over sized transformer help please - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 2nd September 2009, 05:30 PM   #1
diyAudio Member
 
Join Date: Dec 2003
Location: earth
Default over sized transformer help please

I occasionally think of putting a larger transformer in an amplifier, like gettting a small naim and making it into a 250. sort of thing.

Trouble is, how can I judge what is a safe 'over voltage'

Is there a rule of thumb as to what the output devices will take,

and also, please, how will that affect the input and driver stages limits

thanks please reply.
  Reply With Quote
Old 2nd September 2009, 05:54 PM   #2
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Quote:
Originally Posted by lt cdr data View Post
I occasionally think of putting a larger transformer in an amplifier, like gettting a small naim and making it into a 250. sort of thing.

Trouble is, how can I judge what is a safe 'over voltage'

Is there a rule of thumb as to what the output devices will take,

and also, please, how will that affect the input and driver stages limits

thanks please reply.

Without understanding the design from one end to the other there is no safe 'over voltage' - as a rule of thumb the designer will generally choose (or at least I did) a transformer which at max high line and lightly loaded would not produce a supply voltage that exceeded the safe operating voltages (with some derating) of any component in the amplifier.

What you can do with considerable benefit is fit a larger (higher current rating) transformer with the same rated output voltages which will significantly improve the supply voltage regulation under load. You can also fit lower loss rectifiers, and larger filter caps. All will gain you audible improvements in sound quality (at least at near clip) provided that the components originally chosen were not really conservative high quality choices.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 2nd September 2009, 06:58 PM   #3
wg_ski is offline wg_ski  United States
diyAudio Member
 
Join Date: Oct 2007
Quote:
Originally Posted by kevinkr View Post
All will gain you audible improvements in sound quality (at least at near clip) provided that the components originally chosen were not really conservative high quality choices.
Not an improvement near clip - what you get is an improvement when actually driven into clip. With a good stiff power supply you can drive 3 to 6dB into clip on peaks before the sound goes south. With a marginal supply it is painfully obvious the moment of overdrive.
  Reply With Quote
Old 4th September 2009, 01:02 PM   #4
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
If by "going South" you mean deterioration in sound quality then I don't think I would like listening to clipping at near half the peak voltage.

That's why I use a 100W amp playing at an average of ~ 1W.

Even using 1W of average power I can still hear improvements in PSU at the speaker output. I can certainly measure differences in performance when the PSU is improved.
__________________
regards Andrew T.
  Reply With Quote
Old 5th September 2009, 03:22 PM   #5
diyAudio Member
 
mikesnowdon's Avatar
 
Join Date: Aug 2007
Quote:
Originally Posted by lt cdr data View Post
I occasionally think of putting a larger transformer in an amplifier, like gettting a small naim and making it into a 250. sort of thing.

Trouble is, how can I judge what is a safe 'over voltage'

Is there a rule of thumb as to what the output devices will take,

and also, please, how will that affect the input and driver stages limits

thanks please reply.
With Naim amps this is totally plausible due to the fact they all have the same poweramp circuit right through the ranage on older models. The newer ones are still very similar.

As you move up the NAP range the main differences occur in the power supply with increasing transformer size and rail voltage. Some regulated supplies, some with large 22000uF caps some with 4 x 10'000uf etc.

Generally the higher the rail voltage the more output power. So In theory you could get an old NAP90 and add a bigger trafo (ca. 500VA) with higher secondaries (33/35v) giving 46/50v rails. With the NAP90 you would also need to add some bigger smoothing caps and ensure the relevant caps on the board are rated high enough. To make it a true 250clone you need a regulated supply but don't worry about that. Adding a beefier supply makes a huge difference. In fact there is enough room in a NAP90 case to make it dual mono. Internal height is the only limitation.

See acoustica.org.uk, click 'Naim poweramps mods bible' on the left pane. Also if modding Naim amps is something your interested in sign up to pinkfishmedia.net and post in the DIY room your intentions or ideas.

EDIT: Also check out Avondale audio.
__________________
www.drugfreeworld.org

Last edited by mikesnowdon; 5th September 2009 at 03:25 PM.
  Reply With Quote
Old 7th September 2009, 07:09 AM   #6
cbdb is offline cbdb  Canada
diyAudio Member
 
Join Date: Oct 2008
Location: Vancouver
Probably not a good idea to increase the power (voltage) of your amp just by replacing the trnsfrmr. If the amp was designed properly, nothing else will be able to handle that extra power, from the fuse to the heat sinks. What you might want to do is put a bigger transfrmr at the same voltage in, to increase your current but you would want to add more smoothig capacitance also.
  Reply With Quote
Old 7th September 2009, 08:08 PM   #7
diyAudio Member
 
Join Date: Dec 2003
Location: earth
Mike is correct, I know more than enuff about naims to say they can't design another power amp, or won't, as perhaps they have tried to in research and testing, but not released publically,

perhas cos it doen'st sound as good, so they stay with the only power amplifier design they have ever made commercially.

so yes it varies only in power supply size (not incl. the regulated ones)

naim make one amplifier

(((with outputs from depending how you measure around 20-25 watts the green cased nap 90 is appallingly low on power, far outdone by a half shoebox old one of similar rating, strangely

to 70 ish, only altering EFFECTIVELY in power supply size.))))

I am talking old style

Yes that is the total truth hard to believe, REALLY, even new ones are same bar new reg. design in modern amps, not much knowledge on these, but apparently power amp is almost the same

I was merly wondering what I can get away with, ie voltage rail limit

a bit like the fact that proac cannot design another crossover, and living voice cannot design speakers at all.

Last edited by lt cdr data; 7th September 2009 at 08:17 PM.
  Reply With Quote
Old 7th September 2009, 08:27 PM   #8
diyAudio Member
 
mikesnowdon's Avatar
 
Join Date: Aug 2007
I suggest you post your query on PFM:

http://www.pinkfishmedia.net/forum/forumdisplay.php?f=8

I have a DIY dual mono NAIM amp. Its based on genuine NAPA boards from a NAP135 (serviced by Avondale) with dual mono powers supplies consisting of a pair of Avondale audio 'minicap6' modules (6 x 10'000 Kendeil caps in CLCLC) and dual 225VA toroidal (33-0-33 secondaries). Its blows the LM3886 clean out of the water. Tight punchy bass, phenomenal dynamics. No contest

I can tell you that as far as power and grip is concerned I have heard nothing like it. If the apparent 'low power output' of Naim amps is such as issue you have to wonder why they have been so successful dont you? (if it aint broke....). Its not the power that's important but what you do with it that counts.

As regards the NAP90, try some bigger PSU caps (22'000uF) and a higher rated trafo (around 400VA min), aim for 50v rails if you can, or go a tad lower (46v) depending on what caps you can fit in the case. People on PFM report amazing things when increasing the rail voltage to 50vdc

Theoretically you should be getting 70/80watts on 46/50v supply voltage
__________________
www.drugfreeworld.org
  Reply With Quote
Old 8th September 2009, 01:36 PM   #9
diyAudio Member
 
Join Date: Dec 2003
Location: earth
thanks mike, but due respect to the pink fishers, most will not know the limit rails for a std generic 3 stage amplifier bipoliar quasi complimentary output stage, class B.

of which the naim is a textbook example.

they were successful as they were part of a pact between julian and ivor tiefenbrum to initiate one cannot be used without the other, which spread to the dealers and then public.

I didn't say APPARENT was a problem, domestially, I would say AVERAGE is 50 watts or so, minimum you see is around 20-30, and the upper end, well 80 watts is expensive in hifi terms, you rarely go above 100, I would say 120-130 watts is about the upper end of domestic hifi amplification

with a few expections for the extremely well off and stupid who have more cash than sense, and if so lose with it, are likely to lose their cash.

I know this from 10 years of diy audio and hifi, from the back of many magazimes which list the prices of virtually every domestic hifi amplifier, complete with power ratings.

the nap 90 is woefully unqualified to drive some speakers, even in my small room it strained driving some naim credos, I won't go into naim religion etc., that#'s not the discussion

its both a current and voltage thing, the current of the power tx capacity is small, is a tiny cored transistor, as is the voltage capability, ie the rails, and again, transformer core, and winding wire thickness.

just up them, via a decent tx, the caps are adequate fora bit, then you can up them to perhaps 12k uF, or more, if one wishes.

as I said, the amp is the same, a nap 90 is a nap 250/135 circuit, there is NEGLILGIBLE difference.

I was merely wondering on a guidline for an upper voltage limit, I suspect around 250/135 levels, without consulting all the devices/going over the design with a fine tooth comb.

however it may be that lesser transistors are employed, too, you can't be too careful.

I have a massive suspcition its the quasi power stage, combined with the preamp, and certain older devices that gives it THAT punchy driving sound, take that away, and its no naim, hence why we see no new naim amplifier.

ie there is only 1, conclusion, either theyy CANNOT design amplifiers, or

they cannot design anything that sounds better.

most of that, I believe is pretty irrefutable

Last edited by lt cdr data; 8th September 2009 at 01:38 PM.
  Reply With Quote
Old 8th September 2009, 02:10 PM   #10
diyAudio Member
 
mikesnowdon's Avatar
 
Join Date: Aug 2007
Quote:
Originally Posted by lt cdr data View Post
thanks mike, but due respect to the pink fishers, most will not know the limit rails for a std generic 3 stage amplifier bipoliar quasi complimentary output stage, class B.
If its a NAP90 then yes, they will. Some on PFM have been modding Naim amps fopr years. LesW of Avondale for example.

Quote:
they were successful as they were part of a pact between julian and ivor tiefenbrum to initiate one cannot be used without the other, which spread to the dealers and then public.
Whatever

Quote:
didn't say APPARENT was a problem, domestially, I would say AVERAGE is 50 watts or so, minimum you see is around 20-30, and the upper end, well 80 watts is expensive in hifi terms, you rarely go above 100, I would say 120-130 watts is about the upper end of domestic hifi amplification
I know you didnt.

Quote:
I know this from 10 years of diy audio and hifi, from the back of many magazimes which list the prices of virtually every domestic hifi amplifier, complete with power ratings.
Do you actually read that crap? I stopped buying Hi-Fi mags years ago.

Quote:
the nap 90 is woefully unqualified to drive some speakers, even in my small room it strained driving some naim credos, I won't go into naim religion etc., that#'s not the discussion
Eh?

Quote:
its both a current and voltage thing, the current of the power tx capacity is small, is a tiny cored transistor, as is the voltage capability, ie the rails, and again, transformer core, and winding wire thickness.
Yep

Quote:
just up them, via a decent tx, the caps are adequate fora bit, then you can up them to perhaps 12k uF, or more, if one wishes.

as I said, the amp is the same, a nap 90 is a nap 250/135 circuit, there is NEGLILGIBLE difference.
Actually I said that.

Quote:
I was merely wondering on a guidline for an upper voltage limit, I suspect around 250/135 levels, without consulting all the devices/going over the design with a fine tooth comb.

however it may be that lesser transistors are employed, too, you can't be too careful.
None of the Naim modders on PFM seem to go over 50v rails. The output transistors are different on the 90 but I suspect they could easily be replaced by (for example) Sankens. (early NAP140 used Sankens) It wouldnt take much for you to check the datasheets of various parts in the circuit.

Quote:
I have a massive suspcition its the quasi power stage, combined with the preamp, and certain older devices that gives it THAT punchy driving sound, take that away, and its no naim, hence why we see no new naim amplifier.
Many agree.

I use my DIY NAP with a Cambridge 840's preamp stage (whlie I build my SKA preamp) and a CA 640c CD player. It still sounds punchy and dynamic, more so than the chipamp I had before in the same system.

Quote:
ie there is only 1, conclusion, either theyy CANNOT design amplifiers, or

they cannot design anything that sounds better.

most of that, I believe is pretty irrefutable
Please dont come to PFM with this kind of crap. Its off topic and old hat anyway. You asked a DIY question on a DIY forum. I have seen so many threads on this website develop into endless arguments (why I post on, and read mainly PFM now) and I see this one heading that way. These days I only pop on here occasionally and rarely post but I saw you Naim related question and thought I could help you. What your thinking about re the NAP90 is possible, but it will take a little work on your behalf. Start by reading acoustica.org.uk and checking some datasheets. Then put the soap box away and start a thread on PFM if your serious about modding this NAP90.

What are your intentions?


Rgds

Mike
__________________
www.drugfreeworld.org
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Advice needed on big sized bookshelves 18inch Multi-Way 3 30th May 2008 07:48 AM
Atom sized transistor... gmphadte Solid State 1 21st August 2007 06:19 PM
Aleph 1.2 under sized transformer? Steve Fay Pass Labs 10 16th October 2004 08:34 PM
Small Sized Enclosure Design Onur Multi-Way 11 8th July 2003 12:32 PM


New To Site? Need Help?

All times are GMT. The time now is 10:19 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2