power amp help please - Page 2 - 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 10th September 2012, 08:16 AM   #11
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Reduce the voltage from the transformer by adding a few dozen primary turns.
Reduces the temperature of the transformer and possibly makes it mechanically quieter as well.
__________________
regards Andrew T.
  Reply With Quote
Old 10th September 2012, 08:17 AM   #12
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
63V?

75V or 80V would be enough margin for me.

Might do 300W/4Ω for you, sounds like you have a nice project!
__________________
Candidates for the Darwin Award should not read this author.
  Reply With Quote
Old 10th September 2012, 02:34 PM   #13
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
A 40Vac transformer comes out @ 58 to 60Vdc at the smoothing caps.

If you are seeing 63Vdc then that indicates that the transformer is > 40Vac. Maybe a 45vac. This will need 75/80V caps. 100V caps will cost a lot, lot more.
__________________
regards Andrew T.
  Reply With Quote
Old 10th September 2012, 04:33 PM   #14
diyAudio Member
 
Join Date: Dec 2010
Location: wigan
Default Potted centre

Quote:
Originally Posted by AndrewT View Post
Reduce the voltage from the transformer by adding a few dozen primary turns.
Reduces the temperature of the transformer and possibly makes it mechanically quieter as well.
Hi Andrew
Unfortunatley the transformer has a potted centre so not possible to add out of phase or remove in phase windings. The main smoothing capacitors are original and the powered mixing desk was used for background music aswell as live gigs so has done many hours I will be recapping it just for good measure. The main reason i mentiond the caps only being 63VDCis i could not belive a large manufacturer would have fitted these also i am quite surprised they have lasted so long. they even quote 63Vdc caps in the original scematic. As for the price of 100Vdc caps im not too worried as the rest of this amplifier came free of charge.
Regards Mark

Last edited by madtecchy; 10th September 2012 at 04:51 PM. Reason: typo
  Reply With Quote
Old 10th September 2012, 04:50 PM   #15
diyAudio Member
 
Join Date: Dec 2010
Location: wigan
Quote:
Originally Posted by djk View Post
63V?

75V or 80V would be enough margin for me.

Might do 300W/4Ω for you, sounds like you have a nice project!
Hi djk.
The amplifier is rated by the maker as being 350 Rms into 4 Ohm's and 210 Rms into 8 Ohm's. it uses a higher voltage rail at 73 volt to power the front end and Vas. yes it is a bit of a project and has far too much power for my needs . oh yea i nearly forgot as this amplifier has a balanced input can i just take the inverting input to audio ground so i can drive it from a single ended source.

Best regards mark
  Reply With Quote
Old 11th September 2012, 07:16 AM   #16
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by madtecchy View Post
210 Rms into 8 Ohm's.
If this is BJT output stage then that power confirms a 45Vac transformer.
41Vac is very close to the absolute maximum that can be used with 63V capacitors.

I too have a high quality amplifier that uses a 35Vac transformer and 50Vdc capacitors. This practice is a scandal, no matter how good they claim the sound quality.
__________________
regards Andrew T.
  Reply With Quote
Old 11th September 2012, 07:45 AM   #17
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
"The amplifier is rated by the maker as being 350 Rms into 4 Ohm's and 210 Rms into 8 Ohm's."

A 1Khz rating I'm sure (standard for PA), nothing wrong with that.

"can i just take the inverting input to audio ground so i can drive it from a single ended source. "

Yes.

" i could not belive a large manufacturer would have fitted these"

A large manufacturer (that will remain nameless) used to make a PA amplifier with 85V using a 75V cap. Another (very well respected name) hi-fi manufacturer used to run 52V on 50V caps.

When Peavey amplifiers with 52V rails and 55V caps would need replacement I would always use 63V. Same with the Bryston 3B.

I prefer to have 10% margin, and allow another 10% for high line voltage (76.23V for your 63V example, I could live with 75V or 80V).
__________________
Candidates for the Darwin Award should not read this author.
  Reply With Quote
Old 11th September 2012, 07:15 PM   #18
diyAudio Member
 
Join Date: Dec 2010
Location: wigan
Hi Andrew
Yes the amplifier uses BJT MJ 15003 and MJ 15004 two of each . Im not sure how this amplifier will sound . The unit is more like 15 years old and im shocked the caps have lasted this long . Also it only uses two 3300uF caps in parrallel per rail to feed two channels. They look real small too for this power level . Anyway time to stop wondering and time to fire it up . Fingers crossed

Regards Mark
  Reply With Quote
Old 11th September 2012, 08:00 PM   #19
diyAudio Member
 
Join Date: Dec 2010
Location: wigan
Hi djk

Advice apreciated i will use 80 Vdc .Now for the 73 volt rail. It only uses 16Vdc caps for smoothing . The twist is they have smoothed the higher 73 volt rail against the lower 63 volt rail of same polarity and not to ground . from what i have learned form diy audio im really noe sure that is good sound quality practice to me it looks like thay have found a cheap way to screw the last watt out of this amp so it looks good on paper. Aparently it was supposed to be a very good unit in its day But then again it is a PA amplifier . .
  Reply With Quote
Old 11th September 2012, 08:27 PM   #20
diyAudio Member
 
Join Date: Feb 2009
those 16V cap will do fine. they only see the difference between the 63V rails and the 73V rails. so those caps only see 10V.
  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
LTspice tool for power amp power supply component evaluation andy_c Software Tools 2 23rd August 2009 05:10 PM
Adding a 12V power trigger switch to Electrocompaniet Power Amp maxzimum Solid State 0 11th April 2008 01:54 PM
WIll an X-PSU v1 power an SI T-amp &/or TC754 pre-amp? gnostic19 Class D 7 3rd August 2007 01:26 AM
High Freq. AC Power for Filaments of 300B SE Power Amp? snoopyma Tubes / Valves 6 3rd January 2004 06:21 PM


New To Site? Need Help?

All times are GMT. The time now is 12:46 AM.


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