Power amp under development

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#1,643
Mr Q:

I'm going to bother you once again with a couple of questions since i've started building the amp and i'm having some trouble; i went to the electronics store and they don't have some of the transistors i need. Do you have any reccommended replacements for:

2sc1845
mje350
mje340

I'd also like to know why i have to put T8 near the fets in that heatsink, if it's just to dissipate heat or there's another reason.

One more doubt, what program are you using to design the pcb's? because i need to make a pcb but protel 99 is giving me headaches.
Thanks again, and sorry for bothering!!
 
#1,645
Hi Quasi and all the people in this thread

A few days ago I decided to post my preliminary impressions about
the BJT version of your excellent design and this was done right
after I fired the amplifier for the first time with music.

However this was done with the bias still at the point of a tentative
setting. After Quasi told us about the ideal setting (around 65-75
mA) then I thought a good listening would be in order.

Only yesterday I was able to do so and it was an afternoon of pure delight, I've built a few good amplifiers, Symasym included but
with a quasi design in the back of my mind. Built the Cyrus clone
(a good amplifier too) but I wanted a more powerful design and I
ventured to built the quasi bjt version that I had on paper for some
time. I modified the layout for other than TO3 outputs (I think it's
called MT-200) and installed only 6 as opposed to eight the layout
called for.

The supply is +- 62V DC.
But I never thought this amplifier had such a high quality, I don't know the Mosfet version, I didn't built it, I had a good number of
bipolar transistors (2SC3857, Sankens) in my junk box, so that's
what pushed me to build this one.

Transparency, sound stage, strong bass and one of the best
overall quality that I ever heard, these are the best atributes I
can mention to define such a beast. Yes, because the amp is
huge and cumbersome but I am happy enough to have constructed it.
The best amplifier I have, to summarize.
Thanks Qausi for the design and I encourage others to build it
you won't regret it.
 

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#1,646
i'm planning to use +-70v. (rectified voltage)

What's the bjt version of quasi's amp? where can i find the schematic?

I have to add that a friend of mine who's studying electronics engeneering like me, but he's about to finish the career, saw te Nmos 350 schematic and said that it was simply a GREAT design. I have to agree, i think that what quasi has done with this amps is just amazing, and i seriously can't wait to see the Nmos i'm building in action. Once again, congratulations Mr Q for your great work.
 
#1,648
G'day Hernanstafe,

I am glad your amp works well and thank you for the great feedback. You just can't replace power as a major contributor to great sound.

I wonder if you would be so kind to post the information you've submitted here and anything else you can share in the other thread "Brother of Quasi". As you have shown the BJT version has great potential, and when well constucted (as you have done) should be a quality power amplifier.

Well done again your build and happy listening.

Cheers
Q
 
#1,650
jmateus said:
Hi Quasi and all the people in this thread...
Click to expand...

Wonderful to hear your response! I think the Mosfet version has clinical accuracy that would stun many people if they actually listened to it. I'm just getting some feedback from the chap I loaned my build to. He listens to a lot of classical and "modern" (new-ish) jazz. I'm not big on the classical and mostly like dirty old jazz records so his perspective is important to me. The guy is completely blown away with the Quasi Mosfet amp I built! To sum up his words, "it's a 'high-end' sounding amp with tremendous power capability". His words are completely different, I don't even know what the heck he was saying as I'm not into all that. :xeye: I will try to show him the DIY forum on his computer again, as it would be nice for him to provide a post but he doesn't get the whole DIY internet site thing. :whazzat:

Thinking back now and remembering a talk I had with anatech, I talked about one of my old fav power amps. It was the Yamaha P2201/2200 pro series models. I recall clearly from my teen years, before damaging a portion of my left ear, how clean a BIG power amplifier could sound. I always thought the P2001 did not color the sound like so many others amps did. If I was to say one thing about the Quasi Mosfet I built, it would be THAT but at the same time I know it sounds different? I guess I need to rebuild a P2201/2200? Perhaps it is the difference of Mosfet vs. BJT's? I miss that Yamaha...anyone got one going cheap. My collection has lots of room.

jmateus, can you share with us your "board work" & modifications? I too like the TO-3's. 🙂


Long Live Quasi,

Shawn.
 
#1,652
Mr Q:

I haven't built it, jmateus did, you confused the replies🙂 i was just asking you replacements for the transistors, the voltage i'll use for the amp is +-70v. Do you know any good replacements?

I did tho compliment the design, since i've been told by some people who know way more than me about electronics, that it's a really good design.

I'm working on the mosfet Nmos350 amp tho, i'm going to "burn" the pcb tomorrow hopefully, but i need to know the replacements for the transistors i mentioned above so i can start getting the parts.
 
#1,653
hernanstafe said:
Mr Q:

I'm going to bother you once again with a couple of questions since i've started building the amp and i'm having some trouble; i went to the electronics store and they don't have some of the transistors i need. Do you have any reccommended replacements for:

2sc1845
mje350
mje340

I'd also like to know why i have to put T8 near the fets in that heatsink, if it's just to dissipate heat or there's another reason.

One more doubt, what program are you using to design the pcb's? because i need to make a pcb but protel 99 is giving me headaches.
Thanks again, and sorry for bothering!!
Click to expand...


Instead of the 2SC1845 you could try these;

2SC2546, 2SC2547, 2SC1841, 2N5550, 2N5551, 2SC1845, 2SC2003, 2SC2784, 2SC2362, 2SC1775, 2SC2856, 2SD755, 2SD756. Try to choose one with the lowest noise rating.

For the second stage you could try BF469 / 470 instead of the MJE340 / 350.

For the third stage, you'll have to do some research to try and find something similar. The MJE340/350 is a pretty common transistor, have you tried ringing around or mail order ?

The mounting of T8 has nothing to do with keeping it cool. It is there to "measure" the temperature of the heatsink and adjust the output stage bias current to prevent problems. It must therefore be mounted in or on the heatsink as close as possible to the output FETs. Please do not try anything else as it will surely cause you pain.

I use a program called Sprint Layout to draw my designs. It's cheap and good enough for everything I do.
http://www.abacom-online.de/uk/html/sprint-layout.html


Cheers
Q
 
#1,655
Re: Bipolar

TomWaits said:
Perhaps I need to build the Brother of Q to compare?
Click to expand...


You could always run with the idea we explored with the Crown. I.e; You could run with the original output stage board and change the input and driver board. That would make it a Quaon (pronounced simliar to Crayon).

Oh dear .....sorry....Quasi's losing it ....Haaarg Haargh.

Cheers
Q
 
#1,658
Helllo Tom Waits

Are you asking for the modification I made on the original board to
acommodate the HT-200? Because that's what I did, in the link the board is done with TO3 transistors but a I had a lot of those 2sC3857
which are HT-200 I had to modify the board. If you want that (I can supply it, it's just a matter of e-mailing me directly, I'll be glad to
send it to you.

But I think there is a little confusion, I modify the TO3 board for a
board with those I mentioned...

Let me know, my adress is

joaomateus11@earthlink.net
 
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