Thanks sesebe,
The amp (fake Yamaha pictured in post 16) is supposed to be 300W per channel, I cant tell by looking at it if it is or not but there is no way I am using anywhere near that, but my Crown speakers are 8 Ohms so this would drop the amp to 150W X 2 but still, even when my wife used it in the house for karaoke it was still doing the same thing & the volume was a lot less than at the gig.
Looking at the photo in post 16, I know it's not so clear but would you know how I can disable the amp altogether so I can use the "mixer only" with my new powered speakers?
I'm afraid it's no use telling me in technical terms as I'm really not an electronics man & don't know what the amp parts look like, I would like to disable the amp outputs but of coarse keep power to the mixer & vent fan, the reason is I am not home very often as I work around the globe and I'm afraid someone might connect the powered speakers from the amp side of the mixer in my absence.
I know I can cut the red & blue wires off the output sockets but I don't see the point in having the amp on when I'm never going to use it.
Whats the big heavy round thing? Is it a transformer? if so I guess I need to keep this in?
If it's a very technical job then I will just disconnect the wires from the output sockets.
Sorry for being such a newb!
Thanks.
Ian.
The amp (fake Yamaha pictured in post 16) is supposed to be 300W per channel, I cant tell by looking at it if it is or not but there is no way I am using anywhere near that, but my Crown speakers are 8 Ohms so this would drop the amp to 150W X 2 but still, even when my wife used it in the house for karaoke it was still doing the same thing & the volume was a lot less than at the gig.
Looking at the photo in post 16, I know it's not so clear but would you know how I can disable the amp altogether so I can use the "mixer only" with my new powered speakers?
I'm afraid it's no use telling me in technical terms as I'm really not an electronics man & don't know what the amp parts look like, I would like to disable the amp outputs but of coarse keep power to the mixer & vent fan, the reason is I am not home very often as I work around the globe and I'm afraid someone might connect the powered speakers from the amp side of the mixer in my absence.
I know I can cut the red & blue wires off the output sockets but I don't see the point in having the amp on when I'm never going to use it.
Whats the big heavy round thing? Is it a transformer? if so I guess I need to keep this in?
If it's a very technical job then I will just disconnect the wires from the output sockets.
Sorry for being such a newb!
Thanks.
Ian.
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Well I had hoped the description of output transistors with 20 mm wide metal tabs attached to the heat sink, or lozenge shaped steel cases attached to the heat sink would be adequate for a newbie. The lozenge shaped output transistors are about 25 mm long. Your amp should have one or the other in the 300 watt class.
To disable the power amp powertion of a power mixer, you clip the wire from the middle terminal of the plastic ones with the 20 mm tab, or disconnect the wire from the case of the lozenge shaped TO3 output transistors. All of them. Insulate the ends of the wires with tape, you don't want them touching anything grounded, like the heat sink.
If you disconnect the output jack, the transistors will continue to draw power, and if one is damaged, it might eventually draw enough to blow the fuse .
Good luck.
To disable the power amp powertion of a power mixer, you clip the wire from the middle terminal of the plastic ones with the 20 mm tab, or disconnect the wire from the case of the lozenge shaped TO3 output transistors. All of them. Insulate the ends of the wires with tape, you don't want them touching anything grounded, like the heat sink.
If you disconnect the output jack, the transistors will continue to draw power, and if one is damaged, it might eventually draw enough to blow the fuse .
Good luck.
Looking really carefully at the picture of the mixer in post # 16, I think I see four output transistors connected to a heat sink at the top of the picture. These should have 20 mm wide tabs. The middle leg of these is the collector, and should be removed from the circuit board with your soldering iron. Use safety glasses removing things, solder splashes.
You could analyzed the board and instead remove the two wires from the big round capacitors to the two places on the power amp board that connect to the middle pins of the output transistors. This should remove the power. The capacitors have plus signs pointing to one terminal, or minus signs in balls pointing to the other terminal. It appears the biggest capacitors with the highest voltage are on the board, so this may be difficult.
The mixer stages, which are probably on the other board, should have their own winding of the transformer (the 70 to 100 mm diameter toriod). However, if it doesn't and the designer made the +and -15 v for mixer with a regulator from the +-50v? winding, then removing the transformer wires from the bridge rectifier may kill the mixer, too. The bridge rectifier looks like a plastic blob with two wiggles next to two AC terminals, and a + and a - next to two other terminals. The wiggles look like the top left key of a PCAT keyboard.
You could analyzed the board and instead remove the two wires from the big round capacitors to the two places on the power amp board that connect to the middle pins of the output transistors. This should remove the power. The capacitors have plus signs pointing to one terminal, or minus signs in balls pointing to the other terminal. It appears the biggest capacitors with the highest voltage are on the board, so this may be difficult.
The mixer stages, which are probably on the other board, should have their own winding of the transformer (the 70 to 100 mm diameter toriod). However, if it doesn't and the designer made the +and -15 v for mixer with a regulator from the +-50v? winding, then removing the transformer wires from the bridge rectifier may kill the mixer, too. The bridge rectifier looks like a plastic blob with two wiggles next to two AC terminals, and a + and a - next to two other terminals. The wiggles look like the top left key of a PCAT keyboard.
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), much appreciated M8. 
Dear Nicoll: ***PLEASE*** don't butcher that amp based on newbie suggestions !!!
Or misguided "oldie", it's the same.
You don't need to *remove* those power amps , even less to unsolder the power transistors to disable it (craziest suggestion I ever saw)
You simply don't plug your powered speakers (or anything else) into the speaker out jacks and that's it.
If you want to be absolutely safe that nobody can do that by mistake (probably trying to "help" you to set up), cover them with a strip of strong gaffer tape and to boot write on it "don't touch".
Even better: "NO tocar".
Your "Yamaha" mixer *does* have line level outs , probably labelled left and right or Main out , which will drive your powered speakers.
The China Peavey and the Behringer look legitimate, and at the low price they are sold it's not worth faking.
As of the "Yamaha", I have already repaired those under many names, even "Mackie".
I called the local Importer and he told ne they are as generic as can be, and in 50-up lots they will stamp any logo you want on them, so now you know.
They are quite decent for the price, the problem you had before was on the speaker side, very unefficient which required overdriving them to get any volume out of them, and now, since the problem repeats at your home, I'm starting to suspect either a shorted tweeter or a shorted crossover cap, only 2 reasons for the abnormal resistor overheating.
Or misguided "oldie", it's the same.
You don't need to *remove* those power amps , even less to unsolder the power transistors to disable it (craziest suggestion I ever saw)
You simply don't plug your powered speakers (or anything else) into the speaker out jacks and that's it.
If you want to be absolutely safe that nobody can do that by mistake (probably trying to "help" you to set up), cover them with a strip of strong gaffer tape and to boot write on it "don't touch".
Even better: "NO tocar".
Your "Yamaha" mixer *does* have line level outs , probably labelled left and right or Main out , which will drive your powered speakers.
The China Peavey and the Behringer look legitimate, and at the low price they are sold it's not worth faking.
As of the "Yamaha", I have already repaired those under many names, even "Mackie".
I called the local Importer and he told ne they are as generic as can be, and in 50-up lots they will stamp any logo you want on them, so now you know.
They are quite decent for the price, the problem you had before was on the speaker side, very unefficient which required overdriving them to get any volume out of them, and now, since the problem repeats at your home, I'm starting to suspect either a shorted tweeter or a shorted crossover cap, only 2 reasons for the abnormal resistor overheating.
Hi JMFahey,
Thanks for your answer.
We had bands playing on Wednesday, Friday, Saturday & Sunday using my old Crown Speakers with the new Peavey amp and so far the tweeters are still ok. When I use the Yamaha it burns out the 10W6.8Ohm resister almost every night, this is why I come to the conclusion it was the Yamaha mixer that had issues.
Having said that I did replace all the 10W10Ohm and 10W6.8Ohm resisters with new ones I bought from a reputable electrical store so to be sure I will try it once again next Weekend (fri, Sat & Sun) and see what happens, I bought plenty spare ones incase they burn out again!
It would be nice if all was ok after changing all the resistors, but if it burns out the caps again then I am afraid to use it with my new powered speakers from the main out with the amp still working incase it damages my new speakers too!
Pity there is nobody in my small town qualified to check it out for me, the nearest place is an overnight boat trip away, and even they are not exactly filling me with confidence that they know what is wrong - hence I found & asked on this boards.
Lets say that I find there is for sure a problem with the yamaha amp, are you 100% sure that the problem wouldn't effect the main outs (line level)? Thanks again.
Funny you mention overdriving the speakers to get volume - these speakers are suppose to be 300W and have a blue light (LED) that is "almost" constantly on even at lower volumes in the house, it seems to light up with the smallest of sounds, is this some sort of clipping warning? If so then they are clipping a lot, even when using the Peavey this last 3 nights but somehow the tweeters have survived the last 3 nights, I'm very confused.
From the photo's in post 1, what is the crossover caps, I can try replacing them all.
Thanks for your answer.
We had bands playing on Wednesday, Friday, Saturday & Sunday using my old Crown Speakers with the new Peavey amp and so far the tweeters are still ok. When I use the Yamaha it burns out the 10W6.8Ohm resister almost every night, this is why I come to the conclusion it was the Yamaha mixer that had issues.
Having said that I did replace all the 10W10Ohm and 10W6.8Ohm resisters with new ones I bought from a reputable electrical store so to be sure I will try it once again next Weekend (fri, Sat & Sun) and see what happens, I bought plenty spare ones incase they burn out again!
It would be nice if all was ok after changing all the resistors, but if it burns out the caps again then I am afraid to use it with my new powered speakers from the main out with the amp still working incase it damages my new speakers too!
Pity there is nobody in my small town qualified to check it out for me, the nearest place is an overnight boat trip away, and even they are not exactly filling me with confidence that they know what is wrong - hence I found & asked on this boards.
Lets say that I find there is for sure a problem with the yamaha amp, are you 100% sure that the problem wouldn't effect the main outs (line level)? Thanks again.
Funny you mention overdriving the speakers to get volume - these speakers are suppose to be 300W and have a blue light (LED) that is "almost" constantly on even at lower volumes in the house, it seems to light up with the smallest of sounds, is this some sort of clipping warning? If so then they are clipping a lot, even when using the Peavey this last 3 nights but somehow the tweeters have survived the last 3 nights, I'm very confused.
From the photo's in post 1, what is the crossover caps, I can try replacing them all.
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That blue light blinking Is why I thought perhaps your output transistors might be leaking DC voltage. Or the feedback is hosed causing clipping all the time, or any other thing. Hence, if you are not going to check the speaker output for DC voltage, why I think disconnecting output transistors from the power is key to longevity of the rest of the mixer. Disconnecting the main power transformer winding from the rectifier is more direct, but you are too much of a newbie to identify the main winding which could be confused with the the +-16 winding that drives the mixer and preamp sections. this Mixer is almost trash, I'm no respector of the $2 transistors that might be causing the problem anyway.
Using the mixer section of a power mixer with a trashed power output section is the kind of thing I would do if I was blowing speaker crossover parts, was in the middle of nowhere, and didn't have a meter. I'm ex Army, have been to the woods, and got back to base too, despite lots of tired or unreliable equipment. You wouldn't believe how hard it was to find a meter in the field in a 740 man maintenance battallion. Everybody that had a meter was out in a truck somewhere taking care of business, might be back 3 AM three days from now. they didn't let the 550 mechanics have a meter, only the 60 missile techs. The radio guys had special purpose testers, not a set of probes in the whole radio shop. Yet everybody had a generator, a wiring setup, light, hoists, command equipment, and no way to debug the problems if you are the one guy in the maintenance management office with a physics degree and ability to figure out electrical problems.
Using the mixer section of a power mixer with a trashed power output section is the kind of thing I would do if I was blowing speaker crossover parts, was in the middle of nowhere, and didn't have a meter. I'm ex Army, have been to the woods, and got back to base too, despite lots of tired or unreliable equipment. You wouldn't believe how hard it was to find a meter in the field in a 740 man maintenance battallion. Everybody that had a meter was out in a truck somewhere taking care of business, might be back 3 AM three days from now. they didn't let the 550 mechanics have a meter, only the 60 missile techs. The radio guys had special purpose testers, not a set of probes in the whole radio shop. Yet everybody had a generator, a wiring setup, light, hoists, command equipment, and no way to debug the problems if you are the one guy in the maintenance management office with a physics degree and ability to figure out electrical problems.
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Guys, I'm so sorry to be a pain but have another question, I hope this is an easy one!
I have been testing the Yamaha mixer in my home with my powered speakers, when I whisper into the mic the signal does not come through, if I hum quietly still nothing, as I hum slowly louder - the signal all of a sudden kicks in, I am not talking about extremely low volume, this issue is even noticeable in live gigs when the acoustic guitarist is picking a soft part of the song - the signal just dies!
All gain settings are set correctly.
I have confirmed this happens in all 8 channels of the mixer AND from both the power amp outs (to passive speakers) & from the line level outs (to active speakers).
Any idea's?
Thanks guys!
I have been testing the Yamaha mixer in my home with my powered speakers, when I whisper into the mic the signal does not come through, if I hum quietly still nothing, as I hum slowly louder - the signal all of a sudden kicks in, I am not talking about extremely low volume, this issue is even noticeable in live gigs when the acoustic guitarist is picking a soft part of the song - the signal just dies!
All gain settings are set correctly.
I have confirmed this happens in all 8 channels of the mixer AND from both the power amp outs (to passive speakers) & from the line level outs (to active speakers).
Any idea's?
Thanks guys!
This could be a high frequency oscillation, and probably in a stage that is south of the main mix bus -- but probably NOT in the power amp. If it's coming out of the line outs it could damage external powered speakers. If they are bi-amped it is less likely to damage them, but it certainly won't be helping the sound. This oscillation is probably happening when it appears to be silent - cooking your crossover resistors the whole time. The presence of a signal may suppress it and then it appears to work normally.
It could be a faulty op amp - or even a design problem. Those "generic" designs may not even be tested before they go out the door. It could be as easy as swapping an op amp or putting some bypass capacitors on the board where they should have been in the first place. Without an oscilloscope and/or some knowledge of electronics this may be difficult.
Bottom line is, if this is NOT in the power amp (which can be bypassed) and is coming out the line outs, I would dump it NOW unless you have the expertise to fix it. Certainly not worth the couple hundred bucks (or equivalent) that a tech would charge - and if it's a design problem the bill will add up quickly.
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