P
Phil Allison
Guest
Gareth Magennis wrote:
** It's exactly the same as the one I described as "rough as guts".
.... Phil
** It's exactly the same as the one I described as "rough as guts".
.... Phil
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P
Phil Allison
Guest
Gareth Magennis wrote:
** Hmmm - that should not happen.
However, if the amp worked even for a few seconds, the chunky relay next to the PTC closes and bridges it out. If the primary shorted out after that, it is possible the relay contacts became instantly welded closed.
The fault current could then trip the breaker in the 30A ring mains and easily blow any fuse fitted inside power plug.
A subsequent attempt to switch on the amp would result another huge surge and maybe make a track on the PSU board vaporise.
BTW:
IIRC, the secondary voltages and currents are printed on the side of the tranny. The tranny is about 800VA and it ought to be possible to have one made that is close to the same size and ratings for an acceptable cost.
.... Phil
The customer said it had been in storage the past 2 years. He fired it up
today and it blew all the main fuses in his gaff.
So sounds like it may have been short like yours and Phil's, then blew open.
** Hmmm - that should not happen.
However, if the amp worked even for a few seconds, the chunky relay next to the PTC closes and bridges it out. If the primary shorted out after that, it is possible the relay contacts became instantly welded closed.
The fault current could then trip the breaker in the 30A ring mains and easily blow any fuse fitted inside power plug.
A subsequent attempt to switch on the amp would result another huge surge and maybe make a track on the PSU board vaporise.
BTW:
IIRC, the secondary voltages and currents are printed on the side of the tranny. The tranny is about 800VA and it ought to be possible to have one made that is close to the same size and ratings for an acceptable cost.
.... Phil
A
Arfa Daily
Guest
The customer said it had been in storage the past 2 years. He fired it up
today and it blew all the main fuses in his gaff.
So sounds like it may have been short like yours and Phil's, then blew
open.
Gareth.
Er, except customers tend to lie a lot.
He may have tried to boot several times with various size fuses/paper
clips etc.
Gareth.
That would be my feeling. It would seem that when these trannies fail on the
primary, they do it in style. The one in this 5000 is *so* short-circuit, it
blew the fuse in the mains lead plugtop, the fuse in the bench input lead
where it plugs into the heavy duty extension cable, and the fuse in the
extension plugtop. Oh yes, and it popped the breaker in the consumer unit as
well. I've had a few mains shorts over the years, but I can't remember one
that has ever taken out three mains fuses in series, *and* the breaker. Just
goes to show how slow the breaker is though, compared to the cartridge fuses
in the plugs. But then I suppose it is over twice their rating, at 30 amps
....
Arfa
Guest
On Thursday, August 13, 2015 at 5:51:55 AM UTC+1, Phil Allison wrote:
They are. 74/0/74 and 18.3/0/18.3
Cheers,
Gareth.
Gareth Magennis wrote:
The customer said it had been in storage the past 2 years. He fired it up
today and it blew all the main fuses in his gaff.
So sounds like it may have been short like yours and Phil's, then blew open.
** Hmmm - that should not happen.
However, if the amp worked even for a few seconds, the chunky relay next to the PTC closes and bridges it out. If the primary shorted out after that, it is possible the relay contacts became instantly welded closed.
The fault current could then trip the breaker in the 30A ring mains and easily blow any fuse fitted inside power plug.
A subsequent attempt to switch on the amp would result another huge surge and maybe make a track on the PSU board vaporise.
BTW:
IIRC, the secondary voltages and currents are printed on the side of the tranny. The tranny is about 800VA and it ought to be possible to have one made that is close to the same size and ratings for an acceptable cost.
... Phil
They are. 74/0/74 and 18.3/0/18.3
Cheers,
Gareth.
P
Phil Allison
Guest
sound....@btconnect.com wrote:
** The 74-0-74 winding is rated at about 6 amps.
The 18.3-0-18.3 needs only 0.6 amp but is in fact tapped off the main winding.
.... Phil
They are.
74/0/74 and 18.3/0/18.3
** The 74-0-74 winding is rated at about 6 amps.
The 18.3-0-18.3 needs only 0.6 amp but is in fact tapped off the main winding.
.... Phil
Guest
Just start a new thread Arf. Itt is damn hard enough for peopple to keep track of shit without having two separate isssues in threads not specificallty named hat they should be named. If =you do, I won't rip you a new bollocks hole, we got Phil to take care of that.
but seriously seriously here, I almost NEVER had an actual bad power traansformer almost in my life. I had one in a Zenith TV that started getting open connections. First was to the CRT filamentm whichg I fixed by wrapping a wire around the flyback core to get about 22 volts peak to peak which is about 6 volts RMS. Then another linee come loose and it was tjhe center tap for the +/- 24V or whatever fed the vertical, and was on th same wire as the return for the 130 volt lin. It sent the picture offf ceneter and the centering control of course did not work. ALL the currnet pulled by the 130 volt line was going through one of the vertical output transistors. this was another of the myriad of TVs that nobody else could fix. That was my specialty.
But that sounds interesting. Question is, is it distorting ? There are a couple of different ways to implement a clipping detector. If it is actually detecting a ifference between the input and output of the power amp there are several possibilities. High frequency oscillation is possible. Loss of bias couldd do it.
Start a thread, I am not going to fuck this all up. This thread is for this, make that thread for that. See you there.
but seriously seriously here, I almost NEVER had an actual bad power traansformer almost in my life. I had one in a Zenith TV that started getting open connections. First was to the CRT filamentm whichg I fixed by wrapping a wire around the flyback core to get about 22 volts peak to peak which is about 6 volts RMS. Then another linee come loose and it was tjhe center tap for the +/- 24V or whatever fed the vertical, and was on th same wire as the return for the 130 volt lin. It sent the picture offf ceneter and the centering control of course did not work. ALL the currnet pulled by the 130 volt line was going through one of the vertical output transistors. this was another of the myriad of TVs that nobody else could fix. That was my specialty.
But that sounds interesting. Question is, is it distorting ? There are a couple of different ways to implement a clipping detector. If it is actually detecting a ifference between the input and output of the power amp there are several possibilities. High frequency oscillation is possible. Loss of bias couldd do it.
Start a thread, I am not going to fuck this all up. This thread is for this, make that thread for that. See you there.
A
Arfa Daily
Guest
"Phil Allison" <pallison49@gmail.com> wrote in message
news:34019e33-46d1-4b20-8995-8b73b1a44f6c@googlegroups.com...
The owner has decided to 'go for it' so the owner of the shop that it came
in through has gone ahead and ordered in the replacement that was offered at
100 GBP. Should be here this week sometime. While we're on slave amps,
anyone following this thread got the schematic for an Alto Mac 2.2 ? Very
odd fault. Both channels work just fine for a while, then all of a sudden,
one channel starts to indicate 'clip' with the level control just a gnat's
bollock above zero. There seems to be a dual opamp involved in the clip
detect circuit, but before going round in circles trying to see what's
happening and why, it would be handy to have a schematic to see how the clip
detect circuit is designed and what its inputs are. I'll put a new post up
as well to catch anyone that's not following this discussion.
Arfa
news:34019e33-46d1-4b20-8995-8b73b1a44f6c@googlegroups.com...
Gareth Magennis wrote:
Hey guess what?
Today I received a Crown XLS 602.
And guess what?
The mains Transformer is open circuit.
This TX is marked "NRE Electronics Manufacturing Co Ltd.
08/2006"
Dunno if that makes it from the same source or not.
** It's exactly the same as the one I described as "rough as guts".
... Phil
The owner has decided to 'go for it' so the owner of the shop that it came
in through has gone ahead and ordered in the replacement that was offered at
100 GBP. Should be here this week sometime. While we're on slave amps,
anyone following this thread got the schematic for an Alto Mac 2.2 ? Very
odd fault. Both channels work just fine for a while, then all of a sudden,
one channel starts to indicate 'clip' with the level control just a gnat's
bollock above zero. There seems to be a dual opamp involved in the clip
detect circuit, but before going round in circles trying to see what's
happening and why, it would be handy to have a schematic to see how the clip
detect circuit is designed and what its inputs are. I'll put a new post up
as well to catch anyone that's not following this discussion.
Arfa
P
Phil Allison
Guest
Arfa Daily wrote:
** The schem of the 2.3 should be very close:
http://www.mediafire.com/view/bmotmjwznd2/MAC_series_service_manual+8.jpg#
The Alto MAC amps have basically copied early QSC models like the USA850 and 900. Changes include use of a toroidal transformer, flat pack output transistors and SMD for all the small signal stuff.
The topology is very odd with output transistor collectors all tied to chassis ground while the DC rails swing with output signal. Speaker drive comes from the PSU centre points for each channel and the usual driver transistors have simply been eliminated. The short circuit protection scheme is weird too.
Advantages are a low parts count, cheap to make and will not pass DC current into a speaker under fault conditions.
The clip LED is driven by U2-B (half an NE5532 supplying drive to the output stage) via a diode bridge and also triggers the clipping limiter (U1A) via R26 to ground.
.... Phil
While we're on slave amps,
anyone following this thread got the schematic for an Alto Mac 2.2 ? Very
odd fault. Both channels work just fine for a while, then all of a sudden,
one channel starts to indicate 'clip' with the level control just a gnat's
bollock above zero. There seems to be a dual opamp involved in the clip
detect circuit, but before going round in circles trying to see what's
happening and why, it would be handy to have a schematic to see how the clip
detect circuit is designed and what its inputs are.
** The schem of the 2.3 should be very close:
http://www.mediafire.com/view/bmotmjwznd2/MAC_series_service_manual+8.jpg#
The Alto MAC amps have basically copied early QSC models like the USA850 and 900. Changes include use of a toroidal transformer, flat pack output transistors and SMD for all the small signal stuff.
The topology is very odd with output transistor collectors all tied to chassis ground while the DC rails swing with output signal. Speaker drive comes from the PSU centre points for each channel and the usual driver transistors have simply been eliminated. The short circuit protection scheme is weird too.
Advantages are a low parts count, cheap to make and will not pass DC current into a speaker under fault conditions.
The clip LED is driven by U2-B (half an NE5532 supplying drive to the output stage) via a diode bridge and also triggers the clipping limiter (U1A) via R26 to ground.
.... Phil
P
Phil Allison
Guest
Arfa Daily wrote:
** Is there a dummy load connected ?
The clip indicator is probably just showing the channel is being overloaded, as is the rapid heating. Could there be an intermittent short in the output wiring ?
Also, I see there are two PCBS, small signal and power stuff, interconnected by some kind of multi-pin. You must know how reliable they all are...
** I found the Alto schem on a net forum, it looked terribly familiar.
Have you not seen the QSC's USA models or the MX700 ?
... Phil
** The schem of the 2.3 should be very close:
http://www.mediafire.com/view/bmotmjwznd2/MAC_series_service_manual+8.jpg#
Thanks for that, Phil. Much appreciated. Odd how it works for a short while.
Before having the schematic, I gave everything in the area a good dousing
with freezer when it failed, but nothing really that I would say was very
positive. Maybe - and it *was* a maybe - the 5532 was a bit sensitive, but
it was inconclusive. I did notice that when it was wrong, the waveform on
pin 7 I think it was, was much bigger than 'normal' and the output TRs on
that side got quite hot quite quickly.
** Is there a dummy load connected ?
The clip indicator is probably just showing the channel is being overloaded, as is the rapid heating. Could there be an intermittent short in the output wiring ?
Also, I see there are two PCBS, small signal and power stuff, interconnected by some kind of multi-pin. You must know how reliable they all are...
I'll try and find time to get another look today or tomorrow with the
benefit of your schematic. Thanks again.
** I found the Alto schem on a net forum, it looked terribly familiar.
Have you not seen the QSC's USA models or the MX700 ?
... Phil
A
Arfa Daily
Guest
"Phil Allison" <pallison49@gmail.com> wrote in message
news:040210fa-0ca8-4d06-abba-7ebf7cebb8cc@googlegroups.com...
Thanks for that, Phil. Much appreciated. Odd how it works for a short while.
Before having the schematic, I gave everything in the area a good dousing
with freezer when it failed, but nothing really that I would say was very
positive. Maybe - and it *was* a maybe - the 5532 was a bit sensitive, but
it was inconclusive. I did notice that when it was wrong, the waveform on
pin 7 I think it was, was much bigger than 'normal' and the output TRs on
that side got quite hot quite quickly.
I'll try and find time to get another look today or tomorrow with the
benefit of your schematic. Thanks again
Arfa
news:040210fa-0ca8-4d06-abba-7ebf7cebb8cc@googlegroups.com...
Arfa Daily wrote:
While we're on slave amps,
anyone following this thread got the schematic for an Alto Mac 2.2 ? Very
odd fault. Both channels work just fine for a while, then all of a
sudden,
one channel starts to indicate 'clip' with the level control just a
gnat's
bollock above zero. There seems to be a dual opamp involved in the clip
detect circuit, but before going round in circles trying to see what's
happening and why, it would be handy to have a schematic to see how the
clip
detect circuit is designed and what its inputs are.
** The schem of the 2.3 should be very close:
http://www.mediafire.com/view/bmotmjwznd2/MAC_series_service_manual+8.jpg#
The Alto MAC amps have basically copied early QSC models like the USA850
and 900. Changes include use of a toroidal transformer, flat pack output
transistors and SMD for all the small signal stuff.
The topology is very odd with output transistor collectors all tied to
chassis ground while the DC rails swing with output signal. Speaker drive
comes from the PSU centre points for each channel and the usual driver
transistors have simply been eliminated. The short circuit protection
scheme is weird too.
Advantages are a low parts count, cheap to make and will not pass DC
current into a speaker under fault conditions.
The clip LED is driven by U2-B (half an NE5532 supplying drive to the
output stage) via a diode bridge and also triggers the clipping limiter
(U1A) via R26 to ground.
.... Phil
Thanks for that, Phil. Much appreciated. Odd how it works for a short while.
Before having the schematic, I gave everything in the area a good dousing
with freezer when it failed, but nothing really that I would say was very
positive. Maybe - and it *was* a maybe - the 5532 was a bit sensitive, but
it was inconclusive. I did notice that when it was wrong, the waveform on
pin 7 I think it was, was much bigger than 'normal' and the output TRs on
that side got quite hot quite quickly.
I'll try and find time to get another look today or tomorrow with the
benefit of your schematic. Thanks again
Arfa
A
Arfa Daily
Guest
"Phil Allison" <pallison49@gmail.com> wrote in message
news:ab1f9489-bc90-4c6c-9493-1db7413ad2c1@googlegroups.com...
Yes, and embarrassingly, I was even working on one last week ... :-\
Funny how just a different name on the front blinkers you to the obvious. I
was even discussing that odd output topology with a colleague.
Back to the problem in hand. I only had a few minutes to look further today.
In answer to your questions, yes, there was a dummy load on the end that has
a built in power meter. Yes, there are two main boards, each of which has a
power amp and power supply, and one of which also has the driver / clip
sense circuitry for both channels. Initially today, it was giving its
problem. Couple or three volts RMS going in, transformer balanced into the
channel 2 XLR input. As soon as the front panel level control is advanced
just a gnat's cock, on comes the clip light, very solid. The amp still has
output, but it's pretty strangled, as you would expect if the clip limiter
is genuinely coming in. When looking at the output of the opamp on pin 7,
when it's wrong, it's massive, and asymmetric, so I guess that's the reason
for the clip circuit to come in and the light to come on. It's as though the
opamp has suddenly attained 10 times its normal gain. I thought at one point
that maybe the level control was going intermittently open at its groundy
end, but when it's working, with that level of input signal, you can wind
the level pot full up, and not make it clip. It's as though a feedback
resistor is going open intermittently. Trouble is, all of the resistors
around the opamp are those tiny tiny sm devices that are so small you can
barely see them.
Actually, a thought now occurs to me. I wonder if the level control is
actually nothing of the (conventional) sort, but rather a variable feedback
resistor for the opamp, as they sometimes are in some amps. If that went
open, it might allow the opamp to go to full open loop gain. I don't
remember the level control being shown on the section of schematic that you
linked for me. I'll maybe have a look tomorrow if I get time, but today, a
shitload of work has poured in the door, including four Technics SL1210s
that are needed by the weekend, an Evans tape echo, two Voxs and a Marshall
....
As I finished checking around the opamp today, it came back right, and
wouldn't go bad again, with the control as smooth as you like from zero to
flat out, so at that point, it got flung off the bench again to make room
for something else.
Oh yes, and the ribbon. There is one of about ten or twelve ways that links
the two boards, and I have had problems in the past I seem to remember, but
in this case, it seems quite solid, as do all the other connectors. In fact
I haven't found a way to provoke the problem into either coming or going. It
just does it, as and when it feels like it.
Thanks for your input. Any and all suggestions and insights are welcome with
problems like this
Arfa
news:ab1f9489-bc90-4c6c-9493-1db7413ad2c1@googlegroups.com...
Arfa Daily wrote:
** The schem of the 2.3 should be very close:
http://www.mediafire.com/view/bmotmjwznd2/MAC_series_service_manual+8.jpg#
Thanks for that, Phil. Much appreciated. Odd how it works for a short
while.
Before having the schematic, I gave everything in the area a good dousing
with freezer when it failed, but nothing really that I would say was very
positive. Maybe - and it *was* a maybe - the 5532 was a bit sensitive,
but
it was inconclusive. I did notice that when it was wrong, the waveform on
pin 7 I think it was, was much bigger than 'normal' and the output TRs
on
that side got quite hot quite quickly.
** Is there a dummy load connected ?
The clip indicator is probably just showing the channel is being
overloaded, as is the rapid heating. Could there be an intermittent short
in the output wiring ?
Also, I see there are two PCBS, small signal and power stuff,
interconnected by some kind of multi-pin. You must know how reliable they
all are...
I'll try and find time to get another look today or tomorrow with the
benefit of your schematic. Thanks again.
** I found the Alto schem on a net forum, it looked terribly familiar.
Have you not seen the QSC's USA models or the MX700 ?
... Phil
Yes, and embarrassingly, I was even working on one last week ... :-\
Funny how just a different name on the front blinkers you to the obvious. I
was even discussing that odd output topology with a colleague.
Back to the problem in hand. I only had a few minutes to look further today.
In answer to your questions, yes, there was a dummy load on the end that has
a built in power meter. Yes, there are two main boards, each of which has a
power amp and power supply, and one of which also has the driver / clip
sense circuitry for both channels. Initially today, it was giving its
problem. Couple or three volts RMS going in, transformer balanced into the
channel 2 XLR input. As soon as the front panel level control is advanced
just a gnat's cock, on comes the clip light, very solid. The amp still has
output, but it's pretty strangled, as you would expect if the clip limiter
is genuinely coming in. When looking at the output of the opamp on pin 7,
when it's wrong, it's massive, and asymmetric, so I guess that's the reason
for the clip circuit to come in and the light to come on. It's as though the
opamp has suddenly attained 10 times its normal gain. I thought at one point
that maybe the level control was going intermittently open at its groundy
end, but when it's working, with that level of input signal, you can wind
the level pot full up, and not make it clip. It's as though a feedback
resistor is going open intermittently. Trouble is, all of the resistors
around the opamp are those tiny tiny sm devices that are so small you can
barely see them.
Actually, a thought now occurs to me. I wonder if the level control is
actually nothing of the (conventional) sort, but rather a variable feedback
resistor for the opamp, as they sometimes are in some amps. If that went
open, it might allow the opamp to go to full open loop gain. I don't
remember the level control being shown on the section of schematic that you
linked for me. I'll maybe have a look tomorrow if I get time, but today, a
shitload of work has poured in the door, including four Technics SL1210s
that are needed by the weekend, an Evans tape echo, two Voxs and a Marshall
....
As I finished checking around the opamp today, it came back right, and
wouldn't go bad again, with the control as smooth as you like from zero to
flat out, so at that point, it got flung off the bench again to make room
for something else.
Oh yes, and the ribbon. There is one of about ten or twelve ways that links
the two boards, and I have had problems in the past I seem to remember, but
in this case, it seems quite solid, as do all the other connectors. In fact
I haven't found a way to provoke the problem into either coming or going. It
just does it, as and when it feels like it.
Thanks for your input. Any and all suggestions and insights are welcome with
problems like this
Arfa
P
Phil Allison
Guest
Arfa Daily wrote:
** The volume pot is connected in the usual way between the output of the input balancing stage ( U2A ) and the input of U2B.
FYI:
The QSC model that is near identical to your Alto is the RMX1450.
You will find a much more readable schem in the RMX850,1450&2450 manual from Elektrotanya and without the little errors I see in the Alto one.
http://elektrotanya.com/qsc_rmx_850_rmx_1450_rmx_2450.pdf/download.html
..... Phil
Actually, a thought now occurs to me. I wonder if the level control is
actually nothing of the (conventional) sort, but rather a variable feedback
resistor for the opamp, as they sometimes are in some amps.
** The volume pot is connected in the usual way between the output of the input balancing stage ( U2A ) and the input of U2B.
FYI:
The QSC model that is near identical to your Alto is the RMX1450.
You will find a much more readable schem in the RMX850,1450&2450 manual from Elektrotanya and without the little errors I see in the Alto one.
http://elektrotanya.com/qsc_rmx_850_rmx_1450_rmx_2450.pdf/download.html
..... Phil