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I need a phono stage for my system, The L3 phono kit looks really appealing except for one thing. A good friend who is very knowledgeable is concerned that the out put impedance, based on his knowledge of tube circuiry, of the L3 may be too high for my GeorgeMark Audio line stage with an input impedance of something over 100K ohms. Otherwise he likes the design.
Does anyone know the output impedance of the L3 phono? Or can anyone comment on its suitability in my system, either positively or negatively?
Thanks for any info.
Follow Ups:
Allen,
I would estimate that the output impedance of the second stage is 27K-30K (since there is no overall loop feedback with the passive RIAA equalization). Driving a 100K load would not be ideal; a cathode follower or transformer would be needed for best results. Luckily, there is plenty of room in the chassis to add either option. Murray or I can easily draw up a cathode follower to meet your needs
Gary Muffley
Do you realy think it is around 30k output imp.?
Thats realy high!
I used the L3 phono with the L3 pre and that was oke
But i ordered a new preamp and this one have 10k input imp.
I think this will never work together.
What is the best thing i can do now?
Edits: 02/22/12
The tube manuals list the nominal plate impedance of a 12AY7/6072 tube as 44k ohms. The L3 has no loop feedback to lower output impedance, but the cathode bypass cap will lower the impedance slightly. If you run a 12AY7 with 145-150 VDC on the plate with an idle current of 1.0 MA you can calculate the plate resistance to be 27K ohms. If you run more current (3-4 MA), you might be able to get the plate resistance as low as 20K; still, that is not ideal when driving a 100K line stage.
hello Gary
What is a good solution then?
I used the L3 phono a few years with the L3 preamp this preamp has an input impedance of 100k and it sounded very good.
i think there is no problem with driving 100k
But my new pream has 10k input imp.
would a buffer stage then a good option?
are there kits on the internet?
There are two main options: wire up a cathode follower or use a transformer. You can wire up a cathode follower with as little as one tube, one resistor and a capacitor.
Can you please kindly draw up the transformer use?
Thanks and regards
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