xerxes
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Post by xerxes on Apr 26, 2006 3:36:57 GMT
I hope someone can help me with this. I had a little Pimeta headphone amp and a Monica 2 DAC. I wasn't really using either as I have a WNA amp on my main system and I prefer the sound of my CD player with the internal DAC. But the other day I tried the Monica 2 DAC on a cheap, £37.99 DVD player and the results were really good. I came up with a cunning plan, I'd put the Monica 2 DAC and the Pimeta amp in one enclosure and use a 12v SLA battery to power both to give me a neat DAC-Headphone amp combo that I could plug into my cheapo DVD player. All went well until I switched it on. ;D When I have the DAC and the headphone amp running from the same battery, like this: I get a really awful noise, like massive distortion. However, if I run the Pimeta amp from it's own 9v battery, everything is fine. I've tried the amp with another source with 12v and it runs fine. So I can only conclude that there is an "interference" problem when I run the amp and the DAC from the same battery. How can I "decouple" them, should I use a series of caps on the power lines to the amp in the same way as I have for the DAC? To be honest I'm a bit surprised, I wasn't expecting this.
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rickcr42
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Post by rickcr42 on Apr 26, 2006 4:18:16 GMT
Could be the active ground channel which has been the cause of various "glitches' in that type of amp topology
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xerxes
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Post by xerxes on Apr 26, 2006 11:04:58 GMT
OK, how do I fix it?
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rickcr42
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Rest in peace my good friend.
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Post by rickcr42 on Apr 26, 2006 13:22:34 GMT
good question.
I am no fan of the topology or the overly complicated implementation of the simple (multiple parallel buffers where one will do) and never have been.
Because of that have had to go to war for expressing my honest "opinion" with those who own such amps (mostly those with no electronics clue) and the ones who actually designed the amps (well known public wars) so I am likely the last person to ask. I'm not exactly comfortable bashing a legitimate product so many seem to be happy with even though there are many threads pointing to problems that more conventional amps never have to deal with.
I suggest an email to designers and if that does not afford an answer that corrects the problem then I will have at it
rickamundo
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xerxes
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Post by xerxes on Apr 26, 2006 14:32:32 GMT
Well I know sweet F.A. about the relative merrits of the amp design, it sounds OK though.
I tried adding some caps on the power feed to the amp board, no joy, so I'm going to cop out and run the DAC board from the 12v SLA and the amp board from a separate 9v NiMH, as it was originally.
The basic objective of the excercise was to create something that I might use, even if only occasionally, from the amp and DAC which would otherwise just be left lying around. With this little set back, it won't be quite as neet as I would have liked, but still workable.
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rickcr42
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Rest in peace my good friend.
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Post by rickcr42 on Apr 26, 2006 16:25:40 GMT
audio is all about comprimses somewhere and though we would like to do a certain thing sometimes the roadblocks are more trouble than worth so PLAN-B often the rule the three channel amps place certain restrictions on what can be connected to both amp output "common" which is not a true ground as in a traditional amp and the power buss which can be sent into fits under certain circumstances so about as stand alone as it gets without taking steps to isolate any and all interactions. Like anything meant to correct one set of problems more often than not introduces another set and why I like things bullet proof and simple over "on the edge" and complicated.not for everyone but has worked for me for over thirty years of blowing shit up on the bench
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xerxes
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Post by xerxes on Apr 28, 2006 13:40:21 GMT
I completed the Headphone amp and DAC in a single box. I set it up so that both the Monica 2 DAC and the Pimeta headphone amp are housed in the same hammond enclosure, with the Monica 2 DAC running from a 12v SLA and the Pimeta running from a 9v NiMH battery. The Pimeta amp was originally housed in a little plastic enclosure with a 3.5mm jack for both the line input and the headphone output. I replaced the 3.5mm headphone jack with a full size 6.3mm jack and as I had more room, I also replaced the 4 x 470uF 16v Panasonic FC caps on the Pimeta board with 4 x 1,500uF 16v Panasonic FM caps. On the rear of the DAC-Amp I included some RCA inputs and outputs and a couple of switches so that I could use the DAC and amp together or indivitually. One switch selects whether the DAC output goes to a couple of RCA sockets on the rear or to the internal headphone amp. Another switch selects whether the headphone amp takes the signal from the internal DAC or from another 2 RCA input sockets. I'm quite pleased with the results, I listened to several CDs last night and I reckon it comes pretty close to the WNA headphone amp, the WNA sounds a little richer. But connected to the SPDIF output of my cheap, £37.99, DVD player it turns it into very listenable CD player with headphone output.
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rickcr42
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Rest in peace my good friend.
Posts: 4,514
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Post by rickcr42 on Apr 28, 2006 17:07:10 GMT
Cool,glad it it worked out without any pain NEXT PROJECT.....................................
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