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Post by bram on May 27, 2019 12:21:01 GMT -6
I picked up a 1980 Marshall 4140 Club & Country this week. The seller said it had just come off the bench and was biased with new JJ KT77 tubes. Getting familiar with it back home I'm finding that the amp is pretty noisy and has some quirks: (Audio clips are below) 1a. With only the master volume turned up, intermittently there are static/crackly noises (like an old vinyl record). Sometimes it's worse when the amp is warming up, other times it disappears only to return after the amp has been on for some time. 1b. With Channel 1 up, the noises increase in volume. 2. The Reverb channel exhibits similar crackly noises with a much higher intensity. The sound clip is with the reverb channel only up to 3 (10oclock). It's close to unusable 3. If I bonk the top of the amp, its audible through the speakers. Flipping the Bright switch creates a similar sound. Seems to be Ch. 1 related as the bonking is most effective when hitting above the left side of the chassis. 4. The noise with Ch. 1 Boost engaged seems excessive (60hz with strong 120/240 harmonics) 5. If I'm using Ch. 1 and turn up the gain on the unused Ch. 2 , it seems to cancel out the lower 60hz harmonics of the master output. Is this expected behavior? (6.) Ch. 1 doesn't seem to have much clean headroom. This is my first Marshall, so maybe I'm just not understanding the gain staging, but with a single coil strat with vol pot at full, the amp starts to break up at 3'oclock on the Ch. 1 HIGH Input. I was under the impression that the Club & County's were known for their cleans. Compared next to a vintage Music Man 212 One-Thirty (130w from the same era), the input gain on the Marshall is very sensitive. ---------- I've exercised all of the 12AX7 and KT77 tube sockets and gave them a deoxit/bristle treatment. In general, the sockets feel pretty loose and it's easy to shift the tubes around in them, although the individual sockets seem to be tight. I also replaced each 12AX7 with some known working spares and it didn't change any behavior. What might some of the culprits be that are causing these issues? Any guidance would be much appreciated! Photo album of amp and PCB including the missing components
Edit: Legible service manual/Schematic found and uploaded!
https%3A//soundcloud.com/quilts/1-static-noise-ch-1-master%3Fin%3Dquilts/sets/marshall-4140-club-country-noisehttps%3A//soundcloud.com/quilts/2-static-noise-iphone%3Fin%3Dquilts/sets/marshall-4140-club-country-noisehttps%3A//soundcloud.com/quilts/3-reverb-channel%3Fin%3Dquilts/sets/marshall-4140-club-country-noisehttps%3A//soundcloud.com/quilts/4-bonk-test-master-only%3Fin%3Dquilts/sets/marshall-4140-club-country-noisehttps%3A//soundcloud.com/quilts/5-bonk-test-ch-1-master%3Fin%3Dquilts/sets/marshall-4140-club-country-noisehttps%3A//soundcloud.com/quilts/6-boost-noise-bright-switch%3Fin%3Dquilts/sets/marshall-4140-club-country-noise |
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Post by Tbone81 on May 27, 2019 16:04:17 GMT -6
I was going to say tubes, try changing power tubes since you already changed out the preamp/tone stack etc tubes.
Also bad filter caps in the power supply could be adding to the noise.
I’m not familiar with that specific amp but you can also try pulling out the chassis and take a look At the wiring. If it’s point to point check to make sure nothing is loose, and that no braided wiring is accidentally grounding out/not grounded. My JMP was going nuts on me and turned out to be a braided wire that was shorting out with another component. It was so obvious that it wasn’t (if that makes sense).
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Post by bram on May 27, 2019 18:04:44 GMT -6
Thanks Tbone,
I'll need to take a closer look, but upon the first few inspections, I haven't found any loose connections/cold solder joints.
I did notice that 4 components have been clipped: C13 (V2 Pin 3 to GND), R10 (220K, V3 Pin 2 to GND), R14, and R21 (470K, V3 Pin 7 to GND). I'm having trouble finding C13 & R14 on the schematic. Can anyone handy with amp schematics tell me what effect those components have on the circuit? Perhaps that was an intentional mod?
The entire circuit appears to be microphonic (if I'm using that term correctly). Any tap anywhere on the chassis, circuit board, or components gets amplified into the speakers. I'll need to order some KT77's in order to see if those are the culprits.
Also after doing some deep digging, I stumbled across a legible schematic for the 4140, I've updated the first post with it.
https%3A//soundcloud.com/quilts/6-pcb-chassis-tapping
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Post by bram on May 28, 2019 13:24:22 GMT -6
Here's an annotated pic of the missing components:  |
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Post by markfouxman on May 28, 2019 14:09:22 GMT -6
I picked up a 1980 Marshall 4140 Club & Country this week. The seller said it had just come off the bench and was biased with new JJ KT77 tubes. Getting familiar with it back home I'm finding that the amp is pretty noisy and has some quirks: (Audio clips are below) 1a. With only the master volume turned up, intermittently there are static/crackly noises (like an old vinyl record). Sometimes it's worse when the amp is warming up, other times it disappears only to return after the amp has been on for some time. 1b. With Channel 1 up, the noises increase in volume. 2. The Reverb channel exhibits similar crackly noises with a much higher intensity. The sound clip is with the reverb channel only up to 3 (10oclock). It's close to unusable 3. If I bonk the top of the amp, its audible through the speakers. Flipping the Bright switch creates a similar sound. Seems to be Ch. 1 related as the bonking is most effective when hitting above the left side of the chassis. 4. The noise with Ch. 1 Boost engaged seems excessive (60hz with strong 120/240 harmonics) 5. If I'm using Ch. 1 and turn up the gain on the unused Ch. 2 , it seems to cancel out the lower 60hz harmonics of the master output. Is this expected behavior? (6.) Ch. 1 doesn't seem to have much clean headroom. This is my first Marshall, so maybe I'm just not understanding the gain staging, but with a single coil strat with vol pot at full, the amp starts to break up at 3'oclock on the Ch. 1 HIGH Input. I was under the impression that the Club & County's were known for their cleans. Compared next to a vintage Music Man 212 One-Thirty (130w from the same era), the input gain on the Marshall is very sensitive. ---------- I've exercised all of the 12AX7 and KT77 tube sockets and gave them a deoxit/bristle treatment. In general, the sockets feel pretty loose and it's easy to shift the tubes around in them, although the individual sockets seem to be tight. I also replaced each 12AX7 with some known working spares and it didn't change any behavior. What might some of the culprits be that are causing these issues? Any guidance would be much appreciated! Bram, Providing you already checked the tubes and cleaned the sockets next I'd check all mechanical connections, deoxidize/clean all ground connections to the chassis and all pots. If no help next would be 100K plate resistors. While on that I'd also check cathode resistors for drifting. If with volume control the noise goes up it means the problem is before that stage. The R10 and R21 will affect tone controls. C13 most likely the one from anode to cathode of V2a. Best, M |
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Post by svart on May 28, 2019 16:05:59 GMT -6
Just a quick eyeballing, most of the parts removed would affect signal level into the gain stages, but not affect the amount of gain through the tubes.. However, I cannot find C13 and R14 in the schematic either and if those are cathode resistor/cap they could affect gain. Most likely they did this for more distortion as the tubes would be hit with hotter levels.
You could be simply hearing a lot of noise due to the increased signal level (more volume) but that's a lot of hum.. Maybe start by replacing the components you can find and see if that helps at all.
"Bonking" may be a red herring. All tubes have some microphony, but if the gain/signal level is turned up through mods, they might exhibit a lot more than normal.
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Post by Tbone81 on May 28, 2019 16:52:02 GMT -6
The entire circuit appears to be microphonic (if I'm using that term correctly). Any tap anywhere on the chassis, circuit board, or components gets amplified into the speakers. I'll need to order some KT77's in order to see if those are the culprits. https%3A//soundcloud.com/quilts/6-pcb-chassis-tappingIts hard to tell from your recording if the amp tubes are truly microphonic. As Svart said, all tubes will generally relay some sound if you hit them hard enough. Try tapping gently on each tube with a pencil. Does one sound significantly louder than the rest? I know you already swapped out preamp tubes but maybe one of the tube sockets is tarnished?
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Post by bram on May 28, 2019 19:56:47 GMT -6
Thank you for the input everyone. V1 & V2 are both sensitive to tapping directly on the tubes. V3 is silent in comparison, same with the rest of the tubes. It's perhaps worth mentioning that tapping on the circuit board itself creates a louder sound than tapping the tubes.
In any case, I've placed an order for the missing parts and will replace the old Frako electrolytic caps while I'm at it. Will report back once the new components are in!
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Post by johneppstein on May 28, 2019 21:36:56 GMT -6
The entire circuit appears to be microphonic (if I'm using that term correctly). Any tap anywhere on the chassis, circuit board, or components gets amplified into the speakers. I'll need to order some KT77's in order to see if those are the culprits. https%3A//soundcloud.com/quilts/6-pcb-chassis-tappingThat sounds to me like one or more bad solder joints. I'd shotgun it - go over each and every solder joint on the circuit board if not in the entire amp. |
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Post by svart on May 29, 2019 8:44:27 GMT -6
The entire circuit appears to be microphonic (if I'm using that term correctly). Any tap anywhere on the chassis, circuit board, or components gets amplified into the speakers. I'll need to order some KT77's in order to see if those are the culprits. https%3A//soundcloud.com/quilts/6-pcb-chassis-tappingThat sounds to me like one or more bad solder joints. I'd shotgun it - go over each and every solder joint on the circuit board if not in the entire amp. Good advice. I initially missed the part where it was stated that it was a PCB based unit. PCB based circuits are usually pretty bad when connecting the sockets to the PCB. The heat/cool cycles stress-crack the solder and the high-ohmic joints that result can cause the crackling we're hearing in the samples. I'd follow John's advice about reflowing joints, but start with all the tube and power resistor solder joints and add a little rosin/flux or some fresh flux-cored solder on each joint to ensure the tarnished solder is melted and cleaned. |
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Post by swurveman on May 29, 2019 8:56:13 GMT -6
That sounds to me like one or more bad solder joints. I'd shotgun it - go over each and every solder joint on the circuit board if not in the entire amp. Good advice. I initially missed the part where it was stated that it was a PCB based unit. PCB based circuits are usually pretty bad when connecting the sockets to the PCB. The heat/cool cycles stress-crack the solder and the high-ohmic joints that result can cause the crackling we're hearing in the samples. I'd follow John's advice about reflowing joints, but start with all the tube and power resistor solder joints and add a little rosin/flux or some fresh flux-cored solder on each joint to ensure the tarnished solder is melted and cleaned. I'm enjoying the tech talk you guys are having. However, when a seller says, an amp has just come off the bench , I would think that means it doesn't have these kinds of problems. Am I wrong for assuming that in the world of amp buying? My thinking after reading this thread progress was, "why not return the amp and get your money back?". |
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Post by Tbone81 on May 29, 2019 9:01:49 GMT -6
Good advice. I initially missed the part where it was stated that it was a PCB based unit. PCB based circuits are usually pretty bad when connecting the sockets to the PCB. The heat/cool cycles stress-crack the solder and the high-ohmic joints that result can cause the crackling we're hearing in the samples. I'd follow John's advice about reflowing joints, but start with all the tube and power resistor solder joints and add a little rosin/flux or some fresh flux-cored solder on each joint to ensure the tarnished solder is melted and cleaned. I'm enjoying the tech talk you guys are having. However, when a seller says, an amp has just come off the bench , I would think that means it doesn't have these kinds of problems. Am I wrong for assuming that in the world of amp buying? My thinking after reading this thread progress was, "why not return the amp and get your money back?". Your not wrong in your assumptions, but old amps are finnicky beasts. Sometimes its just on bad solder joint, one loose connection etc, and the whole amp goes ape shit. However they're generally really easy to work on so if it was me, I'd try and keep it. |
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Post by svart on May 29, 2019 9:07:53 GMT -6
Good advice. I initially missed the part where it was stated that it was a PCB based unit. PCB based circuits are usually pretty bad when connecting the sockets to the PCB. The heat/cool cycles stress-crack the solder and the high-ohmic joints that result can cause the crackling we're hearing in the samples. I'd follow John's advice about reflowing joints, but start with all the tube and power resistor solder joints and add a little rosin/flux or some fresh flux-cored solder on each joint to ensure the tarnished solder is melted and cleaned. I'm enjoying the tech talk you guys are having. However, when a seller says, an amp has just come off the bench , I would think that means it doesn't have these kinds of problems. Am I wrong for assuming that in the world of amp buying? My thinking after reading this thread progress was, "why not return the amp and get your money back?". True. I assume it might be easier to just try to fix it than take it back and argue about whether it "works" or not. Not all techs are good techs either.. It's ultimately up to Bram on what he wants to do but it sounds like fixing it is the way he's going. |
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Post by audiomaintenance on May 29, 2019 9:37:31 GMT -6
I profess to know very little about this... but a good friend of mine who has fixed countless Marshall amps told me ... noises like this are usually Anode resistors breaking down. hope that helps
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Post by johneppstein on May 29, 2019 12:03:20 GMT -6
Good advice. I initially missed the part where it was stated that it was a PCB based unit. PCB based circuits are usually pretty bad when connecting the sockets to the PCB. The heat/cool cycles stress-crack the solder and the high-ohmic joints that result can cause the crackling we're hearing in the samples. I'd follow John's advice about reflowing joints, but start with all the tube and power resistor solder joints and add a little rosin/flux or some fresh flux-cored solder on each joint to ensure the tarnished solder is melted and cleaned. I'm enjoying the tech talk you guys are having. However, when a seller says, an amp has just come off the bench , I would think that means it doesn't have these kinds of problems. Am I wrong for assuming that in the world of amp buying? My thinking after reading this thread progress was, "why not return the amp and get your money back?". Ir all depends on whose bench it came off of. |
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Post by bram on May 29, 2019 17:30:20 GMT -6
The seller was selling the amp for a friend - allegedly it recently came back from the seller's go-to amp tech. Perhaps 'off the bench" meant, "Yeah he put new power tubes in there and biased it" and that was it. It's difficult to imagine anyone that who does this for a living and takes it sincerely would see the missing components, listen to the reverb channel and greenlight it out the door, but I digress. At any rate it's a cool amp, and even if I need to send it off to a tech, I got it for a good price. It's also a solid opportunity for me to learn more about amps and have some fun. I'm a sucker for taking things apart. If the new parts and reflow don't do the job, I'll take it to a professional. Update: I wen't through and re-flowed all of the tube sockets and non-PCB connections. I'll reflow the PCB when the missing parts arrive. Post reflow, V1 & V2 are still touch-sensitive and plenty of Popcorn remains. A new issue has surfaced, which is an intermittent sub-frequency rumbling that grows in intensity over time when the amp is in play mode, and disappears when putting the amp in standby and back into play. What could be the cause of that? Continued appreciation for everyone's input. 🙏 New noise: https%3A//soundcloud.com/quilts/7-low-freq-noiseAttachments:
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Post by svart on May 30, 2019 7:24:46 GMT -6
The seller was selling the amp for a friend - allegedly it recently came back from the seller's go-to amp tech. Perhaps 'off the bench" meant, "Yeah he put new power tubes in there and biased it" and that was it. It's difficult to imagine anyone that who does this for a living and takes it sincerely would see the missing components, listen to the reverb channel and greenlight it out the door, but I digress. At any rate it's a cool amp, and even if I need to send it off to a tech, I got it for a good price. It's also a solid opportunity for me to learn more about amps and have some fun. I'm a sucker for taking things apart. If the new parts and reflow don't do the job, I'll take it to a professional. Update: I wen't through and re-flowed all of the tube sockets and non-PCB connections. I'll reflow the PCB when the missing parts arrive. Post reflow, V1 & V2 are still touch-sensitive and plenty of Popcorn remains. A new issue has surfaced, which is an intermittent sub-frequency rumbling that grows in intensity over time when the amp is in play mode, and disappears when putting the amp in standby and back into play. What could be the cause of that? Continued appreciation for everyone's input. 🙏 New noise: https%3A//soundcloud.com/quilts/7-low-freq-noiseWhoa, that sounds like motor-boating! That's kinda rare to hear if it is. It's caused by oscillation, usually on the B+. Power tubes biased wrong can cause this, and so can a bad ground. Honestly a bad ground can cause a lot of what you're hearing too, so it might be more likely to look there. Could also just be oscillation in the preamp section. does it change with volume and suddenly get louder as you turn it up? |
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Post by bram on May 30, 2019 16:00:54 GMT -6
Whoa, that sounds like motor-boating! does it change with volume and suddenly get louder as you turn it up? Ok! Getting interesting - I am able to induce the 'motor-boating' by tapping/bumping the chassis only when the Master volume is dimed. The motor boating can also start on it's own accord and initiates with a distorted pop. If I drop the master volume down to 8, the noise stops, and doesn't return immediately when I bring the volume back up to max. The motor-boatin' sound is also affected by Ch. 2's volume and gain controls, but is unaffected by Ch. 1. I've gotten clear on where the missing components are in the schematic. I've drawn them in or circled the components in red, attached below. Svart, you had mentioned earlier that the missing components are most likely affecting the gain staging- The missing C13 (probably 22uf) is connected in parallel with R17 from V2b's Cathode to ground. R14 (470K based on another guts photo) runs after C11 in Parallel with R13/R19/(R21 also missing)/R32. Am I correct in thinking these components would affect the Reverb channel? Mouser order arrives tomorrow. Attachments:
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