Rane MA6S .. all six channels "thump" when amp is switched off.
Thump is pretty large ... moves woofer full Xmas.
http://www.rane.com/pdf/old/ma6sdat.pdf
http://www.rane.com/pdf/old/ma6ssch.pdf
According to the data sheet and schematic, there are relays to shunt the speaker(s) output either by power down or large DC offset.
Finding it a little unusual that all (6) relays are/have become faulty all at once.
Any techs here able to direct my attention toward a component responsible for activating that circuit, or any other cause (pwr. switch?) for something like this?
There is also a very low level buzz (sounds like 60hz) if that is even related here. <---- this isn't a huge deal, unless it is related.
I posted this issue on Rane's forum and the pwr switch was first suggested ... the unit still does this even is unplugged directly (no switch toggled). Next was the relays ... but all six?
Any help is appreciated.
Thump is pretty large ... moves woofer full Xmas.
http://www.rane.com/pdf/old/ma6sdat.pdf
http://www.rane.com/pdf/old/ma6ssch.pdf
According to the data sheet and schematic, there are relays to shunt the speaker(s) output either by power down or large DC offset.
Finding it a little unusual that all (6) relays are/have become faulty all at once.
Any techs here able to direct my attention toward a component responsible for activating that circuit, or any other cause (pwr. switch?) for something like this?
There is also a very low level buzz (sounds like 60hz) if that is even related here. <---- this isn't a huge deal, unless it is related.
I posted this issue on Rane's forum and the pwr switch was first suggested ... the unit still does this even is unplugged directly (no switch toggled). Next was the relays ... but all six?
Any help is appreciated.
IMHO, It's most likely a problem with the relay control circuitry.
Now to wade through the schematic and try figure out what's going on....
when an amplifier starts up or shuts down it will require a few seconds for all divisions of the circuit to balance or simplified load or unload in a proper operating voltage
in between and at both procedures thumps and DC at the outputs is expected that is why circuits exist to delay connect the speakers at start up and quick disconnect at shut down ...
the time line for both procedures is determined by small capacitors in the relay circuit ..still if other like power supply capacitors are too old or leaky may the original designed time frame doesn't work properly and amplifier fails to start up in time or shut down quick enough
Combine this with the buzz which if not a ground issue then obviously is a capacitor issue...
of course the amp might have other problems such is soldering or someone in the past was messing with
Kind regards
sakis
in between and at both procedures thumps and DC at the outputs is expected that is why circuits exist to delay connect the speakers at start up and quick disconnect at shut down ...
the time line for both procedures is determined by small capacitors in the relay circuit ..still if other like power supply capacitors are too old or leaky may the original designed time frame doesn't work properly and amplifier fails to start up in time or shut down quick enough
Combine this with the buzz which if not a ground issue then obviously is a capacitor issue...
of course the amp might have other problems such is soldering or someone in the past was messing with
Kind regards
sakis
The amp doesn't display any issues on pwr ON. That delay works as advertized.
I took a look inside the amp yesterday .. before this thread was posted. I see no indication of "repair attempts" or any leaking components. The amp looks to have been used in a environmentally "friendly" area it's whole life. Very clean. No idea of how many hours on the piece though.
I have not taken any "technical" measurements ... other than to plug it in and use it. Aside from the issue(s) posted here, it works great. (overload, clip, LED indicators work ... no cracking/popping, no overheating, no surging ... everything else really seems to be A-OK).
As a possible indicator here .... the buzz seems to me to be related to the DC chassis fan. It sounds like it is around the same frequency level. ... and is the relay circuit also DC driven?
Could the nature of the problem (being all the relays effected) be confined to DC level component(s) on the power module?
Anything I can check with a multimeter to help narrow this down?
Thanks again.
I took a look inside the amp yesterday .. before this thread was posted. I see no indication of "repair attempts" or any leaking components. The amp looks to have been used in a environmentally "friendly" area it's whole life. Very clean. No idea of how many hours on the piece though.
I have not taken any "technical" measurements ... other than to plug it in and use it. Aside from the issue(s) posted here, it works great. (overload, clip, LED indicators work ... no cracking/popping, no overheating, no surging ... everything else really seems to be A-OK).
As a possible indicator here .... the buzz seems to me to be related to the DC chassis fan. It sounds like it is around the same frequency level. ... and is the relay circuit also DC driven?
Could the nature of the problem (being all the relays effected) be confined to DC level component(s) on the power module?
Anything I can check with a multimeter to help narrow this down?
Thanks again.
Hi,
I was looking at you schematic and all 6 amplifiers are independent of each other. The only common is the power supply. Like you said each amplifier have a relay. I do not think all relays are bad. It is possible that you may have a problem with one of the power supplies. I see a common signal to all of the amplifiers and it is through the zener diode D1. If you follow the signal it's goes to the relay and I think here is were you let the others amplifiers that one amplifier have a problem and need to shutdown. The power +15 volt supply voltage to the zener diode D1 and then goes out to all the amplifiers through pin "B". Here is were you may have a problem in the +15 volts or in the -15 volts. I would check all the power supplies first for DC volts and them AC. Read the +/-60 +24 +/- 15 using the voltmeter in AC. This will tell if you have ripples in the power supplies. I maybe be wrong but if one of the capacitors in one of the power supplies are bad it will discharge faster than the others and that maybe the thumps that you are experiencing. Also the test that you did pulling the plug and you have the same symptom mean that is not the switch.
I was looking at you schematic and all 6 amplifiers are independent of each other. The only common is the power supply. Like you said each amplifier have a relay. I do not think all relays are bad. It is possible that you may have a problem with one of the power supplies. I see a common signal to all of the amplifiers and it is through the zener diode D1. If you follow the signal it's goes to the relay and I think here is were you let the others amplifiers that one amplifier have a problem and need to shutdown. The power +15 volt supply voltage to the zener diode D1 and then goes out to all the amplifiers through pin "B". Here is were you may have a problem in the +15 volts or in the -15 volts. I would check all the power supplies first for DC volts and them AC. Read the +/-60 +24 +/- 15 using the voltmeter in AC. This will tell if you have ripples in the power supplies. I maybe be wrong but if one of the capacitors in one of the power supplies are bad it will discharge faster than the others and that maybe the thumps that you are experiencing. Also the test that you did pulling the plug and you have the same symptom mean that is not the switch.
The output of Z2 (5534) has a bad habit of swinging wildly when powered off. This is caused by the +/- 15V rails collapsing at different rates. Since the amp's supply rails take longer to collapse, the amp's output will swing very high, possibly to amp's supply rails because the base of Q10 (MPSA93) is being injected with DC up to +/-15V.
There are a few ways to remedy this.
1) Shorten the output relay Cut-off time so that the relay opens before the swing. This will obviously also shorten the power-up delay as well.
2) Short the output of Z2 to 0V before it starts to swing.
3) Cut the +/-15V supply instantly.
4) Change Z2 to an opamp that doesn't swing when powered off.
All the above require modifications.
The easiest way is to leave everything as it is.
5) Install another output relay but one that runs off 120Vac. Wire this relay to the power switch of the amp. This will give you instant open/close.
If it's coming from the transformer, it's probably some DC on your Mains.
Right now the question to ask is if this is a day one or it is a recently problem. In the schematic also I see a 4.7K resistor installed in the -60 volts and not in the +60 volts. In the +60 volts it is missing. This will make the discharge of the capacitors uneven. In other word the -60 volts will discharge faster than the +60 volts. Second the speaker output contact it is connected with two diode to -60 volts and +60 volts and the speaker. The relay when powered down it will short the speaker output and the two diodes to ground. Now If the 24 volts take too long close the ground then the speaker will make the "thump" noise. Like Michael Chua already described the problem that will cause if the relay stay longer. I will try to fix the problem by doing these two modification. Add a resistor in parallel to the relay coil to discharge the +24 volts faster and add a 4.7K 2 watt resistor same as the -60 volts to the +60 volts. This will allow the -/+ 60 power supplies to discharge both evenly when the amplifier it is powered down. I will do this to just one amplifier and see if it is fix the problem.
Thanks for your input Mike. I saw this circuit used by somebody and posted on the web. I was curious about it ... as is did seem to be a simple solution.
On the TF, I'd have to check lead length first but was wondering if rotating it might help w/the low level buzz?
@tauro0221 .. I honestly don't know if this is/was a day one condition. (I acquired this amp second hand)
I do know that people @Rane say this should not "thump" like it does now. This is through conversation on their troubleshooting forum. It is also no longer serviced by them (limited parts, etc. I suppose). On the upside, I guess, a workable solution can be implemented without worrying about warranties.
Both you and Mike have my thanks. I'll check the voltage levels as you suggested and go from there.
That's means that the +/- 60 volts are OKAY. What about the +/-15 volts? I would check all the voltages individually to see if they are OKAY.
One thing that I will do to see and does not take to much to do it is to install the 4.7K resistor in the +60 volt. This will balance the +/- 60 volts. This resistor in parallel with the capacitors are use to bleed the capacitors when power down. It will discharge the capacitor faster. Right now the -60 volts is discharging more faster that the +60. Second I would add a resistor to the +24 volt to ground to discharge it faster so the relay open more faster. I will use a 10K resistor. And last I would move the two diodes D18 and D19 to the other side of the contact leaving the speaker alone. I think that is the way I would do it. You can try in this sequence:
1- Add a bleeding resistor to the +24 volts. If this is the problem will fix all the amplifiers.
2- Add a the 4.7K resistor bleeding resistor to the + 60 volt to ground. This will balance the discharge of the +/- 60 volts.
3- Move the Diodes D18 and D19 to the other side of the relay contact.
One thing that I will do to see and does not take to much to do it is to install the 4.7K resistor in the +60 volt. This will balance the +/- 60 volts. This resistor in parallel with the capacitors are use to bleed the capacitors when power down. It will discharge the capacitor faster. Right now the -60 volts is discharging more faster that the +60. Second I would add a resistor to the +24 volt to ground to discharge it faster so the relay open more faster. I will use a 10K resistor. And last I would move the two diodes D18 and D19 to the other side of the contact leaving the speaker alone. I think that is the way I would do it. You can try in this sequence:
1- Add a bleeding resistor to the +24 volts. If this is the problem will fix all the amplifiers.
2- Add a the 4.7K resistor bleeding resistor to the + 60 volt to ground. This will balance the discharge of the +/- 60 volts.
3- Move the Diodes D18 and D19 to the other side of the relay contact.
The 3.2mV dc offset is fine.
I think you are measuring after the relay contact. Take another reading at Point A at the output of the amp, where the zobel is. Your meter should register the DC swing.
tauro0221 brought up a few good solutions. Strange that all the MA-6 models have the 4.7K bleeder resistor on the negative rails only.
Hi,
Disregard the 10K resistor to the relay. I traced back the +24 volt and found they already have a 1.8K bleeder resistor from the +24 to ground. I think that adding the 4.7K resistor to the +60 volts the next thing to try. Last move the diodes to the other side of the relay contact leaving the speaker alone. I do not know why they have to ground the speaker when power down. Why not leaving it open that must people would do.
Disregard the 10K resistor to the relay. I traced back the +24 volt and found they already have a 1.8K bleeder resistor from the +24 to ground. I think that adding the 4.7K resistor to the +60 volts the next thing to try. Last move the diodes to the other side of the relay contact leaving the speaker alone. I do not know why they have to ground the speaker when power down. Why not leaving it open that must people would do.
Does the thump occur the instant the power switch is turned off ? That's a big big clue.
If so the switch may be arcing.
Try pulling the main plug to power it off instead to check.
A quick look at the circuit shows that this seems to rely on the 24 volt rail collapsing quickly to remove power to the relay. C39 (100uf) R39 (1K8). Check the cap is correct marked value and resistor OK (measure it out of circuit). The main amps with all the rail capacitance (the multiple 4700uf caps) should run for a lot longer than the 24 volts rail can power the relay.
The only active switch off for the relay seems to be the discrete thyristor formed by Q19 and Q20 and the input to it marked "D" which is part of the DC offset protection.
So as far as on and off delays go it's down to time constants. The relay should definitely drop out quickly.
If so the switch may be arcing.
Try pulling the main plug to power it off instead to check.
A quick look at the circuit shows that this seems to rely on the 24 volt rail collapsing quickly to remove power to the relay. C39 (100uf) R39 (1K8). Check the cap is correct marked value and resistor OK (measure it out of circuit). The main amps with all the rail capacitance (the multiple 4700uf caps) should run for a lot longer than the 24 volts rail can power the relay.
The only active switch off for the relay seems to be the discrete thyristor formed by Q19 and Q20 and the input to it marked "D" which is part of the DC offset protection.
So as far as on and off delays go it's down to time constants. The relay should definitely drop out quickly.
Measured off the buss far end:
60V(+ -) = 63.2V (all solid + -)
Relay 24V = 22.87V (referenced to the GND between + - 15V)
+15V = 13.75V
-15V = 14.25V
ETA: The relays are closing ... just too slow it seems. The main switch is a rocker ... I can just move it enough to kill the power without it being snapped "OFF". I can hear the relays click ... with a dummy speaker and the slight movement to "OFF" on the switch it "thumps" ... quick back "ON" then fully "OFF" no "thump". So, relays do work.
60V(+ -) = 63.2V (all solid + -)
Relay 24V = 22.87V (referenced to the GND between + - 15V)
+15V = 13.75V
-15V = 14.25V
ETA: The relays are closing ... just too slow it seems. The main switch is a rocker ... I can just move it enough to kill the power without it being snapped "OFF". I can hear the relays click ... with a dummy speaker and the slight movement to "OFF" on the switch it "thumps" ... quick back "ON" then fully "OFF" no "thump". So, relays do work.
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I think the voltage are OKAY. The +/- 15 should be the same but the +15 have the fan connected to it. That's maybe the differences. I would add the 4.7K 2 watt resistor to the +60 volts and see what happen. Any way it should have one. This allow both +/- 60 discharge evenly. I still does not understand why the didn't left the speaker alone in the relay. Why ground the speaker going down and why put the two diode also. I am still thinking in the reason. Maybe somebody have any idea and let's know.
Yes, those are the ones.
You'll have to excuse me, I'm a carpenter by trade ... this is a little new to me.
I'll add that circuit as you suggested. This will help w/the relays .. or no?
Will have to strip out the amp cards to get to the PWR module ... and mark all the connections so I don't bone that up. I'll probably have a couple questions once I get the board out.
Thanks a bunch!
Phil
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