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Old 19th January 2015, 09:18 AM   #1
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Default DIY power amp 250 - 300W @ 4Ohm

Hi people,

I'm concidering getting a two-channel power amp to complement my Rotel RSX1067. It's rated as 100W into 8 Ohms, 4Ohm spec is unknown to me. It's currently driving a pair of Dynaudio Special 25's. I believe these speakers deserve a better power amp with greater current capability, more head room and less distortion. For this power-amp task, there are a few options.

A hifi-store in my town sells a brand new Bryston 4B-SST2 for about €4000,- which, unfortunately, is above my budget. Although it sounds like a steal! Another (more fun) route would be to DIY. I'm looking for something with the stability, sound and reliability of a few well known amplifiers, like Bryston, Musical Fidelity, Myryad, Hegel, etc. All are respected for their sound- and build quality and reliability.

I've seen the thread on the Honey Badger power amp, which seems like good amp with some tuning options.
Another option is a 1996 design from the Dutch magazine Elektuur:

http://www.hobbielektronika.hu/forum...e.php?id=85281

According to the article, this is a potent amp with good specs. What sort of "worries" me, however, is the fact that they state the amp is a trade-off between reliability and simplicity. Sound quality was not the main goal, although it's supposed to sound quite good. But, without hearing it, that's quite difficult to judge. I have a feeling, however, that this amp can also be tweaked and optimised by selecting alternative components that have better audio-related properties (same value equivalents, of course) to make it sound even better. Perhaps more power supply capacity, for starters?
I already have two PCB's for this amp, made them long ago, when I was still studying electronics in school. I've never done anything with these boards, nor have I done much with my education...

I don't have much building experience and - tools. Both amps, I think, are more or less equally challenging to build. My question to you, more experienced builders and electronics engineers, which is the better amp, spec and sound wise? What other things are there to take into account?

Last edited by Jamesblond; 19th January 2015 at 07:37 PM.
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Old 19th January 2015, 07:06 PM   #2
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Since the amplifier is not designed by Giesberts it actually has the potential to be ok ...

Input stage is a fine part
the complete design is simple yet well designed
Combination of rail supply versus ops used is also fine
choice of semis is poor to today's aspects ,,,it could be done better
The presence of a limiter in the output will never make a HI END amplifier and in the way the limiter is designed will not also make a pro amp ...

In general its an OK amplifier expect it to be made easy last for a long time and play very well but not perfect
Remember that for a ""Hifi "" use the limiter might be erased from the circuit Obviously you will have safety issues if the amp is pushed but to make you feel better many of the so called hi end amplifier have not these types of circuits behind them ...

There is room to play in this amplifier and many can be done to alter the sound of the amp for the best. faster outputs , other drivers other types of compensation can make some difference from the first look .


Kind regards
Sakis
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Old 19th January 2015, 07:29 PM   #3
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Hi Sakis. Thanks for your reply!

What would be needed to get the PA300 up to date? Can that be done without altering the pcb? And can the limiter be bypassed without too much hassle and without altering the pcb?

How would the PA300 compare to the Honey Badger? The latter does not use an OpAmp in the input stage. I've been told that's supposed to be "better" in terms of sound quality. But at this point any one of you knows more than me about this stuff. So any and all feedback is welcome.

Thanks!!!

Last edited by Jamesblond; 19th January 2015 at 07:34 PM.
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Old 19th January 2015, 08:17 PM   #4
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That is answer that cannot be given with in 5 minutes ..One have to study and recalculate a few things for a viable suggestion

For the limiter just skip these parts
T4, T5, R20,R21, R22,R23 C15 C16 D3, D4, D5, D6

Many of us do not like to use MJE340 and 350 for VAs application actually a video signal transistor ..likewise drivers MJE 150xx series are notorious for being extremely rugged though very hard on sound and very "metallic"

Many of us prefer 2SA and 2SC series from Toshiba that sound far smoother
TO247 outputs can be also used without serious modifications on the same pcb and using them will give you the ability to work with much higher ft from 3 MHZ of the 15003 to almost 30 that modern transistors offer ...

Altering the semis for the best will make a better sounding amplifier but astronomical speed doesn't come for free Additional compensation in the drivers might be needed and bias scheme might need a touch also to cop with the new drivers...

Kind regards
Sakis
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