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My first DIY amplifier 20 years a go
My first DIY amplifier 20 years a go
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Old 18th August 2014, 10:34 PM   #561
gaborbela is offline gaborbela  Canada
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For coupling caps I do not like large value caps, that would be my correct statement.
If the PS built on a PC board like many commercial amp we have to use what ever need for there.
If you look at my layout you can see if I rotate the capacitors (next to the power transistors) I can use even 2200uFt to.
There is room enough there.
I will see if really necessary to go over 470uF what I think is a decent capacitor for that position.

By the way these is the final layout what I will use at my tests.
The size of the PC board 86 X 82mm
86 wide frame to frame and 82 long.

Greetings
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Old 22nd March 2015, 05:26 PM   #562
Bigun is offline Bigun  Canada
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My first DIY amplifier 20 years a go
Any progress on this project, the dream should not end yet...
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Old 22nd March 2015, 07:34 PM   #563
gaborbela is offline gaborbela  Canada
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It is not over yet.
I prepared to etch several different amplifier PC boards so that is the reason for the long wait.

Greetings G
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Old 23rd March 2015, 01:32 PM   #564
ashok is offline ashok
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My first DIY amplifier 20 years a go
Hmmm....I went off track around mid 2014 and never got back due to a lot of reasons plus side tracked by some new things that came along......usual rant ..
However I do want to complete my stereo version for which I had even bought the transformer and heat sinks ! I think I will do something this year ! In the meantime the L12-2 amp caught my attention . After many months I bought the boards recently on eBay. Making boards myself is becoming time consuming.
The L12 amp is very nice . Will have to compare that with your amp. Since there are some variations possible I'll pick the one I like best to test. Two important factors will be dc offset stability ( with fluctuating supply voltage ) and dc bias stability.
Cheers.
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Old 2nd August 2015, 11:13 AM   #565
gaborbela is offline gaborbela  Canada
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Quote:
Originally Posted by Bigun View Post
Any progress on this project, the dream should not end yet...
Hi
Mosquito simulated the VBE modified version the result he get is very bad.
With these tweak the sim result is (very) good but may be we back to the thermal drift problem.
Who knows
I think I will build these and if there will be problem try to solve it on the actual amplifier.
I waited until now so someone simulate the VBE molded circuit.
Now time to work on the layout and after turn on the soldering station.

Bigun or anyone else who interested please take a look at the latest circuit

Thanks
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Old 4th August 2015, 05:32 PM   #566
Bigun is offline Bigun  Canada
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My first DIY amplifier 20 years a go
I am happy to see this thread coming alive!

Still, I suggest somebody should run quick Spice sim with "TEMP 30 40" to see how stable is bias of output power devices with temperature. More sophisticated simulation needs control over individual devices of course but it's simple enough to do global test whilst you begin some real soldering!

I like this topology and I have reserved many pairs of Sanken Darlington devices for when time is available !

Perhaps good to add a capacitor across Vbe to ensure good a.c. Behaviour.
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Old 5th August 2015, 12:13 AM   #567
gaborbela is offline gaborbela  Canada
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Hi
Bigun I agree with the capacitor across to the VBE
Very likely next to the VR2 we will need a resistor, one side it has 2K2 the other side only a 470VR.
At least for test I made the room for the mentioned components
The resistor marked as a J jumper the capacitor not marked but is there in the layout
Greetings
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Old 5th August 2015, 12:35 AM   #568
nigelwright7557 is offline nigelwright7557  United Kingdom
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One of my first builds was a Maplin amplifier in around 1980.
It was 225WRMS and I used it with four Fane 50WRMS speakers on a mobile disco.
It sounded very good and was very loud when required.

Click the image to open in full size.
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Old 5th August 2015, 05:53 AM   #569
djk is offline djk
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"It was 225WRMS "

Bridged?

Max safe voltage on a 2N3055/2955 pair is 30V.
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Old 5th August 2015, 10:16 PM   #570
Bigun is offline Bigun  Canada
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You've lost me there Nigel, the Maplin circuit has no relevance in this thread??

How to provide thermal stability for Gabor's amp is the question. I think the issue as always is the VAS, the current through it increases with temperature and this simple Vbe causes increase in OPS current. The VAS emitter degenerate helps but may not be enough and increasing it will reduce OLG. Other option is to make the Vbe multiplier immune to VAS current using solution like my TGM5. Or add some temperature variable element to the input stage like VSSA. What other ideas - there are more options?
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