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Old 1st September 2005, 08:02 PM   #11
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by nuvistor
So what are your opinions on the topology I incorrectly described as EAR 834P, specifically, flat gainstage with no NFB, followed by 75us passive, followed by 3180us/318us active?
It depends. When using stuff like ECC83's (poor linearity, poor bandwidth, very high gain) often an active EQ around it is a better choice.

Otherwise I am mainly in favour of split stage of single stage "type b"passive equalisation in valve circuitry, if linearity, output impedance etc. do not cause concern.

I'm not sure if I where to make the 3180/318uS EQ passive or the 75uS, probably the prior, not that latter and probably by varying load with transconductance input stage (no headroom penalty). But if I was I'd probably throw the 75uS back into the mix and be done.

Sayonara
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Old 1st September 2005, 08:18 PM   #12
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Quote:
Originally posted by Kuei Yang Wang
I find that FOR OP-AMP structures ONLY, the single stage design as is the AA/ElCheapo and the more recent RJM is a better choice, objectively and subjectively.
How about a single stage active EQ around two single-ended discrete gain stages? Here is a simple example with resistive loaded stages (L1, R9 represent MM cartridge), mu stages would provide more open-loop gain.
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Old 1st September 2005, 08:29 PM   #13
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Quote:
Originally posted by Kuei Yang Wang
Otherwise I am mainly in favour of split stage of single stage "type b"passive equalisation in valve circuitry, if linearity, output impedance etc. do not cause concern.

I'm not sure if I where to make the 3180/318uS EQ passive or the 75uS, probably the prior, not that latter and probably by varying load with transconductance input stage (no headroom penalty). But if I was I'd probably throw the 75uS back into the mix and be done.
"type b" refers to Jung's 1980 topology paper?

Not quite sure what you mean by the last statement, I take it you prefer 3180/318us passive as part of 1st valve load, followed by 2nd valve with 75us passive?
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Old 1st September 2005, 08:49 PM   #14
Previously: Kuei Yang Wang
 
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Konnichiwa,

Quote:
Originally posted by nuvistor
"type b" refers to Jung's 1980 topology paper?
Nope, not really. Jungs Type A & Type B are from my view the same, both subject to identical problems and hence lumped by me as "type a passive EQ" (in other words generic since the 1940's).

My "type B" (which in the context of Jungs paper would be "type C") looks like this here:

Click the image to open in full size.

It frees you from the tyranny of Lipshitz et al and sets the EQ free, at the cost of one extra resistor....

Quote:
Originally posted by nuvistor
Not quite sure what you mean by the last statement, I take it you prefer 3180/318us passive as part of 1st valve load, followed by 2nd valve with 75us passive?
I mean i would likely lump the 3180/318/75uS EQ directly into the anode/drain/collector load of a pure transconductance stage, tus obtaining a naturally equalised output which is "flat" after the first stage.

Sayonara
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Old 1st September 2005, 08:53 PM   #15
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Konnichiwa,

Quote:
Originally posted by nuvistor
How about a single stage active EQ around two single-ended discrete gain stages? Here is a simple example with resistive loaded stages
In such cases it is very much a tossup. What does the interstage slewing look like. Is the open loop bandwidth sufficiently stable with signal, etc. Some stages require looped feedback to operate well, others don't.

By STRICT GUT FEELING I would opt for passive eq in that specific case, but I'd have to do a more complete analysis to be more certain.

Sayonara
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Old 1st September 2005, 09:39 PM   #16
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KYW -

Regarding your "type B", I hadn't really noticed the extra resistor (I presume 48k7 in your schematic), I can see how this would reduce breakpoint interaction. Do you have any maths to share correlating time constants to R/C values? If not I can derive them from your example.

The example I gave with resistive loading has low open loop gain and a bit high output impedance so I agree that passive is a better practical choice. The version I use has about 72dB open loop gain (mu of 80 ^ 2, using 5755 with CCS/mu follower) so it needs loop feedback with frequency compensation. The 2nd stage Cdom Miller capacitance has the slewing burden, slew rates with only the music signal is of no consequence but scratch or pop signals could challenge slew rate. I think that "excessive" slew rate minimizes pop/scratch noise, mine clocks in at about 40V/us, should be plenty.

My generalizing opinion is that passive EQ is better with linear low gain (30 - 40 dB) stages of known and not necessarily low output impedance, active EQ is better with high gain (>60 db) stages of lesser linearity but require low network and gain stage output impedance for best performance, the final choice depends on your tastes and implementation, there is no one best solution for all cases.

I believe that active EQ is regarded as inferior because of implementations with high network and drive impedances and too low quiescent current, Dyna PAS for example. Graham Slee and Nelson Pass probably do it right given their reputation, they use active EQ.
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Old 1st September 2005, 10:23 PM   #17
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Quote:
Originally posted by Kuei Yang Wang

My "type B" (which in the context of Jungs paper would be "type C") looks like this here:

Click the image to open in full size.

It frees you from the tyranny of Lipshitz et al and sets the EQ free, at the cost of one extra resistor....

What parts could work well in order to get a silicon discrete or IC version to replace the tubes?


Carlos
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Old 1st September 2005, 10:43 PM   #18
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by nuvistor
Regarding your "type B", I hadn't really noticed the extra resistor (I presume 48k7 in your schematic), I can see how this would reduce breakpoint interaction. Do you have any maths to share correlating time constants to R/C values? If not I can derive them from your example.
Well, 31K6//316K = 28k7

28K7 + 48K7 = 77k4

77K4 * 1nF = 77.4uS

The rest is the difference between theory and practice... ;-)

Quote:
Originally posted by nuvistor
My generalizing opinion is that passive EQ is better with linear low gain (30 - 40 dB) stages of known and not necessarily low output impedance, active EQ is better with high gain (>60 db) stages of lesser linearity but require low network and gain stage output impedance for best performance, the final choice depends on your tastes and implementation, there is no one best solution for all cases.

I believe that active EQ is regarded as inferior because of implementations with high network and drive impedances and too low quiescent current, Dyna PAS for example. Graham Slee and Nelson Pass probably do it right given their reputation, they use active EQ.
Yeah, I'm more or less in agreement, high network impedances are not per se bad though.... It's all in the implementation.

Ciao T
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Old 1st September 2005, 10:50 PM   #19
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Konnichiwa,

Quote:
Originally posted by carlmart
What parts could work well in order to get a silicon discrete or IC version to replace the tubes?
Non, most solid state stuff lacks the headroom to use passive EQ well.

Easy calculation, LP nominal = 5cm/S, LP standard maximum = 25cm/S (RMS), so expect normal 14db more output from the cartridge than nominal 5cm/S rating. If you have enough gain your headroom goes unless you go active EQ or push the supply voltages into Valve territorry, where you may as well use valves.

Sayonara
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Old 1st September 2005, 11:16 PM   #20
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Quote:
Originally posted by carlmart



What parts could work well in order to get a silicon discrete or IC version to replace the tubes?


Carlos
Look at -

KYW's L'Pacific Optime

Wonder why he didn't mention it, it's almost the same topology as the tube version.
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