Power amp under development

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#2,981
Wassim, wires are too long and thin, for good bass you need
Short ,fat, 10 gauge wires ,copper bars across your filter caps,
AND I hope that's not your main PS transformer I see there!!
(what are you using?)
Neat, FAT, and short..that 's for power!:wiz: P.S.
these amps sound "tinny" (tried it with my BOQ*)
if there is not enough bias on
the outputs...2sc2240/1845 spec out real close so no
problem there.

A huge transformer (800/1500VA- 50-0-50)..
http://www.antekinc.com/AN-15450.pdf
good for NMOS 600/2 ohm?:dead:
not bad for 60 or 120 US$.

also 12 gauge lamp cord to speakers would help..

By the way I went shopping to buy the best passive
components for these Q amps andhttp://www.newark.com/ has by far the best prices
for the best stuff..:bigeyes: :bigeyes:

Caps..http://www.newark.com/97M5310/passives/product.us0?sku=cornell-dubilier-slpx472m080c9p3

http://www.newark.com/81K0530/passives/product.us0?sku=cornell-dubilier-cd15330jo3f

http://www.newark.com/75M1979/passives/product.us0?sku=vishay-bc-components-2222-373-21105

Bridges..http://www.newark.com/58K8880/semiconductors-discretes/product.us0?sku=fairchild-semiconductor-gbpc2504

All the transistors are there too..IRFP260 ,mje350/40etc.. $0.50
to $3.76
NO fakes ,all from manufacturer...(EBAY is scary)
MUCH cheaper than MCM, PARTSEXPRESS..I think newark is their
supplier anyway.

Roughly 70-80 US$ per NMOS 350 .. including supply caps and
bridge for 1 channel.MY little NMOS (250)'s are only going
to cost me 100$/ pair- w/high temp caps,silver mica,polyester
2% resistors,etc... hopefully these links were helpful.

I think Newark ships internationally,they are a BIG company.😀:wiz:
 
#2,984
smoke 😕

well the amp worked great at low volumes, worked for about an hour. As soon as i cranked it up, smoke. it seems that T9 did something wierd and applied source voltage to the gate's on the positive side. all positive fet's are now dead, T9 is so burnt there arent even pins left on it, and all the 27ohm gate resistors are cactus.... it seems the negative side of the amp is all fine thou...

im still stumped.. could it have been fake fet's? why did T9 go all wierd then? T9 bjt is from a trusted source, highly doubt it was a fake or dodgey. im at a loss... any idea's as to what could have caused that?

anyway, once i know what went wrong i will rebuild it. it was good untill i cranked it up. can supply pics and measurements if anyone wants.
 
#2,988
Hi ostripper,

I think you are right that wires are long and not very thick. I have phonic powerpod and I am using its transformer (but I have to buy one). but just testing the amp with it. It's 500VA 40 0 40 I think.
What about the mid frequencies how can I reduce them.

Regards
 
#2,989
I dont know about the mids.. just short fat wires ..dont starve the amp..only hook one up ,that is all 500VA can handle
(I run 4 output amp from one like yours -NMOS200).
adjust bias 20-40 mv across R29 to 34 ..any 1 resistor
(50-100ma)idle . I may be wrong I haven't built nmos yet just
brother of quasi. I noticed big difference in clean bass
and amp temp.also w/ 40-0-40 /53-0-53dc?change R6
(chart on qausi's site)
Ask Qausi,I think he is here,somewhere.

🙂
 
#2,990
ostripper said:
I dont know about the mids.. just short fat wires ..dont starve the amp..only hook one up ,that is all 500VA can handle
(I run 4 output amp from one like yours -NMOS200).
adjust bias 20-40 mv across R29 to 34 ..any 1 resistor
(50-100ma)idle . I may be wrong I haven't built nmos yet just
brother of quasi. I noticed big difference in clean bass
and amp temp.also w/ 40-0-40 change R6 (chart on qausi's site)
Ask Qausi,I think he is here,somewhere.

🙂
Click to expand...

Thanks Mate I will wait for Qausi's reply

Regards
 
#2,992
Wasim said:
Hi Quasi,

I rebuild the amp nmos350 and it’s working perfectly. I just want to ask one thing.

In this build (Nmos350) I feel that the mid frequency is more prominent than the high frequency and bass is ok not very good. In my previous build the sound was different. Is this because of the transistors? Because three things are different in my new build I used IRFP460 instead of IRFP450, I used 2SC2240 not 2SC1845 and for T8 I use BC546 where as in my previous build I used BC550?

Overall sound is very clear.

Regards
Click to expand...


The amplifier frequency response is ruler flat, extending beyond the audible range, so it in itself should not affect the sound. The 2SC2240 plus the other transistors you have used will not make a difference. The lower end of the amplifiers response can be extended by increasing the input capacitance to say 4.7uF.

So I suspect it's your power supply. That transformer in the picture is way too small to do anything other than power the soft turn on and DC detect circuits. What size capacitors are those in the photo? A 400va - 500va transformer would be a reasonable choice.

I would not get carried away about the thickness of the internal wiring, anything capable of continous 10 amps delivery is ok.

Finally the secret to this amps performance (almost all amps) is the power supply. The amp is simply there to modulate the power supply cleanly, relative to the input signal and hopefully survive.

Cheers
Q
 
#2,993
ostripper said:
.also w/ 40-0-40 /53-0-53dc?
Click to expand...
Something seriously wrong with these numbers.
40Vac should give between 57 and 60Vdc not 53Vdc.
The other replies seem to indicate that your transformer is far too small, this silly DC voltage confirms that something is seriously lacking.
What is the smoothing capacitance you are using?
What is the speaker impedance and sensitivity your are using?
 
#2,994
40Vac should give between 57 and 60Vdc not 53Vdc
Click to expand...
Just a few volts differance, but I have a 45-0-45 right in front
of me w/25a/400V bridge and 12000uf X 2 and get 61v no load
and 57.5 V with amp's load. Using this as a referance I assumed
a 40-0-40 would have 5-7V less. I could be wrong since
different bridge's -(bleeder resistors?)would also be a factor.

Still ,Quasi's 18k R6 is best for NMOS 350's at the upper range
of the voltage spectrum 65-75V and Wasim's transformer
is way :whazzat: too small for 2 amp's of this caliber.
 
#2,995
Hi All javascript:smilie('🙂')
smile,

Thanks a lot for so many replies.

It was my mistake, actually the transformer at the right is only for the DC detect. This transformer is not running the amp. I used a power pod transformer and I just took the connection wire from the box of Power pod to run Nmos350.

That transformer in the power pod is 500VA 40 0 40. And it is giving 53-54 VDC. I am running 8ohm speakers.

The Caps were 10,000Uf 100V. Quasi I will change the power supply and let you know the result. Actually the amp is giving excellent sound but I just mentioned that the sound was somehow different from the previous build. I felt that the mid frequencies were more prominent and bass was not as good as in my previous built?

Regards
 
#2,996
Quasi, I would like to know a little bit more about the
"birth" of the quasi line of amps. What sparked this interest
was the reading of "8 distortions" by Douglas self.As I read
I saw he progressed almost to your exact design topology
as the truely "blameless" amp.(Which by the way has
.008-.01 distortion and bandwidth out to 200k+)

My question is, did you read Douglas self's book to base
your design on and if so would it be a good reference to
further it's development. ?

thank you for a GREAT design 😀 ,OS.


P.S check out my "WWW" many books,designs, etc.
quasi-DXamp-leach are abut the same for total downloads...
(remember the old forrest mims-radio shack 1978 .. books for
curious children ? ..they are here in
electronics/educational/forrest mims/) 😎
 
#2,998
Ravs,
have you looked at Quasi's web pages?
Nmos data shows maximum of 61Vac and output @ 600W into 4r0 is the maximum for a 10FET output stage.

5pair won't even drive 3r0 (zero phase angle) within the 50degC SOAR. This indicates that the worst reactive load it can handle is greater than 6ohm.
How can you expect 5pair to drive 4ohm 60degree phase angle?
 
#2,999
AndrewT said:
Ravs,
have you looked at Quasi's web pages?
Nmos data shows maximum of 61Vac and output @ 600W into 4r0 is the maximum for a 10FET output stage.

5pair won't even drive 3r0 (zero phase angle) within the 50degC SOAR. This indicates that the worst reactive load it can handle is greater than 6ohm.
How can you expect 5pair to drive 4ohm 60degree phase angle?
Click to expand...

thanks
andrewT

wouldnt it be good to add 4 more fets

or should i go with actrk600
 
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