Leach Amp, QSC USA1310 and transistor types 
Author Message
 Leach Amp, QSC USA1310 and transistor types

I'm about to build some Leach Amps, but I've been unable to find MPS8099 and
MPS8599 here in Finland.  I'd like to know if I can use BC639 and BC640
instead.

Also USA1310 has MPS8099s in it's protection circuits.  Can these be
replaced with MPSA06 / MPSA05 or BC639 / BC640?

Thanks

-Kimmo S.



Sun, 02 Feb 2003 03:00:00 GMT
 Leach Amp, QSC USA1310 and transistor types

Quote:

> I'm about to build some Leach Amps, but I've been unable to find MPS8099 and
> MPS8599 here in Finland.  I'd like to know if I can use BC639 and BC640
> instead.

> Also USA1310 has MPS8099s in it's protection circuits.  Can these be
> replaced with MPSA06 / MPSA05 or BC639 / BC640?

> Thanks

> -Kimmo S.

Is this the one you are talking about?

http://users.ece.gatech.edu/~mleach/lowtim/
 http://users.ece.gatech.edu/~mleach/lowtim/graphics/ckt.pdf
http://users.ece.gatech.edu/~mleach/lowtim/part3.html

On the site Leach indicates the MPSA06/MPSA05 as an option.

The BC546 (NPN) and BC556 (PNP) devices look close too (better fit than the
BC639/BC640).

As with any substitutes be careful when you power it up and test it thoroughly.
Check for pin-out difference on the devices.  Don't use your $2000 speaker
system on any amplifier until you know it's OK!

Regards
Rob



Mon, 03 Feb 2003 00:05:20 GMT
 Leach Amp, QSC USA1310 and transistor types


Fri, 19 Jun 1992 00:00:00 GMT
 Leach Amp, QSC USA1310 and transistor types


Quote:
> Is this the one you are talking about?

> http://users.ece.gatech.edu/~mleach/lowtim/
>  http://users.ece.gatech.edu/~mleach/lowtim/graphics/ckt.pdf
> http://users.ece.gatech.edu/~mleach/lowtim/part3.html

It is.

Quote:
> On the site Leach indicates the MPSA06/MPSA05 as an option.

Im interested in how much loss of quality I could suffer, or what is the
final difference between them and 8x99?

Quote:
> The BC546 (NPN) and BC556 (PNP) devices look close too (better fit than
the
> BC639/BC640).

I'll go and have a look

Quote:
> As with any substitutes be careful when you power it up and test it
thoroughly.
> Check for pin-out difference on the devices.

I will.  I can print all possible datasheets before trying anything.

Quote:
> Don't use your $2000 speaker
> system on any amplifier until you know it's OK!

I won't.

But my main concern which this didn't address (also because I made no
mention of it) is that can I replace the USA1310's 8x99 also with BC5x6?
Maybe I should do more work and ask less questions, but it's undeniably
easier this way.

Thanks

-Kimmo S.



Mon, 03 Feb 2003 03:00:00 GMT
 Leach Amp, QSC USA1310 and transistor types

Quote:

> Im interested in how much loss of quality I could suffer, or what is the
> final difference between them and 8x99?

In those positions in the circuit the transistors will have practically
unmeasurable effect on the final signal quality.

Quote:
> But my main concern which this didn't address (also because I made no
> mention of it) is that can I replace the USA1310's 8x99 also with BC5x6?

Well, I would say yes, the match is quite close. If I was building the unit I
would have no hesitation substituting them in the circuit, however testing is
mandatory.  If you want more confidence I can tell you there are plenty of
amplifiers similar to the Leach design that use them.

That amplifier is a well honed design, Leach has refined it over many years so I
would not expect the design to be so marginal that it became unstable (in the
sense that it would oscillate) because of small changes. Nonetheless you never
know, that's why you have to test it, I would be looking for high frequency
oscillations (If you are making a different PCB then you could create
instability problems because of your layout - so don't just blame the
transistors if this occurs).  In the FAQ, Leach actually said he wasn't sure if
the BC5x6's were suitable because he has no experience with them.

I thought Leach gave a very honest account of the design on his web page.  The
fact that he had to remove one of the caps around the protection network and
also had problems with the output impedance stabilizer made me cringe a little,
but I don't know all the details of the circimstances where these  problems
occured.

Quote:
> Maybe I should do more work and ask less questions, but it's undeniably
> easier this way.

There is  no harm in asking.  By the way,  I have *NOT* build this amplifier, I
just went looked over the design about a year ago.

Regards
Rob



Wed, 05 Feb 2003 13:26:10 GMT
 Leach Amp, QSC USA1310 and transistor types


Fri, 19 Jun 1992 00:00:00 GMT
 Leach Amp, QSC USA1310 and transistor types
If you are talking about Q10 & Q11, over current protection transistors, you
may use any general transistor like the 2222 ( NPN) family or the 2907 (PNP)
family, which also say 23904/3906 , 4001/4002.

By the way the protection circuit is borderline and do not have current
adjustment versus output voltage and for that you need a resistor from the
base to ground from both over current protection transistors.

Expanding this borderline statement:

The over current limits for the output transistors is dependent on the
output voltage level and the dissipation of the output transistors (
including the devices (heat sink) temperature).

So the trip current is lower when the output voltage, lets say, 10% of
maximum and much higher when the output voltage, lets say,  80% of maximum.

Ideally D9 & D10 need to be rotated and not connection to output amp and the
common junction of both diodes brought to ground via a resistor that sets
the overall maximum current at maximum output voltage; the sampling current
resistors set the lower current limit when the voltage output is at a
minimum ( like dead short ).

Finally: dead shorted transistor needs power supply removal, so make sure
that your power supply has a set of fuses to blow is such damage occurs.

Regards

H.G.


Quote:
> I'm about to build some Leach Amps, but I've been unable to find MPS8099
and
> MPS8599 here in Finland.  I'd like to know if I can use BC639 and BC640
> instead.

> Also USA1310 has MPS8099s in it's protection circuits.  Can these be
> replaced with MPSA06 / MPSA05 or BC639 / BC640?

> Thanks

> -Kimmo S.



Fri, 07 Feb 2003 13:09:12 GMT
 Leach Amp, QSC USA1310 and transistor types

Quote:

>By the way the protection circuit is borderline and do not have current
>adjustment versus output voltage and for that you need a resistor from the
>base to ground from both over current protection transistors.

I don't advise this modification, producing what is known as 'load-line
protection', unless you do a very thorough design investigation
afterwards. The problem largely arises from the fact that the load is
not likely to be wholly resistive, so that the load line is an ellipse.
But the protection circuit 'thinks' that the load line is close to a
straight line. As a result, the protection may come into operation over
part of a cycle of the signal waveform and this can cause severe
problems, not only {*filter*} distortion but also high-frequency
oscillation.

Peter Baxandall developed a method of measurement for amplifier
protection systems, which can be found in international standard
IEC60268-3. Go to http://www.***.com/ .
--
Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839
Fax +44 (0)1268 777124. http://www.***.com/ I wanted to make a fully-
automated nuclear-powered trawler,but it went into spontaneous fishing.
PLEASE do not mail copies of newsgroup posts to me.



Fri, 07 Feb 2003 03:00:00 GMT
 Leach Amp, QSC USA1310 and transistor types
I built the Leach amp in the early 80's without the power limiter.  As
with many builders, I made changes.  The power supply, use of 10 turn pot
in bias network, metal film resistors throughout, ramp-up audio.  The
power supply is 4 x 50 volt with 9600 uf of capacitance on each supply, so
this involved adding an inrush current limiter.  The essence of the
limiter is to turn on the amp with a 50 ohm resitor in the AC line with
speakers disconnected. When all the supplies are up to about 2/3 of their
final value, the 50 Ohm resistor is shorted out and the speakers are
enabled and the input audio signal is ramped up with an opto-fet in series
with the inputs.

The neeatest thing about the protection circuit is that it functions as
designed if the npn and pnp output devices are reversed by accident with
only the resistor destroyed.  If a rail fuse blows the protection resistor
blows too.  I had one of the 100 uf caps on the rails short once because I
used 50V instead of 100 V units and I accidently switched the NPN and PNP
output transistors.

I loved the amp.  recently I listened to it compared to a couple of tube
amplifiers and my friend said the amp sounded "tubey".

I wish you luck and I hope you don't do what I initailly did.  I made a
mirror image of the PC board and was able to salvage it. I wish I made a

20 amp X  35 V x 2 windings constant voltage transformer which hummed too
much.  That supply made the amp sound much better.

Ron



Fri, 07 Feb 2003 03:00:00 GMT
 Leach Amp, QSC USA1310 and transistor types
John:

The ellipse load line can be generated to follow a desired curve.

What is important is that you need to calculate the max dissipation the
output stage accepts at any Vce- Ic levels, therefore the current limit must
be above the Ellipse Load, within the Vce/Ic limits.
I presented the basic design to the problem that I know is borderline, I
should be aware since Have designed  1 KW RMS amps with just two MOSFETS,
short proof and  load line protected. Range:  Frequency ( 30 Hz to 30KHZ
+ ).

The 5 KW RMS had the same properties. Though much more complicated .

IEC60268-3 is Work in Progress , I could not read anything .

Regards

H.G.


Quote:


> >By the way the protection circuit is borderline and do not have current
> >adjustment versus output voltage and for that you need a resistor from
the
> >base to ground from both over current protection transistors.

> I don't advise this modification, producing what is known as 'load-line
> protection', unless you do a very thorough design investigation
> afterwards. The problem largely arises from the fact that the load is
> not likely to be wholly resistive, so that the load line is an ellipse.
> But the protection circuit 'thinks' that the load line is close to a
> straight line. As a result, the protection may come into operation over
> part of a cycle of the signal waveform and this can cause severe
> problems, not only {*filter*} distortion but also high-frequency
> oscillation.

> Peter Baxandall developed a method of measurement for amplifier
> protection systems, which can be found in international standard
> IEC60268-3. Go to http://www.***.com/ .
> --
> Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839
> Fax +44 (0)1268 777124. http://www.***.com/ I wanted to make a
fully-
> automated nuclear-powered trawler,but it went into spontaneous fishing.
> PLEASE do not mail copies of newsgroup posts to me.



Fri, 07 Feb 2003 03:00:00 GMT
 Leach Amp, QSC USA1310 and transistor types

Quote:

>IEC60268-3 is Work in Progress , I could not read anything .

You cannot read the standard on-line: you have to buy it. What is 'work
in progress' is the next edition.
--
Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839
Fax +44 (0)1268 777124. http://www.jmwa.demon.co.uk I wanted to make a fully-
automated nuclear-powered trawler,but it went into spontaneous fishing.
PLEASE do not mail copies of newsgroup posts to me.


Fri, 07 Feb 2003 03:00:00 GMT
 Leach Amp, QSC USA1310 and transistor types
You can order MPS devices from www.mcmelectronics.com I just recieved
20 of each.



Quote:
>I'm about to build some Leach Amps, but I've been unable to find MPS8099 and
>MPS8599 here in Finland.  I'd like to know if I can use BC639 and BC640
>instead.

>Also USA1310 has MPS8099s in it's protection circuits.  Can these be
>replaced with MPSA06 / MPSA05 or BC639 / BC640?

>Thanks

>-Kimmo S.



Wed, 19 Feb 2003 04:10:23 GMT
 
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