@indianjo I'll try and see if I can tickle it a little more to get it down closer to 4mv.
Out of curiosity (general question), why is 'any' DC acceptable or safe, or even in some cases possibly wanted (or needed)?
Out of curiosity (general question), why is 'any' DC acceptable or safe, or even in some cases possibly wanted (or needed)?
No DC is wanted. It permamently pushes speaker voice coil out of the optimum magnet gap. And it heats the voice coil.
This can not possibly be wanted or needed.
You will always have small amount of DC, no matter how you adjust it due to drift. It changes with thermal conditions. When you start the amp, it will be far off, when it settles thermally, it will be different. When the ambient temp changes, it will be different. When you play no music, or full power, it will be different. There will always be some DC. Few mV is fine.
This can not possibly be wanted or needed.
You will always have small amount of DC, no matter how you adjust it due to drift. It changes with thermal conditions. When you start the amp, it will be far off, when it settles thermally, it will be different. When the ambient temp changes, it will be different. When you play no music, or full power, it will be different. There will always be some DC. Few mV is fine.
Thanks @adason for helping with the info! Really appreciate it. I'll be able to run the amp today for awhile, and will try to lower the measured DC at the speaker terminals again and get it down to as close to 0mv as I can (try for no higher than 5mv, the pots are VERY VERY touchy).
There had been a fair bit of accumulated dust that I carefully blew out and vaccumed (still looks like there's thin layer of attached dust).
Is it possible the pots are gunky? Can I safely spray with deoxit (with amp off and unplugged and caps drained)?
There had been a fair bit of accumulated dust that I carefully blew out and vaccumed (still looks like there's thin layer of attached dust).
Is it possible the pots are gunky? Can I safely spray with deoxit (with amp off and unplugged and caps drained)?
Yes, touchy oxidized dirty pots is why you should not monkey with DC bias to achieve perfection. Yes, you can use deoxit. As adason pointed out, the actual operating point changes with temperature and load history (temperature of the dies in the transistors). 200 mv DC offset is an oft quoted limit.
I clamp the DC bias pot in my units with an appropriate number of series 1n4148 (0.7 v) and maybe a schottky (0.3 v) to clamp the wiper at just above what wiper voltage I find works well. Probably end up at that voltage after the wiper lets go anyway. clamp goes parallel from pot end to wiper terminal.
I clamp the DC bias pot in my units with an appropriate number of series 1n4148 (0.7 v) and maybe a schottky (0.3 v) to clamp the wiper at just above what wiper voltage I find works well. Probably end up at that voltage after the wiper lets go anyway. clamp goes parallel from pot end to wiper terminal.
@indianajo I'll run the amp today for awhile, shut down and drain, then deoxit and run again to set the DC as close to 0.3v as I can and then leave her.
I would still like to get proper replacement resistors for those 8 (four per board) and give them a little stand-off air, but that will come after I do more formal reading and learning first!
I would still like to get proper replacement resistors for those 8 (four per board) and give them a little stand-off air, but that will come after I do more formal reading and learning first!
Ran the amp today from my Black Ice FX Tube DAC via Maclaptop USB, at pretty aggressive volume (with aggressive music) for a couple hours after being on idle for over an hour.
Checked the DC at speaker outputs and got it to +.001 to -.001 on both channels (left was higher initially than right. (was around .010 and .012)
Played some heavy music again for a couple hours at 'loud' volume- lots of bass and strong drums.
RE-checked with the meter, was a little elevated back up to .005+/-.001mv.
Tweaked again, ran again and things seem to have stayed pretty stable at +/-.001mV DC.
I have to say, playing thru a pair of old Epos ES14 speakers, it's been sounding REALLY solid.
Seems to have some amazing control of the 8" woofer and really nails articulate drum hits without any noticeable distortion or break up.
I always felt the tweeters needed to 'come up in level' and frequency a good solid 3-6db before.
But now the speakers sound perfectly balanced and as articulate and detailed as 35+ year old speakers can sound-- way better than just played from a Rega Mira integrated which sounded sort of choked and flubby, like a wet blanket was over the speakers.
I still want to get the 8 large resistors changed out, re-grease the heat sinks, and would love to have an actual technician to test the amp out with a scope and meter to make sure all the caps are solid with good esr, the transistors and fets are solid and not leaking at all, etc etc.
Checked the DC at speaker outputs and got it to +.001 to -.001 on both channels (left was higher initially than right. (was around .010 and .012)
Played some heavy music again for a couple hours at 'loud' volume- lots of bass and strong drums.
RE-checked with the meter, was a little elevated back up to .005+/-.001mv.
Tweaked again, ran again and things seem to have stayed pretty stable at +/-.001mV DC.
I have to say, playing thru a pair of old Epos ES14 speakers, it's been sounding REALLY solid.
Seems to have some amazing control of the 8" woofer and really nails articulate drum hits without any noticeable distortion or break up.
I always felt the tweeters needed to 'come up in level' and frequency a good solid 3-6db before.
But now the speakers sound perfectly balanced and as articulate and detailed as 35+ year old speakers can sound-- way better than just played from a Rega Mira integrated which sounded sort of choked and flubby, like a wet blanket was over the speakers.
I still want to get the 8 large resistors changed out, re-grease the heat sinks, and would love to have an actual technician to test the amp out with a scope and meter to make sure all the caps are solid with good esr, the transistors and fets are solid and not leaking at all, etc etc.
Greetings, Steve Kaiser lived a mile away and we were friends. We were in a local Audio Club. He had brought his amp to my house for a demo. It was an excellent amp and put it at the top of my list "to watch for amps". Meanwhile I bought the Amherst P-2000 preamp. Another great unit. Enjoy your amp & consider yourself lucky.
Happy Sunday @crispycircuit , and thanks for chiming in here!!
I feel pretty lucky to have found this relatively close by, and the shop was VERY kind and generous in helping support my USFS fire station.
Honestly, I really really like this amp for a lot of reasons: it (to my novice experience) looks relatively simple but highly functional and purpose built in layout and component choices...even though allegedly this was "just a tester run of X units to see how they would be, and cost to make en-mass".
I was very fortunate that a member on another forum happened to have talked with Steve years ago, and got a schematic for the more modern but nearly identical sister amp, the KST-150 from "Luminance Audio". Sadly I for some reason can barely read it (very small file, and I don't truly know electronics, so I can't recognize and translate the items easily- sort of 'well that must be a 12w resistor, and that likely says______').
Is there ANY chance you still speak with Steve? Would it be weird/inappropriate of me to ask if you could ask Steve for ANY additional info on his work and concept design for this, and if he could provide a schematic for it?
I really don't want to damage the amp and ruin it if there's something a bit off, and with use would cause full failure destroying the boards or the harder to find components.
I have to say though, in listening to singers like Domanique Fils-Aimé, Lianne La Havas, Jacintha, even Richie Havens (thru Jolida/Black Ice Dac and Epos ES14 speakers), this thing sounds AMAZING, and VERY noticeably different than the Mira integrated amp. It's not the best looking amp (nor cleanest, man look at the first post pics!), but to my ears it's really spectacular.
If it seems the amp is truly stable and functions ok over more time, I'll play it thru my new Legacy Audio Studio HD stand mounts with a REL T5x sub.
Again many thanks for chiming in and saying hi, and offering some other info.
If nothing else tell Steve I greatly admire his amp, and it's inspired me to learn more about electronics and amp design and function!
~alan
I feel pretty lucky to have found this relatively close by, and the shop was VERY kind and generous in helping support my USFS fire station.
Honestly, I really really like this amp for a lot of reasons: it (to my novice experience) looks relatively simple but highly functional and purpose built in layout and component choices...even though allegedly this was "just a tester run of X units to see how they would be, and cost to make en-mass".
I was very fortunate that a member on another forum happened to have talked with Steve years ago, and got a schematic for the more modern but nearly identical sister amp, the KST-150 from "Luminance Audio". Sadly I for some reason can barely read it (very small file, and I don't truly know electronics, so I can't recognize and translate the items easily- sort of 'well that must be a 12w resistor, and that likely says______').
Is there ANY chance you still speak with Steve? Would it be weird/inappropriate of me to ask if you could ask Steve for ANY additional info on his work and concept design for this, and if he could provide a schematic for it?
I really don't want to damage the amp and ruin it if there's something a bit off, and with use would cause full failure destroying the boards or the harder to find components.
I have to say though, in listening to singers like Domanique Fils-Aimé, Lianne La Havas, Jacintha, even Richie Havens (thru Jolida/Black Ice Dac and Epos ES14 speakers), this thing sounds AMAZING, and VERY noticeably different than the Mira integrated amp. It's not the best looking amp (nor cleanest, man look at the first post pics!), but to my ears it's really spectacular.
If it seems the amp is truly stable and functions ok over more time, I'll play it thru my new Legacy Audio Studio HD stand mounts with a REL T5x sub.
Again many thanks for chiming in and saying hi, and offering some other info.
If nothing else tell Steve I greatly admire his amp, and it's inspired me to learn more about electronics and amp design and function!
~alan
If is running hot, priority on checking the idle bias current (F1) at the quoted 300 ma for all 4. Requires a DVM with 2 A scale, and 2 alligator clip leads. Toy much idle bias current, sounds great. Too much idle bias current is not good for long life. Same warning about the pot losing contact.
If the transistors have not been removed, dried heat sink grease is not a problem. Grease makes it flow evenly, but when it was done at the factory the powder that flows the heat has already been spread out evenly.
With tech time running $60/hour up, and capacitors running under $1, not worth checking ESR IMHO. Lots of old unused equipment given a new life runs 6 months for a new enthusiast until the water evaporates out the cracked capacitor seals. ESR tells that the cap has already expired. ESR does not tell that the seal is intact or cracked.
Many e-caps are replaced by shops with 500 hr or 1000 hr service life caps. Good for maybe a year of 16 hours/day running. >3000 hours caps are available, some small ones available in 10000 hours up. Most shops won't pay the extra 40% charge for the long life parts. Most shops won't even keep long life caps in stock. Customer won't have a problem with the cheapest parts for a year at least. I've scrapped out TV's that were obviously repaired by a professional, (sticker on the back) with used e-caps.
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@indianajo I am hoping I am understanding and doing this next part correct.
I got the clip leads for my Fluke 116 meter, and set it to "DC-uA".
Clipping onto the F1 fuse, powering on, no input no load, powering on I got 2.0uA dc on one channel, and 2.2uA on the other channel.
I am CERTAIN I am doing this incorrectly,
I got the clip leads for my Fluke 116 meter, and set it to "DC-uA".
Clipping onto the F1 fuse, powering on, no input no load, powering on I got 2.0uA dc on one channel, and 2.2uA on the other channel.
I am CERTAIN I am doing this incorrectly,
Well, microamps (uA) is not what you are looking for. Text post #4 says "300 ma". So a 200 ma scale of DVM would not be big enough. 2 amp scale would be big enough, would read 0.300 on 300 ma. My DVM doesn't have that it has 10 A scale. Would still read 0.3 A. I don't know where you got the text in post #4, but I'm assuming that is correct.
No input no load attached is correct.
If your DVM is autoranging, then maybe you can start at uA, and it will switch ranges several times until it gets to where 300 ma is not overscale. In that case you have to look at the words on the screen to see what range it actually ended up at. 2.2 doesn't sound right; if it autoranged to 2 amp scale it would read 0.22 for 220 ma. In that case "amps" legend would appear.
If idle bias is actually 220 ma I wouldn't worry about the heat.
No input no load attached is correct.
If your DVM is autoranging, then maybe you can start at uA, and it will switch ranges several times until it gets to where 300 ma is not overscale. In that case you have to look at the words on the screen to see what range it actually ended up at. 2.2 doesn't sound right; if it autoranged to 2 amp scale it would read 0.22 for 220 ma. In that case "amps" legend would appear.
If idle bias is actually 220 ma I wouldn't worry about the heat.
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Yes @BSST that's the issue: the fuse is still in: oops.
@indianajo I figured out the issue. The Fluke meter I have doesn't read amp (or in trying to read thru the manual to find it, I still haven't come across it.)
I have another meter that had a 10A DC option and probe port, and I grabbed that.
In testing F1 with the 10a meter setting, switching the amp on briefly (I really am scared I am going to blow/pop/burn up something), I got a reading of .028 for the Left Channel. .027 for the Right Channel.
Sound a little better?
@indianajo I figured out the issue. The Fluke meter I have doesn't read amp (or in trying to read thru the manual to find it, I still haven't come across it.)
I have another meter that had a 10A DC option and probe port, and I grabbed that.
In testing F1 with the 10a meter setting, switching the amp on briefly (I really am scared I am going to blow/pop/burn up something), I got a reading of .028 for the Left Channel. .027 for the Right Channel.
Sound a little better?
Was hoping you would think that as well. I can't think that a tiny bump up to .30a is going to really make a big difference in the sound quality (I don't care as much about volume at all).
I'm going to take it to the Station and run it for awhile (a full two weeks, left on, ran with music for 1-2 hours a day) and check things again.
I did notice that one of the black 100uF 1000v caps top is a 'little' domed, so I'll keep an eye on it.
When time permits this summer I'll have a work bench at the station that I can set up and pull the heated resistors and replace those 4 small caps and keep it running! Thanks so much for your patience with explaining things and checking my work. Much appreciated.
Now to find the Amherst P-2000 preamp to go with it!
I'm going to take it to the Station and run it for awhile (a full two weeks, left on, ran with music for 1-2 hours a day) and check things again.
I did notice that one of the black 100uF 1000v caps top is a 'little' domed, so I'll keep an eye on it.
When time permits this summer I'll have a work bench at the station that I can set up and pull the heated resistors and replace those 4 small caps and keep it running! Thanks so much for your patience with explaining things and checking my work. Much appreciated.
Now to find the Amherst P-2000 preamp to go with it!