I have friend with a Carver M-500t which puts out what sounds like a dimmer buzz at idle.
After reading the Carver postings here, I've come to the conclusion that it's probably noise from the triac in the Magnetic Field PSU. This can apparently misfire under light load conditions.
Does this cause a buzz at the outputs?
Does anyone know how to fix this?
After reading the Carver postings here, I've come to the conclusion that it's probably noise from the triac in the Magnetic Field PSU. This can apparently misfire under light load conditions.
Does this cause a buzz at the outputs?
Does anyone know how to fix this?
Hi, Yes the buzz sounds like dimmer noise because the main transformer is basically on a dimmer.
there are filters built into the amp, but i'm guessing they're optimised for US mains, or they're just crap.
i have a coulpe of racks of PM1.5's , same problem, although varies from amp to amp!
the usual solution is to fit a good filter Externally in the power cable to each amp.
when i say filter, i don't mean one of those 'power conditioning plugs'
I use some nice filters made my Roxburgh (RS), they come in a aluminium can about 50mm dia. by 75mm tall with a mounting stud on the top. (similar to the ones you find inside washing machines).
These contain a pair of big chokes, 2 Class-X caps and a Class-Y cap.
techninally, you should swap the LOAD and LINE connections round because you are trying to stop interference coming OUT of the amp, not giong in.
I use this 20A one in each of my PM1.5's....
hmm - cant find it.. but here's somethin similar
http://rswww.com/cgi-bin/bv/rswww/s...mkdlmgghcefeceeldgkidhgj.0&cacheID=uknetscape
there are filters built into the amp, but i'm guessing they're optimised for US mains, or they're just crap.
i have a coulpe of racks of PM1.5's , same problem, although varies from amp to amp!
the usual solution is to fit a good filter Externally in the power cable to each amp.
when i say filter, i don't mean one of those 'power conditioning plugs'
I use some nice filters made my Roxburgh (RS), they come in a aluminium can about 50mm dia. by 75mm tall with a mounting stud on the top. (similar to the ones you find inside washing machines).
These contain a pair of big chokes, 2 Class-X caps and a Class-Y cap.
techninally, you should swap the LOAD and LINE connections round because you are trying to stop interference coming OUT of the amp, not giong in.
I use this 20A one in each of my PM1.5's....
hmm - cant find it.. but here's somethin similar
http://rswww.com/cgi-bin/bv/rswww/s...mkdlmgghcefeceeldgkidhgj.0&cacheID=uknetscape
Hi viddipaldi,
I will have a look for the filter i use when i get the new farnell catalogue (they promised last week).
I should clarify: the filters we use are to reduce switching spikes caused by the carver which travel back down the mains cable to more sensitive parts of a touring system, for example PA mixers and the multicore (which in a touring system is 50 - 100M long with the mains feed taped along side it).
We found the buzz worst when using multiple amps in racks.
Although fitting filters to the start of the multicore power feed might would have been effective, the buzz would still pick up in all sorts of places (most annoyingly in the guitars and amps of the bands we were working with).
Buzzes were different with different combinations of carvers in use.
bearing all this in mind....
does the buzz still happen if you use the amp on its own with no input, input pots turned down, away from any other sources of interference (i.e. at home) ?
If this is the case then you probably have a problem with the amp's power supply - possibly dried out caps, leaky rectifier diodes, incorrectly set idle pot or damaged snubbers around the triac.
If you acn be bothered, you should get the amp to a service guy who knows these amps well.
On the other hand, if the buzz is the result of the carver(s) causing interference elsewhere in your system then you should consider using filters - either on every other mains feed from your distro, or as me and most of my colleagus prefer, one large filter per amp.
I hope this helps - i'll have a look for a suitable filter - remind me if i havent posted in 2 weeks
jonathan
I will have a look for the filter i use when i get the new farnell catalogue (they promised last week).
I should clarify: the filters we use are to reduce switching spikes caused by the carver which travel back down the mains cable to more sensitive parts of a touring system, for example PA mixers and the multicore (which in a touring system is 50 - 100M long with the mains feed taped along side it).
We found the buzz worst when using multiple amps in racks.
Although fitting filters to the start of the multicore power feed might would have been effective, the buzz would still pick up in all sorts of places (most annoyingly in the guitars and amps of the bands we were working with).
Buzzes were different with different combinations of carvers in use.
bearing all this in mind....
does the buzz still happen if you use the amp on its own with no input, input pots turned down, away from any other sources of interference (i.e. at home) ?
If this is the case then you probably have a problem with the amp's power supply - possibly dried out caps, leaky rectifier diodes, incorrectly set idle pot or damaged snubbers around the triac.
If you acn be bothered, you should get the amp to a service guy who knows these amps well.
On the other hand, if the buzz is the result of the carver(s) causing interference elsewhere in your system then you should consider using filters - either on every other mains feed from your distro, or as me and most of my colleagus prefer, one large filter per amp.
I hope this helps - i'll have a look for a suitable filter - remind me if i havent posted in 2 weeks
jonathan
Hello Jonathan,
thank you very much for your description. It helped me a lot to understand.
The buzz is also with no inputs, the pots turned down and no other equipment around.
So there are no filters which would help me. I have also tried with a filter from a washing machine, but no change.
If I turn the left pot up the buzz is getting louder and in maximum position it decreases to that noise it is when the pot is turned down.
The right channel is the same but not that much, the buzz is a bit quiter.
I can record a sound sample of it, maybe it can be helpful for diagnostics.
If we play with the band the buzz doesn't matter, you won't hear it anyway, but I think if I am able to find the problem it would be good for the amp itself.
Can you give me any other hint wich components I should try to replace first? Maybe I can isolate the problem swapping several components from left to right channel to hear which components caused more of the buzz in the left channel?
Once more thanks a lot for your time and help, guys
David
Btw. I do have the schematics of the amp, the changes described have been made to my PM 1.5 from the owner before.
I am not the expert but in our company we have two specialists for electronics who are on hand.
thank you very much for your description. It helped me a lot to understand.
The buzz is also with no inputs, the pots turned down and no other equipment around.
So there are no filters which would help me. I have also tried with a filter from a washing machine, but no change.
If I turn the left pot up the buzz is getting louder and in maximum position it decreases to that noise it is when the pot is turned down.
The right channel is the same but not that much, the buzz is a bit quiter.
I can record a sound sample of it, maybe it can be helpful for diagnostics.
If we play with the band the buzz doesn't matter, you won't hear it anyway, but I think if I am able to find the problem it would be good for the amp itself.
Can you give me any other hint wich components I should try to replace first? Maybe I can isolate the problem swapping several components from left to right channel to hear which components caused more of the buzz in the left channel?
Once more thanks a lot for your time and help, guys
David
Btw. I do have the schematics of the amp, the changes described have been made to my PM 1.5 from the owner before.
I am not the expert but in our company we have two specialists for electronics who are on hand.
hi,
i'm actually away from the carver circuits at the moment.
the circuit djk shows is a theoretical model of a type of filter i call a 'snubber', it soakes up the spikes using the resistor, the inductor limits the rate of change of current (i'm a bit rusty, so someone correct me if i'm wrong).
to use this circuit in the amp, you would have to look at the filter /snubber that is already there and decide whether you wanted to change carver's cicuit (or maybe just change a few component values).
Its quite likely that the circuit in the carver is already very similar to this one - its just what you use when you have a triac with a large inductive load.
the problem you describe may just be the inherrent hum and noise in the carver design. (you didn't say how loud the buzz was in relation to the music).
It's almost impossible to design a compact amp without some electro magnetic pick-up from the power supply's transformer this is why some audiophile gear has an external power supply (of course, not practical in a high power amp).
the way the hum goes up when the volume control is away from either end of its travel suggests 3 possibilities to me. possibly interference pickup in the wire leading from the input card at the back, to the pot (carver use 3 wires twisted together rather than screened cables although the signal level is high enough for then to get away with this.
alternatively, there may be a poor groung connection between the pot terminal and the input circuit, thirdly, there may be an earth loop through the chassis.
as i said - i'm no-where near a carver at the moment so i can't see exactly how they're doing things.
problems like this are not easy to solve and its quite likely its just a design shortfall in the amp. (you should hear the PM2.0t - it has a 1kHz buzz ! ).
i hope this has been of some help - or at least interesting.
jonathan
i'm actually away from the carver circuits at the moment.
the circuit djk shows is a theoretical model of a type of filter i call a 'snubber', it soakes up the spikes using the resistor, the inductor limits the rate of change of current (i'm a bit rusty, so someone correct me if i'm wrong).
to use this circuit in the amp, you would have to look at the filter /snubber that is already there and decide whether you wanted to change carver's cicuit (or maybe just change a few component values).
Its quite likely that the circuit in the carver is already very similar to this one - its just what you use when you have a triac with a large inductive load.
the problem you describe may just be the inherrent hum and noise in the carver design. (you didn't say how loud the buzz was in relation to the music).
It's almost impossible to design a compact amp without some electro magnetic pick-up from the power supply's transformer this is why some audiophile gear has an external power supply (of course, not practical in a high power amp).
the way the hum goes up when the volume control is away from either end of its travel suggests 3 possibilities to me. possibly interference pickup in the wire leading from the input card at the back, to the pot (carver use 3 wires twisted together rather than screened cables although the signal level is high enough for then to get away with this.
alternatively, there may be a poor groung connection between the pot terminal and the input circuit, thirdly, there may be an earth loop through the chassis.
as i said - i'm no-where near a carver at the moment so i can't see exactly how they're doing things.
problems like this are not easy to solve and its quite likely its just a design shortfall in the amp. (you should hear the PM2.0t - it has a 1kHz buzz ! ).
i hope this has been of some help - or at least interesting.
jonathan
The GE filter was actually suggested for a light dimmer.
The light dimmer has the same basic problem as an audio amplifier, you don't always know how much current it will draw. With low-current loads the Q of a filter will peak, and can actually make the noise greater. This filter design works over a 10:1 current range.
For 120V AC line the capacitors must have a 200V minimum rating. I used a 16ga cup-core inductor with a very small air-gap. The resistor was a half-watt carbon film type.
The light dimmer has the same basic problem as an audio amplifier, you don't always know how much current it will draw. With low-current loads the Q of a filter will peak, and can actually make the noise greater. This filter design works over a 10:1 current range.
For 120V AC line the capacitors must have a 200V minimum rating. I used a 16ga cup-core inductor with a very small air-gap. The resistor was a half-watt carbon film type.
i've got the circuit diags for the carver 1.5 here - i don't have an actual amp in front of me to double check - but i can see they've been pretty mean.
The AC line comes in and there is a 0.47uF (Class-X) across it. The Live terminal also has a 0.01uF (Class-Y) to earth with a 3.9M / 1/2 W bypassing it.
The live goes through the triac, and then through the transformer primary, and out to the neutral terminal completing the circuit.
the triac snubber was a 0.1uF(X) in series with an 18R / 1/2W (although there is an ammendment drawn on the sheet to say this should be a 51R (possibly for 240V) as the layouts came from the UK service agent.
No wonder it upsets everything !
As for the PM2.0t (with its awful switchmode PSU), we have slightly better filtering...
typically - my circuits for the 2.0 are with the 2.0, in the warehouse, but from memory live and neutral each had an open choke - about 10 turns of 1.2mm copper wire on a 12mm diameter, with a 9mm cube of ferrite glued in the centre.
this was then followed by the usual class x and class y capacitor filter that you would find in any SMPSU.
The 2.0t used a pair of obsolete darlington transistors MJ10025 20A/800V/250W to drive the primary in centre-tapped push-pull mode.
I have never found an equivalent for these, although i did manage to pick some up on ebay.
The snubber arrangement for the psu drivers is 'interesting'.... 2 x ceramic 11W resistors each in series with a class X cap ... all wrapped in a tube of cardboard and literally shoved in loose on some flexible wire.
don't think that would get a CE mark nowadays !
jonathan
The AC line comes in and there is a 0.47uF (Class-X) across it. The Live terminal also has a 0.01uF (Class-Y) to earth with a 3.9M / 1/2 W bypassing it.
The live goes through the triac, and then through the transformer primary, and out to the neutral terminal completing the circuit.
the triac snubber was a 0.1uF(X) in series with an 18R / 1/2W (although there is an ammendment drawn on the sheet to say this should be a 51R (possibly for 240V) as the layouts came from the UK service agent.
No wonder it upsets everything !
As for the PM2.0t (with its awful switchmode PSU), we have slightly better filtering...
typically - my circuits for the 2.0 are with the 2.0, in the warehouse, but from memory live and neutral each had an open choke - about 10 turns of 1.2mm copper wire on a 12mm diameter, with a 9mm cube of ferrite glued in the centre.
this was then followed by the usual class x and class y capacitor filter that you would find in any SMPSU.
The 2.0t used a pair of obsolete darlington transistors MJ10025 20A/800V/250W to drive the primary in centre-tapped push-pull mode.
I have never found an equivalent for these, although i did manage to pick some up on ebay.
The snubber arrangement for the psu drivers is 'interesting'.... 2 x ceramic 11W resistors each in series with a class X cap ... all wrapped in a tube of cardboard and literally shoved in loose on some flexible wire.
don't think that would get a CE mark nowadays !
jonathan
Inside the amp ?
Hi,
I have a M1.5t with a big ground hum. Now id this circuit supposed to go inside the amp - I mean that Transformer in your circuit is the one in the amp, we dont add an external trafo right ?
Thanks.
Srinath.
A typical filter will not work properly with a Carver, try this:
Hi,
I have a M1.5t with a big ground hum. Now id this circuit supposed to go inside the amp - I mean that Transformer in your circuit is the one in the amp, we dont add an external trafo right ?
Thanks.
Srinath.
Hi Srinath, The picture is detailing the snubber around the Triac, so the Triac and transformer are already in the circuit.
I don't have the circuit for the M1.5t, but the principle is the same for many of their amps (with the exception of the 2.0t which uses a conventional SMPS supply running at 1kHz).
You describe the sound as 'ground hum'.
we usually associate ground hum with incorrect earthing or tired filter caps.
the sound we're talking about on this thread is a sharp buzz caused by the triac's switching spikes... these can travel back down the power cable into mixers, crossovers etc.
It's worth getting a scope onto the DC power supply rails and checking them for symmetry with, and without load. The No. 1 fault i find in these amps is dried-out power supply caps (usually the 50V rails, not the 110V ones).
I don't have the circuit for the M1.5t, but the principle is the same for many of their amps (with the exception of the 2.0t which uses a conventional SMPS supply running at 1kHz).
You describe the sound as 'ground hum'.
we usually associate ground hum with incorrect earthing or tired filter caps.
the sound we're talking about on this thread is a sharp buzz caused by the triac's switching spikes... these can travel back down the power cable into mixers, crossovers etc.
It's worth getting a scope onto the DC power supply rails and checking them for symmetry with, and without load. The No. 1 fault i find in these amps is dried-out power supply caps (usually the 50V rails, not the 110V ones).