vintage amplifier repair/upgrade manual

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Thanks for the respond gents , but i need more specifics .


Jack ,

Are you suggesting using an LM4702, LME49811 etc to replace the whole flat amp or just the driver transistors .

Sakis,

I have an situation , due to how the amp is being operated , i would like to have a stronger driver stage . Can i just upgrade to stronger drivers ?


regards,
 
My Pioneer SX-838 which was a 50W design from the early 1970's now sports an LM4702 driving lateral MOSFETs -- I bought the receiver new from Harvey Electronics on 45th St. in NYC when I got my first job out of grad school.

I boosted up the power supply caps as well, redid the power wiring with teflon. This amp was always blowing the output transistors. I did one remake of the preamp/tone control section but wasn't quite pleased with the results -- I've got to get a bipolar supply in there!

Pictures on this thread:
http://www.diyaudio.com/forums/chip-amps/119160-lm4702-meets-pioneer-sx-838-a.html
 
Thanks for the respond gents , but i need more specifics .


Jack ,

Are you suggesting using an LM4702, LME49811 etc to replace the whole flat amp or just the driver transistors .

Sakis,

I have an situation , due to how the amp is being operated , i would like to have a stronger driver stage . Can i just upgrade to stronger drivers ?


regards,

basically it would be wise to make a new thread regarding this issue this thread is to disscus the manual

then again if you state in trhis new thread your problem and your approach you can have my opinion

in a few words if you remove MJE340 /350 yha operate inside one amplifier and replace them with MJ15032 for example almost nothing is going to happen beyond the charcteristics of the specific transitor that might change the sound of your amp for best or worst ( which i dont think that you can hear ) then the only diference will be that 15032 is capable of more curent

how you drive those transitors and what do they have to drive makes the all diference

how your amplifier works , what is exactly your problem or approach , your drivers will have to be stated in some other thread to get some answer

regards sakis
 
Plastic tiger

i have an amp here that was originally 4700ufx2 on the pwr with 2 output transistors per channel(x2)
right now after changing the driver stages to transistors that perform at 1.5A(before it was 1A) ,it has 4 transistors per channel(2sc5200 2sa1943) and 22x4700uf the transformer it's 500va 40 0 40 and it works fine(not to audio sonics extremes)just more power to drive tight and clean bass to 15" black widow(peavey) speakers,.....originnaly the fuse was 4A at 120volt and it's actually the same fuse right now,i play bass guitar on it and it's just fine...for sure the 22 capacitors are a waste but.....they're cheap(63v 4700uf nichikon 3bucks each),so.....
fans,bigger heat sink,
it match
 
Hi all,

Would anyone know where I can find a good, free service manual for a Trio KA 4002, please?

I have tried a good few sites and found schematics but I need a proper manual with a decent picture of the PCB etc.

I have this amp and it is wonderful. The sound is superb but what thrilled me was the sheer amount of connections on the back of it. I have loads of stuff running through it, even the analogue oputput from my PC digitiser ! And even that sounds brilliant.

But it stopped working, no bangs or flashes, no smoke, no smell - no lights or sound, just stopped.

I wonder if I have found all the fuses. I am not a techy...

Cheers,
John
 
Thank you, Simon.

But that site won't let me register except by invite, and I don't even know what language it's in...

I'll try again tomorrow as I was told I can only have two downloads a day unless I register, but then didn't give me the downloads...

I'll see what happens tomorrow...

Story of my life...
 
Dear SAKIS, that was really comprehensive and authentic. Lot of useful information. Still I would like to arise a doubt. How to figure out the exact bias current of an amp about which no data you have?
Again, what you pointed about the usefulness and importance of schematic is correct. I would like to share my experience. Some 15 years before I was in television servicing bussiness. One day, I recieved a set of which the H and V linearity was totally lost. inspecting, no components were damaged, and I fiddled with it for some days. at last found the schematic and comparing with it, it was found that a hand full of caps and resistors in deflection were replaced with spurious components and offset values. But the chassis was soldered like new and there was no trace of any tampring. may be some deliberate work of some crook. once restoring all components as per the schematic, the set was tested okay without any further allignment.
Thank you for the post.
 
For class Ab operation there is many ways to go while all moving around the same axis

For starts i don't recall any vintage amplifiers that schematic or recommended bias value cannot be found Obviously i might be wrong .

One way will be to use a scope to see the spot where crossover distortion gets eliminated Often a bit more is always better . Truth is that experience has a lot to do and combined with choice of semis , heatsink , response of Vbe multiplier together with the style of make , power supply , total power of the amplifier , costumer demands and all of it versus safety will help choose a bias point .

For us at east electronics proper bias point is most of the times according to the manufacturers suggestion. In some occasions after costumer demands we may play a bit more ( hardly ever less ) but this is getting verified by spectrum analyzer and scope to ensure that more or less bias doesn't effect original distortion figures for any reason ..

Increasing the bias in any amplifier will most of the times help the sound of the amp especially in low level listening Still this will alter safety characteristics of the amp and is a thing to be done if needed with caution and study .

Kind regards
Sakis
 
part 2
9- By the same technique (as mentioned above you will be able to notice how well is your outputs matched {especially if more than 2 per channel} by monitoring the voltage drop on every resistor .If voltage drop is equal to all resistors with in a margin of 10% then your outs are very well matched .If voltage drop in one is 10mv and the other 50mv then your outs are very badly selected.


Nice work, Sakis


I really enjoy reading this manual. I got a question about 9. Is there a way to select matched output pairs off the circuit? thanks.
 
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