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Beomaster 8000 preamp

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Saint Beogrowler
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Saint Beogrowler Posted: Mon, Jul 2 2018 9:52 PM
On my Beomaster 8000 I’m having a problem with my FM lacking a channel. The problem swaps sides when I switch 3IC202 and 3IC102. Is there an alternative to this switch?

sonavor
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sonavor replied on Tue, Jul 3 2018 1:31 AM

Hi Peter,

Unfortunately those AD analog multiplex/switches are no longer available from suppliers. One of these days I will have to ask Beolover to make a plug in replacement using moder SMD components. Until then we are stuck with having to use spares from other Beomaster 8000 or get lucky on Ebay or Alibaba Express. If you do come across a source let me though. I am always in the market for those. Wink

John

tournedos
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I couldn't find AD10/278 data sheet anywhere, but functionally it looks like a 4066 would be a drop in replacement - although with a different pinout...

--mika

sonavor
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sonavor replied on Tue, Jul 3 2018 2:59 PM

I haven't found a data sheet for the AD 10/278 either.  From the Beomaster 8000 service manual diagram though the AD 10/278 has three control signals (probably four on the device) that select the input pin to pass to a single output pin. When not selected the input pin is grounded. The TI SN74HC4066 does provide four control signals to independently control four A to B connections. The non-selected state of the input pins is open and the selected state closes pin A to pin B. I'm not sure it would work tying all of the output (B pins) together.

I think a device more like the TI OPA4872 would be needed although it still doesn't look like non-selected inputs are grounded.

sonavor
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sonavor replied on Tue, Jul 3 2018 5:49 PM

It would be nice to find new replacement options for both the AD 10/278 and AD 10/192 analog switch/multiplex devices the Beomaster 8000 uses.

Saint Beogrowler
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I just emailed Analog Devices asking for help or even a datasheet.
tournedos
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Grounding the unused inputs is used to limit crosstalk from non-selected channels. Depending on the impedances of the input and output signals, it may or may not be needed with a replacement, as a 40+ yo original IC certainly won’t be current state of art. A basic 4066 may not be optimal, but If I was faced with this problem I’d certainly try just as a $1 proof of concept - there are any number of better performing analog switches that’d work as an upgrade for a final solution.

--mika

sonavor
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sonavor replied on Tue, Jul 3 2018 11:04 PM

I will try and get some experiments going when I get a break. I do have at least one spare Beomaster 8000 preamplifier board I can test with.

Saint Beogrowler
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sonavor:

I will try and get some experiments going when I get a break. I do have at least one spare Beomaster 8000 preamplifier board I can test with.

I’m excited about what you learn. This is just a bit beyond my skill set and knowledge. Since this is on my spare BM8000 I’d be glad to try what ideas you have. I do use my FM quite a lot as we have some pretty good Public radio stations.
Saint Beogrowler
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Incredibly exciting news!

Installed Sonavor's replacement devices and it works amazing! A drop in replacement. I've been searching for a year now with no luck for a used replacement, I've even bought an auction parts unit BM8000 but the preamp board had been removed. The beolover story https://beolover.blogspot.com/2019/06/beomaster-8000-workbench-unit-testing.html.

All sources work with both channels. I couldn't be happier as I sit here listening to my favorite local jazz FM station.

Saint Beogrowler
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sonavor
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sonavor replied on Sun, Jul 7 2019 8:04 PM

I am really glad the replacement parts fixed your Beomaster 8000. That is a great test!  Thanks for posting that.

I should have a replacement device for the other Beomaster 8000 source select switch (3IC4 - the AD 10/192) ready to send to you next week.

-sonavor

Saint Beogrowler
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Happy to say the Sonavor 10/192 replacement device works exactly as it should installed in my Beomaster 8000. These are some amazing drop in replacements for the long obsolete and unobtainable switches.

Beo_Jean
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Beo_Jean replied on Fri, Jul 19 2019 11:53 PM

Amazing work Sonavor!

You found a nice market here, go for it! Thumbs Up

sonavor
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sonavor replied on Sat, Jul 20 2019 5:55 AM

Hi Beo_Jean,

Thanks.

I don't think there will be too much of a demand and I just build them as I need them. However, I do know that owners like myself will appreciate having the insurance that a failed, obsolete part won't put an end to their Beomaster 8000. 

Besides replacing a failed source switch I was hoping that this low noise switch would solve the problem of crosstalk from the Beomaster 8000 FM source and the Phono source (at high volume). Unfortunately it didn't eliminate that problem. But Beolover's fix appears to work quite well.

-sonavor

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