Hello people of DIYAudio!
I thought I'd join the forum as I found a few posts about this amp so I thought I'd see if anyone that knows anything about these amps is still around and could perhaps give me some pointers.
I have been experiencing an intermittent problem with my 340A whereby only when outputting to loudspeakers (all fine through headphones), the right channel will go quiet and weak, distort or cut out all together. Clear audio will usually come back if I turn up the volume to about half way, kind of like revving an old car when it's about to die, then the audio will kick back in, I'll turn the volume back down to listening level and the audio will play nice and clear thereafter - if I adjust the volume and/or balance knobs the audio will remain clear.
I have tried 'working' the volume and balance knobs in case of dirty pots but seems to make no difference, other than when I mess with the volume knob to get clear sound back when it's playing up. I'm unsure if this would be the cause of the problem anyway since the distortion etc. happens to my R channel and the L is always loud and clear. Sometimes even this method won't work and I have to power cycle the amp a few times to get audio back through the right channel. Sometimes the fault will also happen randomly when the amp has been working fine for a few hours.
I've tried using different input sources through different input selectors, swapped the speaker leads and RCA input cables but this makes no difference.
I've had the amp out of its chassis and had a look at the components - nothing appears to have burnt out and I couldn't see any dry joints. Would it be out of the question to suspect the chip has blown on this channel?
Just for information, the amp was bought used and had been used pretty much daily for around two years now before the fault arose, powering a pair of 4ohm 'studio monitors'. I'd done a little digging on this amp looking for a fix and have seen posts suggesting against 4ohm loads for these amps so maybe that's what's caused my problem!
Anyway thanks for reading. I welcome any suggestions, I'd love to get this amp going again!
Cheers
I thought I'd join the forum as I found a few posts about this amp so I thought I'd see if anyone that knows anything about these amps is still around and could perhaps give me some pointers.
I have been experiencing an intermittent problem with my 340A whereby only when outputting to loudspeakers (all fine through headphones), the right channel will go quiet and weak, distort or cut out all together. Clear audio will usually come back if I turn up the volume to about half way, kind of like revving an old car when it's about to die, then the audio will kick back in, I'll turn the volume back down to listening level and the audio will play nice and clear thereafter - if I adjust the volume and/or balance knobs the audio will remain clear.
I have tried 'working' the volume and balance knobs in case of dirty pots but seems to make no difference, other than when I mess with the volume knob to get clear sound back when it's playing up. I'm unsure if this would be the cause of the problem anyway since the distortion etc. happens to my R channel and the L is always loud and clear. Sometimes even this method won't work and I have to power cycle the amp a few times to get audio back through the right channel. Sometimes the fault will also happen randomly when the amp has been working fine for a few hours.
I've tried using different input sources through different input selectors, swapped the speaker leads and RCA input cables but this makes no difference.
I've had the amp out of its chassis and had a look at the components - nothing appears to have burnt out and I couldn't see any dry joints. Would it be out of the question to suspect the chip has blown on this channel?
Just for information, the amp was bought used and had been used pretty much daily for around two years now before the fault arose, powering a pair of 4ohm 'studio monitors'. I'd done a little digging on this amp looking for a fix and have seen posts suggesting against 4ohm loads for these amps so maybe that's what's caused my problem!
Anyway thanks for reading. I welcome any suggestions, I'd love to get this amp going again!
Cheers
Sometimes people are reluctant to try opening their relays to service them or the dang thing is sealed. This has been answered previously with the OEM part Number and a suitable replacement that's probably easier to find than the original Chinese Massuse brand relay. They're inexpensive so it might be a simpler solution: http://www.diyaudio.com/forums/parts/264555-massuse-me-11-relay-replacement.html
Thank you all! I wouldn't even have thought to check the relay!
It does look to be an ME-11 and unfortunately I think it's sealed so I guess I can't open it up to clean it. I've just tried pulling on the top of it, not sure if there might be some kind of catch accessible from the bottom side (it's still soldered to the board).
I'll have a look for the RM84 mentioned in the linked post, fortunately there's only the one relay so I won't have to find two!
But again thank you guys, really appreciated - I'll let you know how I get on!
It does look to be an ME-11 and unfortunately I think it's sealed so I guess I can't open it up to clean it. I've just tried pulling on the top of it, not sure if there might be some kind of catch accessible from the bottom side (it's still soldered to the board).
I'll have a look for the RM84 mentioned in the linked post, fortunately there's only the one relay so I won't have to find two!
But again thank you guys, really appreciated - I'll let you know how I get on!
Okay, I've had a look around for the RM84 and can't seem to find the right one here in the UK. I don't know much about speccing relays, however I've come across this during my search this evening:
RT424012 | DPDT PCB Mount Non-Latching Relay Through Hole, 12V dc | TE Connectivity
Should I be alright to use it? It has the same 12v coil, 8A (i presume for the 250v?), same physical dimensions with the same 5mm pins and layout. I think this is all okay but just wanted to run it by someone, I don't want to make anything worse!
Here's a link to the datasheet for the original relay I'm looking to replace by the way: Massuse ME-11 012-2Z4 8A 250VAC
Thanks again
RT424012 | DPDT PCB Mount Non-Latching Relay Through Hole, 12V dc | TE Connectivity
Should I be alright to use it? It has the same 12v coil, 8A (i presume for the 250v?), same physical dimensions with the same 5mm pins and layout. I think this is all okay but just wanted to run it by someone, I don't want to make anything worse!
Here's a link to the datasheet for the original relay I'm looking to replace by the way: Massuse ME-11 012-2Z4 8A 250VAC
Thanks again
The Schrack relay (TE connectivity) you picked seems to be out of stock at RS. This model is similar but the sealing method differs and it definitely won't disassemble for cleaning with all that sealing resin: RTE24012 | DPDT PCB Mount Non-Latching Relay Through Hole, 12V dc | TE Connectivity
As a retail customer, you might find CPC Farnell or Farnell has a suitable relay too, as these are widely used parts and there are dozens of types from several manufacturers that would do the same job, provided the coil rating is similar for voltage, current or resistance and the contacts have a min. 30V DC contact rating. A high DC switching rating rather than AC rating is critical to ensure the relay can open under failed amplifier conditions and this is not so easy, as you can see in the different ratings.
As a retail customer, you might find CPC Farnell or Farnell has a suitable relay too, as these are widely used parts and there are dozens of types from several manufacturers that would do the same job, provided the coil rating is similar for voltage, current or resistance and the contacts have a min. 30V DC contact rating. A high DC switching rating rather than AC rating is critical to ensure the relay can open under failed amplifier conditions and this is not so easy, as you can see in the different ratings.
This is an important part of the speaker relay specification.
The sparking when opening damages the contact surfaces.
Some have used mosFETs as solid state relays just to avoid this problem.
Try your new relay and see if that helps in the short term.
If that works then investigate using one of the Forums SS relays for speaker isolation.
They do leak a tiny bit of HF after they open, but that is not a problem.
Strange, it shows as in stock for me! Interesting about the 30V DC though, thank you for pointing that out. Just had a look at the graph on the datasheet and it seems to show it can handle that, though I'm considering going for this one.
G2RL-2 12DC | DPDT PCB Mount Non-Latching Relay Through Hole, 12V dc | Omron
It's much clearer in the datasheet that it supports the 30V DC at 8A and is unsealed for future cleaning (clear to me at least)!
As said, there are literally dozens of similar relays out there that would do the same job so choose the better available pedigree. I don't know that quality is certain among the brands now available and anecdotal evidence is dodgy when it refers to old products. No doubt the original was selected because of the lowest cost in the very competitive Chinese supply market where Cambridge Audio products are assembled.
Where older style power relays are used, access for maintenance is a good thing as it obviates replacement problems for old models. For these tiny disposable parts though, I'm inclined to think that a sealed type is a better option. I would go for it because a service life of 10 years is not exactly brilliant and there will likely be pitting of the alloy faces rather than just contamination, which cleaning won't fix properly. Sealing wont eliminate that pitting but it will at least eliminate atmospheric contamination.
Where older style power relays are used, access for maintenance is a good thing as it obviates replacement problems for old models. For these tiny disposable parts though, I'm inclined to think that a sealed type is a better option. I would go for it because a service life of 10 years is not exactly brilliant and there will likely be pitting of the alloy faces rather than just contamination, which cleaning won't fix properly. Sealing wont eliminate that pitting but it will at least eliminate atmospheric contamination.
You make a good point there. I'm going to order the Omron but in the sealed flavour! I will post back to let you know how I get on.
But thank you Ian, I find it interesting to know about these things. I think I'll be sticking around here to learn more about amps. I find them interesting but daunting to learn about. I've built a class D amp kit (soldered components to a PCB following instructions!) but I'm no expert in electronics like this and I can spend time reading and looking at schematics and things and my brain just gets overloaded. I'm confident there's some info on the forum that's easier for me to digest! Thanks again.
I suggest if you have not covered this in your checks that you re-make the solder joints for the relay pins and check the circuit board traces for hairline cracks.
I located the problem by pressing lightly on the circuit board for a relay problem last year. I wasn't a crack but a solder joint that looked good bad wasn't. The fault would disappear temporarily if a applied a little pressure on the board with my finger near the suspect relay - there were two to choose from in this instance.
I located the problem by pressing lightly on the circuit board for a relay problem last year. I wasn't a crack but a solder joint that looked good bad wasn't. The fault would disappear temporarily if a applied a little pressure on the board with my finger near the suspect relay - there were two to choose from in this instance.
Sorry a few typo's in this. Dry joints happen in older equipment and one cannot always tell by appearances.
I'll have to give it another look. I did have a good look for dry joints but only by eye - I suppose the only real way to check would be to re-solder every component!
I might have a go with pushing on the board, I'd just have to be careful about where I'm touching - I don't fancy a shock! Or I suppose it's all 30v DC on this board away from the power supply and big caps? I do have a schematic I could share but I'm not sure of how best to share it.
The problem area is to do with the relay and that is where you should focus your attention - the headphone connection works so all the electronics that precedes this will be OK.
You will need to identify the in and out pins for the problem channel.
Pressing the top of the relay directly in line with each is suggested - also near the board connection with the relay pins. A safe way to do this is with the eraser end of a pencil.
You can do this with the cover off the amplifier while it is playing music.
If this reveals nothing then you will be faced with a soldering job whether remaking the joins as I have suggested or failing success there, removing the old relay and soldering a new one in place.
If the problem lies with the solder joins rather than the old relay going straight to the second step will be an unnecessary expense.
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Given the usual symptoms of bad relay contacts (output requires a boosted volume level to blast through the gunk) I think the low cost of a new relay is actually a wise investment for an inexperienced repairer, of only about £1.50, for what is an economy grade power relay and you cover all existing possible relay faults in one fell swoop.
I've not yet come across a bad PCB solder joint where contact is restored just by increasing the voltage. Usually, the connection continues to worsen as the solder burns, erodes or even melts away. I really doubt the soldering is a problem but I guess there are always possibilities of strange latent faults in electronics manufacturing.
I've not yet come across a bad PCB solder joint where contact is restored just by increasing the voltage. Usually, the connection continues to worsen as the solder burns, erodes or even melts away. I really doubt the soldering is a problem but I guess there are always possibilities of strange latent faults in electronics manufacturing.
There is still the what if question in regard to the possibility of a hairline crack in the trace between the output and the relay input pin. If there is a joint that has gone cold. The intermittent connection may be due to a combination of the effects of expansion or contraction which metals are susceptible to and ttransmission of the mechanical effects of the relay opening and closing at switch on and switch off. The effects of this on a bad joint over time - these need to be ruled out as a possible primary cause.
I am not denying the possibility the relay may be faulty. The contacts should self wipe as part of the switching and the unit should be sealed to avoid oxidation of the contacts. The proposal for a replacement is not to skimp with the cost. If this amplifier had been repaired sometime in the past - a d.c. current fault involving a large current there could be a concern if the relay was simply a delay dropout strategy rather than for loudspeaker protection against dc current.
I am noting this insight as a clue for the benefit of others who may be looking for answers and come to this thread.
I am not denying the possibility the relay may be faulty. The contacts should self wipe as part of the switching and the unit should be sealed to avoid oxidation of the contacts. The proposal for a replacement is not to skimp with the cost. If this amplifier had been repaired sometime in the past - a d.c. current fault involving a large current there could be a concern if the relay was simply a delay dropout strategy rather than for loudspeaker protection against dc current.
I am noting this insight as a clue for the benefit of others who may be looking for answers and come to this thread.
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Well, I had some free time yesterday so I dug the amp out and had a play.
I plugged it all in and couldn't get it to act up! Had it running for a good few hours, power cycled it a few times, poked at and around the relay with the rubber end of a pencil and all was fine.
I thought I'd just try re-soldering the the relay so I did that, then when I powered the amp up I got my fault, but strangely through the left channel! (it had always been the right that would play up)
I guess that definitely confirms problems with the relay, so I'm going to order one and give that a shot!
I plugged it all in and couldn't get it to act up! Had it running for a good few hours, power cycled it a few times, poked at and around the relay with the rubber end of a pencil and all was fine.
I thought I'd just try re-soldering the the relay so I did that, then when I powered the amp up I got my fault, but strangely through the left channel! (it had always been the right that would play up)
I guess that definitely confirms problems with the relay, so I'm going to order one and give that a shot!
😀
Are you sure you didn't inadvertently swap speakers in the process of testing? In any case, following Mjona's comments, it wouldn't hurt to also (magnifying glass etc.) inspect the copper traces that connect the output signal in and out from the relay. It's a longshot but breaks in the foil can exist from new yet only show up with the repeated temperature cycling and the slight warping that occurs over many years.
As a suggestion for when you do replace the relay, it will be impossible to remove the original without lifting the copper pads from the PCB unless all the solder is removed first from the pins and pads. Use a length of "solder wick" which is fluxed copper braid that sucks up solder when placed between joint and iron tip. It does require more heat than for soldering though, so use small widths of 1.5 -2.5 mm if you only have a small tip. This looks suitable: 10-5L | Chemtronics 1.5m Desoldering Braid, Width 2.5mm | ITW Chemtronics
Brief demo here: https://www.youtube.com/watch?v=BrAJpz9Mdm4