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Class D Switching Power Amplifiers and Power D/A conversion

Beomaster refit - controversial?
Beomaster refit - controversial?
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Old 8th September 2019, 06:49 AM   #1
tallnutt is offline tallnutt  Australia
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Default Beomaster refit - controversial?

Hi All,

I need some opinons from all you experts. I have a 1972 Beomaster 3000 system which is incredibly beautiful to look at but I think it's time to refit it. I've repaired numerous components over the years but I can't live with the intermittent faults, noise and drop outs it suffers from. Also, every time I change components, the traces break becuase they are corroded. It'd be easier to just get a new amp but I don't want this system to just sit unused.

I'm not sentimental about analog amps and I think the class D projects I've bult for boom boxes, garage amps etc. sound much better.

So what I want to do is refit it - keeping the FM/AM tuner board, which works fine, and replacing the preamp and power amps with class D. I also thought putting in a computer PSU could supply all the voltages it needs. I'm not an electronics expert but fairly skilled with a soldering iron and audio builds in general.

What are your opinions about the best pre-made boards to buy for the amp and pre-amp (I need a preamp for my turntable)? The power amp needs to be around 50 W (RMS) per channel for my purposes. I'd also fit a blutooth module. The boards need to have analog pots that I can rewire to the existing slider controls on the front panel (Vol, Bass, Treble).

Thanks!

Theo
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Old 8th September 2019, 08:06 AM   #2
jan.didden is offline jan.didden  Europe
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Sacrilege! ;-)

Jan
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Old 9th September 2019, 02:01 PM   #3
tallnutt is offline tallnutt  Australia
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What I really only need to know is, what is the best diy option for a phono input?


Thanks.
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Old 9th September 2019, 05:33 PM   #4
Mark Tillotson is offline Mark Tillotson
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Well I'm not sure how you'd replace a preamp with class D, surely that's a job for a digital section, ie ADCs and a DSP. A decision to make is does the power amp take an analog or digital signal in?
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Old 9th September 2019, 09:07 PM   #5
tallnutt is offline tallnutt  Australia
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Analog input. The preamp wouldn't be class D. Just need pointers to designs and boards.

Thanks
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Old 9th September 2019, 09:46 PM   #6
Guerilla is offline Guerilla  Denmark
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I would get an amp with aptx-hd for bluetooth. Not just oldfasioned aptx. Maybe try to find one that works good with a 19 volt laptop supply. Or find out which voltage you get from the original PS and find a board that runs well with that.
Cheers!
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Old 12th September 2019, 06:46 AM   #7
Turbowatch2 is online now Turbowatch2  Germany
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Quite a while ago, an, at that time reputable German Audio Magazine, tested expensive Phono pre-amps. The clear winner was a high quality DIYS phono PCB, that was planted directly into the record player, connected to the magnet with the shortest wire possible. The raw-power supply (rectification and first buffer caps) was placed out of the player.
If you find some high grade phono pre, maybe from Pass Labs or else, this would be a very interesting option.
The amplified phono signal can be handled like any line source and is much less prone to beeing disturbed.

Maybe not an idea for anyone, but sure an interesting option.
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Old 12th September 2019, 08:20 AM   #8
Guerilla is offline Guerilla  Denmark
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@Turbowatch2 That sounds like a good idea to fit RIAA by or under the turntable. Tallnutt could search analogue section or ask there for advise which circuit to build or buy.

@Tallnut Did you find out which voltage the Beomasters poweramp section works on?
Cheers!
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Old 12th September 2019, 09:25 AM   #9
tallnutt is offline tallnutt  Australia
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Hi, thanks for the advice. I had thought of putting the preamp in the turntable, I will see how It goes. I don't have a big budget so I ordered one of the Chinese little bears. I plan to keep its power supply separate now. The Beomaster amp runs off 32V I think, but I am not keeping the power supply.. it has a lot of hum, probably due to its age. I already changed the caps and rectifier on it, which blew a few years ago. I have a 20V laptop PSU that I will try out. Waiting for the preamp to arrive at the moment.

I picked up a Technics SA250 amp yesterday to use as a stop gap, but actually pretty impressed by it, although I think the bass is a bit 'flat'.

Theo
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Old 12th September 2019, 10:57 AM   #10
Turbowatch2 is online now Turbowatch2  Germany
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Since I tried some very cheap Alibaba / eBay SMPS boards, Im cured of using these old laptop junk. You never know how it does with audio.
You get these in any voltage and they are remarkable silent.

Example:
DuoWeiSi 36V 250W 7A Switching Power Supply Board Audio Power Supply AC DC Isolated Power Module 220 to 36V-in 3D Printer Parts & Accessories from Computer & Office on Aliexpress.com | Alibaba Group

AC-DC 100V-265V Bis 36V 5A Schaltnetzteil Adapter Switching Power Supply SMPS K1 | eBay
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