70W Class A amp.

[Arick]

Hi everyone I am a newbie, my name is Eric,
I was wondering if anyone had experience with this design. It is a 70W single ended class A, I found in the French magazine LED #118 of April 1994. On fig.1 the IC1 is a LM144H, IC2 LM317L, IC3 LM337L , T1 MPS A 06, T2 MPS A 56. Fig. 2 will show T3 (and T4 for 4 Ohm) as a IRF 150 Mosfet with four LM317HVK.
Happy new year to all!

[analog_sa]

Originally posted by Arick
#118 of April 1994.

70W, huh? The April issue should give you a clue.

[gain-wire]

Well then Eric, welcome to diyaudio! While I'm at it, and since nobody ever does it, I'll take this opportunity to greet you in french: bienvenue à DIYaudio, le meilleur site de renseignements sur l'audio et l'électronique sur l'internet!

So, are you a newbie to electronics, or just diyaudio? If you have not much experinece with audio and electronics, I wouldn' really recommend you start with such a project. But if you understand the schematic and how it works (just those transistors on the regulators for the LM144 are making me scratch my head) then go ahead and give it a try. Bear in mind you'll need a heck of a good transformer...

I love (not!) how the french (les québécois on fait pas ça) don't give you the NECESSARY information on how their ******* circuit works and the style of their litterature. They have a way of writing that seems so, well, philosophical and not technical at all. they like to complicate the sentances, maudit que ça m'écoeure! Ieven I find it bit difficult to understand, especially the fourth paragraph. They also don'T write the values on the components in this magazine. Maybe they have changed that since, I haven't picked up a French magazine in quite a while.

Popular electronics: now there was a magazine that kicked electronic rear-end. I guess the internet killed it. colisse d'internet! take that swearword engine
Oh well, have fun building it!

[Arick]

Hi gain wire,
Thank you for the greeting. This project will be my second project, my first was a tube amp for headphones, from another french magazine.... It turned out well with a bit of effort to find parts and missing info...! As it stands I "think" I have enough info to complete this puppy and I will have a bit of help from a friend who is a electronic technician (although he is busy at times). Could you be more specific regarding your comment about the transistors? Regarding the transformer, I am planning on sticking with a local company who manufactures transformers, as I was very successful using their product in my first project (they also have a good reputation). I will use a toroidal transformer, perhaps adding a choke, if required.
Merci encore,
Eric

[sakis]

construct and let us now

i am also inetersted .... a better and more complete schematic will be a bless also

happy new year

[mjf]

70w single-ended output is a big thing.yuo will need a big transformer and biggest heatsinks -per channel.perhaps you should meditate over this project.
regards..............

[adason]

those two output mosfets will require massive heatsink
schematics look simple, how do you adjust zero volts on output...is it with RV1?

[mjf]

ic1 inverts the input signal(voltagegain is round about r2 divided trough r1).
rv1 is used to adjust the offset at the output.
the outputstage is se-class a without feedback.the voltageregulators ic4 to ic7 seemed to be used as constantcurrentsources(for the bias of the mosfets).
t1 and t2 are used as filter for the supply(capacitance multiplier) . ic2 and ic3 stabilise the supplyvoltage for ic1.
that`s what i presume when looking at the schematic.
regards.............

[Arick]

Hi to all of you,

Originally posted by sakis

i am also inetersted .... a better and more complete schematic will be a bless also

Sakis, the only other schematic is another simple one showing the power supply, If you are interested I can send you a copy of the document buy e-mail.

Originally posted by mjf
70w single-ended output is a big thing.yuo will need a big transformer and biggest heatsinks -per channel.perhaps you should meditate over this project.
regards..............

This amp is designed to be built as two mono blocks, I am already planning to use huge heat sinks, the recommended transformers are 500VA, I might increase that a bit...

Originally posted by adason
those two output mosfets will require massive heatsink
schematics look simple, how do you adjust zero volts on output...is it with RV1?

Zero volt is adjusted with RV1 , after adjusting RV2 output to + 38V and RV3 to -38V. On the subject of heat sinks, I was suggested to keep one component per heat sink, electrically isolating the heat sinks from one other and from the case. Does it make any sense in the audio world???
Than you to all for your constructive comments,
Eric

[Arick]

Almost forgot, I live in Canada where outside temperature go well bellow 0c or 32F and will use it as inside heater as well...