Bowers&Wilkins Upgrade

N

Nick Zea-Smith

Audiophyte
I own a set of Bowers and Wilkins CDM1 speakers. They're a restoration project The crossovers are shot and have gone in the bin, so now in the process of replacing them. Knowing that most of the components are no longer available, I'd like to see if I can make some upgrades. Has anyone tried this, or can offer some advice on the components I can use? Thanks in advance!
 
Swerd

Swerd

Audioholic Warlord
What led you to believe the crossovers are shot? Are they really in the bin? It would have been worth keeping them just to learn the details of the crossover. Is it too late to retrieve them from the bin?

I searched for 'B&W CDM1 crossover schematic', and also for 'B&W CDM1 crossover upgrade', but found nothing useful.

Are you looking to build a replacement crossover, or are you looking for a drop-in replacement?

Are you in the USA? If so, call Madisound in Madison, Wisonsin, and ask them if they have any suggestions.
 
N

Nick Zea-Smith

Audiophyte
What led you to believe the crossovers are shot? Are they really in the bin? It would have been worth keeping them just to learn the details of the crossover. Is it too late to retrieve them from the bin?

I searched for 'B&W CDM1 crossover schematic', and also for 'B&W CDM1 crossover upgrade', but found nothing useful.

Are you looking to build a replacement crossover, or are you looking for a drop-in replacement?

Are you in the USA? If so, call Madisound in Madison, Wisonsin, and ask them if they have any suggestions.
Thanks for the reply. The crossovers aren't there at all! I bought the speakers as a pandemic project and discovered someone decided to 'improve' the design by removing the crossover, terminal tray and any useful internals and create something of their own...
My idea is to build replacement crossovers using components as close to, or better than OEM. Surprisingly, the woofer and tweeter work fine after 20 years of abuse, so the challenge is 'fun'. I've attached the schematic and parts list I'm working to and open to suggestions. I live in Germany, but will source the right bits from anywhere!
 

Attachments

TLS Guy

TLS Guy

Audioholic Slumlord
Thanks for the reply. The crossovers aren't there at all! I bought the speakers as a pandemic project and discovered someone decided to 'improve' the design by removing the crossover, terminal tray and any useful internals and create something of their own...
My idea is to build replacement crossovers using components as close to, or better than OEM. Surprisingly, the woofer and tweeter work fine after 20 years of abuse, so the challenge is 'fun'. I've attached the schematic and parts list I'm working to and open to suggestions. I live in Germany, but will source the right bits from anywhere!
Well the circuit is there. It is first order low pass and third order high pass. Build the circuit as printed. It would be impossible to build a different circuit, without measuring the impedance curves of the drivers, and measuring their acoustic responses. Just use good quality components and build it correctly.

If you can't build it, I can easily. However it would have to be shipped from the US to Germany.
 
Swerd

Swerd

Audioholic Warlord
I have sourced parts from two online vendors in the USA, Parts Express (Dayton brand) and Madisound. I don’t know if they ship to Europe, or what it would cost. There are sources and makers in Europe, but I am not familiar with them.

I don't know how familiar you are with electronics or crossover building, so if I've dumbed this down too much, please accept my apology.

Resistor (R1)
Dayton – 1Ω – 10W –Part 004-1 – $1.49
Madisound – 1Ω – 15W – Part 15r1 – $0.50

Capacitors (C1 and C2)
Do not use electrolytic capacitors. Instead, use only lower priced metalized polypropylene (MPP) capacitors. There are many more expensive MPP caps, but they cost more and provide no audible benefit. Avoid them. These MPP caps are all very good quality and are available in the USA: Dayton or MDL XPP (both made in Taiwan), Solen (France), and Audyn Q4 (Germany). Prices are in US$.

For C1, a 5.3 µF cap is not available. Any capacitor within 10% of 5.3 µF will work in an audio crossover. That becomes anywhere from 4.8 to 5.8 µF. Order the 5.1 µF cap.

C1 5.3 µF
Dayton – 5.1µF – 250V – Part 027-423 – $2.99
MDL XPP – 5.1µF – 250V – Part XPP-5.1 – $2.20

If you must have exactly 5.3 µF, use two caps wired in parallel with each other. Add the two values, 2.0 + 3.3 = 5.3:
Dayton – 2.0µF – 250V – Part #027-414 – $1.73
Dayton – 3.3µF – 250V – Part #027-420 – $1.92
– Or, 4.3 + 1.0 = 5.3:
MDL XPP – 4.3µF – 250V – Part XPP-4.3 – $2.00
MDL XPP – 1.0µF – 250V – Part XPP-1.0 – $0.90

C2 10 µF
Audyn Q4 – 10µF – 400V – Part 027-118 – $4.79
MDL XPP – 10µF – 250V – Part XPP-10 – $4.30

Inductors (L1 and L2) – all Air Core Inductors
L1 0.15 mH
Dayton – 0.15mH – 18 AWG – Part 257-804 – $3.29
Madisound – 0.15mH – 19 AWG – Part .15mhl – $2.70

L2 1.35 mH
Dayton – 1.5mH – 18 AWG – Part 257-832 – $9.49
Madisound – 1.5mH – 19 AWG – Part 1.5mhl – $8.40

For L2, a 1.35 mH inductor is not available. Order the next larger size, 1.5 mH, and unwind enough wire until it reads 1.35 mH on an inexpensive LC meter such as this. Once you have unwound enough wire, cut off the excess wire, but leave enough length to work with.

Please note that in the US, wire thickness is measured in gauge (AWG). In Europe, wire thickness is measured in cross sectional area, mm². 18 AWG = 0.823 mm² and 19 AWG = 0.653 mm².
 
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Swerd

Swerd

Audioholic Warlord
When searching online, I did find a photo (below) of CDM1 crossovers that had been for sale, but are no longer available. It allowed me to see what type or quality of the original B&W parts were.

The two black items are capacitors, clearly marked as 5.3 µF 70V (C1, back corner) and 10 µF 70V (C2, right side). By their size, they look like non-polar electrolytic capacitors.

On the left back corner is the single resistor, R1, a 1Ω sand-cast, white ceramic type.

The two wire coils are the inductors. The larger one on the left (L1) is probably in the woofer circuit, probably a P-Core (Permite) filled with ferrous powder in the core. Strangely, the B&W parts list shows that L1 is 0.15 mH. In the photo, the large inductor on the left looks large for 0.15 mH. I would expect the woofer's low-pass filter would be larger, but that depends on the crossover frequency. Knowing B&W's odd preference for very high woofer crossover frequencies, as high as 3.5 or 4 kHz, that might explain L1's small inductance value.

Similarly, the L2 inductor, in the tweeter circuit, is shown to be 1.35 mH. In the photo, is L2 the small inductor nearby the black capacitors? To me, that value seems high for such as small looking inductor. I wonder if these two inductors values were inadvertently switched in the parts list table? I doubt if B&W would publish a service manual with that type of error. So, the other possibility is that I'm reading the photo wrong.

https://tmraudio.com/old-products/b-w-cdm-1-crossover-network-working-pair-crossovers-from-cdm1-speakers/
1620256472336.png
 
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Swerd

Swerd

Audioholic Warlord
Compare the photo with the crossover schematic:
1620264437307.png
 
N

Nick Zea-Smith

Audiophyte
Thanks for all your help and taking time to look at the schematic. I think you've probably looked at it almost as long as I have over the last few weeks. I've compared your parts list with Parts Express European outlet, Sound Imports (https://www.soundimports.eu/en/) and place an order, with everything arriving this week in Germany from their dispatch center in Holland. The fun starts here.
I looked at the same CDM1 crossover image online for inspiration and came to a similar conclusion that it doesn't look 'right' for some reason, but at least it's given me the layout / position of components on the board.
Hoping to message you later this week, when I've spent some time in the workshop and completed a 'rough assembly'..! Thanks once again Swerd.
 
H

Hebat

Audiophyte
Hi Nick

I am wondering if you did the crossover Work!?
How did you do it (parts...)?
Did it work, how ist the sound?
Do you have a picture?

I have the plan to do just the same with my cdm1.

Greetings an thank you all for the things I have learned from you here!
Chris (Hebat)
 
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