advertisement


Paralleled Output trannies - NCC and HackerNAP

B

bugbear

pfm Member
Given the repeated interest in this, I've tried to gather up the info "to date"

The key threads are:
Pete Maddex on his HackerNap in Jun 2018:
https://pinkfishmedia.net/forum/threads/hackernap-parallel-output-transistors.216188/

And Andrew Sutton, on his Qudos (NCC220) in Mar 2019:
https://pinkfishmedia.net/forum/threads/qudos-parallel-output-transistors.226250/

Others who have "gone parallel" are:

TimH https://pinkfishmedia.net/forum/thr...output-transistors.216188/page-2#post-3590570

TOR https://pinkfishmedia.net/forum/thr...output-transistors.216188/page-3#post-3614729

BugBear
 
Wow 2018 I didn’t think it was that long ago.

Its still sounds good, but soon to be replaced by a fully complementary Hackernap with parallel output transistors.

Pete
 
I hope that I have enough grasp of things...................forgive me if not, and ignore.

There was an informl survey of NCC boards dying a short while ago, possibly on one of the links, and it seemed to be not uncommon. So, paralleling-up the output trannies would seem to be a best practise, apart from any other reason.
 
Hi, I can’t say it is best practice as there are risks associated with parallel output transistors.
The main concern seems to be instability but I have not heard of it happening with Avondale or Hacker amps yet.
Cheers Andy.
 
Paralleling devices is almost always a good idea and offers many potential benefits. Issues are usually when extra devices are added to a circuit not designed for it and no modifications are made to accommodate it where required.
 
Arkless Electronics said:
Paralleling devices is almost always a good idea and offers many potential benefits. Issues are usually when extra devices are added to a circuit not designed for it and no modifications are made to accommodate it where required.
Click to expand...

It depends, in the past power transistors suffered badly from “bipolar gain droop” where at even quite low currents the gain would drop markedly, to get round this transistors were paralleled but today modern transistors can have high gain at much higher currents, so if you listen at sensible levels with moderately efficient speakers then paralleling is not worth it if you use transistors like the 3281/1302 or 21194/21193, of course if your speaker is the kind of load that looks like a starter motor on an old diesel truck on a cold day, you have a large room and like to play air guitar to heavy metal with your mates after downing too many Jack Daniels......
 
russel said:
It depends, in the past power transistors suffered badly from “bipolar gain droop” where at even quite low currents the gain would drop markedly, to get round this transistors were paralleled but today modern transistors can have high gain at much higher currents, so if you listen at sensible levels with moderately efficient speakers then paralleling is not worth it if you use transistors like the 3281/1302 or 21194/21193, of course if your speaker is the kind of load that looks like a starter motor on an old diesel truck on a cold day, you have a large room and like to play air guitar to heavy metal with your mates after downing too many Jack Daniels......
Click to expand...

I completely disagree!! What makes you think greater power was the main thing I was thinking of? There are MANY reasons why a multiplicity of output devices are always a good idea. When applied correctly these can include vastly reduced distortion, much lower output impedance etc.
 
Arkless Electronics said:
I completely disagree!! What makes you think greater power was the main thing I was thinking of? There are MANY reasons why a multiplicity of output devices are always a good idea. When applied correctly these can include vastly reduced distortion, much lower output impedance etc.
Click to expand...

I focussed on bipolar gain droop which is less of a problem with modern transistors.
 
russel said:
I focussed on bipolar gain droop which is less of a problem with modern transistors.
Click to expand...

That didn't even enter into my reasons for using paralleled output devices! Obviously the oft repeated thing in hi fi of a single pair of devices being best is complete arse gravy.
 
Arkless Electronics said:
What makes you think greater power was the main thing I was thinking of? There are MANY reasons why a multiplicity of output devices are always a good idea. When applied correctly these can include vastly reduced distortion, much lower output impedance etc.
Click to expand...

Must admit I'm intrigued as to what is improved by multiple ouput devices if one pair doesn't suffer gain droop and has plenty of SOA. Please let us know.
 
Like I said vastly reduced distortion and output impedance are the main ones. Increased voltage compliance is another one but not that important usually. Note that I'm not in any way referring to Avondale or Naim but generalising and that the advantages only really apply to certain OPS topologies.
 
How do you get vastly reduced distortion?
The voltage gain of the ouput stage is a bit less than unity. Paralleling doesn't change this.
If you are talking about into low impedance loads then that is covered by "more power", whcih you stated you didn't mean. Anyway, one device with a current gain of 100 works the same as two in parallel with a gain of 100 each - within the 'no gain droop' region.

You are a great proponent of "output impedance does not need to be all that low". But if you do want lower o/p impedance, wind up the loop gain!
 
My post was carefully worded.... If totally off topic as it does not apply to these topologies!

Output impedance should of course be as low as possible.
 
Arkless Electronics said:
That didn't even enter into my reasons for using paralleled output devices! Obviously the oft repeated thing in hi fi of a single pair of devices being best is complete arse gravy.
Click to expand...

I don’t see how you can design an amplifier without considering gain droop, given the driving stage sees about half the load of a single transistor with dual transistors it’s not something to do without due consideration of what you are trying to achieve.
 
russel said:
I don’t see how you can design an amplifier without considering gain droop, given the driving stage sees about half the load of a single transistor with dual transistors it’s not something to do without due consideration of what you are trying to achieve.
Click to expand...

;)
 
Les always said that the NCC200 with BUV20 output devices gave "The power and the glory" - I discovered recently that BUV20s are dual-die devices, so technically they're parallel outputs.
 
RonR said:
Les always said that the NCC200 with BUV20 output devices gave "The power and the glory" - I discovered recently that BUV20s are dual-die devices, so technically they're parallel outputs.
Click to expand...

I have been wondering if the BUV20's could be doubled as thats what's in my Voyagers? I know they're supposed to give a bit more power output, but still short of the NCC300's quoted 130watts.
 
KJhWROz.jpg


...like this? Parallel OP section taken from various HackerNAP threads. Questions:
  1. Are extra 100R resistors needed as mentioned here?
  2. Will the MJE243/253 suffice for parallel MJ21194Gs?
 
Last edited:
You must log in or register to reply here.


advertisement


Back
Top