John Curl's Blowtorch preamplifier

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John, Milan, my intent was to add a different perspective (but one based on real-world experience rather than conjecture) on some of the specific issues that have been raised in this thread. Outside of providing the basis for my hands-on observations, I don't think it is appropriate to talk about the Lyra preamps per se in this thread, as this rightfully belongs to the Blowtorch and John.

Besides, I think that somewhere on diyAudio there already is a thread or two about the Lyra preamp.

regards, jonathan carr
 
John,
Jonathan,

I started a thread about the Lyra 4-2L SE which you can find at
http://www.diyaudio.com/forums/showthread.php?s=&threadid=62998&highlight=

Jonathan gave us some bread crumbs, and I tried to make a cake out of those crumbs, but I did not succeed.

I will post some news in that thread.


Sigurd

jcarr said:

Besides, I think that somewhere on diyAudio there already is a thread or two about the Lyra preamp.

regards, jonathan carr
 
Hi Jonathon. From the pictures in Sigurd's link it appears the 4-2LSE audio section is shielded five of six sides, assuming those side panels are metal (hard to tell from the shots.) Is the front panel wood treated in any way for RF rejection? It's an interesting contrast to the Blowtorch chassis.
 
Originally posted by jcarr

rdf, with apologies, but since I consider this to be John's thread, I'm trying to avoid talking overly much about the L-C here.
regards,

jonathan carr

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at least 2 of the forum members here would like to see you start an L-C thread .
 
Who started this madness?

Neither JC started this thread. I doubt if JCarr wants to discuss his linestage.
I may cop his regs on top of the circuit idea though. Putting those discrete regs so close has be help some.
I bought a 12.00 copy of HIFI+ just to drool on the pics of the L-C. Guess another 19,988.00 and I could buy the real thing.

Poor relative George
 
Bob Crump preferred 10K, but we could have used a 1 Meg pot, if we wanted to. This is because the fet input doesn't leak much or get noisy with changes of input impedance.
Most of us chose 25K, because we had tube equipment as sources as well. My unit has a buffered input that is about 50K on one switch selection. I plug my vacuum tube tuner there. Generally speaking, lower impedance pots sounded better to Bob, and he was our guru, when it came to parts selection.
 
PMA said:
John -

I have almost always heard better sound with low value pot, like 10k. My explanation is that it reduces effect of non-linear input capacitance of the input stage. What is your opinion?

Regards,
Pavel

For what it is worth (i.e. almost nothing, I'm affraid), simulation gives 30 times more distortion (0.2%) at the gates of the fets with a 500K source impedance compared with 5k source impedance.

regards.
Philippe.
 
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