Well, guys,
Panomaniac is coming over to my house this weekend, and bringing his quiver of D amps (all Tripath chip, if I am not mistaken), and we are going to audition with the latest version of the Machine.
I have clients on the Machine who have owned and heard the Heavy Hitters in boutique audio, and are ecstatic with their five watt solution. I'm not pitching, I'm just pointing out that we have a pretty good baseline to A-B these D amps with, although not a 'clone. The D amps will be much more powerful, of course, but my own breadboard can have my eardrums kissing and making up in the middle of my skull with the 94dB Fostii, so I don't think that will be a factor.
Now, there's a slight problem here in that I have never properly heard a gain*, but there we go.
Stay tuned, film at eleven.
Aloha,
Poinz
Panomaniac is coming over to my house this weekend, and bringing his quiver of D amps (all Tripath chip, if I am not mistaken), and we are going to audition with the latest version of the Machine.
I have clients on the Machine who have owned and heard the Heavy Hitters in boutique audio, and are ecstatic with their five watt solution. I'm not pitching, I'm just pointing out that we have a pretty good baseline to A-B these D amps with, although not a 'clone. The D amps will be much more powerful, of course, but my own breadboard can have my eardrums kissing and making up in the middle of my skull with the 94dB Fostii, so I don't think that will be a factor.
Now, there's a slight problem here in that I have never properly heard a gain*, but there we go.
Stay tuned, film at eleven.
Aloha,
Poinz
Thank you all for your thoughts, I began to think the thread was dead already 
Anyway, I'm having some difficulties getting my amp together. I think I actually managed to destroy good half of it... All because I was rushing to get it up and running... I know, I should have known better, especially with my experience on computers field - but i have an impression that these new PCs tend to be much more forgiving than an amplifier
What I've done is: I wired and soldered everything just fine (voltages on rectifier's outputs were fine and everything), EXCEPT that I swapped V+ with V- on one of the amp boards. The result was burned copper path on rectifier PCB as soon as I turned the power on (this was the only visible result). I was hoping that everything might still be ok when I replace the board and put the wires as they should be.
Unfortunately, the story pretty much repeated - the same copper path as in the first rectifier went on fire.
I disconnected the rectifier board from amp boards, patched it up with two pieces of thin wire (VERY thin wire, just in case). And it seems that those diodes are tough sons of the (ekhm, ekhm) - the bridge puts out pretty much the same voltage as previously.
My bet is that the initial reverse voltage damaged the chip (and the first rectifier board by the way), and then, the newly-created internall short-circuit in that chip caused fire on the other rectifier board.
So, I was thinking why not try connecting at least a single channell (the one which was wired properly from the beginning). Does it make any sense to do it, or is it best to replace both chips and not risk another fireworks show?
Anyway, I'm having some difficulties getting my amp together. I think I actually managed to destroy good half of it... All because I was rushing to get it up and running... I know, I should have known better, especially with my experience on computers field - but i have an impression that these new PCs tend to be much more forgiving than an amplifier
What I've done is: I wired and soldered everything just fine (voltages on rectifier's outputs were fine and everything), EXCEPT that I swapped V+ with V- on one of the amp boards. The result was burned copper path on rectifier PCB as soon as I turned the power on (this was the only visible result). I was hoping that everything might still be ok when I replace the board and put the wires as they should be.
Unfortunately, the story pretty much repeated - the same copper path as in the first rectifier went on fire.
I disconnected the rectifier board from amp boards, patched it up with two pieces of thin wire (VERY thin wire, just in case). And it seems that those diodes are tough sons of the (ekhm, ekhm) - the bridge puts out pretty much the same voltage as previously.
My bet is that the initial reverse voltage damaged the chip (and the first rectifier board by the way), and then, the newly-created internall short-circuit in that chip caused fire on the other rectifier board.
So, I was thinking why not try connecting at least a single channell (the one which was wired properly from the beginning). Does it make any sense to do it, or is it best to replace both chips and not risk another fireworks show?
uncle_leon said:
I'd double check everything and then give it a go with the other board. You've already uglied up your rectifier boards anyways, so if the voltages are ok after the repair, I don't see much point in replacing good parts.
As far as trying to improve it with fancy parts, I wouldn't even bother. Get it working with standard cheap parts and you'll probably be happy with it the way it is. I've never felt the need to change any of the parts in the standard kit I got from Peter, and when I decided it was time for another amp, I did it point to point with the same parts.
Personally, I think all this stuff about resistors and capacitors sounding different is in peoples' heads (within reason of course).
If you want to blow some money on "bling" for your amp, I think it's better spent on a better volume knob and connectors.
I picked up a "PEC" brand pot from digikey at the recommendation of some others on this board, and am really quite happy with it. Not because I think it sounds better, but because it is solid, and tracks evenly between the 2 channels. Unlike the cheap pots, I expect that it will still be working perfectly in 10 years, and not all scratchy and crackly. When I'm listening very quietly, the balance isn't off centre like with a lot of cheap amps.
Also, I hate RCA connectors, so I used XLRs.
I'm not saying you shouldn't give different caps/resistors a try. I doubt I could tell the difference, and I doubt most people who claim to could recognize anything in an ABX test, but there may be exceptions.
What I am suggesting is that it's probably not the first thing to mess with. Chassis, controls, and connectors are all better places to spend your dough. (Especially if it's in short supply)
-Nick
uncle_leon said:
As Brian says, Shorted is better than open. Open shouldn't cause any problem either, since it's held to ground by 22k in that circuit if I remember correctly, but if it's shorted you know it's at 0, and shouldn't be picking up any noise across the input resistor, so you can measure your DC offset to be sure it's safe to hook up some speakers. Then hook up a cheap throwaway speaker, and play with that until you're confident you've gotten any potentially speaker frying bugs out.
-Nick
My amp sang for me today! Just one channel obviously, but it will give me some idea about its sound.
So, my initial impressions were:
- very expressive, life-like vocal (MJ, Kate Melua)
- well detailed treble
- very tight&controlled bass, extending deep into low frequencies
- sound is a bit on the bright side
- very good instrument separation
But after some more listening, I decided that there is something wrong with tonal balance. Bass seems to lack 'filling'. It does slam nicely, but it is nowhere near richness of my NAD 3225PE.
The other problem is upper-mids - they are screamy and overexposed. Add the fact, that there was way too much trebles, and you have one really shrilly&shouty amp.
And I don't like being shouted at... After hooking speakers back to NAD, the feeling was like if I was sat in an soft padded, comfy armchair. Relaxed, rich, but polite sound, enjoyable even in spite of the lack of that last detail. Gainclone seems to be much more involving, but for now, NAD remains my main amp.
So now I'm wondering WHY? Can anyone please give me a hint as to possible causes of such imbalanced sound?
I also have one less important question, as to optimal temperature for this chip. During normal, moderately loud listening it was getting more than warm, but wasn't burning. But after putting the volume really loud, it got to over 80deg.C. Is it still safe or should I install fan/larger heatsink?
Just one channel obviously, but it will give me some idea about its sound.So, my initial impressions were:
- very expressive, life-like vocal (MJ, Kate Melua)
- well detailed treble
- very tight&controlled bass, extending deep into low frequencies
- sound is a bit on the bright side
- very good instrument separation
But after some more listening, I decided that there is something wrong with tonal balance. Bass seems to lack 'filling'. It does slam nicely, but it is nowhere near richness of my NAD 3225PE.
The other problem is upper-mids - they are screamy and overexposed. Add the fact, that there was way too much trebles, and you have one really shrilly&shouty amp.
And I don't like being shouted at... After hooking speakers back to NAD, the feeling was like if I was sat in an soft padded, comfy armchair. Relaxed, rich, but polite sound, enjoyable even in spite of the lack of that last detail. Gainclone seems to be much more involving, but for now, NAD remains my main amp.
So now I'm wondering WHY? Can anyone please give me a hint as to possible causes of such imbalanced sound?
I also have one less important question, as to optimal temperature for this chip. During normal, moderately loud listening it was getting more than warm, but wasn't burning. But after putting the volume really loud, it got to over 80deg.C. Is it still safe or should I install fan/larger heatsink?
80 degrees is definitely on the hot side.
i found, by attaching a thermocouple at the heat sink right next to the chip, that thermal protection started to kick in at around 85 degrees C (at the time i had quite small heat sinks and my speakers are rated at 6ohms).
into an 8 ohm load the lm3875 does not need a very large heat sink but, if the load is less and the listening level is loud, the heat production definitely can get to levels that need a larger heat sink.
nevertheless, it has been my experience that passive cooling was always able to do the job with the lm3875.
lastly, with my first cobbled together gainclone, i found it was getting quite hot until i discovered that a single thread of my speaker wire was shorting. the amp still sounded fine with the short but the heat production was definitely increased.
hope this helps.
i found, by attaching a thermocouple at the heat sink right next to the chip, that thermal protection started to kick in at around 85 degrees C (at the time i had quite small heat sinks and my speakers are rated at 6ohms).
into an 8 ohm load the lm3875 does not need a very large heat sink but, if the load is less and the listening level is loud, the heat production definitely can get to levels that need a larger heat sink.
nevertheless, it has been my experience that passive cooling was always able to do the job with the lm3875.
lastly, with my first cobbled together gainclone, i found it was getting quite hot until i discovered that a single thread of my speaker wire was shorting. the amp still sounded fine with the short but the heat production was definitely increased.
hope this helps.
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