You can replace the existing switch with a double pole single throw switch and use the extra contact to disconnect the +24 volts. Be careful because you have to timing it right.
I'll check that out tauro0221 ... sounds like that might work great too.
I don't think a toggle is the way to go Mike. I've got family here and just see a scenario where the toggle is left OFF ... the wife cranking the gain wondering why no sound ... then sees the switch. 🙁
This has to be bullet proof.
Tapping the +24V off R52's legs would be easy enough. Will that screw up that resistors value? If so, I'll look for the thermal switch and bypass that. ... just don't see it on the PWR module plan view.
You guys have been great working with me on this. Many thanks!!
Phil
I don't think a toggle is the way to go Mike. I've got family here and just see a scenario where the toggle is left OFF ... the wife cranking the gain wondering why no sound ... then sees the switch. 🙁
This has to be bullet proof.
Tapping the +24V off R52's legs would be easy enough. Will that screw up that resistors value? If so, I'll look for the thermal switch and bypass that. ... just don't see it on the PWR module plan view.
You guys have been great working with me on this. Many thanks!!
Phil
If you want to go in that direction you can cut one of the wire in the front thermal light indicator and connect one of the wire from the light to the switch and from the other side of the switch to the other wire from the light. The thermal light it is coming from R52 through D21 thermal light to the relay.
Can you make another check if you do not mind. Can you check the resistance with the amplifier off between the + side of the speaker and ground. Disconnect the speaker before do the test. This is to check the contact resistance of the relay. It should be zero.
Thanks for clarifying.
That's a strange issue as you have tried powering the amp down via other means to eliminate the switch.
The main rails to the amp ! It might be worth connecting a meter (analogue meter is often best but a DVM will do for this or a scope) to each rail in turn and seeing how quickly they collapse.
It's all very "empirical" but might give a clue. The relay should be dropping out quickly but the rails should remain "high" until the relay drops out due to all that capacitance on them.
Check both the rails to the opamps the same way as well as the main rails.
An amp shouldn't be affected by a fall in supply voltage until it reaches a "critical" level and that could be as low as just a few volts so it's something worth checking. If the quiescent current in one amp were very high for some reason then that could discharge the rails quickly. Similarly a DC offset would draw current via the speaker and do the same (so check that too).
A fault like this is a case of gathering as much info as possible to try and reach some conclusions.
I think we already proved what your are taking when we added the resistor to the +60 volts supply. The thump was dampening. That means it is possible that -60 it is discharging faster than the +60 volts. It is possible that capacitors are weakening in the -60volts ?
tauro0221 ... checked resistance ... got like .001ohm on the meter.
Mooly .. I understand what you're saying just that I'm not able to judge what's "fast" in this context. The experience required to make that type of determination is not something I own right now.
For instance .. I did leave the DMM leads connected out of curiosity and PWR'ed OFF. Meter went to zero ... was it too fast, slow (shrug) .. got me. Certainly fast enough not to be able to apply an everyday clock to the duration.
I know it's not the best way but I'm going to fall back on the more primitive workaround ... switching the +24V circuit, to see if that works here. I know this won't damage anything .. least I wouldn't think so. There's a small hole 3/16" or so in the side panel .. enough to fish a couple wires through to a momentary NC switch. I'll use a rack ear to mount it "temp. like" to see if this is a go.
Only thing I'm not quite sure about is if after measuring the wiring (to and from + the switch) for resistance .. should I change R52 to reflect that additional resistance ... or not worry about it?
Mooly .. I understand what you're saying just that I'm not able to judge what's "fast" in this context. The experience required to make that type of determination is not something I own right now.
For instance .. I did leave the DMM leads connected out of curiosity and PWR'ed OFF. Meter went to zero ... was it too fast, slow (shrug) .. got me. Certainly fast enough not to be able to apply an everyday clock to the duration.
I know it's not the best way but I'm going to fall back on the more primitive workaround ... switching the +24V circuit, to see if that works here. I know this won't damage anything .. least I wouldn't think so. There's a small hole 3/16" or so in the side panel .. enough to fish a couple wires through to a momentary NC switch. I'll use a rack ear to mount it "temp. like" to see if this is a go.
Only thing I'm not quite sure about is if after measuring the wiring (to and from + the switch) for resistance .. should I change R52 to reflect that additional resistance ... or not worry about it?
No problem, good luck with whatever you try 🙂
(If you do come back to this I would have guessed at the speaker relay dropping out within a second or so of powering off.
As to the amps. With all that rail capacitance and a normal sort of quiescent current draw for a Class AB amp then I would guess it [the amp modules] should work for perhaps 3,4 or maybe much more seconds before the amp complained. I would expect the meter to go something like 60 and 50 and 40 and 30 etc at the speed you can say that 🙂)
Puppet I took the liberty to write this recount just in case people want to joint us in fixing your problem. Please accept my apologies.
This is a recount of test done to the amplifier to correct the "thump" when the amplifier is powered off.
1- Amplifier produce a loud "thump" when powered off.- using the power switch
2- test by disconnected the amplifier from the plug - same result
3-test the amplifier using an outlet switch - same result
4- -60 volts does have 4.7K bleeder resistor and +60 volts does not have one. Added one 4.7K resistor - "thump" loudness when down 20%
5- Power supplies read as follow:
Relay 24V = 22.87V
+15V = 13.75V
-15V = 14.25V
60V(+ -) = 63.2V
After these tests were done one possible conclusion is that the relay is not dropping fast enough to prevent the "thump".
Puppet Please add/correct if something is missing.
Puppet A team
This is a recount of test done to the amplifier to correct the "thump" when the amplifier is powered off.
1- Amplifier produce a loud "thump" when powered off.- using the power switch
2- test by disconnected the amplifier from the plug - same result
3-test the amplifier using an outlet switch - same result
4- -60 volts does have 4.7K bleeder resistor and +60 volts does not have one. Added one 4.7K resistor - "thump" loudness when down 20%
5- Power supplies read as follow:
Relay 24V = 22.87V
+15V = 13.75V
-15V = 14.25V
60V(+ -) = 63.2V
After these tests were done one possible conclusion is that the relay is not dropping fast enough to prevent the "thump".
Puppet Please add/correct if something is missing.
Puppet A team
Mooly you do not think that another possible solution to this problem it is add more capacitors to the +/- 60 volts. By doing so the +/- 60 volts will hold longer than the other power supplies. This is another possible solution.
"4- -60 volts does have 4.7K bleeder resistor and +60 volts does not have one. Added one 4.7K resistor - "thump" loudness when down 20%"
Thump loudness didn't go down ... overall power output of the amp went down.
I tried the +24V switch today ... didn't work. I immediately realized as I tried it (on-off) that the relays need 24V to work ... dumb eh.
Thump loudness didn't go down ... overall power output of the amp went down.
I tried the +24V switch today ... didn't work. I immediately realized as I tried it (on-off) that the relays need 24V to work ... dumb eh.
I think Mooly give me a hint for what it happening. This is what I think it is going on.
Scenario 1: -60 volts discharge faster than the +60.
This will allowed to apply a positive voltage from the +60 volts through the resistor R57 and R59 to the +24 volt in the relay. This will hold the relay on longer until the +60 discharged.
Scenario 2 :+60 volts discharge faster than the -60 volts. This will allow the -60 volts goes through the R57 and R59 making the +24 negative making the relay to drop immediately. You should not heard the "thump".
I think that is why the switch didn't work. The switch will drop the +24 but the +60 will still hold the relay for the above explained
Possible solutions:
1-Replace all the capacitors to the power supply. Do not know how old this amplifier.
2- Add some capacitors to the negative -60 volts
3- Add a diode between the R59 and the +24 to prevent feeding voltage to relay.
4- Do nothing
Puppet the only way to fix it is by trying different way. Some will failed but maybe one will be able to fix it.
Scenario 1: -60 volts discharge faster than the +60.
This will allowed to apply a positive voltage from the +60 volts through the resistor R57 and R59 to the +24 volt in the relay. This will hold the relay on longer until the +60 discharged.
Scenario 2 :+60 volts discharge faster than the -60 volts. This will allow the -60 volts goes through the R57 and R59 making the +24 negative making the relay to drop immediately. You should not heard the "thump".
I think that is why the switch didn't work. The switch will drop the +24 but the +60 will still hold the relay for the above explained
Possible solutions:
1-Replace all the capacitors to the power supply. Do not know how old this amplifier.
2- Add some capacitors to the negative -60 volts
3- Add a diode between the R59 and the +24 to prevent feeding voltage to relay.
4- Do nothing
Puppet the only way to fix it is by trying different way. Some will failed but maybe one will be able to fix it.
Certainly to do some checks in that area.
To see how quickly all the rails collapse and to measure the current draw on the rails etc. They have to be the first steps to get an idea of what is going on. If the rail capacitance had become or was low for some reason on one or more rails then that could cause this problem.
Just looking at the circuit again. With 8 * 4700uf caps it's hard to believe there is a problem there but obviously at least check the rate (by timing) of discharge.
The relay with it's 24 volt rail and single 100uf reservoir cap has to collapse quickly and providing the 100uf cap is correct there can't be a problem there.
Also check rate of discharge of C43 and 44, the two 2200uf caps that feed the 15 volt regs. That's an important one to check. Those rails have to remain at something reasonable for longer than the relay drop out time.
(A DC coupled amp shouldn't normally give a thump just because the rails change or drop or are unbalanced. As long as there is sufficient DC to maintain a stable operating point the output should remain at zero volts... no thump... and the speaker relay should have dropped out long before that point is reached).
Just trying to cover all possible bases with this. Are the opamps original types or have they been changed for something else ? Check them.
The relay with it's 24 volt rail and single 100uf reservoir cap has to collapse quickly and providing the 100uf cap is correct there can't be a problem there.
Also check rate of discharge of C43 and 44, the two 2200uf caps that feed the 15 volt regs. That's an important one to check. Those rails have to remain at something reasonable for longer than the relay drop out time.
(A DC coupled amp shouldn't normally give a thump just because the rails change or drop or are unbalanced. As long as there is sufficient DC to maintain a stable operating point the output should remain at zero volts... no thump... and the speaker relay should have dropped out long before that point is reached).
Just trying to cover all possible bases with this. Are the opamps original types or have they been changed for something else ? Check them.
Mooly do not forget that the power supply feed 6 amplifiers at the same time. What you said about that it should be zero at the speaker output your are right but still should hold longer. Right now follow Puppet reading we have an unbalance in the -/+15. They should be the same voltages. Puppet can do a check by reading each individual voltages with the voltmeter when the amplifier it is powered down. He may notice if one it is discharging faster than the others. The best is to use an scope that can recorder the event.
Mooly and tauro0221 ... I intend on checking the discharge rates today. I'll try to enlist a stop watch. Will report back after completed.
Amp parts are all original as far as I can tell. Nobody has been inside this thing before me ... or whoever was had been real careful with the phillips screw heads.
Also going to try and age the amp through Rane w/S/N if possible. Production started in '94 ... not sure how long it ran. I'll find out.
Amp parts are all original as far as I can tell. Nobody has been inside this thing before me ... or whoever was had been real careful with the phillips screw heads.
Also going to try and age the amp through Rane w/S/N if possible. Production started in '94 ... not sure how long it ran. I'll find out.
OK ...
+60V Takes 30 seconds to discharge to 0V (zero)
Approx. 3 seconds per decade (V's) rate. ... (so, +60V .. 3s ... +50V .. 3s .. +40V .. etc)
-60V Takes 3minutes to discharge to 0V
Approx. 7seconds per decade rate.
+24V drops immediately .. residual in mV
+15V drops immediately to .7V residual then gradual decline
-15V drops immediately to 1V residual then gradual decline
+60V Takes 30 seconds to discharge to 0V (zero)
Approx. 3 seconds per decade (V's) rate. ... (so, +60V .. 3s ... +50V .. 3s .. +40V .. etc)
-60V Takes 3minutes to discharge to 0V
Approx. 7seconds per decade rate.
+24V drops immediately .. residual in mV
+15V drops immediately to .7V residual then gradual decline
-15V drops immediately to 1V residual then gradual decline
Indeed they should. The output of the 15 volt regs should be close to the marked value. So that needs a careful check of the input to the regs by measuring the DC voltage across C43 and C44
Brilliant... the 60 volts rails sound good as does the 24.
The 15 volt rails I would say should remain for longer than the 24 volt rail.
Does that make sense ? Once the relay drop out and disconnects the speakers it doesn't matter what the amp does then.
The fact that the 15 volt rails are lower than they should be needs investigation. I think those 2200uf caps have to be proved by substitution with known good ones first.
What is the voltage across each ? The regs need at least 18 volts or so input.
The 15 volt rails I would say should remain for longer than the 24 volt rail.
Does that make sense ? Once the relay drop out and disconnects the speakers it doesn't matter what the amp does then.
The fact that the 15 volt rails are lower than they should be needs investigation. I think those 2200uf caps have to be proved by substitution with known good ones first.
What is the voltage across each ? The regs need at least 18 volts or so input.
- Status
- Not open for further replies.