In Reply to: RE: grid resistors first stage of amp posted by Jim McShane on June 24, 2012 at 13:16:33:
Jim is spot on about the 1:10 rule. We want waveform fidelity, not power transfer in small signal situations.
Another factor to take into account is Miller capacitance. The 470 KOhm parts previously mentioned are fine with a pentode I/P stage, but can easily cause HF info. to be rolled off, with a 12AX7 section in the I/P stage.
Modern, digital, sources will drive a 10 KOhm load, as that's an IHF "standard". FWIW, I use voltage followers in my designs to do that too. The old standby of a 600 Ω line impedance did not come into being by accident. ;>)
Eli D.
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Follow Ups
- RE: grid resistors first stage of amp - Eli Duttman 16:46:55 06/24/12 (15)
- RE: grid resistors first stage of amp - Naz 06:28:51 06/25/12 (3)
- RE: grid resistors first stage of amp - Eli Duttman 18:16:29 06/25/12 (2)
- RE: grid resistors first stage of amp - Tre' 17:17:39 06/26/12 (0)
- RE: grid resistors first stage of amp - Naz 21:36:24 06/25/12 (0)
- RE: grid resistors first stage of amp - Tre' 17:28:15 06/24/12 (10)
- RE: grid resistors first stage of amp - Jim McShane 13:14:33 06/25/12 (9)
- RE: grid resistors first stage of amp - Tre' 14:34:57 06/25/12 (8)
- RE: grid resistors first stage of amp - Jim McShane 15:41:48 06/25/12 (1)
- You may be right - Tre' 15:56:33 06/25/12 (0)
- It dawns on me that the grid resistor does lower the source impedance but... - Tre' 14:55:16 06/25/12 (5)
- A triode driver example - Tre' 15:30:26 06/25/12 (4)
- RE: A triode driver example - Triode_Kingdom 16:26:14 06/26/12 (3)
- RE: A triode driver example - Tre' 20:01:05 06/26/12 (2)
- RE: A triode driver example - hennfarm 21:14:01 06/27/12 (1)
- RE: A triode driver example - Tre' 09:13:50 06/28/12 (0)