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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 20th September 2019, 02:29 AM   #31
Turbowatch2 is offline Turbowatch2  Germany
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The amp in the above configuration is 100% dead silent. It is only a test build up. Use a cordless drill to do the wires like that. It is really important, as it keeps a lot of noise in the wire and away from the amp. Dontīs use left overs from the garbage can. For final installation I use simple house installation, solid copper wires, stripped of the outer insulation and drilled. It will stay the way you put it and has quite some serious diameter. Signal connections may be screened 2-pole wire with the screen only connected at one side (the sending device) or drilled, wire of smaller diameter, as well.
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Old 20th September 2019, 02:38 AM   #32
Turbowatch2 is offline Turbowatch2  Germany
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DSP
As you can see it is fresh from the box. I have to figure out if you can program any pot to act as signal source for the DSP. I hope so, as it is programmable
If not I have to do some serious modding to the remote.

This is DIYS: You plan, collect, try, learn and sincerely hope to finally find the time to put it all together...

Found this at Sure Adau 1701 external Potentiometer - Q&A - SigmaDSP Processors and SigmaStudio Development Tool - EngineerZone

You might get an idea how this DSP stuff works. As I wrote, you do not need to use it more than once...
Attached Images
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File Type: png pot_DSP.png (34.1 KB, 81 views)

Last edited by Turbowatch2; 20th September 2019 at 02:45 AM.
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Old 20th September 2019, 03:47 AM   #33
Turbowatch2 is offline Turbowatch2  Germany
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There is an important "but" to Sigma Studio v. 4.4
It only runs with win 7 64 as far as I know.
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Old 20th September 2019, 05:38 AM   #34
tallnutt is offline tallnutt  Australia
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Thanks for the great explanation! That definitely looks like the setup for me. Just two more questions.. are the pots on the DSP single or dual gang? And what will you do about having a volume pot on the DSP and on the amp? Can the amp pot be set permanently so that only one controls the volume?
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Old 20th September 2019, 09:58 AM   #35
Turbowatch2 is offline Turbowatch2  Germany
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Hi,
here is a link for the 3e amp (the smallest available at time) TPA3251 2x140W 2Ch Class D Audio Amplifier | eBay US$70

Your question is a bit tricky. In theory you can do as you wrote, but this would degrade the sound quality.
See, if you play a CD, at the output you get full resolution audio and can control it analog. No problem. But here things are different: You take analog and convert it to digital, which is done best with full signal strength, just a little before clipping. If you lower volume, you take less steps on the digital ladder. So your analog stages should always run at full distortion free level, like 2 volt rms, to stay near to the 100dB dynamic of the analog to digital converter.

What you can do best:
Remove the volume pot from the new board and connect your pot (slider). This slider will in most cases be logarithmic, not linear.
I would, maybe, parallel both sliders or use the one in best condition. Now they control an AD converter, not the signal!
Then, you have to change the pot-block in the Sigma Studio software, so it accepts a table for the sliders values. Should have been done before by someone, maybe we find an example somewhere.
No problem to measure the slider.
As far as I have seen, you can cut the PCB with the pots in parts, which makes installation more convenient.

This digital level volume control has the huge advantage you do not loose resolution of the ADC which take your 2 volt signal to process it in digital form.

If you listen at low or moderate volume and control it analog before the signal enters the DSP, you only use a fraction of the converters steps which cover 100dB in the ADAU1701 input. This is important, as the DSP is not sampling at 196kHz, but conservative 44 or so, which is absolutely OK for CD audio quality and human ears. The sense of higher than 44kHz digital audio can be questioned, if the CD resolution it is used right.
(The more expensive 196kHz chips are only useful for professional application, where you constantly loose resolution while mixing recorded sounds for example. You can not hear 80kHz audio!)

OK, hope I got it right.
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Old 20th September 2019, 10:45 AM   #36
Turbowatch2 is offline Turbowatch2  Germany
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I just figured out which Beomaster 3000 you got. Nice. If it is in good optical condition, this is a very interesting object to modernize. Design is by Jacob Jensen.
I do not know the internals, but the inputs can be adjusted trough holes in the bottom. This could be a very useful feature to match different sources to the digital level.
The B&O stuff I know was always made with clear to define sub modules. If this is the same with yours, you might be able to use the analog "line in" whith the balance stage and remove most of the rest. Add your pre amp and go digital from there. This way you should inklude the tuner as well. Think about shielding it in metal before it is to late, as it could pick up noise. The FM band is sensible for some harmonics of digital stuff and SMPS.
If you become more comfortable with the DSP software, you could use some of the switches the B&O has for their original functions, but in the digital domain, if they are not too complicated, as the CPU and memory of the DSP have limits.

As I wrote, I had my fingers in some old B&O stuff. As beautiful it was designed, as impossible to repair where these beauties after ages in damp basements. The B&O service in Germany was not willing or able to repair them, as we found out on some occasions. Schematics? Impossible, top secret.
So, for many years, you could find them at the monthly garbage collection, together with old sofas in the better parts of my home town.

I think it is a sacrilege not to modern-digiti-lize it.


PS the 3e-audio amp that goes with the DSP for most is the best high end D-amp chip at time.
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Old 20th September 2019, 01:24 PM   #37
Turbowatch2 is offline Turbowatch2  Germany
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Just read your post again: The little Bear is a phono pre amp, so it has to be integrated between RCA input and source selector, but best would be in the turntable, away from all high frequency stuff. The MM signals are very weak, MC even weaker.
Maybe you can go from the selector to the balance pot and then into the DSP, but it could be better to have a buffer stage in front of the balance. Maybe post some picture of the internals of the Beo? Such a buffer stage is nothing complicated or expensive, just a small PCB, but it needs clean PS.
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Old 20th September 2019, 06:30 PM   #38
planet10 is offline planet10  Canada
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Beomaster refit - controversial?
Quote:
Originally Posted by Turbowatch2 View Post
The clear winner was a high quality DIYS phono PCB, that was planted directly into the record player
I have a buddy that did that on his table — a jFET heas amp right at the headshell.

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Old 21st September 2019, 03:18 AM   #39
Turbowatch2 is offline Turbowatch2  Germany
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There are quite some uncommon options with record players.
Many years ago I had a symmetric MM-pre, as the signal of the cartridge is symmetric in the beginning, eliminating any ground problems. Then the amplified signal left the player with line level, asymmetric as the rest ot the chain.
The pre-amp PCB was just under the tone arm base and the tiny wires went directly into the first stage of it. Worked well for years until I gave the phono away.
I never understood why this concept was not used commercially. Any professional microphone with XLR shows how to do it right. Most probably, when the industry moved from cristal pick upīs to moving magnet, someone decided to put the pre outside, to make the player universal and that was left as is was.
Even as it is none sens to sent this millivolt, micro ampere signal un-amplified through a asymmetric cable, where the screen is also one pole of the connection. Even more stupid to do this with MC signals, that are even weaker.
If you think about it, it is quite amazing how well such a technically imperfect system can sound.
If you have to add a phono-pre-amp to the system anyway, there is the option to do it better in DIYS Hifi and at least move the phono module where it belongs, into the player. Just keep the transformer out of the player, as it might induce noise into the chassis.

To build the first amp stage into the head shell is taking the idea even further, like a electret microphone capsule. Should work well with tone arms on the heavier side. Usually there should be enough room for two small FETīs and maybe an additional wire for the voltage feed if you think about it.

As most of the HIFI business has always been about easy money for the industry through a mass market, they sold what was produced cheapest, not what was best. Anyone who opens up average, commercial HIFI of the pre CD age today, will be amazed how such cheap junk could be sold to the masses so expensive, since PCB boards could be made mostly automated. Only very few manufacturers cared for what was inside. As long as it sold, the less was the better.
I myself, as a juvenile did not build amps by my own because i could, but because really high quality was so expensive at that time. Commercial amps of the 80īs where weak or sounded awful.

The technical optimum was left to the small high end sector and most of it moved to CD at a point when the record disk and pick upīs where about to reach their highest evolution stage. So no one thought about innovations for a dying system.
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Old 21st September 2019, 11:04 AM   #40
tallnutt is offline tallnutt  Australia
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Thanks Turbowatch. The preamp module in the B&O was noisy and had distortion problems.. probably the transistors... But the radio section is good and I have worked out how to power it, so I am keeping that in (there was a full schematic in an envelope taped inside the case). The little bear makes no noise, even inside the B&O so I will keep it in there, inside its metal case. I was thinking of adapting some of the switches and the DSP will give a lot of options.. so all the switches will work.



I'm not sure I understand your answer to the pot question.. The power amp pot wil be replaced by my volume slider? But I don't understand what to do with the DSP volume pot.


Thanks.
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