VERY old school amp

Dan2 · 1st November 2007, 01:44 PM

i have a mosfet amp that looks like it came from the stone age ( well you can see all the parts have been hand soldered in) but it still works well and can drive a pretty decent speaker.

it has the preamp built in - so all u have to do is hook up a cd player, speaker and it plays music.

the only problem is that the amp distorts before it reaches its power limits (i think), because the supply voltage doesn't drop too much (maybe 1 volt) and the bass doesn't thin out, and the amp doesn't even get warm

is this just how mosfet amps work or does it sound like i could get some more power out of this amp?

poynton · 1st November 2007, 02:25 PM

Could the CDplayer be overloading the input ??

A photo and schematic would help.

Andy

AndrewT · 1st November 2007, 02:55 PM

Hi,
Mosfet amps generally perform better with a higher bias current than a BJT amp.
This usually means that it runs warmer. Odd that you say it does not warm up.

I wonder if the distortion is a crossover problem?

Can you identify how to measure the output stage bias current?
Can you estimate the heatsink capacity and temperature rise?
Can you tell us what the output stage consists of? Driver and output device type numbers and number off.

Dan2 · 2nd November 2007, 01:11 PM

i don't have a schematic of this amp, sorry. i can tell u what is written on the mosfets : SGS 9805 DB116 (i think they are mosfets)

i tried looking for the datasheets of the DB116's but no luck.

here are some pics

Dan2 · 2nd November 2007, 01:13 PM

from the side

Dan2 · 2nd November 2007, 01:14 PM

-

Elvee · 2nd November 2007, 01:27 PM

Hi,

Looking at the pictures, it seems pretty sure it is not a mosfet amplifier. In fact, the output devices might even be germanium.
The first thing I'd do is to check the electrolytics : there is a number of them, and after 40y or so, there is a good chance one or two have dried out.
LV

poynton · 2nd November 2007, 02:15 PM

What are the numbers on the other transistors ?

Andy

Dan2 · 3rd November 2007, 11:33 AM

how do you check the electrolytics??? and what happens to the amp when the caps dry out? 'cos it still works well, it just doesn't seem to run at its full potential.

i don't suppose you can guess the power output, maybe??

poynton · 3rd November 2007, 01:42 PM

Quote:

Originally posted by poynton
What are the numbers on the other transistors ?

Andy

Any answer ?

Also what volume control arrangement are you using?

Andy

1st November 2007, 01:44 PM	#1
Dan2 diyAudio Member Join Date: Sep 2005	VERY old school amp i have a mosfet amp that looks like it came from the stone age ( well you can see all the parts have been hand soldered in) but it still works well and can drive a pretty decent speaker. it has the preamp built in - so all u have to do is hook up a cd player, speaker and it plays music. the only problem is that the amp distorts before it reaches its power limits (i think), because the supply voltage doesn't drop too much (maybe 1 volt) and the bass doesn't thin out, and the amp doesn't even get warm is this just how mosfet amps work or does it sound like i could get some more power out of this amp?

1st November 2007, 02:55 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, Mosfet amps generally perform better with a higher bias current than a BJT amp. This usually means that it runs warmer. Odd that you say it does not warm up. I wonder if the distortion is a crossover problem? Can you identify how to measure the output stage bias current? Can you estimate the heatsink capacity and temperature rise? Can you tell us what the output stage consists of? Driver and output device type numbers and number off. __________________ regards Andrew T.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Old School Fan	syncro	Introductions	2	8th May 2009 10:25 PM
Old School F5 by ZM	Zen Mod	Pass Labs	77	27th January 2009 08:03 PM
Old School favorites go bad while I'm out of school...HELP!	HayaBuddha	Car Audio	5	26th March 2007 05:20 AM
Old School Top 5	mgibson	Solid State	7	5th July 2006 05:18 PM
old school fun	chainenoble	Multi-Way	0	21st May 2006 06:23 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

1st November 2007, 02:25 PM	#2
poynton Magneto the Gravity Man diyAudio Member Join Date: Mar 2005 Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)	Could the CDplayer be overloading the input ?? A photo and schematic would help. Andy

2nd November 2007, 01:27 PM	#7
Elvee diyAudio Member Join Date: Sep 2006	Hi, Looking at the pictures, it seems pretty sure it is not a mosfet amplifier. In fact, the output devices might even be germanium. The first thing I'd do is to check the electrolytics : there is a number of them, and after 40y or so, there is a good chance one or two have dried out. LV

2nd November 2007, 02:15 PM	#8
poynton Magneto the Gravity Man diyAudio Member Join Date: Mar 2005 Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)	What are the numbers on the other transistors ? Andy

3rd November 2007, 11:33 AM	#9
Dan2 diyAudio Member Join Date: Sep 2005	how do you check the electrolytics??? and what happens to the amp when the caps dry out? 'cos it still works well, it just doesn't seem to run at its full potential. i don't suppose you can guess the power output, maybe??

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)