes): CV7127 germanium (Super, super smooth at fV .22-.26fV)
D7, 8 (SS2 diodes): 1D507A germanium (my favorite Soviet sleeper @ .27-.28fV)

Guess what; it sounds like the YouTube clips, with maybe a little more grit and character on the SS2 side (the diodes make a big difference on that side).


Other fun:

Duplex Drive graphics (Google it) screen printed at PPP
Micro incandescent bulbs for indicators (100R CLR)
22 AWG pushback cloth wiring

The message inside the back cover is for a friend's son, who is receiving this as a graduation present.

Enjoy!







...and yes, I fixed the stomp wiring

[cajone5]

beautiful

[Manc]

Pretty amazing!
I did changed the values of those resistor, plus your cap swap hint didn't pass unnoticed

I tried a lot of GE diodes, eventually settled on some SI BAT43, and 1N270 for the SS side... pretty happy with the tone, I must admit.

[warriorpoet]

Pretty amazing!
I did changed the values of those resistor, plus your cap swap hint didn't pass unnoticed

I tried a lot of GE diodes, eventually settled on some SI BAT43, and 1N270 for the SS side... pretty happy with the tone, I must admit.

Very cool!

1N270s were my second favorites on the SS2 side, but the 1D507As just have this great gritty character I love. Don't have any BAT43s around; what's the fV? Tried 1N60p, BAT41, BAT46 and BA282s, plus my germaniums (I have a LOT of germaniums...), and all are too dark for my taste on the G2 side over ~.3fV, even 'ol reliable 1n34as! Might need to pick up some BAT43s to try out!

Glad the cap swap worked out for you! I was shocked by how much difference it makes!

[stringsthings]

Really excellent build.  I'll have to do that cap switch to brighten mine up.

[gordo]

Great build!  I love the big electros. I'll have to open mine up to give the parts swap a shot.

[electricb]

That looks amazing. I don't know if I could rearrange the board to fit those massive electros but good for you for making them fit. I'll bet that build sounds incredible. Also, I think your detective work on the cap change is massive. People have been complaining about the G2 darkness since it was traced years ago and it seems like you have cracked it. I'm actually rebuilding my duplex with your changes because I can't wait to try them. Well done all around!

[Timko]

I have a general diode question for you, since you seem to have some oddballs in your build.  I have your standard diodes in my collection from various pedal building sites online.  If I wanted to acquire some of these other diodes, do I just start ordering them off eBay?  Is there a short list of some good ones to have?

[warriorpoet]

That looks amazing. I don't know if I could rearrange the board to fit those massive electros but good for you for making them fit. I'll bet that build sounds incredible. Also, I think your detective work on the cap change is massive. People have been complaining about the G2 darkness since it was traced years ago and it seems like you have cracked it. I'm actually rebuilding my duplex with your changes because I can't wait to try them. Well done all around!

Thank you!  I really appreciate you making this board available; it's an awesome layout!

Please post your impressions after the mod. I've done 3 now with the cap and resistor changes, as well as the diodes in the list above, and all 3 have been very consistent, and almost unbelievably noise-free.

[warriorpoet]

I have a general diode question for you, since you seem to have some oddballs in your build.  I have your standard diodes in my collection from various pedal building sites online.  If I wanted to acquire some of these other diodes, do I just start ordering them off eBay?  Is there a short list of some good ones to have?

Hey Timko,

I have done a lot of experimenting with different types of diodes, mostly out of curiosity. The CV7127s are just mil-spec DO7s, and I discovered the 1D507As by accident when I ordered some mislabeled OTK-254s. Man, am I ever glad I did that!

If you ever want to try a few oddities, PM me, and I'll send you some samples for the 'ol breadboard

[warriorpoet]

Really excellent build.  I'll have to do that cap switch to brighten mine up.

Thank you! Do the cap switch; it's amazing how much difference it makes!

When you couple that with low fV diodes on the G2 side, the difference is just night and day off the original trace.

Great build!  I love the big electros. I'll have to open mine up to give the parts swap a shot.

Thank you! Man, I have such an unhealthy love for giant audio caps

Let us know what you think after you swap things around!

[gordo]

Opened it up tonite and did the swap. Very nice!  Really opens up the tone control with bright sounds starting at about noon and useable over its full sweep. I stuck with the diodes in the build docs. Highly recommended.

I really like all 3 of electricb's double drives: dual bluesbreaker, maxon/Klon, and this cornish

[JC103]

Very interesting re: C5! We built one up with Wima caps and A113 diodes for the G2 (with fv of .26). Sounds great, the best G2 build I've tried yet... but it's dark for sure. Even with the treble all the way up it doesn't get those bright tones heard on the youtube videos. Not complaining, sounds great with my amp, and a Cornish buffer into a Compulator pre G2 brings the goods. Will have to the try cap swap.

[JC103]

PS: Good work, and great build! Love the graphic and knob choices.

[warriorpoet]

Very interesting re: C5! We built one up with Wima caps and A113 diodes for the G2 (with fv of .26). Sounds great, the best G2 build I've tried yet... but it's dark for sure. Even with the treble all the way up it doesn't get those bright tones heard on the youtube videos. Not complaining, sounds great with my amp, and a Cornish buffer into a Compulator pre G2 brings the goods. Will have to the try cap swap.

Awesome!

The cap swap is incredibly effective. Be sure to post back when you do swap; I'd like another point of verification, if possible