Pre Amp - Modifications

[unclejed613]

Is it power amp volume or loudness volume?I see 4 pins in the volume..!!

"loudness" change the tone balance as the volume control is turned up. below the tap on the volume control, bass and treble are boosted because at low volume the ear's response to bass and treble aren't as good as at midrange frequencies.. there is somewhat of a "standard" loudness contour, but the reason most high end systems either don't have a loudness switch or a loudness control (some high end preamps do have a loudness control) is that the filters used to do the loudness compensation often add unwanted phase shifts to the audio, especiall y between about 3khz and 20khz. a good explanation of loudness compensation is https://diyaudioprojects.com/mirror/members.aol.com/sbench/freqres3.html

 

[unclejed613]

I have never seen a TL082 or a lousy old 741 opamp in anything

TL07x and TL08x op amps both have nearly the same noise spec 16nV/sqrt Hz for the TL072 and 18nV/sqrt Hzfor the TL082. they differ by open loop gain, Aol for a TL072 is 200k, and Aol for a TL082 is 100k.

https://www.ti.com/lit/ds/symlink/tl082-n.pdf

https://www.ti.com/lit/ds/symlink/tl072.pdf

 

[audioguru]

I think TI invented the TL08x opamp with Jfet inputs but found a wide variation in noise and distortion so they "selected" the low noise and low distortion ones and called them TL07x. Many hifi manufacturers and I have always used only TL07x ones.

Although they both have the same minimum gain, the TL07x has a slightly lower typical gain but maybe that is why its distortion is much less than the TL08x.
Their test conditions are different. The conditions for the TL07x were selected for better numbers.

 

[crutschow]

I know exactly what it's for, but better quality gear doesn't use it.

So you don't have a point to your comment, just an observation?

 

[crutschow]

the loudness compensation often add unwanted phase shifts to the audio, especiall y between about 3khz and 20khz

Unwanted is not the same as undesirable.
My understanding is that the ear is not sensitive to phase (or are you referring to the proverbial golden ear).

 

[Nigel Goodwin]

So you don't have a point to your comment, just an observation?

The point is obvious, high quality audio gear doesn't provide loudness compensation, which is a kind of distortion (the signal is no longer what it was) and against the ethos of high quality.

 

[dr pepper]

I odnt think the o/p is building really expensive gear.
A long time ago I had a walkman style cassette playey, it had dynamic bass boost, occaisionally you heard the bass distort then the bass boost cut back, I like it as you could mess with the volume to get loud sound without distortion.
I googled it but couldnt find an example, but I dare say there will be some out there.