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Old 7th December 2008, 04:47 PM   #41
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Don't be so fast in your judgement, PMA.

Your test does not say anything. You need to test your amps with different transformer sizes and transformer types.
I would recommend trying a large Rcore for ex. and maybe even try using two transformers - one for each channel.

Could it be that some amps are more affected by transformer size than others?

A few years back you would not have said that you could hear that a 10 cm wire can sound different from another 10cm wire.




Sigurd

Quote:
Originally posted by PMA


Superstition.
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Old 7th December 2008, 05:13 PM   #42
syn08 is offline syn08  Canada
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Quote:
Originally posted by jgedde
Syn08, That board sure is handsome. Did you etch it yourself? How did you do the solder plating and have it so smooth and level?

John
I don't etch my own boards, but order from (shipping next day):

- www.apcircuits.com (Canada) for small sizes (2 pcs. minimum order).
- www.barebonespcb.com (US) for large sizes (5 pcs. minumum order).

Shipping from US is outrageous ($75 FeDex plus 13% Canadian taxes), while apcircuits costs are much higher. I built a spreadsheet with cost/sizes and found the threshold (depending on size and number of boards). For cost reasons, I don't do solder masks and silkscreens.
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Old 7th December 2008, 05:16 PM   #43
syn08 is offline syn08  Canada
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Quote:
Originally posted by analog_sa
Cute and probably not bad sounding. Power transformer is about 20 times smaller than what i use Jung regs or not this is quite audible.
The whole thing draws 80mA from the +18V supply and 40mA from the -18V supply. Filtering is 10,000uF per rail (2 x 4,700uF). If anybody has a good reason why a large power transformer would be required, speak up. "sounds better" is not good enough for me.
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Old 7th December 2008, 05:24 PM   #44
syn08 is offline syn08  Canada
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Default Re: Re: Hps 2.0

Quote:
Originally posted by Sigurd Ruschkow
Good to see that you decided to improve the design!

The huge red caps in the upper right corner and in the middle, what types are those?

Ideas for improvement could be to have adjustable gain, and adjustable input resistors for MC cartridges (although doing this manually might be the best solution).

BTW,
what gains do you have,
and what are the overload margins?



Sigurd


The huge red caps are SuperCap polypropylene C6 in the schematic. Sorry, they are 10uF/250V not 22uF. 22uF is an overkill.

Adjustable gain could be done by just another DIP switch, will think about if there will be another release (little reason so far).

I don't think it's reasonable to adjust the input impedance externally. It could be done via relays and sone decoding logic, but price and complexity could be prohibitive. BTW, I think this design pretty much closes the discussion about good quality (and wisely used) reed relays as not good for the ultimate performance. Just another legend...

Gains are (as in the previous design) 46dB for MM and 64dB for MM. Haven't looked at the overload margins but the opamp swings are the limiting factor and the supplies are +/-18V. Due to the FB loop, the input gain stage output swing is very small.
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Old 7th December 2008, 05:27 PM   #45
syn08 is offline syn08  Canada
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Quote:
Originally posted by scott wurcer

BTW, did you really have no use for the little bit of distortion removal via the 50pf extra cap on the first amp? It's possible there is little or no difference in this circuit.
Scott,

If you are looking closely at the signal board you'll notice a couple of unused holes close to each opamp. These are provisions for the distortion cancelling caps. I may install them one day but, to my experience, the impact here will be negligible.

BTW, for noise reasons, AD797 is really required only in the input stage. For the rest, I was unable to find any measurable difference to other good quality opamps (tried lots, from OPA211 to LME49710). I liked though more AD797 in the second stage and LME49710 in the output stage.

And another BTW, the power supply uses LT1115 and I got 7nV/rtHz output noise.
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Old 7th December 2008, 08:22 PM   #46
PMA is offline PMA  Europe
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Quote:
Originally posted by Sigurd Ruschkow
[B]Don't be so fast in your judgement, PMA.

Your test does not say anything. You need to test your amps with different transformer sizes and transformer types.
Especially present audiophiles were perplexed by the test result, considering price, power input (not output), capacitors and weight of the competition device.
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Old 7th December 2008, 09:36 PM   #47
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Quote:
Originally posted by PMA


Especially present audiophiles were perplexed by the test result, considering price, power input (not output), capacitors and weight of the competition device.

At the risk of repeating myself comparing different topologies is completely meaningless with respect to the transformer effect. Glad that your amp managed to perplex. Imagine how much further the perplexion would have gone with a proper PS
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Old 7th December 2008, 11:30 PM   #48
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With this kind of phono stage, a very good way of measuring noise is NOISE FIGURE. Yes, just find an equivalent resistor that, when placed on the input, gives a 3dB noise figure. Works for me, and it takes in EQ, and everything.
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Old 8th December 2008, 12:02 AM   #49
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But audio is rarely a match terminated affair (i.e. you have minimal control over your source impedance), noise figure is more useful maybe if you are using transformers.

If you mean taking an audio band RMS meter and increasing the source until you get +3dB, that is a good way to eliminate gain and frequency response from the measurement. But the presense of 1/f noise can give errors, especially with the low boost of RIAA.
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Old 8th December 2008, 05:46 AM   #50
Bonsai is offline Bonsai  Taiwan
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I've just stumbled back into this thread. Great execution Syn08 - I like your FE tweaks especially. Happy listening!

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