RE: How low do we have to go???

Posted by Paul Joppa (P) on November 19, 2014 at 17:06:12

In Reply to: How low do we have to go??? posted by TomWh on November 19, 2014 at 08:39:35:

#1 (theory) transients such as the thwack of a tympani or pluck of a bass guitar string actually have no practical lower limit - they have at least SOME energy pretty much all the way down.

#2 (experiment) the human ear loses sensitivity as the frequency drops, but the threshold of hearing does not meet the threshold of discomfort until 2Hz.

#3 (theory) the small signal response is relative to the parallel combination of the plate resistance and the reflected speaker load. However, the large signal response (power band) is determined by the load impedance - when the inductive impedance equals the load impedance, the tube has to deliver 1.4 times the normal current, which it usually can't if the amp is designed for maximum efficiency at the design impedance.

#4 (in my experience) A value of 3 henries per kOhm load, or around 10 henries per kOhm plate resistance, usually sounds adequate on most music most of the time but it's not hard to find occasions or music which show the limitation. Twice that makes it hard to detect as a bass-specific issue and the improvements with further inductance increase have a different, more subtle character.

#5 (in my experience) I built a parafeed preamp (6BL7 into Magnequest nickel B7s at 5K nominal) with switcheable inductance and compared 20-24-40-48 henries plate choke and a current source load. The differences were subtle but audible, and several people all came to the same conclusion - more impedance is better.

#6 (theory/experience) transformers get very big very fast when you increase inductance, and the treble response suffers, one way or another. In my experience, the best treble I've heard came from a 3K transformer with only 10 henries inductance.

Not much help, was it? :^)

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Follow Ups Full Thread

Topic - How low do we have to go??? - TomWh 08:39:35 11/19/14 (26)

RE: How low do we have to go??? - drlowmu 11:23:23 11/23/14 (12)

RE: How low do we have to go??? - Lew 12:00:17 11/24/14 (1)

RE: How low do we have to go??? - drlowmu 15:11:55 11/24/14 (0)

Never trust listening tests alone for this - Triode_Kingdom 23:36:52 11/23/14 (9)

+1 (nt) - Tre' 12:47:25 11/24/14 (0)

RE: Never trust listening tests alone for this - drlowmu 10:54:49 11/24/14 (7)

RE: Never trust listening tests alone for this - Triode_Kingdom 21:08:28 11/24/14 (4)

Do you ever get tired ?? - drlowmu 21:30:01 11/24/14 (3)

RE: Do you ever get tired ?? - Triode_Kingdom 21:42:53 11/24/14 (2)

RE: Do you ever get tired ?? - drlowmu 15:47:19 11/25/14 (1)

RE: Do you ever get tired ?? - Triode_Kingdom 10:22:22 11/26/14 (0)

RE: Never trust listening tests alone for this - cpotl 16:53:04 11/24/14 (1)

RE: Never trust listening tests alone for this - drlowmu 21:13:48 11/24/14 (0)

RE: How low do we have to go??? - Sherwood Forest 08:50:49 11/20/14 (1)

see my post below - Ralph 09:16:13 11/20/14 (0)

Solution (mine at least) - Chip647 06:51:28 11/20/14 (5)

You got that he's talking about phono reproduction, right? nt - Ralph 09:12:27 11/20/14 (3)

No, I guess that the concept of choke loading plates on a phono stage - Chip647 15:35:26 11/20/14 (1)

RE: No, I guess that the concept of choke loading plates on a phono stage - Donald North 23:38:26 11/21/14 (0)

Sorry about that, nt - Lew 14:27:07 11/20/14 (0)

In a similar vein - Lew 07:26:23 11/20/14 (0)

RE: How low do we have to go??? - DanK tubes 18:34:06 11/19/14 (1)

Thanks for the link, however - Ralph 09:10:44 11/20/14 (0)

RE: How low do we have to go??? - Paul Joppa 17:06:12 11/19/14 (0)

RE: How low do we have to go??? - Ralph 09:26:59 11/19/14 (1)

You summed it up (no pun intended!) correctly... - Dman 05:50:21 11/20/14 (0)

Follow Ups

RE: How low do we have to go??? - Paul Joppa 17:06:12 11/19/14 (0)

RE: How low do we have to go???

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