The lettering looks correct compared to mine. The ones I have are pulls from an old Pioneer SX-1010 so I know they legit.
Craig
Craig
Followed advice of lowering series resistor to the trim pot from 1491 to 1469. The trimpots were so touchy I replaced with bourns to fine tune values. The problem now is if I go by service manual & adjust to 50ma after 4 minutes then I get bias runaway sort of speak.(this is on both channels) Got 65ma after 30 minutes following service manual. It also seems that if I go over 47.5 mamps after it's been on say 10 minutes or more bias current will just keep increasing. That seems to be sweet spot. I'm just wandering if it's this heat sensitive if I will have problem under load. Is is 47.5 OK?
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I usually keep adjusting to the spec until it settles down at the spec. Eventually everything will get to even temperature and stay where you put it at idle at least. That's sort of what the SM is saying. After you are satisfied at idle run it for a while into a load then check your idle current again. Some amps are overcompensated, meaning when it's hot the idle will less than what set it for but should settle to where you set it. Then some amps are the opposite, when hot the idle will be higher than what you set it but settle again at idle.
Craig
Craig
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Ran it awhile and sounds good but I did notice something that may be out of norm. I had DC offset adjusted to 1mv but at idle but under a load with volume up I was hitting some peaks of .6 volt. I know this is not the way you normally measure but is that something to be concearned about?
Connected to good speakers now. I'm hearing a real low buzz out of both channels when no music is being played. What could that possibly be?(it doesn't sound like hum but buzz).
Does the volume control change the level? Hum, 60Hz, is usually associated with ground issues. Buzz, 120Hz, would be power supply related. An o'scope would be nice here.
Craig
Craig
The buzz is unaffected by volume-I only get a little hiss when all the way up which seems to drown out buzz some. I do have a scope that's a bit flakey and my meter has freq counter.
The original caps in this measured about 20% over rated value. If it possible a lack of original capacitance value could be causing the buzz? New caps measure right at stated value(thanks to modern cost cutting I'm sure).
The buzz could be from the power supply. Has it been recapped.
Was the buzz there b4 your recap effort?
Was the buzz there b4 your recap effort?
having a similar problem with a G-7500 receiver. faint buzz coming from the pre-amp.
not sure if it was there before my major mod. But I have yet to change the ecaps in the power supply and the tone amp.
put in a new PS, from a pioneer sx-1050 as the orig transformer blew and the PA had smoked multiple times.
added pre-out/power-in rca connectors, the amp, a LME49830/ALF16N_P16W is as quiet as a mouse. Method of elimination it seems for me on that pre-amp buzz.
not sure if it was there before my major mod. But I have yet to change the ecaps in the power supply and the tone amp.
put in a new PS, from a pioneer sx-1050 as the orig transformer blew and the PA had smoked multiple times.
added pre-out/power-in rca connectors, the amp, a LME49830/ALF16N_P16W is as quiet as a mouse. Method of elimination it seems for me on that pre-amp buzz.
Whats happening here with the hum noise is that you need to have bigger regulating capacitors, you probally have 10 000uf factory but to have zero hum noise you need to have a much higher value
For the 0.6V in speakers when you crank it up, that is related to capacitance you have, more regulating caps the more stable your dc speaker voltage is when you crank it up.
I know DC voltage in speakers indicate one side is using more current or gaining more, so when you set your idle current you need to have 0 Volts or near zero volts DC in the speaker
If you monitor your idle current and you can get it up higher and have safe temps then go for it, it should sound better and it will give your a more stabe DC voltage at speakers when you crank it up
For the 0.6V in speakers when you crank it up, that is related to capacitance you have, more regulating caps the more stable your dc speaker voltage is when you crank it up.
I know DC voltage in speakers indicate one side is using more current or gaining more, so when you set your idle current you need to have 0 Volts or near zero volts DC in the speaker
If you monitor your idle current and you can get it up higher and have safe temps then go for it, it should sound better and it will give your a more stabe DC voltage at speakers when you crank it up
Main caps are 6800uf which I did not replace(didn't hear any hum just buzz). I replaced power board caps, driver board caps and most tone board caps(few that I was out of). Since replacement caps are less than originals measured do you think bypassing them with additional 20% of value would be good idea? I did get DC low at idle .1mv in one channel and 3 mv in other. Bias current ended up being 45ma which would raise to about 48ma after being on 30minutes. If I went higher it would run up to about 60+ma. Main transistors do not get too hot but the little driver board transistors do and understand some of them are not easy to find so that was my main concearn.
Well if your little ones get hot then you should back off a bit, I think 48ma after a long idle is great.
So you managed to get the idle current same on both sides? .1mv and 3mv is a really good dc voltage in the speakers. and it shouldn't cause much or any diffrence at all with idle current
I have a few amps and I know with 20 000UF for a single channel I can hear a hum or buzz noise if I put my ear to the sub woofer and with about 60 000uf there is zero noise at the speaker.
With the regulating caps, it should be safe to give it 100 000uf for a single channel amp.
I had tried 120 000uf before and used that amp for a year and worked fine
With other caps, some times they are feed back caps or signal path caps etc. Those ones you should use orignal values(unless you know what you are doing), and use caps for music if you can get some.
So you managed to get the idle current same on both sides? .1mv and 3mv is a really good dc voltage in the speakers. and it shouldn't cause much or any diffrence at all with idle current
I have a few amps and I know with 20 000UF for a single channel I can hear a hum or buzz noise if I put my ear to the sub woofer and with about 60 000uf there is zero noise at the speaker.
With the regulating caps, it should be safe to give it 100 000uf for a single channel amp.
I had tried 120 000uf before and used that amp for a year and worked fine
With other caps, some times they are feed back caps or signal path caps etc. Those ones you should use orignal values(unless you know what you are doing), and use caps for music if you can get some.
What I actually Think more important than same current both sides npn pnp, is that you measure the BE voltage of your output trasntiors, Both trasnisotrs should have same voltage, BE voltage indicates how turned on the transitors are, more BE voltage more idle current it is drawing.
Some times theres a extra pnp or npn trasnitor used, so its we want to have same BE voltage not same idle current both sides.
Some times theres a extra pnp or npn trasnitor used, so its we want to have same BE voltage not same idle current both sides.
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