Corey Y's Sunn Concert Bass

VOLVO))) · September 08, 2011, 01:27:04 AM

So, Corey Y sent me this busted Concert bass. Upon first inspection, I noticed someone wired the main output of the amp to be a speakon connector. This is probably where the problem lies, in the first place. If someone did a botch job with the wiring, (it's on there with female spade clips, no solder.) If it just fizzled out, I'm going to assume it had something to do with the modification.

So, first order of business, throw the most likely parts at it. Output transistors.

THE SAGA BEGINS.

spookstrickland · September 08, 2011, 03:10:51 AM

Post some pics each step of the way that would be super cool!

You rock

Hemisaurus · September 08, 2011, 08:15:03 AM

You don't have a scope? Before you throw the parts at it?

VOLVO))) · September 08, 2011, 11:50:46 AM

Quote from: Hemisaurus on September 08, 2011, 08:15:03 AM
You don't have a scope? Before you throw the parts at it?

Negative. They're cheap, available at the shack, and they're the most common cause for these sombitches not working. I'll "diagnosticize" if it doesn't work. I already have a few other suspicions, a cap that looks suspect, and that mod for the speakon jack. Anyone else have one of these Silverface Concert basses that would be willing to shoot some pics of the output scheme? It looks funky to me. Traced the wires around a little bit and they don't seem right.

grimniggzy · September 08, 2011, 12:07:54 PM

Quote from: SunnO))) on September 08, 2011, 11:50:46 AM
Quote from: Hemisaurus on September 08, 2011, 08:15:03 AM
You don't have a scope? Before you throw the parts at it?

Negative. They're cheap, available at the shack, and they're the most common cause for these sombitches not working. I'll "diagnosticize" if it doesn't work. I already have a few other suspicions, a cap that looks suspect, and that mod for the speakon jack. Anyone else have one of these Silverface Concert basses that would be willing to shoot some pics of the output scheme? It looks funky to me. Traced the wires around a little bit and they don't seem right.

No silver CB, but I have a Coliseum & a Slave that are silver era I can take pics of if you think it'd help.

If you get this fixed I have 2 SS Sunn guys that don't put out any sound. Might have to hit you up for advice, or if I get too stumped commence with some shipping.

Hemisaurus · September 08, 2011, 12:14:56 PM

You checked the Sunn Shack and ampage.org for service manuals? I forget here I originally got those Beta books from.

I do have a spare scope, if you're up for a trade

You can probably check the output trannies with a meter, see if the rail is sitting on the collectors, if yeah, probably OC. If the rail is sitting on the output, probably SC

That's how I melted a speaker once, amp slapped the DC rail on the output terminal whilst I was out in the shed, came back and smelt burning. Man that sumbitch was hot, even after I left it an hour to cool and then took the driver out, it still burned me

VOLVO))) · September 08, 2011, 12:26:36 PM

I PM'd the techy mod fellow, I'm about to post it on the forum.

I need to figger out how to put the outputs back to stock. It looks simple enough, they took the main jack, and made it a speakon, the original quarter inch is still paralleled to it, but I'm not sure if they crossed a wire, or switched something that caused it to fizzle. Once it's back to stock, I can really start to trouble shoot.

Isn't that scope like a trillion pounds, Herbie?

Chris, What do you have that isn't workin'? I'm always up for projects, gotta get that experience from somewhere...

grimniggzy · September 08, 2011, 12:32:26 PM

The aforementioned Silver Slave & a Red Concert Lead (one of those weird MIM ones). I bought them un-working and just never got around to having them looked at since I've always had more than a few working ones.

This is the neighborhood amp guy up in my hood. I called him once and he seemed really out of it on the phone.

Somehow I don't trust him, haha. I'm sure hes fine and all but he seems more than a little crazy and probably more familiar with tube stuff.

VOLVO))) · September 08, 2011, 12:33:57 PM

YOU HAVE A SOL O)))?

I really want that, Chris, are all the controls in Spanish?

grimniggzy · September 08, 2011, 12:36:19 PM

Nah, I don't think so. Theres some spanish on the back though I think. It still says Sunn and the knobs read in english (I think)

VOLVO))) · September 08, 2011, 12:42:22 PM

Damn it! They had ones where all the controls were in spanish. I want one. Badly.

We added "o" to the end of all of my puerto rician buddy's concert bass controls without his knowledge. Hehehehe

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grimniggzy · September 08, 2011, 12:46:12 PM

I'd be down for changing them on this. I mean it is from Mexico and its never worked so when I get around to sending it & I get back and its all in spanish and working I'd be thrilled.
You could paste the Dos Equis guys face on it for all I care.

VOLVO))) · September 08, 2011, 01:56:51 PM

We have output! It's just a loud hum, but there is output! I have yet to fix the jack situation, there are some questionable cap ties in there, shitty cold joints I hit... gonna redo the caps that look dildos, and fix that jack. Should be good to go.

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VOLVO))) · September 08, 2011, 02:56:42 PM

Ditched the speakon connector. WE HAVE ACTUAL GUITAR SIGNAL! with that shitty buzz.

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justinhedrick · September 08, 2011, 03:15:46 PM

hopefully that dildo cap job fixes the hum!

Slow · September 08, 2011, 03:45:57 PM

Alright, my buddy is playing guitar through it, it doesn't seem as loud as it should, but there is strong signal going throughout. Nothing I touch with the chopstick fixes the hum/buzz. I found a trim pot on the board that harnesses it down to a simple ground buzz kind of, but it's ever present, and very annoying. I see a few more questionable things I'm going to desolder and redo. Someone hotglued one of the connections in place, and that was what caused the original failure. Fixed the speakon debacle, used a regular 1/4 jack, reused the spades with a fresh solder job, put 'em directly to the terminals. The main jack and parallel jack both make noise, good sweet low endy growly noise, when the buzz isn't blowing it out of the water for volume. I think that questionable cap, and the few other things I saw are what's causing it. The shack doesn't carry 220uF 65V axial caps. Shithole.

Hemisaurus · September 08, 2011, 04:13:20 PM

What is the power through that cap? Shack does 50V caps, I'd drop 1000uF 50V in there, if it's just doing a power thing, and the rail is under 50V

Scopes are heavy, I can bring it through when you play with Justin

Found schematic

http://www.prowessamplifiers.com/schematics/post/sunn_concertbass.pdf

VOLVO))) · September 08, 2011, 04:43:20 PM

I'm looking for it on the schematic... It actually may be the wrong cap. It's obviously smaller than the original cap that was in it's place. The other two nearbys are 1000uF/50v or something close.

Found it, the cap that's in there 220uF/63V. Supposed to be 1000uF/50v or a 75. I'll have to check and see what else is around it to confirm. Would that cause the buzz? I've already dug up all the questionable joints, and hit 'em all. It's definitely in the power section. So, nothing in the preamp is to blame.

Edit: Shit, I found a nearby 250/60v cap, and that could be what I'm looking at. I'll post pictures. Goddamn it. At least i get good loud signal, that's a start. I didn't even throw any parts at it, yet.

Hemisaurus · September 08, 2011, 07:30:56 PM

The schematic for the Concert Lead is split into pre and power the power should be common to both but it looks different to me, it is labelled new.

Hemisaurus · September 08, 2011, 07:44:22 PM

There does seem to be a 250 bypassing the cathode on Q302.

Oddly on the PDF schematic, it looks like it goes to ground, on the schematic in the Sunn museum it's going to the base of Q1.

It does appear to be in circuit with the 1000uF 50V cap, so it can probably be dropped to a 50V, but changing the value drastically will change the response of that section, so stay within the 220-330 range.

VOLVO))) · September 08, 2011, 07:50:41 PM

I understand that, but its most definitely out of place... ill shoot you a pic when I get home, to show you what I mean.

Took this earlier. Maybe you can see what I mean from that.

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VOLVO))) · September 09, 2011, 02:41:44 PM

Found some scans from the original manual. C306 is 250uF/64v. This is annoying. Ill post a video of the buzz so you can hear it.

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VOLVO))) · September 09, 2011, 07:27:19 PM

I suspect this socket is bad, when I yank the white wire off the terminal, the buzz goes away, somewhat.

Hemisaurus · September 09, 2011, 07:39:03 PM

Why the socket, you could just be cutting the signal from elsewhere? Just wondering?

VOLVO))) · September 09, 2011, 07:49:24 PM

Quote from: Hemisaurus on September 09, 2011, 07:39:03 PM
Why the socket, you could just be cutting the signal from elsewhere? Just wondering?

good point, it was a mistake originally when It popped off and the buzz went away. I can't think of anything else. I feel like I'm pretty close to solving the issue, but... eh. Any ideas?