English Channel Voltages

[mrsage]

I just built the English Channel off ROG, but my voltages aren't quite right.

I've got the right voltages for most of the "D" pins on the J201s, but on Q1 and Q2, the voltages for the "S" pins are off.

Q1:
D 4.49
S 0.29
G 0

Q2:
D 4.45
S 1.16
G 0

Q3:
D 8.96
S 4.55
G 4.48

Q4:
D 4.61
S 1.27
G 0.78

Q5:
D 4.6
S 0.20
G 0

That's on a battery that measures 8.98 volts.

Any suggestions? I've tried swapping out a few different J201s for Q1 and Q2, but it hasn't fixed things...Should I just keep swapping them out? Or are there resistors I should be changing?

And the voltages seem to jump a bit on Q2. Sometimes I have to hold the multimeter against the pin and let the voltage come to a resting place. Is that normal? I checked the connections and it looks okay...

[mrsage]

And I'm getting no output at all when I plug it in.

Seems like I should get something, even with voltages that are slightly off.

I ran an audio probe, and the sound does okay up until the 47pf capacitor (after the "S" leg of Q3). That cap seems to suck a lot of the volume out of the signal. Same with the 100k resistor that leads to the 22n caps. Plenty of volume before; not so much after.

Then the signal just gets weaker and weaker as it goes through the rest of the circuit, until there's nothing by the time it reaches Q5.


This is my first perf board, so any suggestions would be helpful. (I know...I probably should have tried something simpler)

[B Tremblay]

Carefully check your tonestack wiring.

The Q1 source voltage looks OK, it's within the range of acceptable given the variation in FETs.

Q2's source looks a little high for a J201.  I've seen voltages near that level in the Fetzer Valve when using an MPF102 (its single stage is identical to the Q1 and Q2 stages in the English Channel), but can't remember a J201 doing it.

[mrsage]

Okay, thanks!

Two questions:

1) What is the tonestack?   :oops:  (newbie here)

and

2) If that's too high for a j201, should I replace the j201 or rewire or change out my components?

[B Tremblay]

The tonestack is the section between Q3 and Q4: the Bass and Treble pots, along with their associated caps and resistors.

I'd try other J201 (you did use sockets, right?) to see if their source voltage can get closer to the recommended value.  Remember, Q1 and Q2 are identical stages, so if their voltages aren't reasonably close, something may be amiss.

[mrsage]

Thanks for the tips!

I checked the first two stages, and they weren't the same, so I did some careful tracing. It's easy to lose track of wiring on perfboard.

Anyway, I got it running, and thought I'd post a clip. I'm not sure if this is what it's supposed to sound like, so I'd appreciate any feedback you all could give me. Sounds very compressed to me, at least at the higher gain settings.

The clip starts out with the stock circuit (Brilliant Channel), gain turned all the way up. Then I flip the switch and turn on the "Normal Channel." Finally, I just did a little strumming with the gain turned down a bit.

Anyway, give me some feedback...Does it sound okay, or do I need to tweak the trimpots or something?

[clip deleted to save my bandwidth]

[mrsage]

By the way, it's recorded Strat -> English Channel -> direct to sound card

[RDV]

If the voltages look right(1/2 of supply voltage) at the trimpots you're good to go. It's not a high-gain fuzzbox kind of circuit but rather a sort of preamp simulation sort of thing. I enjoy mine a great deal feeding the normal channel of my Marshall for a bit of Vox flavour. I just leave mine on the brilliant and turn down the treble if needed.

RDV

[mrsage]

All the voltages are right, but I'm still getting a lot of clipping...It just doesn't sound as nice as I expected (based on what others were saying). It sounds fine at lower volumes, but I can't turn the Master up that much before it starts sounding like I've overloaded my sound card's input...which isn't the case at all! All my recording levels are fine.

Here's an example (since I deleted my first file):

http://s2.yousendit.com/d.aspx?id=A6FA4B38B52DA710EF3137DE53A2DF46

It sounds okay at first, but if you skip to the end, I hit the last chord hard and it's not the Voxy distortion I was hoping for.

Any suggestions? Is this a trimpot/bias problem? Or do others do this as well?

[RDV]

It sounds like recorder overload to me at the end. I like that sound, are you using any kind of speaker sim on that?

I think there's a certain compression and graininess to all the various JFet distortions. I think that's why some people like them so much. I want a bit more hedroom than they afford sometimes. I'm using them though, cause when you get the right balance of amp pre & JFet there's some really good stuff in there.

RDV

[mrsage]

There was no speaker sim, just Strat -> Eng. Ch. -> delay -> direct

It almost definitely wasn't the recorder, though...I recorded through Cakewalk and was watching the inputs. They barely got into the red, and definitely didn't top out.

Hmm...I'll try it through my amp and see if it's any better.

I really like the sound when it's not overloading though! Thanks for a fun project, ROG!