NAD 3240PE (Integrated Amplifier) and 7240PE (additional FM Stereo Unit) - from Power Envelope Series - Pros and Cons
The fact that issues resp. failures can be observed with this amplifier more often than average - go to the wide range of threads listing in post #5 under
https://www.diyaudio.com/community/threads/nad-3240-pe-issues.333339/prompted me to find out why.
At first glance, it is noticeable that numerous parts in different areas get so hot that the circuit board is more or less colored black - go to my images from post #4 under the same URL
The main benefit of this used topology (close to Class-G) is the fact, that the peak power output is briefly so large that there is 6db more headroom available (nearly 4 times the value for power output compared to the nominal value) - check out the details in the attached PDF file, where are to find the circuit description and theory of operation in detail - so as this thread:
https://www.diyaudio.com/community/threads/nad-power-envelope.377320/
But a great disadvantage is the fact, that the front-end (LTP/folded cascode and first stage of triplet push-pull output power follower) does operate permanently on the high voltage rails (+/-70V) and not only temporarily i. e. only while the short time, where the peak power is necessary. As a result, many parts of the front end have too high idle power and thus thermal stress as to see in the above mentioned images.
Best solution from my view is the acceptance of the lack of 4–6 dB increased peak power.
To realize this in such kind, that thermal stress isn't longer present, two main steps are necessary:
A: removing the +/-70V rails (desolder bridge rectifier BD502 so as Q431, Q435 and D421 (replace by wire) for the pos. rail and
Q433, Q437 and D423 (replace by wire) for the neg. rail
B: Disconnecting the front end from the +/- 70VDC rails and connecting to the +/- 40VDC rails (R465 and R467)
On the actually necessary reduction of the resistor values for R441 (47K Uref for CCS) so as R447/449 (15K for zeners - offset adjust)
can possibly even be dispensed with (then the zeners run less hot).
check out regarding schematic drawing error in one of different service manuals around R466 from right channel post #67 under
https://www.diyaudio.com/community/...repair-nad-3240pe-advice-needed.256520/page-3
But what about the zeners D405/406 (15V) in series of the supply voltage rails for the soft clipping unit between the main input and the input of the complementary LTP ?
How works this unit, if the switch for "soft clipping" is in the "off"-position (check out the attachment in post #9) ?
R413/414 and 423/424 runs very hot independent of position from this switch.
Maybe best solution it is to remove the whole unit and replace C401/403 by a 470nF MKP.
Thank you for some advice.
The thread
https://forums.stevehoffman.tv/threads/what-does-nads-soft-clipping-actually-do.316284/don't provide the wanted information.
The fact that issues resp. failures can be observed with this amplifier more often than average - go to the wide range of threads listing in post #5 under
https://www.diyaudio.com/community/threads/nad-3240-pe-issues.333339/prompted me to find out why.
At first glance, it is noticeable that numerous parts in different areas get so hot that the circuit board is more or less colored black - go to my images from post #4 under the same URL
The main benefit of this used topology (close to Class-G) is the fact, that the peak power output is briefly so large that there is 6db more headroom available (nearly 4 times the value for power output compared to the nominal value) - check out the details in the attached PDF file, where are to find the circuit description and theory of operation in detail - so as this thread:
https://www.diyaudio.com/community/threads/nad-power-envelope.377320/
But a great disadvantage is the fact, that the front-end (LTP/folded cascode and first stage of triplet push-pull output power follower) does operate permanently on the high voltage rails (+/-70V) and not only temporarily i. e. only while the short time, where the peak power is necessary. As a result, many parts of the front end have too high idle power and thus thermal stress as to see in the above mentioned images.
Best solution from my view is the acceptance of the lack of 4–6 dB increased peak power.
To realize this in such kind, that thermal stress isn't longer present, two main steps are necessary:
A: removing the +/-70V rails (desolder bridge rectifier BD502 so as Q431, Q435 and D421 (replace by wire) for the pos. rail and
Q433, Q437 and D423 (replace by wire) for the neg. rail
B: Disconnecting the front end from the +/- 70VDC rails and connecting to the +/- 40VDC rails (R465 and R467)
On the actually necessary reduction of the resistor values for R441 (47K Uref for CCS) so as R447/449 (15K for zeners - offset adjust)
can possibly even be dispensed with (then the zeners run less hot).
check out regarding schematic drawing error in one of different service manuals around R466 from right channel post #67 under
https://www.diyaudio.com/community/...repair-nad-3240pe-advice-needed.256520/page-3
But what about the zeners D405/406 (15V) in series of the supply voltage rails for the soft clipping unit between the main input and the input of the complementary LTP ?
How works this unit, if the switch for "soft clipping" is in the "off"-position (check out the attachment in post #9) ?
R413/414 and 423/424 runs very hot independent of position from this switch.
Maybe best solution it is to remove the whole unit and replace C401/403 by a 470nF MKP.
Thank you for some advice.
The thread
https://forums.stevehoffman.tv/threads/what-does-nads-soft-clipping-actually-do.316284/don't provide the wanted information.
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I have the 2200PE and it has been a fairly reliable amp short of some cold solder joints that I needed to re-solder and the speaker relays that I still need to replace but over all I kind of like the amp. Why go through all the trouble of neutering the amp. Once you remove the power envelope you won't be left with much. I know that there is some phase inversion going on with regards as to how the signals are fed to the rails. I forget exactly how it works but one side is flipped and that would need to be addressed I would imagine. I don't know much about how amps work but I have looked into this one (2200PE) and I assume that it is the same general circuit topology in the 3240PE as they are both Power Envelope amps are they not?
never had a problem with any of the 'pe' models ive had or repaired and i drive my amps pretty hard
i wouldnt alter what is a good product
i wouldnt alter what is a good product
About 15 years ago I picked up a 7225 from the gutter. Every single transistor in it was blown or off spec. It cost around $12 in parts at the time to repair. Since then it's had the type of makeover I give vintage amplifiers (recap, earth layout redesign, transistor choice, etc). Few mid-range amplifiers I service better it, but sure good ones certainly do. This is my bench amp in the repair lab, and rates pretty well in output capability and transparency than an awful lot of other stuff.
I had every one of those at some point. That speaks more for pros. Always reliable, always sound good and always have problems with the volume pots. Then and now. Except then the balance turned inside of the volume dial.
I play them loudly, I never had one clip. Perhaps I listen before they get a chance to clip. Because I play all amplifiers loud.
I upgrade them, I always have one or the other, or two of them. The PD always sounds good, with the dynamic sludge hammer all Nad amps posses to go with the clarity and the musicality. The volume makes static and the speaker posts don't except spades so it makes changing speakers a bigger chore. But Nad like always are worth keeping. New ones, and old ones alike.
I play them loudly, I never had one clip. Perhaps I listen before they get a chance to clip. Because I play all amplifiers loud.
I upgrade them, I always have one or the other, or two of them. The PD always sounds good, with the dynamic sludge hammer all Nad amps posses to go with the clarity and the musicality. The volume makes static and the speaker posts don't except spades so it makes changing speakers a bigger chore. But Nad like always are worth keeping. New ones, and old ones alike.
Attachments
By the way some of them make pretty good preamps and have very good switchable phono set ups, mm/mc, that punch very well above the modest costs.
I have one of their preamps. I forget the model #. It's in storage right now but it was the one that was matched and usually sold with the 2200PE. Solid preamp. It has your standard 2 volt RCA outs as well as 10 volt RCA's for hooking it up to pro/studio gear. It still works fine but It needs a serious deoxification and maybe even a recapping. I really don't use it any more as I use my PC as a preamp.
again the question : how works this soft clipping circuit ?
In the attached file you will find a redraw for better tracking of the signal path .
Attachments
The soft clip works on the input signal using the two diodes and a set DC voltage to bias them. Knowing the voltage gain of the power amp means the input level needed for clipping is already known. The switchable clipping circuit simple clamps the input level to below that where the output stage will hit the rails.
I see - thank you very much.
In post #68 under
https://www.diyaudio.com/community/...repair-nad-3240pe-advice-needed.256520/page-4
there rises up additional question. Please have a look if you have time - thank you.
The NAD manuals can be confusing and there do seem to be many variations. I've nothing different to the commonly available manuals from the usual sources I'm afraid.