I have a full POA6600A manual with the idle current setup procedure but since the 6600 is a dual super non-nfb curcuit and the 6600A is optical class A.... I don't think the 6600A procedure would be any benefit 
Has anyone got any ideas? Is there a tech whizz that could give me a rough idea from looking at the schematic?
Has anyone got any ideas? Is there a tech whizz that could give me a rough idea from looking at the schematic?
Hi Bigred,
I would think your DC offset adjust control would go for minimum DC voltage from the audio output to ground. Less than 10 mV since it is adjustable.
Bias current is another issue. Most products tend to sit from 10 mA to 30 mA per device.
If you have the schematic in electronic format, could you email it to me please? bhome at sympatico dot ca.
-Chris
I would think your DC offset adjust control would go for minimum DC voltage from the audio output to ground. Less than 10 mV since it is adjustable.
Bias current is another issue. Most products tend to sit from 10 mA to 30 mA per device.
If you have the schematic in electronic format, could you email it to me please? bhome at sympatico dot ca.
-Chris
Hi Kevin,
The procedure for setting bias simply warms the heat sink up to what would be close to a known temperature. Adcom and a few other people do things in a similar way. Just follow the same procedure and check the value and placement of the test points so you can correct for any differences.
Your DC offset should be very close to zero. If this channel has been repaired before, it's possible the J-Fets were damaged. Also, check your +/- 15 VDC supplies for the front end.
To match J-Fets, you first measure a bunch for IDSS and separate them into piles having similar values. From each pile you can run them through a matching test jig I made. You can also use the jig for testing NPN pairs or even individual beta.
Note that I reversed the current select scale listed. It goes from right to left instead of the other way around. Measure between TP 1a and TP 1b for the lowest reading to get a match. I normally run the drain voltage around 10 VDC.
-Chris
Edit: Brain Fart! It's the POA-6600A that I do not have. Can anyone help me out here?
The procedure for setting bias simply warms the heat sink up to what would be close to a known temperature. Adcom and a few other people do things in a similar way. Just follow the same procedure and check the value and placement of the test points so you can correct for any differences.
Your DC offset should be very close to zero. If this channel has been repaired before, it's possible the J-Fets were damaged. Also, check your +/- 15 VDC supplies for the front end.
To match J-Fets, you first measure a bunch for IDSS and separate them into piles having similar values. From each pile you can run them through a matching test jig I made. You can also use the jig for testing NPN pairs or even individual beta.
Note that I reversed the current select scale listed. It goes from right to left instead of the other way around. Measure between TP 1a and TP 1b for the lowest reading to get a match. I normally run the drain voltage around 10 VDC.
-Chris
Edit: Brain Fart! It's the POA-6600A that I do not have.
Can anyone help me out here?Attachments
The one 6600 mono block was in protection and had the 2sa1492 and 2sc3856 complimentary pairs done along with a 15v zener in front end, some smoked resistors (can't remember exact ones) and spkr relay 701 (contacts MELTED!! lol). I dont have the means to have handfulls of transistors for matching purposes unfortunately. It is back pounding but runs a little warmer than the other and has the -14mv dc-offset (cooler amp +1mv). So the search on how to setup idle current continues. One other note: After amp was back running, found the amp would go into protection with loud pop thru spkrs if you switched it from normal to balanced mode. Since normal mode was only ever used and amp functioned just fine until output prob, it is not known how long this circuit has been faulty(cause, coincidence, result who knows). In any case I traced it back to opamp NJM2068(IC401) and replaced. I dont have a balanced capable preamp to fully test but no more protection and pop. Even though its not used, I wouldn't feel good giving back until I fully check so am gonna borrow my buds preamp with balanced outputs after I am confident with the idle current and neutral point voltage setup. Looks like I will have to jar loose and grab the SM from servicemanuals.net since its not available from Denon anymore.
Hi Bigred,
With damage like that, it is very possible to damage the front end. Check the feedback resistor in case it got overheated as well. The case is simply that those fets have been damaged and should be replaced. They should not be expensive and if you pick up 20, you should get a few good pairs out of that. One point is that this channel may have higher noise and distortion (almost guaranteed!). It may also fail later on.
Understand that enough current went through the fets to wipe out a zener. That should be reason enough right there.
-Chris
With damage like that, it is very possible to damage the front end. Check the feedback resistor in case it got overheated as well. The case is simply that those fets have been damaged and should be replaced. They should not be expensive and if you pick up 20, you should get a few good pairs out of that. One point is that this channel may have higher noise and distortion (almost guaranteed!). It may also fail later on.
Understand that enough current went through the fets to wipe out a zener. That should be reason enough right there.
-Chris
Well I have confirmed all resistor values are within tolerance and all expected voltages are pretty well spot on. There MIGHT be some fatigued components but I do not think this amp is in any dire need of more repair. Yes the offset should be ZERO but I didn't think 14mv is worth the trouble of building a jig and matching handfuls of fets etc. I may be wrong with this thinking and am open to being convinced otherwise.
I have since learned there are 3 adjustment procedures needed to be performed with the 6600
1: Idle current 2: Neutral Point voltage 3: Distortion factor. The 6600A has no mention of distortion factor. So I will be more at ease when I get the 6600 manual and confirm these adjustments. The only thing confusing at the moment is the fact for the 6600A version all it says for the adjustment of neutral point voltage is to hook meter up to terminals and confirm the voltage indicates within +/-100mv value. THATS IT!! If I'm understanding correctly... any reading +/- of upto 100mv is acceptable here. So if I got 99mv reading or neg.99mv its good. I happen to be gettin -14mv so I assume its well within "spec". It puzzles me that the manual is calling it "adjustment of neutral point voltage" but no actual adjustment procedure just to confirm the +/-100mv value. What if I got 150mv for example??
I have since learned there are 3 adjustment procedures needed to be performed with the 6600
1: Idle current 2: Neutral Point voltage 3: Distortion factor. The 6600A has no mention of distortion factor. So I will be more at ease when I get the 6600 manual and confirm these adjustments. The only thing confusing at the moment is the fact for the 6600A version all it says for the adjustment of neutral point voltage is to hook meter up to terminals and confirm the voltage indicates within +/-100mv value. THATS IT!! If I'm understanding correctly... any reading +/- of upto 100mv is acceptable here. So if I got 99mv reading or neg.99mv its good. I happen to be gettin -14mv so I assume its well within "spec". It puzzles me that the manual is calling it "adjustment of neutral point voltage" but no actual adjustment procedure just to confirm the +/-100mv value. What if I got 150mv for example??
Hi Bigred,
Now the really sad thing is that I used to have that manual, and I've worked on those units. This procedure sounds very familiar. I'm sure I've suffered it before.
This is one of those things that would come rushing home if I was looking at that unit on the bench or peering at the manual. Maybe it's one of those things I didn't want to remember.
If you measured 150 mV, you would stop and recheck your adjustments. If they were okay you would fix the problem (because there would be one). Even if you measured 99 mV, it's time to perform the above. I'd be looking if it was 50 mV.
The fact that you lost a zener diode means those transistors were greatly abused. That may not be reason enough for you, it is for me. It's not the offset that bugs me as much as your reported damage.
-Chris
Now the really sad thing is that I used to have that manual, and I've worked on those units. This procedure sounds very familiar. I'm sure I've suffered it before.
This is one of those things that would come rushing home if I was looking at that unit on the bench or peering at the manual. Maybe it's one of those things I didn't want to remember.
If you measured 150 mV, you would stop and recheck your adjustments. If they were okay you would fix the problem (because there would be one). Even if you measured 99 mV, it's time to perform the above. I'd be looking if it was 50 mV.
The fact that you lost a zener diode means those transistors were greatly abused. That may not be reason enough for you, it is for me. It's not the offset that bugs me as much as your reported damage.
-Chris
BELIEVE ME...I know better than to use nte or ecg unless its an ABSOLUTE last resort and then I just make sure its not a mix and match pc. together. I use Global Electronics in Mississauga as its the only supplier that I know of that is within hours of me with NO minimum orders. I also can go and pick the parts up that day. Pacific is $50 minimum order. Next time I need a bunch of stuff though I will try Pacific (the outputs I paid $9ea. and Pacific has em for $2ea!!!)
I coulda rebuilt the whole damn amp at Pacific for what I paid at Global for the outputs and such
I coulda rebuilt the whole damn amp at Pacific for what I paid at Global for the outputs and such
Hi Bigred,
Well, it's a tiny world.
About Global. I met the original owner, Ali, many years ago. I started buying from him, then rented him an office in my shop. Before this, Jerry was my partner in Micron Electronics. It didn't work out and he eventually partnered with Ali. Another ex-employee named Hamlet popped in there now and again. I began dealing with Ali's supplier, Premier Parts Source. Faster, cheaper, almost always had stock.
Somewhere along the way, Ali started buying remarks (fake parts). I watched from the sidelines laughing. Jerry also had a history of this. He tried to market MR series parts (Micron Replacement - or something like that). I never used them, but other people did. Jerry was always about the catalog and he still makes the same spelling mistakes to this day. Pretty funny really. Ali forced the Global sale to Jerry, and he is still the sole owner to the best of my knowledge. Jerry makes a good living at this.
So, today Global is the fake capital of Mississauga. My supplier closed due to the dropping sales figures. Smart man. He always bought from Japan. The real thing. Global also buys from ......... Pacific Semiconductor! SO you never know what you're going to get there.
More trivia. Bob (my guy), Pacific and Global started as partners for each market. Global failed in Montreal and only dealt with the clients Bob didn't want. All the problem and low sales places after he moved to the Toronto area.
-Chris
Well, it's a tiny world.
About Global. I met the original owner, Ali, many years ago. I started buying from him, then rented him an office in my shop. Before this, Jerry was my partner in Micron Electronics. It didn't work out and he eventually partnered with Ali. Another ex-employee named Hamlet popped in there now and again. I began dealing with Ali's supplier, Premier Parts Source. Faster, cheaper, almost always had stock.
Somewhere along the way, Ali started buying remarks (fake parts). I watched from the sidelines laughing. Jerry also had a history of this. He tried to market MR series parts (Micron Replacement - or something like that). I never used them, but other people did.
Jerry was always about the catalog and he still makes the same spelling mistakes to this day. Pretty funny really. Ali forced the Global sale to Jerry, and he is still the sole owner to the best of my knowledge. Jerry makes a good living at this.So, today Global is the fake capital of Mississauga. My supplier closed due to the dropping sales figures. Smart man. He always bought from Japan. The real thing. Global also buys from ......... Pacific Semiconductor! SO you never know what you're going to get there.
More trivia. Bob (my guy), Pacific and Global started as partners for each market. Global failed in Montreal and only dealt with the clients Bob didn't want. All the problem and low sales places after he moved to the Toronto area.
-Chris
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