BUZ-amp

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
fab said:
Argo,

Trying to figure out your intent based on your comments on this thread, here is what I began to have in mind before I got to sleep yesterday.

You will recognize your symetric diff input stage (MPA30) and mosfet in voltage gain configuration ( Megalith output stage) with local feedback. Also, it has a VAS to increase open loop gain and the Megalith output stage. It has bias current adjustment to go either class AB or up to class A. Since you can adjust resistors values to your needs ,you are able to either have a very low feedback or high feedback design. It is just an adaptation from your original concept and I do not pretend that it can give outstanding results (but it could too!). What do you think?

Fab


argo said:
Sorry for delayed respond

Fab
Thanks for schematic. I need more time to ponder about it.

Argo


Hello,

http://www.diyaudio.com/forums/attachment.php?s=&postid=403402

This diagram, on the principle, resembles that of the AXL classifies A (Elektor) and very near also to the very known Palouda diagram. This diagram AXL was an evolution of very known Mini Crescendo, unfortunately it did not have the success discounted (it sounds less better with my taste) like these Mini diagrams and Crescendo. To also see the version of JMP.


http://www.mif.pg.gda.pl/homepages/tom/files/70MOS.gif Mini Crescendo

http://perso.wanadoo.fr/francis.audio2/Rds236_palouda.gif Palouda

http://perso.wanadoo.fr/jm.plantefeve/nrds2.jpg JMP


@ + Jean-François
 

fab

Member
Joined 2004
Paid Member
Bonjour Jean-François

Thanks for your interest.

Your posted circuits diagrams are fine but are quite different from the "fab concept based on argo"; the output stage (mosfet in inverting gain with associated driver bjt in inverting gain also, local feedback on output stage, cascode input stage) is not part of the listed circuits in your post.
The mini-crescendo is a standard mosfet follower output stage.
The Palouda is an inverting gain with associated driver bjt in inverting gain also but using power output BJTs instead of power mosfets.
The Jean-Marc Plantfeve has a standard mosfet follower output stage.

So it is not possible to compare the sound of a "non built amplifier" (fab based on argo) with the ones you have listed.

Thus, I suggest that argo continues to "...ponder about it."

Merci

Fab
 
Fab

Thanks again fab. To tell you a truth I haven’t got around of your circuit yet. I started to consider your pervious warnings about highish output impedance of this kind of output stage because my next speakers I am planning to build (MTMWW) will probably have a impedance drop as low as 2.5 - 3 ohm and I decided to build more convenient amp to power them.
So here is another circuit "to ponder about".
This circuit is a modified version of one well regarded amplifier kit. The original circuit has BJTs in the first stage with corresponding current sinks and voltage regulator and has servo to stabilise the DC offset. The modification is suggested by one of our forum member and my friend and consists of replacing the first stage circuitry with only a pair of jfets. He has built the original version and the sound of the amp is one of the best I have heard so far. I’ll try to build this simplified version for a comparison.


argo
 

Attachments

  • buzamp2.gif
    buzamp2.gif
    7.6 KB · Views: 1,105

fab

Member
Joined 2004
Paid Member
Hi Argo

Getting back to our theoritical design, the "inverting" mosfet output stage is used in Hafler 9500 and 9505 power amps and the latter got a very good review from Jean Hiraga in an audiophile magazine.

Your last posted circuit appears to have a similar topology to another posted schematics on this forum:
http://www.diyaudio.com/forums/showthread.php?postid=379920#post379920
...if you remove the Hawksford error correction circuit, cascode input stage, darlington VAS, DC servo and replace the output BJTs with mosfets.
I have not built a "no overall feedback" amp but I wonder how such a design can have a low and stable DC offset at output without a DC servo (which by the way is a 100% overall feedback at DC and very low sub audio frequencies).
To do a fair comparison with the "well regarded amplifier kit" (which one is it?) you may try to use regulated voltage for the all the driver circuit before the output mosfet.

Good luck with your new project!

Fab
 
argo said:
... . He has built the original version and the sound of the amp is one of the best I have heard so far. I’ll try to build this simplified version for a comparison.

argo


Hello,

Welcome with the Club, is it by chance which it resembles a diagram JMP, between Zenquito Evolution and Amperotron without negative feedback.

http://perso.wanadoo.fr/jm.plantefeve/sche.html http://perso.wanadoo.fr/jm.plantefeve/dipolex.html

http://www.diyaudio.com/forums/attachment.php?s=&postid=431898
One needs that R8 and R9 are variable to regulate the tension continuous of exit (Offset), Fet having rather important disparity, it will be necessary to make the appairage as well as possible...

Good listening

@ + Jean-François
 
fab said:
Hi Argo

.......
I have not built a "no overall feedback" amp but I wonder how such a design can have a low and stable DC offset at output without a DC servo (which by the way is a 100% overall feedback at DC and very low sub audio frequencies).

Well, I am very curious about the DC offset behaviour as well. The only way to find that out for me is to build it.

fab said:
To do a fair comparison with the "well regarded amplifier kit" (which one is it?) you may try to use regulated voltage for the all the driver circuit before the output mosfet.
Good luck with your new project!

Fab


Yes I intended to use regulated voltage.
I don’t know if I will violate some copyright rules if I post the original schematic here. If so, I ask moderators to correct me and remove my last posts. Anyway here it is (the newer, Mk III version has some slight changes) http://www.tnt-audio.com/gif/a18a.gif


JFG67 said:

..........
One needs that R8 and R9 are variable to regulate the tension continuous of exit (Offset), Fet having rather important disparity, it will be necessary to make the appairage as well as possible...

Good listening

@ + Jean-François

Yep, R8 and R9 will be variable and iput jfets will be matched. Learnt that by hard way by building Mr Lannes amp and Ampereton.

Argo
 
Well, my buzamp_2 http://www.diyaudio.com/forums/attachment.php?postid=431898 is up and running.
DC offset at output wanders around +and - 100mV.
Still need to hassle with power supply and with speakers (they are in rebuilding state as well) to give a adequate impressions of the real sound. But so far it sounds pretty nice. Soundstage is much bigger then with my pervious JLH amplifier.
While the amp is not totally finished yet, I stumbled across another similar schematic from Hawk Audio http://www.hawkaudio.nl/amppic/hb30sch.JPG
I did a bit additional cutting of the schematic and run some simulations. The sim results are promising and far better from the circuit I have already built. So I thought, why do I need that hassle with input stage jfets matching - this should be sufficient? Ok, it has servo but...then I don’t have DC offset to worry about.
Well the sims have one story to tell and real practice another. So I thought to ask you guys for another opinion before I run to scrap my buzamp_2 amp without giving him a due time prove his worth.

Argo
 

Attachments

  • buzamp_3.gif
    buzamp_3.gif
    17.1 KB · Views: 698
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.