Home Propeller Head Plaza

Technical and scientific discussion of amps, cables and other topics.

To John Curl, andyC and those who want a real technical discussion

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 floor

So 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:
  Parts Connexion  


Topic - To John Curl, andyC and those who want a real technical discussion - morricab 03:45:05 03/15/07 (51)


You can not post to an archived thread.