Harmonic percolator build sounds too clean

[disorder]

I built a harmonic percolator using Mr. Madbeans Pepper Spray board. Followed the "Albini" schematic, used the proper silver mica and tantalum where they were supposed to be, film everywhere else, and resistors all measure to spec. 2N404A measures ~150 hfe with leakage <100. 2N3565 measures ~230 hfe. The circuit works, both controls work as they would expect and there is a TON of gain on tap, just not much distortion. I am using the 1N695 from small bear both measure right around 0.225V for Vf.  Could I have damaged these guys while soldering or handling them? I broke one of these diodes just by bending the leads too close to the body and it shattered. I'm thinking I have the circuit working right but the diodes just aren't doing their jobs?

Any fresh ideas here would be appreciated! I played with it late into night and didn't get anywhere and my brain is all foggy now. I am going to get some bias readings at lunch time and will report back then.

[midwayfair]

If you're using the pepper spray board, you should have a toggle switch installed to select between two sets of diodes. Is there a difference when you flip the switch?

[disorder]

I neglected the switch and extra diodes. This build is going to a friend and he's not the kind of mess with stuff. Two knobs is more than enough. Thinking about socketing the diodes when I get home (as well as socketing Q1 to try lower hfe there). This thing just sounded not that great, more like a clean boost with a little touch of blues grind.

[mth5044]

Did you jumper the switch pads to connect the diodes? That would cause a clean boost without clipping.

[midwayfair]

You can't just leave out the switch .... it actually connects the diodes to the audio path. Gotta jumper them.

[disorder]

You guys saved the day. I finished this thing up around 2AM after a full days work yesterday and was loaded on black coffee and candy. Didn't actually follow the schematic just assumed leaving the switch out meant it was leaving out the EXTRA diode pair not the stock ones.

[disorder]

Here's the voltages anyways...

Q1 --- 2N404A (140hfe, low leakage)
E - 4.04V
B - 3.97V
C - 3.95V

Q2 --- 2N3965 (230hfe)
E - 4.04V
B - 3.97V
C - 5.6V

[Bret608]

Were you able to get this sorted? What Jon and others mentioned is the case, you basically have it in the "no diodes" position without the switch or a jumper. Which for the Albini specs, actually doesn't sound very good. Even if your friend doesn't like to mess with things, you could even use a SPDT on/on switch. This would give you germanium diodes on the right, silicon or whatever you choose on the left, and no "diodes off" middle position, which really is only useful with the "stock" specs anyway.

For what it's worth, your voltages are correct for the Albini specs.

[disorder]

I havent had a chance to fix it but yeah it makes total sense. If all I'm using is the stock diodes then I have to jumper across what would be the common of the switch to the pole that has the stock diodes on it. Can't wait to get home and try it out. Thanks for the confirmation on the voltages as well Bret. Gotta love this forum!

[mac]

Bases should not be at the same voltage.

And even with the diodes not connected the thing distorts. Some members like it without them.

mac

[hellwood]

I had the same problem until I plugged in transistors with insane amounts of leakage by mistake.

[waltk]

I've built several HPs; a couple on the PepperSpray layout, and a few on my own SMD layout.  I've used Ge transistors with varying Hfe, and silicon.  On all my builds, there has been boatloads of gain AND distortion - and I always leave out the diodes completely (cause I like it better that way).  As mac said, you should have plenty of distortion even without the diodes.

Your plan to socket the transistors is a good one - just to try some different ones.  If you don't have a bunch of spare Ge transistors around, try some silicon tr.  If you don't get some decent distortion with them, you should look elsewhere on your build for solder bridges, etc.

[nordine]

percolators are almost never "too clean", post pictures of solder side