I disconnected the amp boards today, still got 58VAC from the PS and 27VDC. So, looks as if I blew the caps when I shorted it....my bulb tester ignorance really bit me. Is there another way to test to make sure it's the caps? My DMM doesn't have a capacitor test mode.
Also guys, does this look like the correct Cap? The manual says
10,000uF 50V - Panasonic TS-U 35x30mm capacitors
Digikey
Also guys, does this look like the correct Cap? The manual says
10,000uF 50V - Panasonic TS-U 35x30mm capacitors
Digikey
Cheap multimeter?
Some would incorrectly indicate ~2 x the DC voltage when measuring Vdc with the meter set for Vac. It may do it only with the probes attached one way (e.g. red to + and black to -).
Try measuring a 9 V battery with the meter set for Vac. If it reads 0 Vac, swap the probes around and make sure it still reads 0 Vac...
That should work for transformers outputting 32 V RMS or less.
You can test capacitors with the resistance (ohm) setting on the multimeter. Discharge the cap with a resistor. Connect the DMM to the cap. It should read near 0 Ω and increase as the cap charges. Reverse the polarity and you'll get a (usually large) negative value. Some multimeters (such as my bench top HP 34401A) reports a largish positive value when the polarity is reversed.
Seriously?! That's wrong on so many levels. 1 V DC = 1 V RMS, so I could see the meter reading the same on the AC and DC settings. But twice? Really?!
My expectation would be that the ACV setting has a high pass filter with a cutoff below 10 Hz and provide a true RMS reading above that. But then again, I'm not one to buy my tools at Harbor Freight or similar bottom-of-the-barrel outfits.
A Fluke 73 is more multimeter than you're likely to need for DIY audio projects and can be had for $30~60 + shipping on eBay in good condition. So seriously?! Why bother with the el-cheapo meters that give you wrong results. I still use the Fluke 73 I picked up in 1992.
~Tom
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I have a GE DMM, dont remember how much it was, but it was in the 30 dollar range. Tried the 9V thing today, shows 18VAC...wow. Ok, borrow a friends CenTech....18VAC. I absolutely can't believe this. thanks though, you steered me clear of purchasing 4 new caps today that would have been a complete waste of my time and money.
Ok, so back to where we were, reinstall the caps, finish replacing the diodes, disconnect floating PS (PS2) (my boards are starting to look like they were part of the Normandy landing). Surprise, hum completely gone (using only PS1 to power both amps), "quiet as a dead mouse". Hook PS2 back up as floating to confirm, hum is back only in that channel. Hook PS2 back to trafo, hum is louder. So, slow and steady wins the race. It seems we have narrowed this to an offending PS.
Recommendations? The 8 diodes on PS2 are new. Is there any part that people would think would be particularly likely to be bad? I can purchase an entirely new PS from chipamp.com with a new board for $30, which is looking pretty enticing considering I have been troubleshooting this for over a month now.
Ok, sufficiently frustrated. I went out tonight and couldn't reproduce what I was showing the other night, that the hanging PS was the issue. If we are calling amp1/ps1 the channel that has the hum, I moved amp1 to ps2, and vice versa. The hum actually moved with the amp board...so now is amp 1 the issue? I thought maybe it was the speaker, swapped those, the hum stays with amp1. It STILL only occurs when both amps are on separate PS. If I put them on either PS in parallel, hum is gone. I've never had so an issue troubleshooting something in my life. Does anyone have any further advice? I am about 2 hours awa from throwing this thing out the window.
Hello.
It's never a good idea to use two different setups of power supply boards like in the first post. All diodes are not created equal and they have different Vf (even if just some mV)
If you want to go for dual mono you better use another identical transformer to power the other rectifier+cap arrangement (or a transformer with 4 secondaries will do it too) With only 2 secondaries transformer stick with only one power supply board, or at least only one rectifier arrangement.
Better to put one capacitor on each rail at each TDA-chip and use one rectifier for both channels then try to to separate the channels with different rectification for each channel.
It's never a good idea to use two different setups of power supply boards like in the first post. All diodes are not created equal and they have different Vf (even if just some mV)
If you want to go for dual mono you better use another identical transformer to power the other rectifier+cap arrangement (or a transformer with 4 secondaries will do it too) With only 2 secondaries transformer stick with only one power supply board, or at least only one rectifier arrangement.
Better to put one capacitor on each rail at each TDA-chip and use one rectifier for both channels then try to to separate the channels with different rectification for each channel.
option - 1
the best way to solve this,use one power supply circuit.
option - 2
if u whant to use two power supply circuit you should use two trasfomers.
option - 3
isolation amplifire
I never try this,I cannot say this is 100% working
but you can try if you whant.
Low Phase Noise Design: Isolation Amplifiers
http://www1.futureelectronics.com/doc/ROHM/ROHM BA3121N.pdf
XXXXXXXXX
Kenwood KACX810D Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
the best way to solve this,use one power supply circuit.
option - 2
if u whant to use two power supply circuit you should use two trasfomers.
An externally hosted image should be here but it was not working when we last tested it.
option - 3
isolation amplifire
I never try this,I cannot say this is 100% working
but you can try if you whant.
Low Phase Noise Design: Isolation Amplifiers
http://www1.futureelectronics.com/doc/ROHM/ROHM BA3121N.pdf
XXXXXXXXX
Kenwood KACX810D Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
Then do that. I actually suggested this a while back...
If you only have one transformer, the best way to wire it is to have one supply feeding both channels. If you had two transformers (or a transformer with four secondary windings) you could use two supply boards.
~Tom
Then do that. I actually suggested this a while back...
If you only have one transformer, the best way to wire it is to have one supply feeding both channels. If you had two transformers (or a transformer with four secondary windings) you could use two supply boards.
~Tom
Isn't the benefit of having separate PS to get better channel separation? I could go with 1 PS I suppose.
Allan from Chipamp.com called me yesterday 2 hours after I sent an email and is working with me to troubleshoot. Darn good customer service.
I suppose part of the reason I'm so relentless with this is that I'm still puzzled how WWWJD over at parts-express forum can have the exact same rig and no noise.
The same argument can be said for having separate transformers, separate enclosures, separate mains circuits, etc. How much channel separation do you need? How much are you getting with one supply? How would the performance be if you used all the supply caps in one supply feeding two channels?
I see no reason it shouldn't work. My guess about the mismatch between diodes is a bit far fetched. You should be able to make it work with one transformer, two supply boards.
You could also set up a simulation in LTspice with two rectifier bridges, caps, and mismatched current loads. See if that provides any clues to what's going on.
~Tom
I find when using a floating mobile phone or mp3 player I need to earth the zero volt line of my amplifier.
The other point I have had problems with is making sure the flow of wires through the rectifier and smoothing is split between the input side and amp side.
If you mix these the charging impulses into the smoothing caps will modulate your zero volt line.
The other point I have had problems with is making sure the flow of wires through the rectifier and smoothing is split between the input side and amp side.
If you mix these the charging impulses into the smoothing caps will modulate your zero volt line.
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