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.
Post some pics each step of the way that would be super cool!
You rock :)
You don't have a scope? Before you throw the parts at it?
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.
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.
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 ;D
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 :(
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...
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.
YOU HAVE A SOL O)))?
I really want that, Chris, are all the controls in Spanish?
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)
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
:D
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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.
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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Ditched the speakon connector. WE HAVE ACTUAL GUITAR SIGNAL! with that shitty buzz.
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hopefully that dildo cap job fixes the hum!
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.
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 ;D
Found schematic
http://www.prowessamplifiers.com/schematics/post/sunn_concertbass.pdf (http://www.prowessamplifiers.com/schematics/post/sunn_concertbass.pdf)
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. :D
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.
(http://sunn.ampage.org/site/schematics/SunnConcertLeadNewPoweramp.GIF)
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.
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.
(http://i1234.photobucket.com/albums/ff409/enslavedinrot/2011-09-08_12-56-56_999.jpg)
Took this earlier. Maybe you can see what I mean from that.
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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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(http://i1234.photobucket.com/albums/ff409/enslavedinrot/2011-09-09_17-55-13_743.jpg)
(http://i1234.photobucket.com/albums/ff409/enslavedinrot/2011-09-09_17-55-34_648.jpg)
(http://i1234.photobucket.com/albums/ff409/enslavedinrot/2011-09-09_17-55-44_226.jpg)
(http://i1234.photobucket.com/albums/ff409/enslavedinrot/2011-09-09_17-55-50_257.jpg)
I suspect this socket is bad, when I yank the white wire off the terminal, the buzz goes away, somewhat.
(http://i1234.photobucket.com/albums/ff409/enslavedinrot/2011-09-09_17-56-13_723.jpg)
Why the socket, you could just be cutting the signal from elsewhere? Just wondering?
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?
Was I right in thinking the buzz is affected by the EQ?
Have you tried preamp out into a different power amp, and vice versa? If the hum is affected by EQ, it probably originates in the preamp. Does it hum with a shorted jack in the input?
It isn't the preamp, none of the controls effect it. All i did in the video was turn the volume up and down. The bias pot effects the hum, higher on the dial is louder, lower on the dial (to a certain point) makes it quieter. It's a 100k linear trim pot. (R310) I've ran preamp out into my peavey poweramp and it was a clean signal. No buzzzzzz. It's only when it's plugged into a cab that it has to power. otherwise, solid signal with no noise from the preamp.
I replaced all the output transistors. That's what originally gave me my output back.
It doesn't sound like a grounding issue, either... I don't know : \
The volume on what? The volume on that beast is in the preamp, have you tried bypassing the preamp and plugging into the power amp jack with a boost pedal?
Have you checked for a DC level on the output, with a meter if you've tweaked the bias pot?
I did use the poweramp in and an active bass to check the poweramp. It buzzes. The preamp does not buzz when run into a separate poweramp. I marked the bias pot before I moved it, it's where it was when I got it. How do I meter the output? Put it to the + side of the output, and ground?
What would you do? I don't really have a developed process, since I'm not experienced enough to have one. I usually just clean shit before I do anything else. I did that. Cleaned every jack, pot, switch, etc. Looked for cold joints, and suspect looking shit, fixed all of that.
How would you process? How should I go about diagnosing? I agree with not throwing parts at it, but I had a pretty educated guess as to those transistors being part of the problem. (since they're usually the main cause of it not having sound.)
(LISTEN UP FUCKERS, TIME FOR YOU TO LEARN SOMETHING.)
I'm digging this thread. you guys are really giving me a good education.
Thanks please keep posting all the pics and vids you can.
You have a meter, yes?
Check for AC voltage, on the DC power rails first. Honestly at this point I'd be using a scope and seeing exactly where the hum starts in the circuit, usually it's bad power or a bad ground. I'm not good at this fault finding by proxy :-[
Oh and keep a shorting jack on the power amp in, until you've fixed the hum, it'll help :)
Have you done the biro test? Poke each component with a non conductive tool (including those spade terminals) whilst the amp is running and see if anything makes it better or worse (ONE HAND ONLY, KEEP OTHER HAND CLEAR, SIT ON IT!) and be suspicious of any tantalum capacitors in the problem area, they fail in weird ways. Without a scope these are methods I'd try.
Oh, and that cap was replaced by a lazy tech, or someone in a hurry. Snip out the old component, leave the leads free, twist the new component leads to it, solder in place, and the glue for a bit of extra strength, it works, saves you disconnecting a bazillion wires. It doesn't make it more suspect, except for the fact it's a new repair.
I'll put it to you this way, I'm somewhere between total retard and complete prodigy. I can do most simple things, some advanced things.
I've have indeed done the Biro test. Nothing I've poked changed anything, save for popping off that white wire by accident. That changed/eliminated the hum. I eliminated the spades terminals, direct soldered them to the jack. Basically, anything that looked like complete bullshit, I've fixed already, and it has only done ~good~ to the amplifier. I'm really good at cleaning up circuits, odd looking wiring jobs, and that type of shit. (you should see what I can do to those low rent Korean 49CC scooters :D) I have to get a scope, if I'm going to do this, I understand that, but for now, I can't afford one/don't know how to work one. I've got these for reference, as well as the original schem, Via the Sunn forum. There are some discrepancies than I can't explain between the CB I have and these layouts. Mine is missing things, but there's no place, and no traces for them. (for example, C303 isn't on my board, at all. No place for it, either. In it's general area, R313/R311/R314, and C311 are there, but no C303.)
(http://file:///C:/Users/O)))/AppData/Local/Temp/Sunn_Concert_Bass_Preamp_PCB_2.GIF)
(http://sunn.ampage.org/sdp/index.php?action=dlattach;topic=4515.0;attach=574;image)
(http://sunn.ampage.org/sdp/index.php?action=dlattach;topic=4515.0;attach=570;image)
Am I checking for AC to eliminate caps from my search? Where should I poke the probe? EDUCATION! All of us need it... haha. Also, just leave a jack in the poweramp in?
You're checking for AC on the DC for noise, which would point to bad power supply caps.
The jack in the power amp in should be a shorting jack, get a jack solder tip to sleeve, you now have a shorting jack, don't use a cable or a regular jack, the point is the short won't pick up stray noise from outside, and in this case isolates any hum in the preamp, even if you think there isn't any, it's good practice :)
Engh. Now one of my beta leads is acting up. It's intermittent and a slight tap on the amp stops it.
Anyways, where do I test the DC from? The Tranny, last component in line, eh?? Somewhere on ze board?
Test it on your heart. It will show you the way - and if it does not, I cannot help you...
This will be my last post...
...until my next one.
I've been on vacation, so I just read all the way through. I'm glad it got there in one piece. My packing was so-so, but it couldn't get much more broken. What an epic saga, fraught with twists and suspense. I'm interested to see if you can bring the old girl back to life.
Herb, when I'm ordering caps (the shack, and the local electronics surplus store doesn't have dick, for anything I need,) what tolerances should I be using in the poweramp? I looked on Weber, and there's no 1000MFD/50V caps, so I'm reduced to Mouser, which is convoluted and is going to end up fuckin' me up. I'm gonna replace that lazily done cap job, and those two next to it. It's old, it needs to be one anyways, so I'll just do it. as for those monstrous metal coke can caps... where can I dig those up?
Right, the voltage is a working voltage rating, so when replacing you normally need that voltage OR ABOVE, unless you know the working voltage of the circuit is under that. So don't be scared to use 1000uF @ 80V or whatever or 1000uF @ 700V if you have such things.
The shack seem to have them? It's in stock in all the Shacks around Jacksonville, FL ;D
http://www.radioshack.com/product/index.jsp?productId=2103627&filterName=Type&filterValue=Electrolytic+capacitors (http://www.radioshack.com/product/index.jsp?productId=2103627&filterName=Type&filterValue=Electrolytic+capacitors)
Also you can double up, capacitors in parallel are additive, so 2 x 470uF = roughly 1000uF in a pinch.
I can over-rate voltagewise as long as the farad is the same? Sweet. life is easier... Those things are huge, though, size doesn't matter?
Capacitors have gotten smaller as manufacturing methods have improved. Todays 1000uF 50V capacitor will be considerably smaller than those from the 70's, and yes, long as you keep the new cap at or above the working voltage of the old cap.
Any new progress?
Ordering parts tonight!
Oh and caps are the opposite of resistors, caps in parallel increase in value, so 2 100uF caps in parallel = 200uF ;D
Do voltages stack? Are caps in series subtractive? 300 in series with 40 =260?
No it's not addition and subtraction, it's C1xC2/(C1+C2) like resistors in parallel.
So if you wire 4 1000uF 50V caps in series parallel you have 1000uF 100V, but it's best to add a bleeder network to make sure the voltages are evenly distributed. I don't know the math for DC if you use different Farad values in series off the top of my head.
Anything new? I'm really waiting to hear that Sunn come to life again!
Did Corey's Sunn ever get fixed??????
It's put back together, and was working. Then died again. I'mma drop it off at the local shop for shits and giggles, he does diagnostic work for me for free because I occasionally do work for him. I'll drop back in once I know more!
have you looked the ground plane over? maybe some filter components are cold soldered or failed open to the ground.
have you rung all the test points? like bias levels and the collector/emitter voltages wrt the rails? you will find a leaky component that way if the voltage is pulled up or down too far as the dividers arent working correctly from a leak. bogus biasing could monkey up the gain
SS is all dc except for the signal. hums are almost always ground related
is shielding or a grounded shield removed anywhere? was there a metal piece or some farraday cage thing that has been removed?
is pretty crude circuit there actually, especially that 15v zener clamp heh. there's brute force for you.
edit: check those diodes on the op transformers too.
editz: maybe im way late to the party heh
Beats me, I got it to work, with no hum, playing loud and clean. Then it fizzled out, again. I haven't opened it back up. I'll drop it off to him, and let you guys know once I get it back.