An initial watt revision of a classic little amp - 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 7th February 2010, 06:16 PM   #1
diyAudio Member
 
Parasonic's Avatar
 
Join Date: Dec 2009
Location: Suncoast
Default An initial watt revision of a classic little amp

Hello,
I am new here--what a great fountain of info. I found Sir Hall's Pentonlector amplifier circuit on the web about 5 or 6 years ago http://www.radioconstructors.info/sd...or/circuit.jpg and since then have put the circuit together a few times trying out different output iron. I could never quite zero in on the sound I had hoped to get. The circuit still remains interesting, and recently I have revised the circuit to exclude the transformer and include a two transistor current source load. The results in my humble opinion are worth continuing on with. The current source seems to be a decent load for the amp, and one interesting feature is that R4 sets the midpoint voltage which seems to remain stable. I left this amp turned on accidently overnight the other evening, and all voltages were stable the next morning. I will try to post the circuit diagram for those interested. Apologies if it doesn't attach properly.
Attached Images
File Type: gif Enhanced Hall Amplifier.gif (14.0 KB, 904 views)
  Reply With Quote
Old 8th February 2010, 12:24 AM   #2
Bigun is online now Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
This looks very interesting. I see that the full anode - cathode voltage is across the base-collector of the output transistor. Can you indicate some of the voltages on your circuit ?
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 8th February 2010, 01:06 AM   #3
diyAudio Member
 
Parasonic's Avatar
 
Join Date: Dec 2009
Location: Suncoast
Hello,
I'd be glad to list the voltages after about 10 minutes of warm up time. And, I'd like to humbly acknowledge the true creator of this circuit the late Sir Douglas Hall, whose work I admire very much. All I did was modify an already elegant circuit. I measure with Vcc at +32VDC:

15.7 V at midpoint m (this moves up or down with change in R4)
Q1 collector/ V1 K at 2.5v (I thought this may cut off the tube but it works fine)
V1 screen at 31.8 V
MPSA18 collector at 16.7 V
2N3055 emitter at 16.1 V
MJ2955 base/ V1 plate at 15.0 V

there is approx 800ma of quiescent current flowing. As Sir Hall indicated in his original article, there is tremendous feedback established via the Q1 V1 interface. I have not yet substituted any parts for different ones, except origially I had a 2N3053 where the MPSA18 sits, however the MPSA18 works much better. I wish I had more test equipment. As I sat with a cold one the other night and pondered this circuit's merits, I wondered if the MPSA18 was acting like a common base amplifier which would apply a 180 degree out of phase signal on the top of R3. If it does, I don't see how it could possibly hurt anything by doing so---at any rate, without trying to describe the sound, I just like it.
  Reply With Quote
Old 8th February 2010, 01:30 PM   #4
Bigun is online now Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
I Q3 see it acting as a servo for Q2, keeping some control over the current, making the top half of the circuit a constant current source. You might be interested in a simple but interesting 'upgrade' to your circuit by converting this current source to an Aleph current source. Go and have a look at the Zen amplifier papers by Nelson Pass: http://www.passdiy.com/pdf/zen-ver2.pdf


here you will find the reason behind my interest in your circuit - we appear to be treating similar ground but I never got any further with this than some initial thoughts....

SET amp using Triode-FET complementary feedback pair ?
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

Last edited by Bigun; 8th February 2010 at 01:32 PM.
  Reply With Quote
Old 8th February 2010, 11:16 PM   #5
diyAudio Member
 
Parasonic's Avatar
 
Join Date: Dec 2009
Location: Suncoast
Thanks Bigun,

Wow, I have visited Pass DIY but never knew there was such extensive info on his current sources. The Aleph design is extremely interesting. Almost everything I was sitting there wondering about is explained very well. Dang, it seems that every time I work with Mosfets though, I blow 'em up! In trying to make the Hall amp work, I first found 2 transistor current source on an EDN link from Discover Circuits. Later I found good info from Rod Elliot's site. And have wondered how the dynamic impedance of the current source translates multiplied by the Q1 beta as the V1 plate load. It would be an odd mix indeed to have tube/bipolar/mosfet marriage. The only reason I have stuck with the Hall amp is it's utter simplicity, high input impedance and decent sound. It does have servo action, in that, if the Q1 collector current increases excessively, it will increase the tube bias accordingly. I have a lot to learn, and more test equipment is definitely needed, but will also need to spend more time at Pass DIY. On your circuit, have you got one up and running? Thanks again for the heads up on the Zen current sources.

Terry
  Reply With Quote
Old 14th February 2010, 12:09 AM   #6
diyAudio Member
 
Parasonic's Avatar
 
Join Date: Dec 2009
Location: Suncoast
Default Thanks Bigun

Finally had a little time to try out the suggestions you posted re: Nelson Pass current sources. I altered the CCS by splitting the 4.75K resistor and adding a bootstrap capacitor ala Pass. There is a great big difference in the output now. More clarity, far better bass. Mind you, this amp would require efficient speakers. There is something here worth working on further. I don't say its the ne plus ultra or anything but it has musicality. Also trying to figure out the cathode resistor, its function when changed causes the quiescent current to go up or down.......don't really get that yet, as I thought the CCS had command and control over the Iq. The current setup is happily playing some 70's music on the workbench (that is-----the inglorious basterd of workbenches!!)
Well.......cold beer here..........as the Stan Ridgway song says: "I'll do it tomorrow!"

Have a good one Bigun
  Reply With Quote
Old 14th February 2010, 01:59 AM   #7
Bigun is online now Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
Wow, you don't hang around, good to see you making progress.

I'm still playing with metal work. I don't enjoy that as much as I should so I'm trying to get the amplifier hardware sorted out before I play with the fun bits. Today I was breaking drill bits, filing and hacking bits around to install a volume potentiometer on the front panel of each box (I'm making 4 boxes - so I can play with 4 different designs).

I have set myself the challenge of using junk box parts, no orders to Digikey allowed. I can't think of a good reason for this, must be some truth in the old adage about 'mad dogs and Englishmen...'

But my junk box has a couple of Russian Nuvistors :-)
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 14th February 2010, 02:44 AM   #8
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
I don't uderstand the reason for the complexity of the Pass modulated current source outputs

the output stage in this sim shows a simpler approach with the same push-pull 50% efficient Class A result (sized for headphone amplifier)

Quote:
Originally Posted by jcx View Post
...

Click the image to open in full size.

...Q1,3 cfp has similar current gain but lower distortion than the complemetary Darlington/"Diamond" output

Q2,4 is a feedback ccs with a twist - tapping the current sense resistor R1,2 in the middle gives push-pull Class A output, ~170mA quiescent - >300mA pk output but does give hard current limit at 2x quiescent...
  Reply With Quote
Old 14th February 2010, 12:24 PM   #9
Bigun is online now Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
There are many different ways to 'skin the cat' and obtain a PP output. Nelson has explained his method well, tested it and documented it so that it is accessible to the DIYer regardless of skill level.

I started simulating the circuit you posted a few months back, although I had the modulated CCS on top and the CFP on the bottom and I put a resistor in series with C3 to control the balance between upper/lower current swing rather than split R4/5 - I like your split R4/5 approach. I like CFP too, I had the modulated CCS drive a CFP so that the output had a CFP at both top and bottom. The circuit has never been built though.
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 14th February 2010, 03:28 PM   #10
diyAudio Member
 
Parasonic's Avatar
 
Join Date: Dec 2009
Location: Suncoast
Default Nice looking circuit jcx

Well, have not gotten into push-pull circuitry for a long while, but I see your point.......I guess what interests me is preserving as much as possible the signal without chopping it in half, inverting the phase, etc. It was very interesting and enlightening reading Pass. The analogy of the operation of single ended type amps to air pressure (asymmetry) was very interesting. Its not that one way is any better than the other. The beauty of Mr. Pass's CCS designs to me are the fact that the load allows the output device to function to the extremes of its capability----until someone invents an output device that perhaps operates on some other principle. With the devices we have to work with, those designs are as advanced as it gets. As far as this little Hall amplifier goes, its just fun to see what can possibly squeezed out of it performance-wise. Its fun---no more and no less.

Bigun, I'll be watching for your progress--good luck

Terry
  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
Initial Project: 300W Power Amp bharfhy Solid State 13 6th January 2010 08:25 PM
B&G NEO8 PLANAR TRANSDUCER crossed to two Dayton classic 8"(DC200-8) nunayafb Planars & Exotics 28 13th April 2009 08:28 AM
Northcreek Okara Revision Question mevaniuck Multi-Way 3 2nd July 2006 07:15 AM


New To Site? Need Help?

All times are GMT. The time now is 03:40 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