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Creating a BM7000 switch to allow the pre-installed RIAA to be switched on/off

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rotspot
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rotspot Posted: Mon, Nov 25 2013 12:09 AM

Is it possible to leave the optional RIAA pre-amp in place in the BM6500/7000 and add a switch to allow it to be used or bypassed? I have the RIAA installed in my BM7000 and a BG7000 both the RIAA in place but clearly I only need one in total. I do however want to leave the optional RIAA in place in the BM7000 so I can use a different player without one.

 

Many thanks

Peter

Beobuddy
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Beobuddy replied on Mon, Nov 25 2013 7:14 AM

If you use the original BG7000 with the BM7000, then another recordplayer with build in RIAA could also be connected to the Tape2 socket.

I would not cut any traces on the board. It is possible, but distortion could be a side effect.

tournedos
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tournedos replied on Mon, Nov 25 2013 8:24 AM

Beobuddy:
If you use the original BG7000 with the BM7000, then another recordplayer with build in RIAA could also be connected to the Tape2 socket.

If I remember right, you will need to remove the Datalink pins (and disable remote control functions) from the DIN plug to do that. Otherwise, the Beomaster will switch to the CD input every time you start the Beogram as it is using Beogram, not Beocord type of datalink commands.

Or, use the CD input if you don't have a CD deck in the system.

--mika

Die_Bogener
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Zitat: "If I remember right, you will need to remove the Datalink pins (and disable remote control functions) from the DIN plug to do that. Otherwise, the Beomaster will switch to the CD input every time you start the Beogram as it is using Beogram, not Beocord type of datalink commands.

Or, use the CD input if you don't have a CD deck in the system."

Correct! If the Beogram is connected to the Tape (1/2) Inputs and Datalink Pins are not removed from the Begram plug, the BM7000 will Switch always to Phono Inputs when the Beogram is used.

But removing the Pins will also result in not beeing able to control the Beogram by a remote control, just by the beogram itself.

But it is possible to Keep the Beogram plugged in the Phono socket.

1.) The BM7000 has usually no RIAA inside. This is an Option. If it is installed, there is usually no possibility to connect a BG7000... 2xRIAA does not work. So the Option is to remove the RIAA out of the BM7000 and to repair 2 cut wires.

2.) Remove the RIAA out of the BG7000... what a terrible waste of time and Money.

3.) Install a Switch inside the BM7000, activating or deactivating the installed RIAA inside the BM7000. This Option is undocumented... but possible.

There are 2 wire bridges on the preamp board, J21 and J22. These wires are cut, if a RIAA ist installed or closed, when no RIAA is used in the BM7000.

If the optional RIAA inside the BM7000 was installed and you wish to use it without the RIAA, then unsolder the capacitors C1 and C28. This deactivates the Output of the RIAA. If you install 2 small Pins of a chip carrier and a WIMA 1uf foil capacitor then you can switch it on or off just by plug in or out these small caps. On the other hand, you must open or Close the to wire bridges to enable the Inputs without the RIAA... and this can be also done with a pin of a chip carrier and some wire.

Since one pin of the caps and of the wire can always stay connected, nothing gets lost. You just plug in the wire and remove the cap or vice versa. Activate or deactivate the RIAA... and the RIAA stays inside the BM7000.

Easy done in some minutes... but it means, that the BM must be opened and modified.

 

rotspot
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rotspot replied on Tue, Nov 26 2013 12:37 PM

Thanks for all the help guys. In the end I took out the RIAA in the BEOMASTER, replaced the two wires and connected pins 6 & 7 on the phono output. Although the solution from Die_Bogener seems elegant, I just don't have access to the parts needed to do a good job. Just getting my hands on the basics here in the Philippines is a nightmare so I've opted to go 'standard' and remove the RIAA board in the BM7000. Sad but true. The good news is that I now have an RIAA board for a BM6500/7000 going spare. Is there much interest for these? 

 

Cheers

 

Peter

Die_Bogener
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Yes! 

These RIAA are really rare, very rare parts...

Sell it on Ebay or any other market.

 

rotspot
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rotspot replied on Wed, Nov 27 2013 1:13 PM

Excellent. I'd rather sell it to someone here who I feel certain would use it well. Any takers?

 

rotspot
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rotspot replied on Wed, Nov 27 2013 1:13 PM

Excellent. I'd rather sell it to someone here who I feel certain would use it well. Any takers?

 

joeyboygolf
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I have one advertised in the for sale section of this website for some time and no interest whatsoever so far, same story on ebay!

Regards Graham

rotspot
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rotspot replied on Wed, Nov 27 2013 1:55 PM

Oh wow. I may just hang on to it for now then. Thanks for letting me know.

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