Posted on: 31 May 2001 by Andrew L. Weekes
Hon,
quote:
Glad to hear that you share the same experience with your old Naim amps. My 32/250 are so old that they don't worth much at all, re-selling is not that feasible since I doubt if anyone will buy them. Hence renewal of the out of spec components by myself is a sensible route to enjoy the Naim experience.
My sentiments exactly, I have a full complement of 5 series kit I'd never dream of touching, but the older stuff upstairs is an interesting educational tool, that I can enjoy listening to into the bargain. I bought it for two reasons, to allow me to experiment with active Linn Kans, and to listen to some of the fantastic, late night, radio broadcasts available in the UK.
Bear in mind though that even old Naim kit can be brought up to current spec by Naim, particularly the 250, so there would be plenty of people willing to buy it at the right price. Also since we are not privy to the internal calibration details of the amps (e.g. bias current) these parameters could drift and affect sound. Fiddling with this setting could lead to problems if not careful (thermal runaway).
quote:
The volume and balance pots of the 32 are making a noise when they are turned, so I will replaced the volume pot with something from Alps or Panasonic. I never use the balance pot, so I will bypass it completely. I have also taken out one of the two pairs of phono boards and wire the phono socket directly to the input, making the RCA phono sockets a "straight line" input. In this way, I can use the phono sockets as another source input.
If the volume pot is a carbon type as in my 42XO, it wasn't possible to directly fit an Alps 27mm type directly to the PCB, as the height and spacing from the front panel is wrong (Alps part RK2711120K - 20K log).
It is possible to fit one with careful addition of legs to the pot, then forming them to fit the PCB without stress - a time consuming and difficult task to do to a high standard, but well worth the effort. Replacing just the old volume pot made such a massive transformation to the amp I find it difficult to believe! Channel balance at low levels (the reason for me doing it) is much better also, important for late night listening.
I've also done the mod to the phono inputs - there are genuine Naim link boards available also, to perform the same function.
quote:
I haven't touched the 250 yet, but the amp would definitely benefit from a service. I intend to renew the two reservoir caps first with standard industrial type Aerovox of the same dimension. I haven't decided the capacitance yet, most probably go for 22000 or 33000 uF. I will check the 250 amp and regulator boards to see if any old caps requiring attention.What reservoir caps have you used for your 110?
There were two types, one for the pre-amp supply (not applicable to 250's) and one for each rail of the amps (three caps total).
I used BHC Aerovox ALT22 series for the pre-amp supply and ALS30 series for the PA supplies. Be wary of increasing capacitance above the original design. It can increase surge currents at switch on, and transformer heating, due to the reduced conduction angle of the rectifiers (I squared R losses). Naim know what they are doing when it comes to power supplies, the new capacitors will have much lower impedance across a wider bandwidth than those you replace - and consequently a significant performance improvement.
The 110 doesn't use screw terminal types normally, but I fitted some heavy duty tags to the existing wiring and then fitted the ALS30 types (which were smaller and required padding to fit the existing capacitor clamp). Future recaps are now a very simple job, requiring just a screwdriver and spanner!
There are other BHC Aerovox types that are the same form factor as the original fit, but these weren't so readily available to me, so I elected to use the ALS30's.
Have fun and be careful!
Andy.
Andrew L. Weekes
alweekes@audiophile.com
[This message was edited by Andrew L. Weekes on THURSDAY 31 May 2001 at 13:37.]
