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

[dehughes]

Soooo, this is my 2nd build, and a bit more ambitious (albeit less work) than my first build (AC30 monstrosity).

Basically it is a Brown Deluxe preamp paired with a Komet Constellation 6SN7 channel run in parallel into a Brown Deluxe PI which runs into a 5E3-ish cathode biased 6V6 power section. 5AR4 rectified. AC heaters (for now...).

I fired it up and nothing exploded. Good. The PT is hummy...but it is a Mercury Magnetics clone of a Brown Deluxe PT, so I guess they cloned the hum as well. B+ voltages read out properly on all the tubes and throughout the line. Heater voltages read out at correctly as well. All grounds look to be solid. No solder joint issues that I've noticed.

Essentially, I turn it on and hear a fairly pronounced (though not terribly loud) AC hum (low, deep, powerful...not buzzy or fizzy hash from gain issues), and when I play through it no sound comes out. At first I figured something was wrong with how I coupled the two channels, but then I suspect maybe an input jack issue?

Again, this is just my 2nd build, so I'm sure I (obviously) screwed something up...but I'm so close I can taste it....but I just can't hear it.

Attached are copies of the schematic and a few pics of the build. Lemme know if you see anything suspect. I'm off to get a new soldering iron tip tomorrow (figures it would break after literally the LAST solder joint) so I can get to troubleshooting....

MANY THANKS!

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[billyz]

That is such a tidy build I am humbled by the precision and beauty of it.

The first thing that comes to my mind is , It looks like an Anodized chassis. If so, you did grind off the anodizing where your grounds are? your Pots and jacks appear to be friction grounds to the chassis, might also do a ground buss. I usually run a ground wire to everything that needs grounding and use a star point or buss . Keeping it to several known good locations for various parts of the amplifier.

Sorry, I just saw the ground buss wires. Everything is so straight and perfect I mistook them for another wire. Nice build.

[Phil_S]

I can't really see whether you wired the input jack correctly. I have built 10 amps so far, and wiring the input jacks is something that I have trouble wrapping my mind around. I find the attached drawings have saved me a pile of wasted time.

It is easy enough to test the inputs. Lift the grid input wire from V1. Power the amp and touch it with your DMM probe set to measure volts. You should get a pop or maybe a hum.

Also, while you are at it, probe the grid on the power tube as that should give you some output as well.

These are simple diagnostics and will help you eliminate your suspicions.

BTW, it is intimidating to give advice to anyone who can build such a tidy amp. I suggest, if you really want people to give you advice, that you should not build them so meticulously. <for the record, a tongue in cheek compliment of the highest order>

[Phil_S]

On the hum, is this PT vibration or hum coming from the speaker?

For vibration, you can see about inserting some rubber washers on the bolts between the PT and the chassis. Anything will do...plumbing washers, rubber grommets.

If speaker hum, 60Hz or 120Hz? Your low A#/B on the guitar is about 60Hz.

[Sonny ReVerb]

Have you seen Jack Darr's book:

http://www.pacificrecone.com/JackDarrBook.html

Check out Chapter 4, Page 4. It shows how to go about troubleshooting starting at the output tubes and working back to the inputs. Essential reading.

Beautiful work, btw!

[billyz]

I still don't see where your input jack is grounded other than the friction to the anodized chassis. I like to ground the buss with the control pots and the input jack to the chassis ,close to the input jack . If you have shielded the input to V1 then ground the shield only at the input jack side. I also ground the preamp tube cathodes to the same buss.

[Wayne]

Thought I had something but then re-read your explanation of symptoms, so I'm afraid I can't offer much help. I did want to chime in with others, though, to tell you how insane you are! That is one super-clean looking build. Equipment built that neatly is a joy to work on - too bad you have to learn that so soon.

W

[Structo]

I can't tell from your picture if you have a switching or shorting jack on the input but this is how I wire mine and also how I groung the buss wire.
It is only grounded at the input end.
I would make a probe with a cap on the end and play some audio through it and touch it to the various grids to see where your problem lies.

[Phil_S]

I still don't see where your input jack is grounded...

This comment got me to take a closer look. I wasn't paying attention before. I think you need to go over all the grounds and make sure they are actually appropriate and functioning. That yellow barrel cap on the tone pot is soldered to the back of the pot, but it isn't grounded! I don't think your input jack is grounded. Incidental contact grounds made by bolting the pot or jack to the chassis don't count. Everything needs to go to the buss or a bolt through the chassis. The buss needs to be grounded to the chassis only at one end. Any chassis ground requires you to sand off the finish to assure a good contact.

A missed or non-functional ground = no sound.

[dehughes]

Thanks for the replies, guys.

This chassis came from some old stock stuff I picked up from Top Hat. These are super old Club Deluxe chassis, and I've essentially copied the ground scheme from the Top Hat line. I didn't sand off the metal to make the ground, as I've owned many Top Hats (about 8 or so...) and none of them had this done, and all were super quiet and hum/hiss free. As such, I'm wondering if my issue has to do with something other than ground points.

Regarding the input jack, I only wanted one, but the chassis was cut out for two, so I just went with two jacks though I only wired in the "high" jack. The other is just sitting there for looks. The "high" jack has a 1M from tip to short/ground....but when I test the jack I get a solid ground connection regardless of whether the tip is open or shorted....weird... Maybe that's the issue? I put the 33k resistors right on the grids of the 6SN7 and 12AX7 for a change...heard good things about that method.

Two questions, then, before I start un-doing things:

1) When I test the input jack, if I separate the tip from the short I should NOT have any connectivity to ground, yes? That's a stupid question, but I tripple checked my input jack when I wired it, so I'm curious as to why I keep measuring ground connectivity even when it's "open".

2) Does there appear to be anything not right in the schematic? I kinda ad-libbed some of the channel mixing stuff (I'm no EE...obviously...) so I'm hoping that's all correct.

As well, I'm getting changes in hiss/tone when I turn the volume knobs and tone knobs, and I'm getting pops/clicks when I test plate voltages on the preamp tubes, so I know signal is coming through/out of the amp, it's just not getting from the input jack through the rest of it. If I could get SOME guitar signal through, I'd be able to tell what else needs to change, but as of now nothing is getting through....

[Sonny ReVerb]

I don't think that chassis is anodized, it's been chromated. My Z28 chassis had the same treatment.

http://en.wikipedia.org/wiki/Chromate_c ... on_coating

And, from another site:

Chromate Conversion is unlike anodic finishes in that the alloy's electrical conductivity is maintained.

I agree, there should be an independent ground to the input, pots, etc. but the coating should not be a problem.

[Sonny ReVerb]

Also, for question #1>

With the power off / unplugged, I would pull the preamp tubes and measure the resistance from the tip (separated from the shorting prong) to ground. You should read the 1M resistor. If your getting a ground reading (~0 Ohms) then you have a problem with the input jack wiring.

It sounds like that may be your problem with the other indications (tone changes with knob adjustments, etc.). You're just sending your guitar signal to ground at the input.

[ampdoc1]

You should get conductivity to ground with nothing in the jack. Put an unconnected plug in the jack then measure from the tip connection of the jack to ground,..it should be infinite (no connection to ground).
If you still get a reading to ground, you have probably wired the jack incorrectly, or your input line is grounding someplace.

ampdoc1.

[dehughes]

Thanks Sonny and ampdoc. Much appreciated. I did open up the jack and take the measurement, but there wasn't a cord plugged in. I'll check that when I get home...

[dehughes]

So, with a spare Switchcraft make 1/4" plug I have lying about plugged into the input, I get a reading from tip to ground of essentially no resistance. As well, I'm only getting a reading of 33k to ground from the grid of V1a, which makes sense in that it is a 33k resistor on the grid, but there's no way it should be shorted to ground...

I suspect something is wrong at the jack then? I can tell that the 1M resistor is wired in correctly, so I'm at a loss as to what the problem might be. Stray strand of wire somewhere? Confusing... I'll have to take the jack out and have a look...