In Reply to: RE: Where does the current come from? posted by dave slagle on August 26, 2012 at 18:16:28:
All good points...
1. "...large value caps as the last element do not give me a sound I would call musical."
I believe that's very possibly a result of hysteresis, a common characteristic of electrolytic capacitors. Regardless of the specific cause, there's a straightforward test to determine whether the last capacitor is performing correctly. Simply sweep the amp over frequency at a reasonable power level, say 1/3 - 1/2 its rated power, and monitor the last filter cap with a high sensitivity oscilloscope. Any significant audio energy present at that cap represents imperfect bypassing, leaving open the possibility of coloration. Conversely (and this is the point I really want to stress), if the audio frequency voltage across that cap is zero (or in practice, only a very tiny fraction of the voltage swing at the anode of the output stage), the cap will not color the sound. That's true even if it's 50 years old, exhibits terrible leakage, ESR and hysteresis, and has only 0.1 uF of capacitance remaining. If no audio signal appears across the last filter cap, it is physically impossible for that cap to be the cause of amplifier coloration.
2. The change of inductance over frequency (for all the reasons you mentioned) is understood. The important question is whether sufficient rejection is maintained. I believe this isn't generally a problem, if for no other reason than the decreasing XC of the last filter cap with increasing frequency. If the overall effectiveness is in doubt, one solution would be the addition of a smaller value inductor in series with the primary choke. Adding a small value "HF grade" cap in parallel with the last filter cap might also be beneficial.
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Follow Ups
- RE: Where does the current come from? - Triode_Kingdom 08/26/1220:29:36 08/26/12 (50)
- RE: Where does the current come from? - cpotl 04:26:27 08/27/12 (15)
- RE: Where does the current come from? - Stephen R 06:06:34 08/27/12 (13)
- rant warning - Tre' 08:22:20 08/27/12 (12)
- RE: rant warning - dave slagle 16:35:16 08/27/12 (6)
- RE: rant warning - Tre' 19:05:04 08/27/12 (5)
- RE: rant warning - cpotl 05:28:43 08/28/12 (0)
- RE: rant warning - dave slagle 19:29:38 08/27/12 (3)
- RE: rant warning - Tre' 20:11:25 08/27/12 (2)
- RE: rant warning - dave slagle 20:33:13 08/27/12 (1)
- RE: rant warning - Tre' 08:22:27 08/28/12 (0)
- RE: rant warning - tube wrangler 14:15:05 08/27/12 (2)
- RE: rant warning - Ray Moth 22:28:42 09/1/12 (0)
- RE: rant warning - gusser 14:53:53 08/27/12 (0)
- RE: rant warning - Stephen R 09:27:35 08/27/12 (1)
- Amen! - gusser 11:22:46 08/27/12 (0)
- RE: Where does the current come from? - Triode_Kingdom 05:53:19 08/27/12 (0)
- RE: Where does the current come from? - dave slagle 21:27:58 08/26/12 (33)
- RE: Where does the current come from? - Triode_Kingdom 05:44:21 08/27/12 (32)
- RE: Where does the current come from? - dave slagle 08:28:26 08/27/12 (4)
- RE: Where does the current come from? - Triode_Kingdom 12:36:17 08/27/12 (3)
- RE: Where does the current come from? - dave slagle 16:29:56 08/27/12 (2)
- The Last Cap - Triode_Kingdom 17:38:19 08/27/12 (1)
- RE: The Last Cap - dave slagle 19:52:43 08/27/12 (0)
- Answer number ONE of two, 2007 - drlowmu 07:39:48 08/27/12 (11)
- Absolute nonsense - Triode_Kingdom 08:17:43 08/27/12 (2)
- RE: Absolute nonsense - amnesiac 17:48:23 08/28/12 (0)
- RE: Absolute nonsense - drlowmu 09:40:33 08/27/12 (0)
- RE: Answer number TWO of two, 2010 - drlowmu 07:46:41 08/27/12 (7)
- RE: Answer number TWO of two, 2010 - mikeyb 10:45:19 08/27/12 (0)
- The circuit is wrong - Triode_Kingdom 08:26:53 08/27/12 (5)
- RE: The circuit is wrong - drlowmu 09:38:12 08/27/12 (4)
- You're in way over your head - Triode_Kingdom 12:48:36 08/27/12 (2)
- RE: You're in way over your head - drlowmu 13:23:35 08/27/12 (1)
- Yeah, yeah, heard it all before... - Triode_Kingdom 17:52:36 08/27/12 (0)
- Yes, it does! - mikeyb 10:46:26 08/27/12 (0)
- RE: Where does the current come from? - Stephen R 06:11:07 08/27/12 (14)
- Yes, yes, yes - Triode_Kingdom 08:35:22 08/27/12 (13)
- RE: Yes, yes, yes - grindstone 22:34:17 08/27/12 (0)
- RE: Yes, yes, yes - hennfarm 19:12:17 08/27/12 (0)
- RE: Yes, yes, yes - dave slagle 16:41:17 08/27/12 (0)
- RE: Yes, yes, yes - Stephen R 08:49:02 08/27/12 (9)
- RE: Yes, yes, yes - Triode_Kingdom 12:42:59 08/27/12 (0)
- RE: Yes, yes, yes - Tre' 11:17:40 08/27/12 (7)
- RE: Yes, yes, yes - Stephen R 11:30:40 08/27/12 (6)
- RE: Yes, yes, yes - Tre' 11:53:06 08/27/12 (5)
- RE: Yes, yes, yes - Stephen R 12:04:17 08/27/12 (4)
- RE: Yes, yes, yes - drlowmu 13:13:31 08/27/12 (2)
- Then Get Real - Triode_Kingdom 15:43:50 08/27/12 (1)
- RE: Then Get Real - drlowmu 21:56:51 08/27/12 (0)
- RE: Yes, yes, yes - Tre' 12:15:55 08/27/12 (0)