Hello! I've just got a Valvestate 8080 for a decent price (a good deal, but not cheap) and unfortunately found out a bit too late that when turned on, with nothing plugged in and all knobs to 0, it has a constant, relatively loud buzzing sound (my fault for buying without testing!). The buzz goes away when the loudspeaker is disconnected. I've tried a few outlets too but no luck.
I took the head out and cleaned all the pots with contact cleaner but that didn't do very much (though it's probably good maintenance anyway). Visually nothing seems to be amiss, but I know very little about electronics and amp repairs. One thing to note maybe is that the transformer doesn't appear to be original.
Is there something obvious I should try? This happens on all channels, with a guitar plugged in or not. On similar thread (here and across the internet) people suggest to replace the valve but I'm not sure it's the issue since it happens even on the clean channel which as I understand doesn't use the valve.
Could it be the power supply/transformer? Is there something I can look at that involves minimal soldering? (I can do it, just not very confident with an iron that's all!) — I guess what's puzzling is that it disappear when the loudspeaker is disconnected...
When turned off, it also gives a sharp pop sound. I unplugged the reverb and that seems to fix it. Any way I can get the reverb not to do that?
Here are some pictures before the clean
I took the head out and cleaned all the pots with contact cleaner but that didn't do very much (though it's probably good maintenance anyway). Visually nothing seems to be amiss, but I know very little about electronics and amp repairs. One thing to note maybe is that the transformer doesn't appear to be original.
Is there something obvious I should try? This happens on all channels, with a guitar plugged in or not. On similar thread (here and across the internet) people suggest to replace the valve but I'm not sure it's the issue since it happens even on the clean channel which as I understand doesn't use the valve.
Could it be the power supply/transformer? Is there something I can look at that involves minimal soldering? (I can do it, just not very confident with an iron that's all!) — I guess what's puzzling is that it disappear when the loudspeaker is disconnected...
When turned off, it also gives a sharp pop sound. I unplugged the reverb and that seems to fix it. Any way I can get the reverb not to do that?
Here are some pictures before the clean
well if it's not that one of the diodes in the bridge rectifier is bad then it's the usual problem of bad solder joints on the power resistors that are feeding the low voltage supply for the pre-amp stages. it's a bad design if you ask me those dropping resistors run smoking hot because they're dropping a whole lot of voltage as they are taken from the high voltage supply (R 101,R102 330 or 270 ohm depending on whether it's an 80 or 100 watt model) and the solder on those gets to near the melting point. if the amp is played hard turn off and moved or subjected to shock those solder joints will fail!!
i still have an 8080 which i repaired by using a separate transformer to supply the low voltage.
i still have an 8080 which i repaired by using a separate transformer to supply the low voltage.
@turk 182 Thanks for this, I have to say, I am mostly clueless about electronics. I've located R101 and R102 and from the top they look solidly anchored and not moving. I can't seem to remove the board (couldn't find any videos online and working out on my own, I found 3 plastic pins but even then, it wouldn't come off) and sticking my phone on the side didn't offer up much more insight.
@JMFahey The buzz is through the speaker and doesn't respond to any control. The only way to remove it is to unplug the loudspeaker. Does that help?
@JMFahey The buzz is through the speaker and doesn't respond to any control. The only way to remove it is to unplug the loudspeaker. Does that help?
Is it a LOUD buzz or just annoying? Can you still hear the music despite the buzz?
It isn't surprising that disconnecting the speaker makes it stop. The speaker is where the sound comes from in general.
First susects are the main filter caps - either the caps themselves or the solder to them.
It isn't surprising that disconnecting the speaker makes it stop. The speaker is where the sound comes from in general.
First susects are the main filter caps - either the caps themselves or the solder to them.
@Enzo Yes, that makes sense. I suppose I was putting the emphasis on it as some of the other thread on similar issues seem to reference the buzzing happening even when the loudspeaker is attached.
When someone plays, the buzz is pretty much drowned out so in that sense it's maybe not so much of an issue, but I was hopping to use it to record some stuff eventually and it would become a problem then. Attached is a sample of the noise up close. It's definitely very noticeable when not playing, louder than a fridge (~40db?).
Is there a way to test if the caps are dead or if the solder needs redoing before I try to take everything apart? (excuse the newbie question!) Would I do that with a multimeter? (which I don't have but could try to get one)
When someone plays, the buzz is pretty much drowned out so in that sense it's maybe not so much of an issue, but I was hopping to use it to record some stuff eventually and it would become a problem then. Attached is a sample of the noise up close. It's definitely very noticeable when not playing, louder than a fridge (~40db?).
Is there a way to test if the caps are dead or if the solder needs redoing before I try to take everything apart? (excuse the newbie question!) Would I do that with a multimeter? (which I don't have but could try to get one)
you'd have to remove all the jack nuts the knobs and potentiometer nuts and washers then those plastic rivets but if the disassembly of this thing befuddles you stop...you may need help....while those resistors will feel mechanically solid trust me the carbon in the solder joint crack from arcing will affect circuit operation and produce noise!
there was a period of time that i serviced so many Valvestate 8080's that it wasn't funny but money is money...
i'll try to upload some pics of the one i have here if your interested in modding it.
there was a period of time that i serviced so many Valvestate 8080's that it wasn't funny but money is money...
i'll try to upload some pics of the one i have here if your interested in modding it.
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Same here in Buenos Aires
My main thing is manufacturing but do some servicing on the side, half to keep awake and learning (same reason I´m here, to keep updated), half because I "owe" it to some good Customers, meaning Distributors, Music Shops, rehearsal studios, equipment rentals, etc. , plus it fills some holes in slow times, but as you found, it was not funny.
Official Marshall (and Gibson and Morley and 1000 other brands) distributor here, Import Music, sent me so many repairs, in and out of Warranty, that it seriously chopped my manufacturing time, so I asked them to keep dead amps in a corner of their huge warehouse, and I visited them once a Month.
They put them in rows on long tables, couple "Industrial High School" kids opened them, pulled chassis out so I made preliminary measurements and tests and if needed pulled board out (13 pots plus half a dozen jacks each!!!, THE big time waster), I diagnosed and repaired what´s needed , the beauty of repairing many same model is that failures tend to repeat a lot, so actual servicing was real fast, a few minutes, I did anything from 15 to up to 50 amp batches.
Another important cash cow from same Importer were JCM900 with blown/shorted OTs.
Wound with "self soldering" enamel wire, the kind which evaporates without residue under molten solder temperatures , great for $1 wall warts, 1 second saved in assembly makes all the difference, but have NO PLACE inside a High Voltage Vacuum Tube amplifier, even less a Guitar one which is often used clipping full tilt for hours, son in the end I straight wound batches of 10-20 OTs, knowing I would use them.
Of course mine were wound using Class F or H electric motor wire, good for up to 180C under high stress and vibration, even more inside an OT.
Oh well.
@turk 182 Beffuddled is the word! I think I'll leave it be for now, as it's not that much of an inconvenience for what I want to use it for right now. I have an MG100 as well that needs a new fan and right now the fan noise is even louder than the buzz sooo... no point in fixing the 8080 if the other one is louder still haha
That said, much appreciate all the inputs from everybody and will try to find someone local to take a look. Thank you!
That said, much appreciate all the inputs from everybody and will try to find someone local to take a look. Thank you!
Hi, I just bought one of these amps and I'm experiencing the same hum. Did you manage to find a solution to the problem? Or should I accept that this amplifier is so noisy?
Maybe it's a late answer, but I had the same experience with my 8080. It seems hum is not caused by malfunction, but rather poor PCB design.
I could significantly reduce hum by creating new ground path for the preamp section:
I could significantly reduce hum by creating new ground path for the preamp section:
- I removed original jumper from PCB
- Added a new grounding wire (solder points on the top of the picture were also bridged)
Attachments
Hey @kikikaka I am trying to do this same modification to eliminate the buzz in the same amp. Could you tell me what you mean by "remove the original jumper" here? Which jumper is that? Do you mean from the PCB to the chassis on the input jack side?
I tried this ground workaround from another forum - similar to yours - but it didn't do anything for me.
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