Picked up a M45 and the forum was helpful with manual and display issues. Once I tried powering elec crossed subs the Yamaha was woefully weak. Thought I was only running class A mode-idle,maybe not switching into to B operation. I did a bias check and that showed voltage for both modes (I used the manual) had acceptable bias voltages. Not dead equal but good. Hooked up paradigm center speaker to check each channel. Amp drove it great,just a slight(barely audiable) raspy artifact on one channel. Rehooked subs to M45 unit was weak,but my 80 watt kenwood amp has no problem with same subs. So off to checking circuits on a haunch. Found the main caps are barely at 17,400and 17,600 uf but are rated at 22,000. I am guessing weak caps here. I am an old hand with custom crossovers but just got into amps at the board level. Any second opinions as to this spec for this amp, any body have any good caps at 70 plus volts 22,000uf ?
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Without a physical size thie request goes in the round file.
Check the frequency response first, it is more likely that a cap in the signal path is dried up. Always check the caps in the feedback loop to ground, the gain drops like a rock when these dry up.
Check the frequency response first, it is more likely that a cap in the signal path is dried up. Always check the caps in the feedback loop to ground, the gain drops like a rock when these dry up.
Yamaha 45 low power output
I pulled all caps off the board checked with a cap meter and did charge up leak down anlg meter check before posting .Main caps are 3in tall 2in diameter 69 volt 22,000 uf each -1 pair. Was looking for more of an opinion about how the main caps are at bottom of a 20% tolerance,even a little under. You are on track in that a couple of other caps were also marginal,but not open or killer low( in uf),but I have a ready supply of those. I am more concerned about the higher expense a bit harder to find main caps.
I pulled all caps off the board checked with a cap meter and did charge up leak down anlg meter check before posting .Main caps are 3in tall 2in diameter 69 volt 22,000 uf each -1 pair. Was looking for more of an opinion about how the main caps are at bottom of a 20% tolerance,even a little under. You are on track in that a couple of other caps were also marginal,but not open or killer low( in uf),but I have a ready supply of those. I am more concerned about the higher expense a bit harder to find main caps.
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" I am more concerned about the higher expense a bit harder to find main caps. "
Why? It's probably not the main problem. It should put out full power with a lot less capacitance than what you measured.
IIRC, that amp sounded bad the instant it clipped anyway.
Why? It's probably not the main problem. It should put out full power with a lot less capacitance than what you measured.
IIRC, that amp sounded bad the instant it clipped anyway.
The point of main caps is that they filter ac to dc in concert with the diode bridge. Audio equipment needs clean dc and nothing in a audio circuit likes dirty dc including switching transistors or output transistors. IIRC do you like the sound ac leakage,what amp sounds good clipping? I can't at this moment guarantee to what degree the filtering is affected. I may rescope it after caps and find nothing different ,but your mocking attitude is not nesessary. "Doubt"- I cold respect that ,but mocking is a sign of arrogance,and this is meant to be group sharring and problem solving. Through Darwinian selection I choose to read you,but not to deal with you.
"but your mocking attitude is not nesessary. "
The guilty flee when no one is pursuing, you read somthing in that was neither said nor implied.
"what amp sounds good clipping? "
Lots of them, just not this series from Yamaha.
"I can't at this moment guarantee to what degree the filtering is affected. "
You have already determined that they measure over 17,000µF, that amp will put out full rated power with a lot less filtering.
" I choose to read you,but not to deal with you. "
Your loss, and you sir are very thin skinned and take offence where none was offered.
The guilty flee when no one is pursuing, you read somthing in that was neither said nor implied.
"what amp sounds good clipping? "
Lots of them, just not this series from Yamaha.
"I can't at this moment guarantee to what degree the filtering is affected. "
You have already determined that they measure over 17,000µF, that amp will put out full rated power with a lot less filtering.
" I choose to read you,but not to deal with you. "
Your loss, and you sir are very thin skinned and take offence where none was offered.
M45 low power issue.
Well I finished putting together my test area,and scoped this amp as planned so things are clearer now. I am posting this for anyone who may run into a similar condition. Before even diving in I had noticed resistors to op transistors were changed at some points clue of a big repair. Its good not to assume too much,so after checking with someone who has worked on this very model I knew the main caps were low mfd but should be ok. I then checked the op transistor numbers corresponding to the resistors,and they were replacements,not originals,that makes you go-oh-nooo. This amp scoped out with oscillations. Its not detectable by ear but its there. I may delve in and check transistors and get correct replacements but when an amp has been poped its never fun cleaning up the mess. Oscillating explains the partial power loss some 100 watt amps only put out 10 to 20% power if its bad enough. This may explain why the amp is a bit anemic with larger power demands,fine with smaller speaker power demands. It may not have even oscillated when first repaired but who knows? It may have been tested by ear and someone declared mission accomplished?
Well I finished putting together my test area,and scoped this amp as planned so things are clearer now. I am posting this for anyone who may run into a similar condition. Before even diving in I had noticed resistors to op transistors were changed at some points clue of a big repair. Its good not to assume too much,so after checking with someone who has worked on this very model I knew the main caps were low mfd but should be ok. I then checked the op transistor numbers corresponding to the resistors,and they were replacements,not originals,that makes you go-oh-nooo. This amp scoped out with oscillations. Its not detectable by ear but its there. I may delve in and check transistors and get correct replacements but when an amp has been poped its never fun cleaning up the mess. Oscillating explains the partial power loss some 100 watt amps only put out 10 to 20% power if its bad enough. This may explain why the amp is a bit anemic with larger power demands,fine with smaller speaker power demands. It may not have even oscillated when first repaired but who knows? It may have been tested by ear and someone declared mission accomplished?
I can't think of any amplifier that actually sounds good when it clips, thus I hereby delegate that point as complete moot. As to the capacitors, there is the possibility that they should be replaced, but only an ESR test can validate that. The quoted capacitance that your meter is reading is fine for normal listening, and is more than some amplifiers with more power have. People put way too much thought into capacitor replacement as a pseudo fix-all, which it is not. It doesn't correct an issue where none exists. The problem that your amp is displaying has nothing to do with them, provided their series resistance is appropriate. What you need to identify is the magnitude of the oscillation, where it originates, and the current being sinked for that portion of the circuitry. I would also focus the effort at this point on some frequency response and step response measurements to determine if there is another problem once the oscillation problem is addressed.
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Descent advise kouiky I am going to put this amp aside for a while because I have a hafler dh200 that needs some attention,and I already made a start on it,so I will dive back into that before tying up test bench space with another amp.
"I can't think of any amplifier that actually sounds good when it clips"
Leach LSR&D 101, APT Model 1.
Leach LSR&D 101, APT Model 1.
kouiky you have inspired me to order an esr checker for transistor, coils and caps. Why just assume when you can fix like a pro?
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