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Old 29th September 2004, 11:42 AM   #1
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Default Re: New error correction amp

Last night, between my arrival to and departure from Prague, I had the privilege to listen to Pavel’s (PMA) new amplifier, discussed in the thread with similar title: New error correction amp

As I started enthusiastically writing this thread, I realized that I would be unable to share my impression with the sound of the amplifier because English, as well as many other languages, is lacking adjectives and adverbs describing sound. The best I can do is to present some parallels and hope that some of you had similar experiences, thus will be able to understand.

We have listened to Beethoven’s “Emperor’s,” which starts with a piano. My initial impression listening to the amplifier was similar to a relevation that I had had when I had replaced lower efficiency (86 dB/1W/1m) speakers with high efficiency (105 dB/1W/1m) ones. The timing when the hammer hitting the strings was clearly defined; the amplifier introduced no “uncertainty” and “fuzziness” about or “smearing” of the notes/tones.

After the piano introduction, the orchestra joins in, and the same feeling of “non-fuzziness”, “non-confusion” of the sound, so difficult – at least in my experience – to achieve, was still present. It reminded me of the one time when I heard and saw Wiener Philharmonics. Watching the violinists, they all started and stopped the bows' movement precisely at the same time. There was no “smearing” caused by some of the violinists starting and others joining in later on or vice versa. The word precision comes to mind, both for the Wiener Philharmonics and Pavel's amplifier.

Before the “bottle-head” crowd misreads the term “precision” as “dry and analytical, typical of solid state”, please be advised that I had on an extended loan several of Steve Bench’s tube amplifiers (http://members.aol.com/sbench101/) and I own Hugh R. Dean’s AKSA 55, all amplifiers generally renowned for excellent musical quality. And with due respect to both Steve and Hugh, to me Pavel’s amplifier is preferable.

Because Pavel generously published the schematics, those of you who have the skills to build the amplifier from scratch can do so, and judge for themselves, whether my impression coincides with theirs. As I am not in such a category, I must just hope that Pavel will find some time and build an amplifier for me. (Hint, hint).

M
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Old 29th September 2004, 05:53 PM   #2
ppl is offline ppl  United States
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Default Dynamic Biasing

I noticed similer result going from a standard Dimond Buffer to ine of the dynamic bias type using the same semi's, I belive this type of ouitput stsge offers signifigent sound inhancements over a conventional Class Ab1 Bias. The icq in the output transistors were set the same for a faire comparrison.

Measurements of my standard Dimond buffer result in a THD of .08%@ 1V driving the 63 ohm Sony MDR7505 Headphones, to .0042% driving 300 ohm Koss Pro4AAT.

Measurements on the Dynamicaly bised version results in a constant THD of abour 0.005% with both the sony and the Koss. This would imply the dynamic biasing is doing its job and maintaining an ideal bias at any point in time and over a wide impedance range.

The sound is improved alot with Grados, Bass on some headphones sutch as the Grados HP-1 appeared to go about an octave deeper. another unexpected bennifit is on the Senn HD588-HD600 headphones. These transducers are typicaly rolled off at the top, however the Dynamic bias version qappears tooffer and extended frequency response at the top that really brings thgese heardpones to life.

The down side to the Dynamicaly Biased version is its less stable than a standard class Ab Dimond buffer
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File Type: pdf triad dynobias v 1.4a schematic.pdf (31.6 KB, 721 views)
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Old 30th September 2004, 08:31 AM   #3
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Dear ppl,

is the buffer in your attachment the one that replaces the Intersil HA3 in the "PPA" headphone amplifier?

Thank you,

M
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Old 30th September 2004, 08:58 AM   #4
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No that is the Dyno Bias version that head wize member is Beata testing . the Buffer larry makes is the attached 1.0A
see this post on Head-fi for that Beta testers preliminary comparrisons to the normail biased 1.0A http://www6.head-fi.org/forums/showt...light=DynoBias
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File Type: pdf ppa triad sch v 1.0a.pdf (29.0 KB, 468 views)
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Old 30th September 2004, 12:00 PM   #5
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Dear ppl,

thank you for the information and the link.

M
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Old 11th September 2005, 05:01 PM   #6
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How did you like it, John W?
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Old 11th September 2005, 08:34 PM   #7
JohnW is offline JohnW  Hong Kong
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Being a Hi-Fi designer is much like being a cobbler, whose children have no shoes – not one piece of my “system” is - shall we say complete.

Anyway, I need a “Analogue” amplifier for listing tests during FPGA evaluation & development of digital filters – and my old “Sample 104” a simple design for a Cambridge Audio amplifier who’s retail would have been about GBP129 (back in 1992) was REALLY not cutting it anymore – no matter much I have beefed up the PSU over the years.

For such a very simple design it’s incredibly good, it’s a dual Mono layout – with small independent PSU’s per channel, with bulk reservoir caps of only 4700uF per rail. Now I intended to use this amplifier to drive my Martin Logan Aeons – which being electrostats are never going to be the easiest load (and not with an amplifier with less then 20000uF Bulk caps) – but this little amp drove them remarkably well, with the deepest controlled base and very good treble transients (cymbals etc). This goes to show advantages of error-correction power stages, that even with a “small” PSU, the amplifiers performance can still be extremely good.

This amp completely blows away my old “Sample 104” – and with a much simpler design – what do I miss?

If anything is lacking it’s the VERY fine detail – I have that voice in the back of my mind saying “typical OPAMP sound”. I love electrostats because they can resolve everything, such as background voices in recording studio (if you sit in that 5mm wide “sweet spot” and with your head bolted in a vice) – I can just about still hear them – but only because I know they are there – highlighted by earlier systems. I would bet that replacing the OPAMP with a discrete circuit would gain that extra missing dimension of detail.

But no question about it – for the next couple of weeks, this amp will be singing its little heart out, helping me design the over-sampling filters for my digital amplifier! I might even try it on my Martin Logans CLSIIz – if I'm brave and search for them under the staircase cupboard! Who’s knows - what are they 0.5 Ohms at 20 KHz?…. And driving them with an Amp with less then 20000uF caps and about ~ 20W…. hey its doing a remarkable job with the Aeons!

Pavel, thanks very much for the chance to try your amp – a real great little design!

Its nice to listen to another designers product & have respect!

John
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Old 12th September 2005, 03:11 PM   #8
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Hi, JohnW,

You built NP-PMA? Original NP-PMA consist of current feedback front end and NP-PMA EC itself. Which contributes more to the sound you are hearing, the current feedback characteristic, or the NP-PMA EC characteristic?
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Old 12th September 2005, 03:48 PM   #9
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Quote:
Originally posted by lumanauw
Hi, JohnW,

You built NP-PMA?
No, he borrowed mine.
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Old 12th September 2005, 03:51 PM   #10
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John,

nice to read your small review, thank you. I am very glad that the amp can help you.

I am thinking about lending you a preamp as well, good active preamp is very important.

Cheers, Pavel
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