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Old 13th December 2006, 05:24 AM   #1
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Default Question about the pearl RIAA stage

Hi.

I've recently aquired some pearl pcbs (nice!), but I have a question about the riaa filtration capacitors.
Compared with other phono stages, the values of these caps is quite large (as large as .15uf !), ruling out the use of 1% capacitors (such as silvered mica, or those vishay polyester ones).

What's with the large values, and are there other recommended capacitors besides the panasonic 2% caps (which I'll have to source from overseas )?
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Old 13th December 2006, 11:33 AM   #2
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The important caps seem to be .12 and .33uF. I see no reason the RIAA network cannot be recalculated for higher resistance/ lower capacitance. Some people seem to have a preference for the sound of low resistance networks but i have never been convinced. Your other option is to hand select an accurate cap out of a large batch or using a parallel combination of smaller caps. Nothing wrong with either approach.
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Old 13th December 2006, 01:18 PM   #3
lineup is offline lineup  Sweden
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thanks analog_sa
for good info in this matter


Another thing I have read from some RIAA project:

- It is a bit more important
that the RC components for left and right channel are very close in match.
than
- The actual RC resulting value (... = how close the curve follows RIAA)

analog_sa
Can there be any valid point in this?



Of course, the ideal is
that BOTH channels match AND the riaa curve follows standard closely.
But sometimes, even if parallel or series components
is not possible to achieve absolute perfect values.
It is possibly, in my opinion,
a bit easier to select out two almost identical value Capacitors, for left resp. right channel
than is to find a combination that gives exactly 75uS performance in circuit.

I would say that listening, we may more easily detect difference between left right sound/phase
than detect if the RIAA is 1 or a couple dB from standard curve.

Human hearing is using left / right ear differences- like phase and delay, I guess,
to locate from what direction a sound is coming and the distance to sound source.
We have a developed apparatus for this.
( this is one good reason we have 2 ears and 2 eyes )

Old people with not much left in hearing in one ear
will have difficulty locate a sound source, without using vision.
And if they are half-blind, too.
Only sight of one eye, then is not very funny for them.


Regards
lineup on his way gettin' old man, half deaf and half blind, hopefully!
(who would want to die too soon ...)
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Old 14th December 2006, 12:00 AM   #4
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The argument for lower resistances is based on noise. Lower values contribute somewhat less noise than higher ones--this is one of several reasons that tube circuits are noisier than solid state ones; the resistances are much, much higher.
None of which stopped me from using higher resistances and lower value caps in a phono stage I did last winter, precisely because I wanted to use 1% caps in the RIAA eq. The RIAA is pretty close to perfect. There is some noise. In an ideal world, I'd have enough time to build another circuit using low resistance/higher capacitance for comparison purposes, but I've got other circuits that are more interesting to me at the moment.

Grey
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Old 14th December 2006, 03:29 AM   #5
lineup is offline lineup  Sweden
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Arrow low noise riaa lineup analog_sa hansen grey grollins

Hello, Mister Grey

GRollins

I guess we both have to wait for
analog_sa ......... isn't this Mister C. Hansen ... ?
as you probably know as little as me
the answer to my follow up question (see post above)
in this subject


Regards
lineup 1st Chief Low Noise Engineer
at
Lineup Audio Phono Lab Designs Inc.
http://lineup.awardspace.com/

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Old 14th December 2006, 07:23 AM   #6
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Default Re: low noise riaa lineup analog_sa hansen grey grollins

Quote:
Originally posted by lineup

analog_sa ......... isn't this Mister C. Hansen ... ?

Sadly, it isn't.
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Old 14th December 2006, 07:45 AM   #7
lineup is offline lineup  Sweden
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Default Re: Re: low noise riaa lineup analog_sa hansen grey grollins

Quote:
Originally posted by analog_sa

Sadly, it isn't.



Click the image to open in full size.
Charles 'Charlie' Hansen

Quote:
I n t e r v i e w

Phillips:
And, you finally have the K-1 preamplifier to flesh out the line.

Hansen:
We're really happy with the K-1
—it disappears more than just about any preamp I've ever heard.
If you had to pick one thing that contributes to that more than any other, it would be that volume control. Everyone knows that a stepped attenuator is superior to a pot, but they've got two things against them: they're expensive and the steps are too coarse. We solved the second problem by doubling the number of steps to 46—unless you've got some really weird gain situation in your system, our stepped volume control is virtually indistinguishable from a pot. Cost is another thing entirely [laughs]. It's probably the most expensive volume control ever made—it has solid silver wipers and solid silver contacts. Everything else is second-rate in comparison.

I strongly believe in balanced circuits. The only way to accomplish volume control in balanced circuitry is to use a stepped attenuator—at least the way I figure it.

We are fanatical about the components we use.
We match every transistor we use on a circuit board
—each circuit board in a K-1 has 24 matched transistors on it.

That's a lot of work, and the phono section is even worse. Of course, that's because we use no feedback in the circuit. If we used feedback, we wouldn't have to go to so much trouble. I'm convinced that feedback is a bad idea—at best. In the best case, it's not too bad; in the worst case, it's really awful.

Phillips:
Take a minute and describe the K-1's circuit topology.

Hansen:
All FET, completely balanced from input to output, and as simple as we could make it.
It has an input stage, then a cascode, and then source-followers to give low output impedance so that you can drive things in the real world—that's it. Basically, the signal only goes through three transistors from input to output. Everything is direct-coupled; the line stage is a true DC amp.


... 24 matched (FET) transistors ...
... completely balanced from input to output ...
... as simple as we could make it ...


Yeah!
making a preamp
is pretty simple, isn't


lineup - simply



-----------------------------------------------
Reference.
( Weblink: http://stereophile.com/interviews/610/index1.html )
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Old 15th December 2006, 12:09 AM   #8
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lineup,
I'm sorry, but I'm not clear on what your followup question actually is. If you can rephrase it, I'll try to answer it.
You can either have high resistance and low capacitance, or low resistance and high capacitance. One percent resistors aren't all that difficult (or expensive) to find, but tight tolerance caps are a problem--particularly if you want some sort of film caps. I went with the polypropylene/foil 1% WIMA caps. This allowed me to have virtually perfect RIAA eq, albeit at the expense of slightly higher noise.
I have yet to find a manufacturer who makes polypropylene or polystyrene capacitors in larger values in tight tolerances.

Grey
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Old 15th December 2006, 05:39 AM   #9
steenoe is offline steenoe  Denmark
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Quote:
as you probably know as little as me
You may know little, but I am sure Grey knows what he is talking about.
That was some hell of a statement.
Somehow I found that post offensive. If you have to wait for someone to answer, why not do just that?

Steen.
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Old 15th December 2006, 05:54 AM   #10
lineup is offline lineup  Sweden
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Thumbs down steenoe

steenoe
i have read your post

i leave it to mr grey rollins to eventually report my post
or bother at all if he finds this necessary

he was kind enough to reply
and i am fully aware of his enormous knowledge
in some audio matters


anyway
he who knows it all
is not yet invented
lets not pretend he is


i am not shy to admit there are things i do not know
i am strong enough to admit my weakness
if i find it is there

as well as i am not shy to admit my ability my good knowledge
if i find it really is at hand


for sure,
i wont put my candle under cover
whatever anyone may try with me
at our 97.41% nice forum
of www.diyaudio.com


kindest regards you could imagine
from
lineup
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