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 28th November 2012, 05:12 PM   #1
diyAudio Member
 
monty78pig's Avatar
 
Join Date: Aug 2011
Location: London
Send a message via Skype™ to monty78pig
Post First amp I ever built - An excellent simple class A amp for beginners

Here's a slightly improved variant of the first amplifier I ever built, I was clearing some hard disk space when I found it and thought it would be worth sharing.

It's a very simple amp, with just 3 active devices, but worked very well when I built it at 14. I originally built just one channel using parts that were mostly scavenged from broken amps I'd been given and used it with a big old wharfedale speaker I'd bin raided out of an electricals bin. I used it with my pc and with an old autochanger and two transistor preamp to play 78rpm records.

The design isn't completely original as I'd copied some parts of the topology from a few amplifiers featured on the Elliot Sound Products website but worked out the component values myself. I've changed a few of them and added a zobel network, although it behaved well enough without it at the time. I've also added an ESR to prevent ground loops from becoming an issue.

The design is very simple and I've included a power supply schematic if anyone wants to build a stereo version. The one I built gave about 15 watts or more output power and had a gain of roughly 27dB, and I'd imagine the THD would have been less than 0.1%. The amp is simple enough to build point to point (I built it originally on thick cardboard and mounted it inside an old radiogram), none of the parts are at all difficult to find or big and expensive, its very easy to troubleshoot, no adjustment is required once it is built and you don't have to worry about having an 'on' light (although the LED used for the reference in the constant current source must have a forward voltage of 1.9V to 2.0V)!

It should make a very rewarding amplifier, should anyone new to DIY choose to build it, I have stated all the necessary component ratings on the diagram. For the number of active devices used performance should be excellent.
Attached Images
File Type: png Begginers Amp PS.png (18.8 KB, 414 views)
File Type: png Begginers Amp.png (28.9 KB, 427 views)
__________________
With perfect linearity, it is impossible to go off on a tangent. Also; My Sziklai pairs are better than your MOSFETs/Darlingtons/Pentodes/Triodes

Last edited by monty78pig; 28th November 2012 at 05:16 PM. Reason: errors
  Reply With Quote
Old 26th July 2013, 08:59 PM   #2
diyAudio Member
 
monty78pig's Avatar
 
Join Date: Aug 2011
Location: London
Send a message via Skype™ to monty78pig
LOL - No comments?
__________________
With perfect linearity, it is impossible to go off on a tangent. Also; My Sziklai pairs are better than your MOSFETs/Darlingtons/Pentodes/Triodes
  Reply With Quote
Old 26th July 2013, 09:32 PM   #3
diyAudio Member
 
vacuphile's Avatar
 
Join Date: Apr 2011
Location: Right behind you.
Still building.
__________________
Everything eats everything else, given appetite and opportunity.
  Reply With Quote
Old 27th July 2013, 07:35 AM   #4
Bonsai is offline Bonsai  Taiwan
diyAudio Member
 
Bonsai's Avatar
 
Join Date: Jul 2003
Location: Taipei, Taiwan
Very nice and simple! I like the overall concept.
__________________
bonsai
Amplifier Design and Construction for MUSIC! http://hifisonix.com/
  Reply With Quote
Old 27th July 2013, 08:34 AM   #5
diyAudio Member
 
Join Date: Apr 2011
Location: Pretoria
Only three transistors? Nice.

Could it be improved by the use of a split supply so that the 4700uF on the output can be left out?
  Reply With Quote
Old 27th July 2013, 09:39 AM   #6
diyAudio Member
 
Join Date: Apr 2011
Location: Pretoria
To answer my own question - I ran the circuit numbers in LTspice and it turns out that there is still a significant DC offset on the output with a split supply.
  Reply With Quote
Old 27th July 2013, 10:23 AM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
R3/R4 can be used to set the output offset of a DC coupled output.

I recommend you keep it as a single polarity, AC coupled output, Single ended, SS amplifier. In this you use R3/R4 to adjust the output DC voltage before C6 to ~ half rail voltage.

This design really needs a speaker delay relay (either solid state or mechanical).
If not used, the charging of the DC blocking capacitor will send a high current through the speaker.
Once this protection is added, I would experiment with adjusting the value of C6 to suit the speaker passband. For bass reproduction maybe 10mF to 15mF, for mid duty maybe 1mF to 2200uF, for treble duty maybe 10uF to 220uF

There is no compensation shown.
Where would be the places it can be added, if it's discovered that some stability compensation is required?
__________________
regards Andrew T.
  Reply With Quote
Old 27th July 2013, 10:25 AM   #8
diyAudio Member
 
monty78pig's Avatar
 
Join Date: Aug 2011
Location: London
Send a message via Skype™ to monty78pig
Yes, the Vbe of Q1 and the current running through R7 make a small offset. Improvements can be attained by swapping L1 for a 3.3V zener diode and adjusting R9 accordingly. I'm presenting the circuit here as I first built it, though.

I saw the output cap as a bonus at the time, short circuit protection . You can short the output, put whatever you want into the amps input and it'll be just fine .
__________________
With perfect linearity, it is impossible to go off on a tangent. Also; My Sziklai pairs are better than your MOSFETs/Darlingtons/Pentodes/Triodes
  Reply With Quote
Old 27th July 2013, 05:36 PM   #9
diyAudio Member
 
monty78pig's Avatar
 
Join Date: Aug 2011
Location: London
Send a message via Skype™ to monty78pig
Never needed any compensation although - a cap of about 100pF or so could be placed between the base and collector of Q3 if any problems arose.

I never had much trouble with turn on thump - I think the slow charging of C2 brings the output up slowly without too much audibility.

4700uF is more than enough (I think I may have originally used 2200uF) gives a cuttoff of about 4 Hz into 8 ohms or 8Hz into 4 ohms. This circuit was designed for 6 ohm operation.
__________________
With perfect linearity, it is impossible to go off on a tangent. Also; My Sziklai pairs are better than your MOSFETs/Darlingtons/Pentodes/Triodes
  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
simple class D amp latala Class D 22 28th November 2012 10:24 PM
simple Class A amp muddasirwaheedmalik Solid State 5 4th February 2012 12:49 PM
Built a Cheap Class D amp dano12 Class D 0 15th July 2009 03:40 PM
link to class d amp kit built 20 yrs ago steven344 Class D 2 19th November 2005 03:56 PM
Beginners Project: Need a schematics for a small simple EL84 SE (or PSE) amp Erik Johansson Tubes / Valves 2 15th May 2002 11:35 AM


New To Site? Need Help?

All times are GMT. The time now is 05:46 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