So I may be in the market for a new amplifier... I accidentally grounded the output of my Kinergetics KBA-280. What it was (if I can't fix it or have it fixed):
Class A amplifier spec'd at 140wRMS into 8 ohms, measured it myself: 250 watts continuous.
A stereophile review measured it at about 350 into 4 ohms, 500 into 2, and over an entire thousand into one ohm. The single ohm measurement was different, a 10ms tone burst (fuses blew otherwise. Current delivery of 32A at 1 ohm)
It's SNR A weighted is 102db at 8 ohms. Excellent, considering that the noise is of the benign kind from Class A operation.
There are 10 output transistors in parallel per channel (I forget which model right now). They're all operating well within their linear range. I'm not an expert on amplifier design, but I assume that because of this, feedback would be low.
The amp exudes power. Excellent bass, silky smooth highs, great transients. Not a complaint I could make about it, other than maybe its heat output and fan. The heat is excessive, but the fan is quiet. You can barely tell it's on in a silent room. If you didn't know it had a fan and you never got any closer than 4 feet, you probably wouldn't discover it.
In case I can't have it fixed, I've been looking at possible replacements, and damnnnn! I want something on par, and from what I'm seeing, it doesn't exist. At my local hifi shop, the two highest end options in my target price range:
Moon 240i with LM3886? $3500
NAD M10 SNR 86db/w @5w: $3500!!!
Those are the two options, nothing else unless over 5k or under 1.5.
I want to support them because I've gone there since I was in high school and they've always been helpful. One guy taught me about things when I was new to the hobby. But I can't buy either one of those amps. I'd be unhappy for years. So maybe my next DAC will come from them, but my Babyface Pro is still new and a great source which I use at full level through the simplest passive preamp, so that might be in a bit.
Anyway... I'm relatively new to DIY audio. I'm thinking, if I can't find a good enough high powered amp for less than the price of an Impala, maybe I could make a low powered Class A amp myself for quieter listening. I could take a few of the transistors from the Kinergetics and make an amp. They're all in working order, plus 6 brand new old stock spares that I bought for a shop near me to use to try to fix my amp (they've been unsuccessful thus far).
I have a couple of really great linear power supplies. Fully regulated, extremely quiet, and fast. So fast. Switches to CC mode at 5.1A
+-62v at 5A.
I also have 4 caps total 120,000uf 63v !!8 mOhm!!
Are there any open source, easy (I can hope), high performance, Class A designs online which would benefit from the power supply I have? 150+ and 150- per side. Also, if anyone has suggestions for an off the shelf amp, I'd appreciate it greatly
Class A amplifier spec'd at 140wRMS into 8 ohms, measured it myself: 250 watts continuous.
A stereophile review measured it at about 350 into 4 ohms, 500 into 2, and over an entire thousand into one ohm. The single ohm measurement was different, a 10ms tone burst (fuses blew otherwise. Current delivery of 32A at 1 ohm)
It's SNR A weighted is 102db at 8 ohms. Excellent, considering that the noise is of the benign kind from Class A operation.
There are 10 output transistors in parallel per channel (I forget which model right now). They're all operating well within their linear range. I'm not an expert on amplifier design, but I assume that because of this, feedback would be low.
The amp exudes power. Excellent bass, silky smooth highs, great transients. Not a complaint I could make about it, other than maybe its heat output and fan. The heat is excessive, but the fan is quiet. You can barely tell it's on in a silent room. If you didn't know it had a fan and you never got any closer than 4 feet, you probably wouldn't discover it.
In case I can't have it fixed, I've been looking at possible replacements, and damnnnn! I want something on par, and from what I'm seeing, it doesn't exist. At my local hifi shop, the two highest end options in my target price range:
Moon 240i with LM3886? $3500
NAD M10 SNR 86db/w @5w: $3500!!!
Those are the two options, nothing else unless over 5k or under 1.5.
I want to support them because I've gone there since I was in high school and they've always been helpful. One guy taught me about things when I was new to the hobby. But I can't buy either one of those amps. I'd be unhappy for years. So maybe my next DAC will come from them, but my Babyface Pro is still new and a great source which I use at full level through the simplest passive preamp, so that might be in a bit.
Anyway... I'm relatively new to DIY audio. I'm thinking, if I can't find a good enough high powered amp for less than the price of an Impala, maybe I could make a low powered Class A amp myself for quieter listening. I could take a few of the transistors from the Kinergetics and make an amp. They're all in working order, plus 6 brand new old stock spares that I bought for a shop near me to use to try to fix my amp (they've been unsuccessful thus far).
I have a couple of really great linear power supplies. Fully regulated, extremely quiet, and fast. So fast. Switches to CC mode at 5.1A
+-62v at 5A.
I also have 4 caps total 120,000uf 63v !!8 mOhm!!
Are there any open source, easy (I can hope), high performance, Class A designs online which would benefit from the power supply I have? 150+ and 150- per side. Also, if anyone has suggestions for an off the shelf amp, I'd appreciate it greatly
Last edited:
First it’s not Class A producing 150W, the heatsinks would weight 30+ pounds, it’s a Class A/B.
Of course the Honey Badger from the DIYA store would give you 150 @ 8ohms and 250 @ 4 ohms and sound great, boards available and easy to find parts, best of all a great build guide and a thread dedicated to providing support if you need it.
Also search Blameless amplifier as it is scalable by adding outputs and more voltage and could easily get to 250w at 8 ohms and close to 400w at 4 ohm.
Truly there are a multitude of options so Google is your friend and read reviews.
Of course the Honey Badger from the DIYA store would give you 150 @ 8ohms and 250 @ 4 ohms and sound great, boards available and easy to find parts, best of all a great build guide and a thread dedicated to providing support if you need it.
Also search Blameless amplifier as it is scalable by adding outputs and more voltage and could easily get to 250w at 8 ohms and close to 400w at 4 ohm.
Truly there are a multitude of options so Google is your friend and read reviews.
Yes, it is indeed a class A amplifier.
Fred Pham, Kinergetics Research technician/designer, does repairs of KR products.
Pham can be reached via e-mail at tpham84002@aol.com, or (310) 408-7597.
Fred Pham, Kinergetics Research technician/designer, does repairs of KR products.
Pham can be reached via e-mail at tpham84002@aol.com, or (310) 408-7597.
This is diyaudio.
What you do, is measure the most likely parts to blow up into a short, to see if you damaged them.
After any (unlikely) speaker fuses, IMHO, those are output transistors. You look to see if the bases are shorted to the collectors and emitters, if BJT. Same test on gate for mosfet. Good BJT will read .47 to .75 voltage drop base to E & C. mosfet will read infinity ohms to S & D unless a protection diode, then .5 to .75 v. You do the test with the diode scale of a DVM. I buy the ones from farnell, non-autoranging is more convenient I find. Klein makes a competent meter for sale at HD or Lowes, but the probes are **** for working on amplifiers. **** probe tips disappear unless you are pressing on something. You should never use 2 hands working on an amp powered up, 24 v across your heart can stop it. Use an alligator clip lead on the black probe. Which you can also buy @ farnell.
How big is the heat sink? how many fins. Would settle the question of whether class A or not. I don't see the point of class A. I spend my big bucks on the speakers, not on the amp. My speakers were $600 each, new. I paid $200 each used. HD 20 db under output for 2nd harmonic @ 5 w frequencies 54-14 khz. . My $194 CS800s amp produces .03% HD @ 240 w/ch. My supermodified ST120 sounds exactly the same @ 1 W.
Personally, I find with efficient (101 db 1w1m) speakers in my living room, 1 watt is fine for base level listening, with 70 W available for volume peaks like the cannon shot in 1812 overture. But I've always protected my ears with earplugs in high noise environments, and am not HiFreq deaf like all the "real men" I know.
What makes an amp unrepairable is a transformer or switcher supply damaged. Which is pretty rare. Some switcher supplies can be repaired. I've repaired 4.
If you want to practice your solder skills on something that costs less than $3500, buy a Peavey M-2600 or PV-8c for parts or repair for <$100 and repair that, first. Schematics readily available, on eserviceinfo.com for example.
What you do, is measure the most likely parts to blow up into a short, to see if you damaged them.
After any (unlikely) speaker fuses, IMHO, those are output transistors. You look to see if the bases are shorted to the collectors and emitters, if BJT. Same test on gate for mosfet. Good BJT will read .47 to .75 voltage drop base to E & C. mosfet will read infinity ohms to S & D unless a protection diode, then .5 to .75 v. You do the test with the diode scale of a DVM. I buy the ones from farnell, non-autoranging is more convenient I find. Klein makes a competent meter for sale at HD or Lowes, but the probes are **** for working on amplifiers. **** probe tips disappear unless you are pressing on something. You should never use 2 hands working on an amp powered up, 24 v across your heart can stop it. Use an alligator clip lead on the black probe. Which you can also buy @ farnell.
How big is the heat sink? how many fins. Would settle the question of whether class A or not. I don't see the point of class A. I spend my big bucks on the speakers, not on the amp. My speakers were $600 each, new. I paid $200 each used. HD 20 db under output for 2nd harmonic @ 5 w frequencies 54-14 khz. . My $194 CS800s amp produces .03% HD @ 240 w/ch. My supermodified ST120 sounds exactly the same @ 1 W.
Personally, I find with efficient (101 db 1w1m) speakers in my living room, 1 watt is fine for base level listening, with 70 W available for volume peaks like the cannon shot in 1812 overture. But I've always protected my ears with earplugs in high noise environments, and am not HiFreq deaf like all the "real men" I know.
What makes an amp unrepairable is a transformer or switcher supply damaged. Which is pretty rare. Some switcher supplies can be repaired. I've repaired 4.
If you want to practice your solder skills on something that costs less than $3500, buy a Peavey M-2600 or PV-8c for parts or repair for <$100 and repair that, first. Schematics readily available, on eserviceinfo.com for example.
Last edited:
You get LM3886 boards here for $20 each...thousands of dollars is silly money.
That sounds impressive, your amp specs, but it is frankly an oddity, not for newbies, unlikely to be easy, and quite possible that you will end up doing further damage.
Buy a small amp for listening, $100 is tops, and either send this out, or gain some knowledge before starting on this.
That sounds impressive, your amp specs, but it is frankly an oddity, not for newbies, unlikely to be easy, and quite possible that you will end up doing further damage.
Buy a small amp for listening, $100 is tops, and either send this out, or gain some knowledge before starting on this.
Back to topic:
I do not see any hint of LM3886 here but Sanken output transistors.
No speaker relays, but at least five fuses, four of them for the dc supply.
OP will be able to check some details if he owns a multimeter and
knows how to use it, quite a few members here will be able to help.
I do not see any hint of LM3886 here but Sanken output transistors.
No speaker relays, but at least five fuses, four of them for the dc supply.
OP will be able to check some details if he owns a multimeter and
knows how to use it, quite a few members here will be able to help.
The Kinergetics usually have fuses on the outputs. Did you check them?
More generally, I still fail to understand the practical use of a 140W/channel class A amp.
Its constant power consumption should be close to 10A, even you play it at <10W (normal listening).
With due respect, the OP shouldn´t be messing with that monster of an amp but straight deal with an experienced Tech.
One has been suggested above by Rayma, that alone is a good endorsement.
Parts look hard to find and we are surrounded by fakes which look real, a specialized Tech will certainly have access to reliable parts suppliers, a great asset today.
One has been suggested above by Rayma, that alone is a good endorsement.
Parts look hard to find and we are surrounded by fakes which look real, a specialized Tech will certainly have access to reliable parts suppliers, a great asset today.
Oh it's Class A. If you read my post before typing yours you would have seen it has a fan
Yes 🙁
No, relay is fine. And fuses 🙁
I wrote to him before, no reply. I think he's done supporting things. I'll call when my migraine is gone, but I think the number is out of service.
LM3886 is in the Moon 240i for $3500. Yes, Sanken transistors, I got 6 legit replacements, buy all the transistors turn out work fine.
Yes, I checked them. I get -60V on both channels 🙁
The speakers I drive are 85db/w and in a medium sized room. Plus I like loud rock sometimes
It draws about 400w, 550VA constantly. It heats the room. It'd be great if I could turn down the voltage occasionally, but I don't mind. It sounds so good, I can pay the electricity. It's only an extra $10-15 per month.
Upon power up, it takes 12-1300 watts, 1500VA, which, over 5 minutes, falls down to 400w /550VA, where it sits (no matter what it's output). Obviously this is when it's working.
I haven't hooked up lower impedance speakers to it, but I assume it would fall to a higher number.
Last edited:
"I get -60V on both channels" - is this the speaker output ?
You did not care to describe the nature of the suspected failure so far.
This way the thread is open for all sorts of speculation.
You did not care to describe the nature of the suspected failure so far.
This way the thread is open for all sorts of speculation.
Then it could be that the positive power supply is out, check that with a meter.
There are rail fuses for each power supply polarity, per channel, four total.
Last edited:
Sorry, I got a migraine and couldn't really reply. I still feel like hell, so I should probably come back when I've recovered. When the amp worked, unhooking the power to the transistors which drive the parallel output transistors also resulted in -60v output (I recapped the psu for them, 4x8200uf caps which physically leaked and made hum). The amp was fixed and working, it broke when I accidentally soldered a speaker when the amp was on and connected.
It's Class A. When the one transistor which drives the output transistors is off, the outputs fall to nothing, which makes -60v on the output
When you feel better - tell us what you have checked, i.e. fuse, power supply voltages, etc. so we know where to start.
Also give us an idea of your electronics competency - obviously we will use more layman terms where possible if needed
Also what repair equipment do you have, if any - scope, DMM, bench power supply, etc.
I would fully expect you are better to repair, have repaired, because you will not find a beast like this now-days without a commission to a qualified designer for a bespoke build. Good luck!
Also give us an idea of your electronics competency - obviously we will use more layman terms where possible if needed
Also what repair equipment do you have, if any - scope, DMM, bench power supply, etc.
I would fully expect you are better to repair, have repaired, because you will not find a beast like this now-days without a commission to a qualified designer for a bespoke build. Good luck!