Hi,
I have a faulty Audiohead AH-1000 amp which is the same internally as the C-Mark and Thomann units - which were made ( in China ) by Source Manufacturing and distributed in Europe by anyone who wanted to buy them. The name on the front panel was added by the distributors, but the top cover is embossed with the manufacturers name and a non-functional website address.
My amp has one dead channel which keeps frying the replacement transistors I fit despite having tested every component on the board seperately. ( yes, I really have taken them ALL out and checked them ) I think I've got a hairline crack in the board but I can't find it...
My next step will be to try the channel module on a smaller supply - preferably with some current limiting for safety - I can't afford many more devices.
Does any one have a schematic?
Source Manufacturing won't supply one, and so far I have had no luck with any of the companies in Europe who bought them.
The circuit is really simple - a dual op-amp on the input which floats with the signal and a pair of driver transistors followed by 4 pairs of power devices, but I can't seem to get a handle on the fault.
Any help gratefully appreciated.
Graham
I have a faulty Audiohead AH-1000 amp which is the same internally as the C-Mark and Thomann units - which were made ( in China ) by Source Manufacturing and distributed in Europe by anyone who wanted to buy them. The name on the front panel was added by the distributors, but the top cover is embossed with the manufacturers name and a non-functional website address.
My amp has one dead channel which keeps frying the replacement transistors I fit despite having tested every component on the board seperately. ( yes, I really have taken them ALL out and checked them ) I think I've got a hairline crack in the board but I can't find it...
My next step will be to try the channel module on a smaller supply - preferably with some current limiting for safety - I can't afford many more devices.
Does any one have a schematic?
Source Manufacturing won't supply one, and so far I have had no luck with any of the companies in Europe who bought them.
The circuit is really simple - a dual op-amp on the input which floats with the signal and a pair of driver transistors followed by 4 pairs of power devices, but I can't seem to get a handle on the fault.
Any help gratefully appreciated.
Graham
I'm in the same boat, I have a ah1400 for repair with one channel down - all o/p devices shot. I emailed Thomann and got this reply :
Hello,
sorry, schematics are pateted,
We can help you if there are any problems via mail
mfg, best regards
Reinhold Meißner, Werkstattmeister
Musikhaus Thomann
Musikhaus Thomann
Inhaber Hans Thomann
Treppendorf 30, 96138 Burgebrach
HRA Bamberg Nr. 8988
Have you tried asking them directly about the particular problem ? [ Pretend your amp is a Thomann
]
I emailed
werkstatt@thomann.de.
Let me know if you get any insights, I've ordered spare devices from Profusion as they were cheaper than Farnell - as to whether they're any better...?
Wish I'd found the other thread on this topic before I ordered, though.
Hello,
sorry, schematics are pateted,
We can help you if there are any problems via mail
mfg, best regards
Reinhold Meißner, Werkstattmeister
Musikhaus Thomann
Musikhaus Thomann
Inhaber Hans Thomann
Treppendorf 30, 96138 Burgebrach
HRA Bamberg Nr. 8988
Have you tried asking them directly about the particular problem ? [ Pretend your amp is a Thomann
]I emailed
werkstatt@thomann.de.
Let me know if you get any insights, I've ordered spare devices from Profusion as they were cheaper than Farnell - as to whether they're any better...?
Wish I'd found the other thread on this topic before I ordered, though.
Hi Graham, have you looked at the schematic for the QSC RMX 1450 ? The output devices are the same and the 3 pots are bias and 2 x current limit. Worth a look, -from another thread on here about the behringer a500.
http://www.qscaudio.com/support/library/schems/rmx1450.zip
http://www.qscaudio.com/support/library/schems/rmx1450.zip
Audiohead amplifier fault.
Thanks for the links - I did eventually get a circuit for the Audiohed amp from a firm in the west midlands who wouldn't give me a name I could find in directory enquiries - it seems that they were service agents for these amps for a while, but don't do it any more... Their engineer who now only works one day a week had a copy of the generic diagram for the whole range, but said they never knew where they were with these amps because every batch was different...
By the time the diagram arrived, I had already traced out the entire circuit and devised a method of test using one pair of output devices and some large external resistors as current limiters.
The fault turned out to be an intermittant open-circuit on the bias adjuster pot, so of course, it measured OK with no current flowing...
The circuit designer should be shot for putting the pot in the wrong way, so that a failure blows up the output stage. I remember back in the '60's when vbe multipliers first appeared in amps, the advice was to put the adjuster in the 'fail safe' leg of the voltage divider - pehaps that never got translated into chinese.
The replacement power devices I used come from Semelab ( through Farnells ) and are relatively cheap. So far, I've had no more problems. I think the originals were genuine Toshiba parts, though I've heard that there are some cheap copies around...
If I can help anyone else, feel free to contact me through grahaprie@aol.com.
Thanks for the links - I did eventually get a circuit for the Audiohed amp from a firm in the west midlands who wouldn't give me a name I could find in directory enquiries - it seems that they were service agents for these amps for a while, but don't do it any more... Their engineer who now only works one day a week had a copy of the generic diagram for the whole range, but said they never knew where they were with these amps because every batch was different...
By the time the diagram arrived, I had already traced out the entire circuit and devised a method of test using one pair of output devices and some large external resistors as current limiters.
The fault turned out to be an intermittant open-circuit on the bias adjuster pot, so of course, it measured OK with no current flowing...
The circuit designer should be shot for putting the pot in the wrong way, so that a failure blows up the output stage. I remember back in the '60's when vbe multipliers first appeared in amps, the advice was to put the adjuster in the 'fail safe' leg of the voltage divider - pehaps that never got translated into chinese.
The replacement power devices I used come from Semelab ( through Farnells ) and are relatively cheap. So far, I've had no more problems. I think the originals were genuine Toshiba parts, though I've heard that there are some cheap copies around...
If I can help anyone else, feel free to contact me through grahaprie@aol.com.
Audiohead schematic
Hi,
I'm afraid all I have is a very poor photocopy which probably won't scan, so I'll need your postal address to send it.
I've now looked at the QSC reference mentioned earlier, and the circuit is significantly different - for a start, there are a lot less devices in it, and the centre-tap of the power supply IS the output terminal - the common connection of the power devices is actually GROUND. i.e., the whole PSU swings with the signal! Naturally, each channel has its' own PSU...
Send me your contact details to the mail address I gave earlier, and I'll post you a copy of the diagram.
Graham.
Hi,
I'm afraid all I have is a very poor photocopy which probably won't scan, so I'll need your postal address to send it.
I've now looked at the QSC reference mentioned earlier, and the circuit is significantly different - for a start, there are a lot less devices in it, and the centre-tap of the power supply IS the output terminal - the common connection of the power devices is actually GROUND. i.e., the whole PSU swings with the signal! Naturally, each channel has its' own PSU...
Send me your contact details to the mail address I gave earlier, and I'll post you a copy of the diagram.
Graham.
thanks, i'll make i note of which resistors they are - one looks like part of the bias network, but i havent looked in detail.
its quite possible the the values will be different on the ah1400 (the whole design may be different too) but i'll post up here in a few days when i get a chance to sit down with the cards.
j
its quite possible the the values will be different on the ah1400 (the whole design may be different too) but i'll post up here in a few days when i get a chance to sit down with the cards.
j
Thanks picturevalve, i've had a look at the ah1400 (= QSC RMX1450) and i'm afraid its a totally different design.
To help anyone in a similar situation:
AH1400 = Behringer EP1500 = QSC RMX 1450 Class AB Straight boring Bipolar amp.
AH2400 = Behringer EP2500 = QSC RMX2450 Class H (Rail switching) Bipolar with FET rail switches.
AH4000 = QSC RMX 4050HD Class H (Rail switching), basically a beefed-up version of the 2450.
Berhinger use SMD small signal components, QSC / AH use standard discrete's.
Behringer wont give me Schematic (Even though 10 years ago, they begged me to be their UK service centre).
so i'm going to get hold of the QSC ones instead.
Give me a month to cross check them with the AH module, then i'll be happy to share what i have.
To help anyone in a similar situation:
AH1400 = Behringer EP1500 = QSC RMX 1450 Class AB Straight boring Bipolar amp.
AH2400 = Behringer EP2500 = QSC RMX2450 Class H (Rail switching) Bipolar with FET rail switches.
AH4000 = QSC RMX 4050HD Class H (Rail switching), basically a beefed-up version of the 2450.
Berhinger use SMD small signal components, QSC / AH use standard discrete's.
Behringer wont give me Schematic (Even though 10 years ago, they begged me to be their UK service centre).
so i'm going to get hold of the QSC ones instead.
Give me a month to cross check them with the AH module, then i'll be happy to share what i have.
Hmmm.. replying to myself again...
people may find this of use...
http://www.qscaudio.com/support/library/schems/rmx4050.zip
404 Page Not Found
or try...
http://www.qscaudio.com/support/library/schems/rmx4050.zip
should drop you throug to a useful list of schematics
people may find this of use...
http://www.qscaudio.com/support/library/schems/rmx4050.zip
404 Page Not Found
or try...
http://www.qscaudio.com/support/library/schems/rmx4050.zip
should drop you throug to a useful list of schematics
(still talking to myself...)
this is the circuit to the QSC RMX4050hd...
http://www.qscaudio.com/support/library/schems/Current/RMX Series/rmx4050hd.pdf
i can now see that this uses a triple-rail class-H, which is different the the AH4000 (i'll check when i get home).
but the bias network should be similar (which is the bit that's burned on mine)
i'll update when i have more news
this is the circuit to the QSC RMX4050hd...
http://www.qscaudio.com/support/library/schems/Current/RMX Series/rmx4050hd.pdf
i can now see that this uses a triple-rail class-H, which is different the the AH4000 (i'll check when i get home).
but the bias network should be similar (which is the bit that's burned on mine)
i'll update when i have more news
Hi Andrew,
I should clarify i'm really talking about the topology here, actual resistor values may vary (but only by 1 or 2 degrees.. ie - a 43 Ohm in one product may be replaced by a 47 Ohm ect..).
also, i had a good look at the AH4000 last night, its not the same as the qsc4050. (the qsc one is a better design with triple power supplies). the AH4000 is really a QSC RMX2450 with an extra 4 output devices, the drivers have been upped to larger devices, and the single FET per side on the qsc, has been replaced by 4 in parallel.
I'm guessing the C-Mark 2350 is just a qsc 2450 with a smaller psu.
The 2450 is a dual-rail class-H, easily identifiable because there will be 2 distinct PSU's
ie, 2 sets of high power transformer secondary windings--> 2 seperate high current rectifiers, 2 sets of smoothing caps. (usually something like a 100V pair, and a 63V pair).
on the main board, you should be able to see some rail-switching FETS (they are usually hi speed switches, such as IRF640), and the flyback diode near the FET.
The trick to repairing these amps is to power them up from a variable AC power supply, and monitor them carefully !
If you just replace output devices and switch it on cold... you just threw away your money :-(
I hope this helps
I should clarify i'm really talking about the topology here, actual resistor values may vary (but only by 1 or 2 degrees.. ie - a 43 Ohm in one product may be replaced by a 47 Ohm ect..).
also, i had a good look at the AH4000 last night, its not the same as the qsc4050. (the qsc one is a better design with triple power supplies). the AH4000 is really a QSC RMX2450 with an extra 4 output devices, the drivers have been upped to larger devices, and the single FET per side on the qsc, has been replaced by 4 in parallel.
I'm guessing the C-Mark 2350 is just a qsc 2450 with a smaller psu.
The 2450 is a dual-rail class-H, easily identifiable because there will be 2 distinct PSU's
ie, 2 sets of high power transformer secondary windings--> 2 seperate high current rectifiers, 2 sets of smoothing caps. (usually something like a 100V pair, and a 63V pair).
on the main board, you should be able to see some rail-switching FETS (they are usually hi speed switches, such as IRF640), and the flyback diode near the FET.
The trick to repairing these amps is to power them up from a variable AC power supply, and monitor them carefully !
If you just replace output devices and switch it on cold... you just threw away your money :-(
I hope this helps
Audiohead AH4000
I'm Currently working on an AH4000, just for the benefit of anyone else...
the AH4000 is almost component for component a QSC RMX 2450 - with the following exceptions...
The output devices have been upped to 7 per rail.
The switches have been paralelled upto 4 per rail.
Various resistors have been upped to reflect the larger power.
The input limiter is missing.
The nasty output crowbar has been replaced by a relay.
Commonly burned resistors are:
R34/R199 = 1K8 3W
Driver emmiter resistors are 12R 1W (should've been fusibles).
R15 = 3R3 3W (should've been fusible)
R56 not present
R48/R109 = 10K 3W
R2 is not connected at one end !! (should go to the input ground nearby)
the 8 voltage dropper resistors are 18K 3W
R58/R108 = 3K 3W
Replace the bias and drive limit presets as standard !
IC1 = uA7824 reg
other IC are 5532, 311, 311
small transistors are 2N3904/3906 (totem poles!)
look for a burned via under R3 as the input ground get trashed.
R3 was burned beyond recognition on both channels, but the QSC diag suggests
its a 390R / 0.6W
The HT fuses are a waste of time! (20A in 5A holders.. niice !)
I'd reccomend replacing the 12R's with 10R Fusible + 2.2R. find a combination of standard and fusible res, to replace R15. (you need to get your calculator out).
Cut the HT feeds to the driver stage (thin tracks with no solder resist running outermost along each long edge of the board, and insert a T2A wire ended fuse in each.
This will reduce fires in the driver stage, next time it goes tits up (it will! ;-)
good luck
I'm Currently working on an AH4000, just for the benefit of anyone else...
the AH4000 is almost component for component a QSC RMX 2450 - with the following exceptions...
The output devices have been upped to 7 per rail.
The switches have been paralelled upto 4 per rail.
Various resistors have been upped to reflect the larger power.
The input limiter is missing.
The nasty output crowbar has been replaced by a relay.
Commonly burned resistors are:
R34/R199 = 1K8 3W
Driver emmiter resistors are 12R 1W (should've been fusibles).
R15 = 3R3 3W (should've been fusible)
R56 not present
R48/R109 = 10K 3W
R2 is not connected at one end !! (should go to the input ground nearby)
the 8 voltage dropper resistors are 18K 3W
R58/R108 = 3K 3W
Replace the bias and drive limit presets as standard !
IC1 = uA7824 reg
other IC are 5532, 311, 311
small transistors are 2N3904/3906 (totem poles!)
look for a burned via under R3 as the input ground get trashed.
R3 was burned beyond recognition on both channels, but the QSC diag suggests
its a 390R / 0.6W
The HT fuses are a waste of time! (20A in 5A holders.. niice !)
I'd reccomend replacing the 12R's with 10R Fusible + 2.2R. find a combination of standard and fusible res, to replace R15. (you need to get your calculator out).
Cut the HT feeds to the driver stage (thin tracks with no solder resist running outermost along each long edge of the board, and insert a T2A wire ended fuse in each.
This will reduce fires in the driver stage, next time it goes tits up (it will! ;-)
good luck
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