Tube-Buffered Gainclone - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 31st May 2008, 07:37 PM   #1
diyAudio Member
 
sorenj07's Avatar
 
Join Date: May 2006
Default Tube-Buffered Gainclone

Hi, first post in this neck of the woods I've got a 2x30V 300VA Hammond toroid kicking around. Would it be suitable for building a gainclone using the standard LM3875T chips? I usually see secondaries around 18-22V being used. I would probably have a rail voltage of around +- 42V. On the other hand, I could wire the dual primaries in series to put out +-21V or so, but this seems a little low... Speakers used would be 8 ohms.

Does anyone happen to know the input impedance of the LM3875 by the way? It'd be useful in designing the cathode follower which would feed the volume control.
  Reply With Quote
Old 31st May 2008, 07:43 PM   #2
diyAudio Member
 
Greg Erskine's Avatar
 
Join Date: Jan 2002
Location: Sydney/Australia
http://www.national.com/ds/LM/LM3875.pdf
__________________
Greg Erskine
  Reply With Quote
Old 31st May 2008, 08:06 PM   #3
diyAudio Member
 
sorenj07's Avatar
 
Join Date: May 2006
Am I right in assuming, then, that 42V will be ok into 8 ohms since it's well under the maximum rating of 80V or so? I'm new to these "solid state" things I assume I should try to mount them to a heatsink, right?
  Reply With Quote
Old 31st May 2008, 10:01 PM   #4
diyAudio Member
 
ionomolo's Avatar
 
Join Date: May 2007
Location: Los Angeles
Send a message via MSN to ionomolo
Quote:
Originally posted by sorenj07Am I right in assuming, then, that 42V will be ok into 8 ohms since it's well under the maximum rating of 80V or so? I'm new to these "solid state" things I assume I should try to mount them to a heatsink, right?
Yes, you need a big one! there is an application note on heatsinking national amplifiers and some information on the datasheet.
  Reply With Quote
Old 31st May 2008, 10:06 PM   #5
diyAudio Member
 
sorenj07's Avatar
 
Join Date: May 2006
All right. Do you think some CPU style heatsinks with a mounted fan would work all right? I have no clue about dissipation ratings and the like, but I will take another look at the datasheet. It's just so long
  Reply With Quote
Old 31st May 2008, 10:33 PM   #6
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
Quote:
Originally posted by sorenj07
All right. Do you think some CPU style heatsinks with a mounted fan would work all right? I have no clue about dissipation ratings and the like, but I will take another look at the datasheet. It's just so long
Not a chance.... They dissipate about 60W with fans blowing like mad. If at all possible issolate the heatsink from the case, then mount the chip useing only a little thermal grease... but you are going to need a much sturdier sink than that...
  Reply With Quote
Old 31st May 2008, 11:25 PM   #7
diyAudio Member
 
sorenj07's Avatar
 
Join Date: May 2006
There are some interesting-looking options for the tweaker market..
http://www.newegg.com/Product/Produc...page=1&bop=And

Either some of the more crazy ones, or I start looking for massive blocks. Pity, I figured that these chips wouldn't need that much sinking.
  Reply With Quote
Old 31st May 2008, 11:55 PM   #8
DC Dave is offline DC Dave  United States
diyAudio Member
 
DC Dave's Avatar
 
Join Date: Feb 2004
Location: Washington DC
Quote:
Originally posted by sorenj07
Am I right in assuming, then, that 42V will be ok into 8 ohms since it's well under the maximum rating of 80V or so? I'm new to these "solid state" things I assume I should try to mount them to a heatsink, right?
Wait a minute.

That is going to be to high. 42+42=84V. The 80V maximum referred to is the sum of the + and -. You are going to want a lower voltage for that chip.
  Reply With Quote
Old 1st June 2008, 12:12 AM   #9
Zigis is offline Zigis  Latvia
diyAudio Member
 
Join Date: May 2005
Location: Riga, Latvia
With this trafo you can use regulated PS, to regulate voltage down.
LM338 regulated snubberized PSU for audio amplifiers
  Reply With Quote
Old 1st June 2008, 05:58 PM   #10
diyAudio Member
 
sorenj07's Avatar
 
Join Date: May 2006
Hey, looks perfect!
Click the image to open in full size.

What do you make of using the following schem for the signal part?
http://www.geocities.com/rjm003.geo/...io/diy_gc.html
specifically, this:

Click the image to open in full size.

Or should I just use the textbook example from the datasheet, under "Typical Application"? Anyone have any recommendations?
  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
Buffered, balanced gainclone kits. jamikl Chip Amps 2 1st March 2009 03:51 PM
Tube Buffered Non-Inverting Gainclone Design mwl6m Chip Amps 0 31st July 2007 03:26 PM
Tube-buffered Gainclone for a guitar amp? Spasticteapot Chip Amps 6 4th May 2006 06:42 PM
tube buffered gainclone with cpu fan and heatsink steven344 Chip Amps 0 21st November 2005 06:01 PM
valve buffered gainclone questions moonshow Chip Amps 1 10th July 2004 08:31 AM


New To Site? Need Help?

All times are GMT. The time now is 05:35 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