Hi all.
I have an old amplifier class A, or so says the electrical diagram, and I
want to update to the affection that I have, but first I would like to know
whether it is a class A.
and would like your opinion.
regards.
http://img393.imageshack.us/my.php?image=schematicamplifierszj1.jpg
I have an old amplifier class A, or so says the electrical diagram, and I
want to update to the affection that I have, but first I would like to know
whether it is a class A.
and would like your opinion.
regards.
http://img393.imageshack.us/my.php?image=schematicamplifierszj1.jpg
Re: Re: Possible Class A Amplifier
From Q1 to Q7 it is in class A. Working regime of output stage depends on bias current setting (set it with VR2). With 1,2A running through output stage you'll have 25W in cl. A (@ 8 Ohms load) and about 120W thermal dissipation per channel without signal - that's cl. A.
widi said:
From Q1 to Q7 it is in class A. Working regime of output stage depends on bias current setting (set it with VR2). With 1,2A running through output stage you'll have 25W in cl. A (@ 8 Ohms load) and about 120W thermal dissipation per channel without signal - that's cl. A.
Re: Re: Re: Possible Class A Amplifier
I know that you know ...... that before doing that ( cranking it up ) - is very wise lowering PSU voltage , and installing sufficient sum of capacitance in PSU filter .......
also - without pics of actual amp , we can't say - is it needed to ensure better heatsinking for driver stage
juma said:
I know that you know ...... that before doing that ( cranking it up ) - is very wise lowering PSU voltage , and installing sufficient sum of capacitance in PSU filter .......
also - without pics of actual amp , we can't say - is it needed to ensure better heatsinking for driver stage
It is not class A at the rated output of 100W/8R, thus it is not a class A amp. Or if it is, it will only last a very short time 🙂
I seem to recall a Class A power amp with 2 pairs of MJ15003/4 devices, running on ~37Vdc rails.
Sounded like something Otto said in Fish called Wanda : K-k-k-k-Ken.
Sounded like something Otto said in Fish called Wanda : K-k-k-k-Ken.
Although the voltage readings shown at the bases for the output devices look pretty light, I don't see any reason you couldn't fiddle the bias up into class A territory if you're willing to invest enough in heat sinks and power supply.
Grey
Grey
Thank you all for your opinions, whether GRollins, the PSU has a large toroidal transformer 600W and four capacitors 30.000uf rail in each of the PSU and eight ultra-fast diodes 50A.Lo I want is to replace MJ15003 / 4, by MJL3281A and MJL1302A so that I occupy less space.
Where can I find this change of transistors?
Where can I find this change of transistors?
Beware...changing output devices may lead to instability problems. It's not that it can't be done, but I would suggest checking the amp thoroughly on an oscilloscope to make sure everything is okay before putting it into your system.
Grey
Grey
No es clase A, o al menos no clase A pura simplemente por utilizar transistores de potencia complementarios MJ15003 y MJ15004. Para clase A pura tendrías que ir a esquemas asimétricos del tipo Zen de Nelson Pass con muy baja potencia y elevadísimos consumos. Si de verdad fueran 100 w en clase A necesitaría un toroidal de más de 23kg,
http://www.passdiy.com/pdf/articles/powersupply.pdf
Supongo que, como mi viejo musical fidelity A1 debe estar un poco subido de amperaje en la polarización, con lo cual una pequeña parte de sería clase A. Mide el amperaje en los transistores de potencia, uno de ellos debería marcar algo en reposo y creo que así podrías calcular hasta dónde es clase A, es lo que hacen en esta página:
http://www.mhennessy1.f9.co.uk/mf_a1/technical.htm
http://www.passdiy.com/pdf/articles/powersupply.pdf
Supongo que, como mi viejo musical fidelity A1 debe estar un poco subido de amperaje en la polarización, con lo cual una pequeña parte de sería clase A. Mide el amperaje en los transistores de potencia, uno de ellos debería marcar algo en reposo y creo que así podrías calcular hasta dónde es clase A, es lo que hacen en esta página:
http://www.mhennessy1.f9.co.uk/mf_a1/technical.htm
esos transistores los tienes en rs:
http://es.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=MJL3281A
pero no sé si suponen una mejora de sonido, los que llevan aguantan mayores temperaturas, amperajes y potencia, yo los he usado para actualizar el MF A1 y van muy bien.
http://es.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=MJL3281A
pero no sé si suponen una mejora de sonido, los que llevan aguantan mayores temperaturas, amperajes y potencia, yo los he usado para actualizar el MF A1 y van muy bien.
Caballero muy graciosamente,
Class A has no bearing to either Single Ended or Push Pull output stages, and Pure Class A is merely an annotation that refers to the level of Class A biasing.
Biasing that power amp to the full 100W in Class A would be a piece of cake with a fan and a high performance heat sink, even at a Die temperature that is considered the standard.
Class A has no bearing to either Single Ended or Push Pull output stages, and Pure Class A is merely an annotation that refers to the level of Class A biasing.
Biasing that power amp to the full 100W in Class A would be a piece of cake with a fan and a high performance heat sink, even at a Die temperature that is considered the standard.
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