250watt 8ohm need an opinion

[prorms]

i dont think that this amp is perfect the wattage is high enough for me
?
but the treble , bass and midrange are not at a balance were one is stronger the the other when you run a cd player threw the amp?

the other one is are all the parts at the right setting?

is this realy a perfect circuit for this style of amp ?

better semiconductors ?

anything that you see wrong with poweramp?

i would real like to read your true opinion on this poweramp?
bad or good

i do not suggest that you use amp at 2 ohm setting!!!
the circuit can not handle it !

[edl]

You ask: bad or good...

Hey, it's one of the worst amplifier designs that I've ever seen...

Bad. Really bad.

I'm sure the "designer" not into audio.

Forget this amp, it's a sh*t.

Sorry, but that's the reality.

[prorms]

what do think i should change

[lineup]

Originally posted by prorms

what do think i should change
.

hello prorms!

it is actually not so bad amp schematic

however,
you may have to tweak a number of components a bit
and you should not expect more than like 60-100 watt into 8 ohm,
if you are lucky
( more would need more than 1 pair MJL21193-94 and higher voltage power supply )

============================

See my attachment of circuit.

At a quick look:

1. C3(100uF) should be ~ 470uF-1000uF

2. You may need a little ceramic disc capacitor
across R9 (22k) in feedback. 47pF / 100pF could be a good value.
This is for to ensure stability. And avoid oscillations.

3. You should put a resistor between emitters of drivers, from Q9-Q11.
Select a resistor value, that makes 20-50mA run from Q9-E to Q11-Emitter

4. R4(1.2k) and R5(1.2k) should be something 820-1000 ohm
to make better balance in sharing of current in input pair Q1, Q2
This is very important for high quality = hifi.
That these runs 50%+50% of the current coming from CCS source Q3.
When each Q1,Q2 have 50% of this current
we call it:
Input differential pair are in PERFECT BALANCE

To make sure this, you measure voltage across:
- R7 (220 ohm)
- R5 (for example value 1000 ohm(=1 kohm), just for easy measuring)

Say you have 0.66V across 220 ohm = 0.003A = 3.0mA
Then you should adjust R4 value!
until you read 1.50V across R5.

Because 1.50V / 1000 ohm = 0.0015 = 1.5mA
And if 1.5mA in Q2, then (3.0mA-1.5mA) in Q1

And then we can be sure:
Q1 = 1.5mA
Q2 = 1.5mA
Sum= 3.0mA = Current from current source Q3
= Current in R7(220 ohm)


Regards
lineup

[lineup]

.



BD139 / BD139 are 80 Volt transistors,
80V, 15 Watt ,TO126
And you have 2x47V = 94 Volt.

You can use 2N5400 / 2N5550 instead.
Same as in your input stage! ( they can take 0.625 Watt )
But do not run these TO92 more than max 0.400 - 0.500 Watt!
For example, MAX, 47V x 10mA = 0.470 Watt

You can also use MJE340 / MJE350
300V, 20 Watt,
and they are TO126, like BD139 / BD140

*******************************

Note, the only difference between
2N5550 and 2N5551 is Max Volt Collector-Emitter

For your amplifier this makes no difference.
You can use anyone of them:
2N5400 - max 120V .... 2N5550 max 140V
and
2N5401 - max 150V .... 2N5551 max 160V

lineup

[v-bro]

Wow Lineup, I admire you for that info! Great post.

[lineup]

Originally posted by v-bro

Wow Lineup, I admire you for that info! Great post.

thanks, v-bro
you are kind to express your positive opinion
if you can think like that, about me, some other may too

I am often doing my best
to share what little I know (actually I know more than average do)
but one should never long for getting up on high horse
unless be prepared to take the fall, that will come - sooner or later

by the way, I have spent 15-20 years of my life handling
my stallion horses and female horses, too
and I know very well how to
- drive horse in wagon, 2-wheel racing wagon = trotting racing horse
- ride horse, with or without saddle
- put shoes onto them horses feet
can be a very tough job! if horse is not nice to you
... you use hammer and nails to do this job, as you know
while, hopefully, horse will stand nice on his 3 other legs ..........
Things can happen!
---------------------------------------------------------------

By the way, to be nice to you, in return:
I hadn't bother to explore your website before
http://www.41hz.com/
Looks like a Great Music & Audio site

I have to spend some hour there
to find some new and interesting things about audio amplifiers.
I put it in my favos.
Go there later when I get more time.


Thanks again
And much regards from
lineup

[v-bro]

Wow, admiration again lineup, I've always been a bit scared of horses...
And thanks again Lineup, but placing a link to that site is also out of mere kindness... Jan designs very nice amps and has been so supportive that I thought he deserved to have a link to his site placed in my signature..

And I thought prorms might only be looking for a good amp, or are you rather looking to learn more about amps prorms?

[darkfenriz]

A resistor between emitters of Q9/Q11, say 100R would be useful.
Remember to adjust proper bias of output stage, 30mA minimum.
Add a cap across D1/D2.

[lineup]

Originally posted by lineup

3. You should put a resistor between emitters of drivers, from Q9-Q11.
Select a resistor value, that makes 20-50mA run from Q9-E to Q11-Emitter

Regards
lineup

Originally posted by darkfenriz

A resistor between emitters of Q9/Q11, say 100R would be useful.
Remember to adjust proper bias of output stage, 30mA minimum.
Add a cap across D1/D2.
.

when 2 people say the same thing, without knowing what the other just said
you may put great trust in what they say!

this is why, before a trial at court
witnesses and suspects involved often are kept separate
until there has been a primary hearing and questioning
of the same persons
This way one will not know what the other say
and so possibly influence and/or tell the same,
just for sake of it

thanks darkfenriz,
for confirmation and some additional advice

lineup - praise all independent sources of audio information