Brown Deluxe/Constellation build...help please...

[Structo]

By the way, great looking amp.

I had an amp looking just about that good on a first build.
I didn't really have too many start up problems but I started modding things and soon it didn't look so nice.

I'm sure you'll figure it out soon, it's probably something really simple.

The other day I did some mods to an amp, put it all back together turned it on, nada.
Not even any hiss. Complete silence....
Then I noticed the main ground wire for the board laying there with one end not connected to anything....idiot.

[dehughes]

Sooooooo, get this: I took out my neatly wired input wires...and found that some solder had flowed from the conductor to the shield right where it connects to one of the 33k resistors. Apparently I didn't give myself enough length on the conductor to keep it away from the shield. LAME. That explains why the tip was reading "ground" regardless. So, I'll have to re-do the entire input wiring, but at least I found the problem...it wasn't the jack, or the ground connection, just my own careless mistake.

I'll get to it tomorrow or Monday and check back in...

[Phil_S]

Properly routed, you don't need shielded on that input wire. You have plenty of room in your chassis and where you presently have the white wire to V1 is very nice. I would use plain wire there.

I'm not quite clear, as it looks like you've got a second white input wire from that same jack to V2. I think you need to get rid of that. Maybe I didn't read the photo correctly, so please explain. I don't see that on the schematic and it doesn't make sense to me.

I only resort to shielded input when necessary. From what I see, you should not need it and it is an unnecessary complication. Use plain wire. If it is noisy, you can always "fix" it.

[Structo]

Have you used the "cut control" before?

I'd like to hear what you think of that when you get it going.

Am I right that this amp does not have negative feedback?

[dehughes]

Phil: Yeah, I probably could...but I'd rather do more work than necessary now than have to re-do it again when I find it to be noisy. That said, this isn't a particularly high-gain amp (especially the 6SN7 side...), so you're probably right. I like to overbuild, though... There are two wires going from the jack...one to the grid of the 6SN7, and the other to the grid of the first 12AX7. Think Komet Constellation...the ability to run two dis-similar preamps in parallel, mixing the two with the turn of the volume knobs. In theory, it should work out fine, as they'll be in phase with each other. It's on the schematic...far left....

Structo: I've used this cut control before, though not in this amp (obviously). No negative feedback on this....you're correct. Again, we'll see how this works with the Brownface PI setup....maybe great, maybe not. That's the problem with doing stuff that's not "standard".

[Phil_S]

Re: shielded cable, this isn't a matter of more work or over built. The shield sucks tone. Try it without. Route the input to V2 under the board so it clears the 6.3v filament wires.

[brewdude]

Re: shielded cable, this isn't a matter of more work or over built. The shield sucks tone. Try it without. Route the input to V2 under the board so it clears the 6.3v filament wires.

While I tend to agree and prefer to use as little shielded cable as possible, It seems to me, at the risk of showing the full degree of my ignorance, that a half a foot of shielded cable at the input of the amp is not unlikely to suck any more tone than another half foot of guitar cable would before the input jack.

Regarding the parallel inputs, I was curious why it wouldn't be better to simply run a jumper wire from the grid of V1 to the grid of V2?

But then again, there are many nuances about amp building that I am still trying to fully comprehend.

[Phil_S]

Re: shielded cable, this isn't a matter of more work or over built. The shield sucks tone. Try it without. Route the input to V2 under the board so it clears the 6.3v filament wires.

While I tend to agree and prefer to use as little shielded cable as possible, It seems to me, at the risk of showing the full degree of my ignorance, that a half a foot of shielded cable at the input of the amp is not unlikely to suck any more tone than another half foot of guitar cable would before the input jack.

The guitar cable is outside the chassis and needs shielding of it's own. Inside the chassis, the chassis is the shield. This is simplistic, but short and sweet. People use shielded inside the chassis to compensate for problems they can't solve with lead dress.

Regarding the parallel inputs, I was curious why it wouldn't be better to simply run a jumper wire from the grid of V1 to the grid of V2?

The parallel input doesn't make much sense to me either, but what do I know? Certainly, it seems that a jumper would be very tidy and I don't see why not.

[dehughes]

Interesting....a jumper would be easier, but I wonder if that would need shielding...?

What makes me think that parallel wires is the way to go is that I've looked at pics of the Komet Constellation, and they used parallel shielded wires to each grid (and DC heaters as well...which I may have to do...but that's another subject). I figure those guys are way better engineers/builders than I, so I'm just copying what I see.

[Structo]

Isn't the jumper just a short shielded patch cord?

[dehughes]

Isn't the jumper just a short shielded patch cord?

Dunno...if it is shielded, where to?

[Phil_S]

I admit freely to my amateur status and lack of formal technical training. With that disclaimer in mind, it seems to me that a wire less than 2" long doesn't need to be shielded as long as you route it away from the a/c filament wires.

If you insist on shielded, the shield can be grounded anywhere on the chassis. It's function is the same as the chassis. Ground one end on any handy screw or bolt (the small screw that holds the socket in place), but do not put it on the circuit ground buss.

[dehughes]

Well, I re-wired the input jacks and it is much better now...that is, it works! No more stupid mistakes on my part regarding wiring oversight. Eesh. It does sound really good so far....the two channels are dissimilar enough to be worthwhile, which is nice, as I didn't know what I'd end up with.

However, it still is reeeeeally hummy....like strong AC hum. NOT hissy....hummy. The PT audibly hums on its own just idling there....and I'm not talking about through the speaker, but just sitting there on its own. It hums when it's on standby, but not much. Turning it off standby really kicks in the hum, but what's interesting is that the hum doesn't increase with the volume knobs...that is, it's level doesn't change.

I pulled the 6SN7 tube, and that helped a lot, but the PT is just hummy and it's transferring in to the signal path somehow. Granted, my idea of quiet is pretty strict....I like amps to be dead quiet....but so far I seem to pick hummy PTs as my AC30 build was like this. Perhaps this is just a function of a "cloned" PT (mine is cloned from a '61 Brown Deluxe), but I wager there is more I can do about it.

One thing I've considered is grounding the AC input to the same point as the PT grounds (heater and recto center taps) which is the same ground for the filtering caps. Worthwhile, or should I start somewhere else? (See the pics on page 1 for what I'm talking about...) OR, should I just start with DC heaters for the 6SN7 and the 1st 12AX7? I'd like to start with the option that is easiest and most likely to be the solution....

[Phil_S]

Some PT's hum, that's just the way they are. I would want to find out if it is because of the way it's mounted, for example, is the chassis flexing underneath? Maybe it needs some reinforcement. Or is it just the nature of the item? I suggest pulling the PT off the chassis, bolting it to a wood plank, and plugging it in with no load on the secondaries. Find out if it hums when you do that. If it is quiet, then you know it is how you mounted it. If it continues to hum, then try mounting it on rubber stand offs and see if that helps. It sounds like you are dealing with a physical problem rather than a circuit problem. By pulling the PT off the chassis, you will more easily determine what to do, including whether you need a different PT.

It does not seem like converting heaters to DC is necessary. The work involved in doing this isn't worth doing, IMO, unless really necessary.

Do not mix the mains ground with the circuit ground. Check with someone who is knowledgeable about the NEC and I think they will tell you this is forbidden.

Good work fixing those jacks!

[dehughes]

Interesting. The PT has nylon T-washers which act as a ferrule for the mounting bolts as well as standoffs between the PT and the chassis, and the chassis shows no signs of flexing, etc. My instincts say there's an electrical reason that the hum is getting into the signal...not just a physical one...but what do I know...

Regarding mixing the mains ground with the PT grounds...I've seen this done many times, and those amps have always been very quiet and hum-free. I think I'm going to give it a shot and see if it changes anything.

Also, does everything on the schematic look correct? I'm wondering if I geeked something in the design which might be causing hum to be induced....?

Thanks for your help...much appreciated...