I was playing around with Cheever's results and plugging some 1Khz test data I have for a pretty good measuring SET amp (KR audio VA340) into his formulae. Interesting results. He claims a TAD of around 100 sounds excellent and most SS amps with feedback fall in the 1000+ range with his equation (a higher number is worse as it relates to % deviation from his derived Aural harmonics.Based on the TAD number I calculated for this amp (around 150) it should sound superb...speaker permitting (it is only a 20 watt amp). My own personal experience with this brand confirms its essentially invisible character (or lack thereof...a very good thing). This TAD suggests that the distortion this amp generates is essentially inaudible at the level I calculated it for.
Now some background:
1)
I found a FFT distortion spectrum for this amp at 1 watt output. The spectrum contains only harmonics up to 5th, with a really tiny 7th.
n=2 -50 db
n=3 -72 db
n=4 -95 db
n=5 -107 db
n=6 below noise floor (ie. -125 db in the measurement)
n=7 -118 db
n=8 below noise floor
n=9 below noise floor
n=10 below noise floorSo essentially no higher harmonics were present. The calculated THD for 1 watt from this amp is 0.31% and the S/N ratio is 98db.
2)
In using Cheever's TAD I calculated his so called Aural Harmonics using a 87 db SPL level. I chose this because 1 watt into an average sensitivity speaker, which JA from STereophile says is about 87 db/watt, gives 87db. I figure you gain 3 db for a stereo pair and if you sit about 3 meters away you have a normal listening level.
I will try to plug in some values for other amps on the market to see how they compare to this and also look a bit at their reputation for sound in the marketplace to see if there is some agreement on them sounding good and having a low TAD.
This post is made possible by the generous support of people like you and our sponsors:
Topic - To John Curl, andyC and those who want a real technical discussion - morricab 03:45:05 03/15/07 (51)
- You're talking to the wrong guy about Cheever :-) - andy_c 17:15:11 03/15/07 (1)
- Re: You're talking to the wrong guy about Cheever :-) - morricab 17:24:40 03/15/07 (0)
- Re: To John Curl, andyC and those who want a real technical discussion - john curl 15:26:21 03/15/07 (1)
- Re: To John Curl, andyC and those who want a real technical discussion - morricab 16:18:11 03/15/07 (0)
- Re: To John Curl, andyC and those who want a real technical discussion - john curl 15:16:46 03/15/07 (3)
- Re: To John Curl, andyC and those who want a real technical discussion - morricab 16:09:13 03/15/07 (2)
- 2x1W is good enough for a 91db/m speakers for a small room. - cheap-Jack 08:04:47 03/16/07 (1)
- Re: 2x1W is good enough for a 91db/m speakers for a small room. - morricab 13:53:01 03/16/07 (0)
- Are the amplifier measurements made in silence? - Al Sekela 09:45:17 03/15/07 (39)
- Re: Are the amplifier measurements made in silence? - morricab 10:07:12 03/15/07 (38)
- But then should they be? - Al Sekela 13:39:00 03/15/07 (37)
- Agreed. Here what I've done against vibrations. - cheap-Jack 09:12:47 03/16/07 (0)
- Re: But then should they be? - morricab 16:24:40 03/15/07 (35)
- Simple solution: - Al Sekela 15:45:45 03/16/07 (0)
- I have raised this question too - Jon Risch 18:30:23 03/15/07 (33)
- Re: I have raised this question too - morricab 03:08:33 03/16/07 (31)
- Where to draw the line to obtain data from "non" to "extremely reactive loads? - cheap-Jack 08:36:50 03/16/07 (30)
- worms, worms, worms. - jneutron 09:48:30 03/16/07 (29)
- The worms go in, the worms go out. - Dan Banquer 10:29:38 03/16/07 (28)
- Hey there Dan. - jneutron 06:38:52 03/19/07 (27)
- Re: Hey there Dan. - Dan Banquer 10:02:36 03/19/07 (26)
- Re: Hey there Dan. - jneutron 10:44:59 03/19/07 (25)
- Yo John - Dan Banquer 05:19:59 03/21/07 (24)
- Re: Yo John - jneutron 06:17:29 03/21/07 (19)
- Re: Yo John - Dan Banquer 06:48:46 03/21/07 (18)
- Re: Yo John - jneutron 07:13:23 03/21/07 (17)
- Re: Yo John - Dan Banquer 07:37:53 03/21/07 (16)
- Re: Yo John - jneutron 08:51:29 03/21/07 (15)
- Re: Yo John - Dan Banquer 09:55:39 03/21/07 (14)
- Re: Yo John - jneutron 10:05:43 03/21/07 (13)
- Re: Yo John - morricab 03:31:08 03/22/07 (5)
- Re: Yo John - jneutron 06:20:46 03/22/07 (4)
- Re: Yo John - morricab 15:25:02 03/22/07 (3)
- Re: Yo John - jneutron 06:34:23 03/23/07 (2)
- Re: Yo John - morricab 08:56:56 03/23/07 (1)
- Re: Yo John - jneutron 11:34:23 03/23/07 (0)
- Re: Yo John - Dan Banquer 11:05:33 03/21/07 (6)
- Re: Yo John - jneutron 11:46:10 03/21/07 (5)
- Re: Yo John - Dan Banquer 11:53:52 03/21/07 (4)
- Re: Yo John - jneutron 12:07:04 03/21/07 (3)
- Re: Yo John - Dan Banquer 12:17:56 03/21/07 (2)
- you have mail. Do us a favor, start a new thread - jneutron 13:20:02 03/21/07 (0)
- Re: Yo John - jneutron 12:44:01 03/21/07 (0)
- Come to think of it.................. - Dan Banquer 06:04:47 03/21/07 (3)
- Re: Come to think of it.................. - jneutron 07:03:06 03/21/07 (2)
- Re: Come to think of it.................. - Dan Banquer 07:29:38 03/21/07 (1)
- One subthread, dan..the other one..nt - jneutron 08:46:23 03/21/07 (0)
- Re: I have raised this question too - john curl 02:24:06 03/16/07 (0)
- Did you listen before you measure the amps or vise vera ? - cheap-Jack 07:14:39 03/15/07 (1)
- Re: Did you listen before you measure the amps or vise vera ? - morricab 07:26:54 03/15/07 (0)
- Did some more using Soundstage 10 watt data - morricab 06:35:04 03/15/07 (0)