NAD! Champ 600 being converted to my Woodchipper :)

[midwayfair]

Traded Chris (CK1) for this over the weekend, and immediately set to work making a few improvements.



I'll be replacing the speaker grill with something that air can actually pass through as soon as possible. I want to get a new speaker, too.

Flip it around and it's got three knobs and only one input now ...


The paint scraped off pretty easily, allowing me to avoid an awkward moment where I don't know what the heck the knobs are doing.

And here's the revised guts as of right now:


I ditched/jumpered several resistors that do nothing but lower the gain of the circuit, increased the negative feedback to 10K, and then ripped out the tone control and revised the preamp stage to something pretty much like the woodchipper schematic I posted. The mids control is a variable cathode bypass cap (470nF), and the treble is a variant of the stupidly wonderful tone control, with a treble boost at ~1K being rolled in at the same time the treble cut is reduced.

It sounds really good right now (and it's crazy loud for such a tiny speaker). The tone controls are fairly mild overall, but it gets a little more glassy at the highest settings on the tone controls, and there's a good setting with all my guitars. The highest setting on the mids is much tighter breakup than it was with the 22uF.

I did several things to reduce noise, like put real tubes in (EHX 6v6 and a Tube Store matched 7025), repositioning some wires, shielding the heater and input wires (just wrapped in copper tape with a ground connection). Once I get a parts order in, I can increase the size of the filter caps, increase the resistance on the droppers, and hopefully kill the hum this amp is "known for" permanently.

Right now I have the cathode bypass cap still in on the second half of the 12AX7, but I might pull it out later.

No clips just yet. I plan on putting another recent gear purchase in front of it soon though ...


Which is a really awesome sounding mic. I gave the AT2020 to my friend and bandmate so that he could have a condenser, too.

[haveyouseenhim]

Ha. I read the title and thought I would see an amp in a woodchipper.   If I had a thread with this name that's probably what would be happening.

[Leevibe]

Ha. I read the title and thought I would see an amp in a woodchipper.   If I had a thread with this name that's probably what would be happening.

Would that be after seeing time at the shooting range?

[rullywowr]

Nice amp and upgrades, Jon!  Looking forward to hearing it.

[Morgan]

Awesome!

The mids control is a variable cathode bypass cap (470nF)

How is that working out? Which triode did you do it on?

[midwayfair]

Awesome!

The mids control is a variable cathode bypass cap (470nF)

How is that working out? Which triode did you do it on?

I did it on the first triode. I left the 22uF in the second one to drive the power tubes a little harder. It's kind of overkill right now (breaks up around 5, and I get a little speaker cry there, too), but I plan on biasing the 6V6 a little colder ... it's VERY hot right now. I shouldn't need to do it when I build a 1x12 version. I am also wondering what will happen when I drop it to 150V -- the B+ is over 300V in this right now, barely below the power tube. That seems to be a very high preamp tube voltage from what I'm seeing.

Took it to practice today. It can definitely overpower an acoustic piano, but it sounds awesome at about 5-6 right now! I'm really happy with how it's taking most pedals. The only thing that's really a little uninspiring is a tremolo in front; I can't get a hard sine wave when I'm pumping up against the headroom of the amp, but square wave stuff works really well. One spot where a vibro champ definitely has an edge.

Some really good sounds with the mids and treble cranked. Added a dirt pedal (the Snow Day) and some delay and it did a convincing Vox.

I'll be adding a bright cap, though. It's a tiny bit dark unless I crank the treble and mids at practice volumes. I'm also going to try a permanent presence boost at 5Khz with a 22nF (or perhaps 33nF) in parallel with the mids bypass. It'll have very little overlap with the 470nF according to the chart, and I think it'll help with darker guitars. I like a lot of treble, though, so I think people who play with a pick would be pretty happy with what it's like right now. [Edit: Yeah, those did it, probably don't need both, though.)

Onward.

[midwayfair]

Quick update: My Weber Signature 6 arrived today (and the 12 I ordered the same time). Really fast on those! I guess they don't make the signature series one at a time. I got the ribbed cone for late breakup.

Also picked up a nice oxblood cloth off Ebay and replaced that.

I can't express how much of an improvement it is -- the treble is worlds clearer, the bass is less muddy, and no cone cry.

The other new thing is that I put the negative feedback on a switch so I could have three settings: A 33K, a 33K + 680nF in series (the 'bandpass' setup in the negative feedback tone control thread), and a lift in the center. The different negative feedback also changes the reaction of the mids pot and the second half of the treble, adding quite a big of extra interest to the controls.

[Leevibe]

Very cool.