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Old 18th June 2012, 05:11 PM   #291
RNMarsh is offline RNMarsh  United States
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[QUOTE=Telstar;3063927]Currently the only option for close matching is to use monolithic dual jfets of a single polarity, such as LSK389, which are in production.
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I have a few of the LSK389. Need the complements that really are good complements.
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Old 19th June 2012, 10:05 AM   #292
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Originally Posted by RNMarsh View Post
Rats! All out of that one from my arsenal. I'll have to restock. But. If you dont come up with a working, different topology in, say, a week, then I'll take same type but from Rosebank (1979 - last year in production - Scotland).
Why does it have to be a different topology, the prerequisite of no caps or servo would automatically make me think of the 80s type french circuit with obvious use of Jfets. I would obviously start there and try to reduce the circuit to two stages. The french circuit is the same circuit overall than the JLH except for the use of Jfets anyway.

Ive just thought of a way to get rid of the two caps in JLH circuit although it will probably worsen noise figure, this is one parameter your H amp cant come close to the performance of JLH though. Ill just have to check the THD figures first but I can see them being same as original circuit.
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Old 19th June 2012, 01:52 PM   #293
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I should have sent a note out with the PCB's I had made up. The Node "0", traces are cruciform, connecting the input, output and electrolytic grounds together. I provisioned that the copper pour could be attached to Node "0" nearer the input, nearer the output, or to the chassis.

Mine are humming along quite nicely with separate LT1963A/LT3015 Regulators for each channel.

Click the image to open in full size.
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Old 19th June 2012, 02:04 PM   #294
Telstar is offline Telstar  Italy
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Quote:
Originally Posted by RNMarsh View Post
Quote:
Originally Posted by Telstar View Post
Currently the only option for close matching is to use monolithic dual jfets of a single polarity, such as LSK389, which are in production.
I have a few of the LSK389. Need the complements that really are good complements.
I meant to use a single differential, like done here:
PRE4 N-JFET preamplifier
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Old 19th June 2012, 06:35 PM   #295
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by homemodder View Post
Why does it have to be a different topology, the prerequisite of no caps or servo would automatically make me think of the 80s type french circuit with obvious use of Jfets. I would obviously start there and try to reduce the circuit to two stages. The french circuit is the same circuit overall than the JLH except for the use of Jfets anyway.
Ive just thought of a way to get rid of the two caps in JLH circuit although it will probably worsen noise figure, this is one parameter your H amp cant come close to the performance of JLH though. Ill just have to check the THD figures first but I can see them being same as original circuit.
I dont see any point to using same topology but different transistors. Its the topology that allows such excellent performance and is the best basic topology I've found for audio... IMHO. You can optimize it for low noise, better psrr, high voltage, cascoding, rf and all the rest. This one was for headphone amp but also to try the second part of the article on auto EQ of headphones which is even more audible. -RNM

Last edited by RNMarsh; 19th June 2012 at 06:39 PM.
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Old 19th June 2012, 06:44 PM   #296
RNMarsh is offline RNMarsh  United States
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Originally Posted by Telstar View Post
I meant to use a single differential, like done here:
PRE4 N-JFET preamplifier
very nice and a possible contender -- schematic somewhere?
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Old 20th June 2012, 11:44 AM   #297
Unomas is offline Unomas  Spain
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Quote:
Originally Posted by jackinnj View Post
I should have sent a note out with the PCB's I had made up. The Node "0", traces are cruciform, connecting the input, output and electrolytic grounds together. I provisioned that the copper pour could be attached to Node "0" nearer the input, nearer the output, or to the chassis.

Mine are humming along quite nicely with separate LT1963A/LT3015 Regulators for each channel.

Click the image to open in full size.
Hi Jack, could you please elaborate a bit more about this? When is the hum appearing, when no connection done or when connecting and, in this late case, in which of the three possibilities?

Your advice is to connect on both points as in the attached photo?

Thanks for your advice and great work with PCS's

Javier
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Old 20th June 2012, 01:29 PM   #298
coluke is offline coluke  Italy
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Well, I know I'm not going to win the Glenlivet bottle, nevertheless this simple CFA almost meets Richard's requirements. Beware: I'm talking about simmed figures (with Cordell's models) - still have to try it to see if it works that well even with real components.

1. about 60 dB loop gain up to 20 kHz or so
2. 0.0013% THD from 20 Hz up to 20 kHz @ 1 Vrms into 30 ohm
3. only a couple of bootstrap caps, and another couple to bypass transimpedance emitters stage (needed to keep OLG high)
4. DC offset and drift good (although not amazing) even with pure DC coupling and no servo
5. Aargh! 10 active components...
6. about -110 dB of S/N ref 1 Vrms out - could probably be improved employing low noise BJTs
7. harmonics above 3rd are < -140 dBc @ 1 Vrms into 30 ohm
8. closed loop gain 12 dB
9. Zout < 10 milliohm (approx)
10 . so it seems
11. ultra low cost parts, and quite easy to obtain

Needs further development, but it seems promising (and it could drive low Z headphones, too... ).

Ciao,

L.
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Old 20th June 2012, 01:36 PM   #299
Telstar is offline Telstar  Italy
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Originally Posted by RNMarsh View Post
very nice and a possible contender -- schematic somewhere?
unfortunately not public (and I dont have it).
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Old 20th June 2012, 04:29 PM   #300
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Originally Posted by Unomas View Post
Hi Jack, could you please elaborate a bit more about this? When is the hum appearing, when no connection done or when connecting and, in this late case, in which of the three possibilities?

Your advice is to connect on both points as in the attached photo?

Thanks for your advice and great work with PCS's

Javier
It was Joan Sutherland doing the humming last night...I only meant to use the verb "figuratively".
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