ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Yes - I know this is not of very high interest for most people!
But – I would like the possibility to connect a Moving Coil cartridge to my Beolab 5000.
I could buy a passive step-up transformer – like someone perhaps already have done.
But for me a true Bang and Olufsen solution would be better - much better.
I would like to have a solution so I could be sure to have the fantastic sound of the Beolab 5000 also when I play Moving Coil – vinyl music.
Perhaps someone think – this is not possible – well it is!!!
The Beolab 5000 of 1967 type 5303 is a fantastic design.
Too points why this is possible.
1. The Beolab 5000 microphone input . B&O have used a high quality step-up transformer for this input. This transformer have the very same technical specifications as the expensive step-up transformers produced today (or better).
2. This is a secret - the Beolab PHONO input. There is a switch which have a LOW and a HIGH position. In low position you have the RIAA correction amplifier as everybody know. In high position you have a linear amplifier without any corrections. Sensitivity like the AUX input.
I am going to design a product like this:
1. Input for Moving Coil cartridges with the B&O stepup transformer
2. Input for MM cartridges with the original Beolab 5000 RIAA amplifier (because I want the real sonic quality of the Beolab 5000)
3. The RIAA amplifier will be connected to the moving coil part.
This means a true Beolab 5000 module for MC and MM cartridges with build in RIAA correction.
(Also other cartridges can be used of course like Ortofon – correction circuits will be build in)
The box for this will be the same size as the Stereo Width Box and can be next to Beolab 5000 as a natural extension like the Stereo Width Box.
If this is of interest for you – please send me a PM.
/Frede
Interesting Frede.
Now wouldn't it be possible to actually use the MIC transformer inside and re-route the signal within the Beolab so that the MC signal would arrive at the input of the normal phono circuit? Not much to do then. Just wiring. Possibly a change of two resistors.
So the MIC input nobody uses would be an MC input - just erase the I
Jacques
chartz: Interesting Frede. Now wouldn't it be possible to actually use the MIC transformer inside and re-route the signal within the Beolab so that the MC signal would arrive at the input of the normal phono circuit? Not much to do then. Just wiring. Possibly a change of two resistors. So the MIC input nobody uses would be an MC input - just erase the I
An interesting view of course, but not possible.
B&O designed the preamplifiers by using the very same circuits but with different application setup. So when the function switch MIC is pressed, the RIAA part of the preamp do not function - the RIAA correction parts are not active.
The needed changes to re-wire the Beolab is very complicated inded, I prefer to leave the Beolab as original and use the circuit in an outside module.
Sorry but I really don't understand what you are going to do....
I will try to explain a little more.
I am going to design a box (like the stereo with box).
The box will have these inputs:
Phono input (for MM cartriges like B&O)
Phono input for MC cartridges like Ortofon
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Inside
... a circuit for Moving coilcartridges and the RIAA compensation + a circuit for RIAA compensation (MM cartridges).
All these circuits are excact kopies of the original Beolab 5000 circuits
The MC part is a stepup (transformer) in front of the RIAA / preamplifier.
The very special thing is, actually in the Beolab such a transformer is used for the microphone input.
I am using this transformer (from a Beolab 5000 PCB)
The conclusion
I have a MC device to connect to my Beolab 5000 based on the original Beolab circuit and parts. The Beolab 5000 sound is still possible which is one of my targets.
The moving coil module for Beolab 5000 is build and playing. I am really surprised – the sonic quality of a vinyl record played by a Moving Coil cartridge like the famous Ortofon and my new moving coil RIAA module with stepup transformer (the original microphone transformer from a Beolab 5000) is very very good.
A B&O cartridge like the SP9 gold with a high quality diamond (from Axel) sounds fantastic when it is played on a Beogram 3000 / Thorens TD 124 MKII, but I have to say the (for me) new setup:
Beogram 3000 / Thorens TD124 MKII with an SME tonearm and an Ortofon moving coil cartridge connected to the moving coil (stepup) module and my Beolab 5000 (restored with audio grade parts) – this is even more fantastic.
This is great!
In France, such a combination has been highly regarded since the late seventies. In Japan, even before that, they insisted that a properly set SPU on a 124, possibly at the end of a 3012-R was the ultimate in LP reproduction.
Hi Frede, I hope you're feeling a bit better.
As I've ordered the Beogram 3000 Thorens TD124MkII combination from you, I may be interested in one of these modules - of course, it depends on cost and availability.
Dave.
Dave Farr: Hi Frede, I hope you're feeling a bit better. As I've ordered the Beogram 3000 Thorens TD124MkII combination from you, I may be interested in one of these modules - of course, it depends on cost and availability. Dave.
Hi Dave,
Thank you very much - yes, I hope to start one week from now - I am much better now. Your Beogram 3000 will be one of the first tasks to do. I actually received it fully restores and re-veneered and re-painted last week. The freelance engineers are working though.
The Moving coil module.
I have not calculated any costs yet - it will be expensive. Building takes a very long time and I have to find one Beolab 5000 to scrap for every module because of the microphone transformers, and the are really a lot of expensive parts too.
I didn’t realize some else was interested but I would love to build some more and specially I would like to build one for you. I will have a look of the cost and send you more information during August .