transformer and transistor question - Page 4 - 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 3rd January 2009, 06:46 PM   #31
rtill is offline rtill  United States
diyAudio Member
 
Join Date: Sep 2006
after more research, my transistors are fakes! I am assuming the pinouts are different.

http://images.google.com/imgres?imgu...%3Den%26sa%3DN


Any substitutes I could use in place of these?
  Reply With Quote
Old 3rd January 2009, 06:46 PM   #32
diyAudio Member
 
Nico Ras's Avatar
 
Join Date: Nov 2005
Location: East Coast of South Africa
http://digisec.co.za/ras/music/RAS%2...mp%20Rev02.zip

is the link to the project file and includes current PCB as built by several people.

The biggest problem I have had in the past is guys laying their own PCBs, but making mistakes when capturing the circuit diagram - I am not saying you did, but that is most common.

Keep in mind that this amp is not 300 watt as what is claimed on the web-site you got it from. I am not sure why this guy said so in the first place, maybe to attract people to his site.

Here is the link to the 340 watt 4 ohm version of this amp.

http://digisec.co.za/ras/music/300w%20MOSFET%20AMP.pdf

Kind regards

Nico
  Reply With Quote
Old 3rd January 2009, 06:50 PM   #33
rtill is offline rtill  United States
diyAudio Member
 
Join Date: Sep 2006
Thanks for the links and help! I'm only looking to get 100-150 watts anyways - but more power is always better!

Any substitutes I could use for the mosfets?
  Reply With Quote
Old 3rd January 2009, 07:00 PM   #34
diyAudio Member
 
Nico Ras's Avatar
 
Join Date: Nov 2005
Location: East Coast of South Africa
Quote:
Originally posted by rtill
after more research, my transistors are fakes! I am assuming the pinouts are different.

http://images.google.com/imgres?imgu...%3Den%26sa%3DN


Any substitutes I could use in place of these?
This circuit was designed for Lateral Mosfets, but with some component value changes it can be made to work with Hexfets. What have you got?
  Reply With Quote
Old 3rd January 2009, 07:02 PM   #35
rtill is offline rtill  United States
diyAudio Member
 
Join Date: Sep 2006
I would have to see what the local electronic store has.... any examples I could use and if so, what values would be changed?
  Reply With Quote
Old 3rd January 2009, 08:15 PM   #36
rtill is offline rtill  United States
diyAudio Member
 
Join Date: Sep 2006
found some.... KD998 and Kb778 mosfets in an old 225 watt car amp. Can't find any info on these though.
  Reply With Quote
Old 3rd January 2009, 09:18 PM   #37
diyAudio Member
 
Nico Ras's Avatar
 
Join Date: Nov 2005
Location: East Coast of South Africa
Quote:
Originally posted by rtill
I would have to see what the local electronic store has.... any examples I could use and if so, what values would be changed?
Okay here goes, probably not the highest-fi but now it uses more common MOSFETS IRF140 and IRF9130 and good for about 120 watt rms into 8 ohms using +-55V rails.

The BD139/140 are running at 350 mW and may need small heat sinks.

R7 could be a 1 K trim pot to set the quiescent current. With the resistor value shown it is about 350 mA.

Hope this satisfies your needs.

Kind regards

Nico
Attached Images
File Type: jpg 120 w mosamp.jpg (65.7 KB, 89 views)
  Reply With Quote
Old 3rd January 2009, 09:23 PM   #38
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally posted by rtill
I would have to see what the local electronic store has.... any examples I could use and if so, what values would be changed?

I used IRFP240 and IRFP9240 pairs on my amp.
You can get them on ebay for a couple of pounds.

But you would need a proper bias circuit otherwise you will get either crossover disotrtion or the amp taking a lot of standing current.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 3rd January 2009, 09:32 PM   #39
Account disabled at member's request
 
Join Date: May 2006
Hi Rtill,

The kd998 and kb778 are not mosfets, beware, dont even try, the are high power audio bipolars second source manufactured by most probably KEC.

As for your problem with fakes please help yourself and others from falling into these traps with fakes. Return them to the shop, insist on a refund or their replacement with originals. If they get funny with you tell them you going to file a complaint and announce them all over the internet on consumer protection sites specially in the usa. Also that you will be informing Renaces of this situation, Renaces is original manufacturer. If they were selling these unknowingly they will refund immediatly, even if we are only talking of only a few dollars here youll be doing the electronics world a favour. Save all email correspondence with them especially their reply, if they dont act contact me and Ill give you a site to report this. Then send them a email to let them know that you have done this. We need to stamp this kind of b..lls...t out. At least they were charging less for them but its still decieving the consumer and misrepresentation, some charge the price of originals and give you fakes. If I were in usa I would personally give you a hand with this, I am sick and tired of being decieved too, I buy larger amounts and when someone does this to me I go after them.

Start a thread in electronics and parts and tell others of the situation so they dont fall into this trap too if you fail to have any response from them.
  Reply With Quote
Old 3rd January 2009, 11:16 PM   #40
diyAudio Member
 
Nico Ras's Avatar
 
Join Date: Nov 2005
Location: East Coast of South Africa
Quote:
Originally posted by Nico Ras


Okay here goes, probably not the highest-fi but now it uses more common MOSFETS IRF140 and IRF9130 and good for about 120 watt rms into 8 ohms using +-55V rails.

The BD139/140 are running at 350 mW and may need small heat sinks.

R7 could be a 1 K trim pot to set the quiescent current. With the resistor value shown it is about 350 mA.

Hope this satisfies your needs.

Kind regards

Nico

Quote:
Originally posted by nigelwright7557



I used IRFP240 and IRFP9240 pairs on my amp.
You can get them on ebay for a couple of pounds.

But you would need a proper bias circuit otherwise you will get either crossover distortion or the amp taking a lot of standing current.
As you can see that bias can be adjusted quite accurately using a single pot of about 1k and 25 turns. I run mosfets at about 250 mA bias current and there is no crossover distortion.

The fixed resistor is set a little higher and you should never encounter cross-over distortion in this setup.

You can also see from the graphs that the system is stable under varying temperature conditions. It clearly shows that at higher temperature, the bias backs down.

This remains a very simple and robust little amp.

Nico
Attached Images
File Type: jpg untitled7_crop.jpg (50.6 KB, 67 views)
  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
Transistor Question Tripmaster Chip Amps 33 10th February 2009 09:55 PM
Transistor testing question woody Solid State 0 10th October 2008 04:08 AM
The ultimate single ended class a transistor transformer?! dave_gerecke Solid State 3 8th March 2008 11:00 AM
transistor question mike49504 Car Audio 9 10th April 2007 10:59 PM
transistor circuit to replace transformer in ribbon mic? ubertar Instruments and Amps 1 14th August 2004 09:42 AM


New To Site? Need Help?

All times are GMT. The time now is 04:26 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