Source for Transistors-NAP110
Posted by: leslie on 30 April 2002
After a mishap I need to replace both power transistors(TO3 Package) marked SM 0882 on one channel of my 110. Does anyone know of a source for these? If not is there an alternative-I assume in this case I would have to change all 4 to keep both channels the same.
Posted on: 30 April 2002 by jcc
Hi leslie,
The best advice I know of is to contact your local Naim dealer or distributor. It will cost less in the long run....
Cheers
jim
The best advice I know of is to contact your local Naim dealer or distributor. It will cost less in the long run....
Cheers
jim
Posted on: 30 April 2002 by Andrew Randle
Firstly, the transistors used for Naim amplifiers are specifically made for them (probably by Sanken).
Secondly do you have the test equipment to match the hfe for the NPN and PNP transistors in the output stage? I thought not. Simply put, the hfe is the input-to-output current gain of the transistor, these vary wildly.
If you don't match them, then the positive half of the signal is likely to be bigger than the negative half of the signal (or vice-versa). Thus causing significant distortion.
Like most manufacturers, Naim measure the hfe on specific lab equipment (I forget the name of this, ALW please remind me!). The best manufacturers throw at least 90% of their transistor stock away because they don't have the required hfe value - thus contributing to the expense of the amplifier.
So you've got three options:
1) Fork out £1000's for a machine that accurately identifies the hfe of the 100 transistors you have bought in to test and select.
2) Don't bother testing and do a hashed-up job of it.
3) Send it to Naim for no more than £160. They can update it to NAP140 status for you for £160, which probably means you get the transistors changed anyway.
I'd go for option 3, even if I'd be a hard-up student.
Andrew
Andrew Randle
Currently in the "Linn Binn"
Secondly do you have the test equipment to match the hfe for the NPN and PNP transistors in the output stage? I thought not. Simply put, the hfe is the input-to-output current gain of the transistor, these vary wildly.
If you don't match them, then the positive half of the signal is likely to be bigger than the negative half of the signal (or vice-versa). Thus causing significant distortion.
Like most manufacturers, Naim measure the hfe on specific lab equipment (I forget the name of this, ALW please remind me!). The best manufacturers throw at least 90% of their transistor stock away because they don't have the required hfe value - thus contributing to the expense of the amplifier.
So you've got three options:
1) Fork out £1000's for a machine that accurately identifies the hfe of the 100 transistors you have bought in to test and select.
2) Don't bother testing and do a hashed-up job of it.
3) Send it to Naim for no more than £160. They can update it to NAP140 status for you for £160, which probably means you get the transistors changed anyway.
I'd go for option 3, even if I'd be a hard-up student.
Andrew
Andrew Randle
Currently in the "Linn Binn"
Posted on: 01 May 2002 by John Luckins
A long time ago in days of extreme poverty I decided to try and build a NAP 250 cos I couldn't afford to buy one. The only items I couldn't get were the power trannies which I think are the same in the 110. These were marked with SM001 on the T03 can. I discovered that they were from a supplier called Semelab and were made specifically for Naim and not otherwise available. The nearest equivalent were BDY 58R. These have an unusually high Gain-Bandwidth Product at high Power levels. I was told that the early Naim power transistors were in fact selected BDY58's. I do have a couple of unselected ones kicking around in a cupbord somewhere which I could dig out but quite frankly I would just get Naim to do the job and have peace of mind and lower cost in the long term.
The design is quasi complementary because PNP transistors are not available in this speed, voltage and power rating.
John
The design is quasi complementary because PNP transistors are not available in this speed, voltage and power rating.
John
Posted on: 01 May 2002 by Paul Ranson
quote:
The design is quasi complementary because PNP transistors are not available in this speed, voltage and power rating.
That's a rather bold statement.
Paul
Posted on: 01 May 2002 by John Luckins
Paul
You're right, bold and a little speculative. Do you disagree? I think the gain bandwidth was probably only part of the reason for Naim using quasi complementary configuration, but I spent quite a lot of time researching the PNP alternatives and they really are much slower for the same power. Nothing comes remotely close to the BDY 58 in PNP. There is a trade off here as positive and negative halves are not fully balanced in terms of gain and switching with "quasi comp". I'm sure Naim considered this to be less important than the non-symmetrical bandwidth and stability of complememntary.
My god, don't I sound like a geek.
J
You're right, bold and a little speculative. Do you disagree? I think the gain bandwidth was probably only part of the reason for Naim using quasi complementary configuration, but I spent quite a lot of time researching the PNP alternatives and they really are much slower for the same power. Nothing comes remotely close to the BDY 58 in PNP. There is a trade off here as positive and negative halves are not fully balanced in terms of gain and switching with "quasi comp". I'm sure Naim considered this to be less important than the non-symmetrical bandwidth and stability of complememntary.
My god, don't I sound like a geek.
J
Posted on: 01 May 2002 by Andrew L. Weekes
I think the argument for using matching devices involves answering the following question: -
Have you ever found a complementary pair of devices with the same charactersitics.
They just don't exist.
A.
P.S. The Naim o/p devices were a 'standard' device, repackaged to make it suitable for Naim's application. I'm not sure if Semelab were involved (they designed the NAP500 o/p devices). The Sanken devices (as used in early amps and NAP150's are badged as such, and have different package style).
P.P.S. Matching hfe can be done with simple kit, but it takes time, it's quicker with the right gear.
P.P.P.S Any circuit that relies on a specific hFe to work is poor! It's a very inconsistent, variable, parameter - particularly with temperature.
Have you ever found a complementary pair of devices with the same charactersitics.
They just don't exist.
A.
P.S. The Naim o/p devices were a 'standard' device, repackaged to make it suitable for Naim's application. I'm not sure if Semelab were involved (they designed the NAP500 o/p devices). The Sanken devices (as used in early amps and NAP150's are badged as such, and have different package style).
P.P.S. Matching hfe can be done with simple kit, but it takes time, it's quicker with the right gear.
P.P.P.S Any circuit that relies on a specific hFe to work is poor! It's a very inconsistent, variable, parameter - particularly with temperature.
Posted on: 01 May 2002 by Manu
O/P transistors don't need to be marched on Naim amps.
The only severely matched are the input pair.
Emmanuel
The only severely matched are the input pair.
Emmanuel
Posted on: 02 May 2002 by Paul Ranson
I believe the Naim power amp circuit was derived from a standard 'app note' suggestion from the late 1960's. The 'RCA Transistor Book' rings a bell. At that time PNP power transistors were really crap and complementary outputs weren't a viable option for decent power outputs, and once Baxandall invented his diode quasi arrangements produced very good performance. AFAIK that isn't really the case for the last couple of decades. But it's not broken....
Paul
Paul
Posted on: 02 May 2002 by bam
Leslie,
The choice of the two npn output transistors on each channel and the mirroring diode is crucial to the sound quality and electrical stability of the Naim design. That is all that is really unique about the NAP circuit. To avoid disappointment I would recommend you ask Naim for replacements or get Naim to do the work.
BAM
The choice of the two npn output transistors on each channel and the mirroring diode is crucial to the sound quality and electrical stability of the Naim design. That is all that is really unique about the NAP circuit. To avoid disappointment I would recommend you ask Naim for replacements or get Naim to do the work.
BAM