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-   -   old school amplifier Pioneer GM4200 SQ (http://www.diyaudio.com/forums/solid-state/213047-old-school-amplifier-pioneer-gm4200-sq.html)

muddasirwaheedmalik 21st May 2012 12:52 PM

old school amplifier Pioneer GM4200 SQ
 
hi
I have this GM 4200 pioneer car amplifier 120W per channel 4 ohm, which i plan to install to run my fronts in car, however its RCA input IC is damaged and is dead, however it has pioneer propriety DIN input as well, so it used a DIN connector for RCA leads, but it gives huge alternator and EM noise, so i used the isolation transformer, the noise is gone, the fronts are crossed in 80 Hz HP, the mid range is outstanding just like warm tube sound but the mid bass has gone a lot down i think its due to transformer. but i like the sound its smoother than Focal FP 2.150 LE rated 150 W per channel. the pioneer is way better.

Question, i put both amplifiers on without load or signal the pioneer takes 6A continous whereas the Focal takes 2.5 A, the Pioneer is built like a tank , at least three times heat sink voulme and weight than focal and has compulsory fan cooling.

Is it correct to assume that the higher queisscent current in pioneer is more of its high forward bias and more into class AB thus resulting in beyond question better SQ. ??? If yes then can we further bias the o/p transformers at cost of more warming, lesser efficiencey, lesser power but greater SQ ???

Ian Finch 22nd May 2012 02:52 AM

You may have gotten a useful reply by posting in the car audio forum.

Car audio amplifiers won't be designed to operate at any setting apart from the specification. You may well be able to adjust bias right up to class A but how long will it last with inadequate cooling and thermal runaway likely?

muddasirwaheedmalik 22nd May 2012 08:25 AM

Agreed. but does higher quiescent current draw from mains means higher bias and better SQ?

Ian Finch 22nd May 2012 10:35 AM

Quiescent current
 
First, there is no guarantee that higher quiescent current (bias) will automatically mean higher SQ - it is only a generally accepted maxim.
At high SPL, it may not seem any better at all. The bias is for two purposes; to force the devices to operate in their most linear range and have a
smooth switching transition at the crossover point for p-p pairs. This is always a compromise, assessed usually by lowest distortion measurement.

Second, amplifiers using different technology such as classes AB and D can have widely varying efficiency. A class D amplifier may draw as little
as half the current of a linear class AB amplifier for the same power output. Since modern class D car audio systems seem to operate with negligible bias current, it is reasonable that sound quality, particularly at low SPL, might seem quite poor.

Third, amplifiers of the same class with greater numbers of output devices and higher power ratings require greater bias current and power anyway.
So far, just the condition of optimum bias is discussed . The infinite possible combinations of bias, class A and subjective SQ is something for all the other threads here that already argue about this continuously ;).

muddasirwaheedmalik 22nd May 2012 12:44 PM

impressed and agreed.
But does anyone compared an old school high bias class AB amp with new trumpted amps like Focal 2.50.
P.S i bought Pioneer Gm 4200 some 20 years ago for $600, focal 2.50 today is some $400 ???

Ian Finch 23rd May 2012 01:58 AM

You need to post that question in the car audio forum to get comparisons from people who know the brands.
Car audio is a very different market and product to domestic Hi-fi and pro. amps usually discussed here.

Certainly the price of modern car audio is very cheap, just like the SQ! :D:


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