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It is currently 19 Oct 2018, 09:40

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PostPosted: 09 Mar 2017, 03:57 
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Joined: 09 Mar 2017, 03:51
Posts: 2
Hello everyone,

As I'm building the classical Super Class A 30W amplifier, I was wondering if the supply could be built with these two components :

TRANSFORMER :
http://www.ebay.com/itm/371662652155

RECTIFIER:
http://www.ebay.com/itm/141914755629

The output current of the transformer (hich is quite big and heavy !) is 10A and seems to me to be very high..
If you have any opinion, let me know.

Thanks in advance for your help,
Camille


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PostPosted: 24 Mar 2017, 00:31 
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Joined: 23 Feb 2017, 02:02
Posts: 204
the transformor is 25v ac
this means after your recftier board you'll get approx 35V-36V DC


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PostPosted: 27 Mar 2017, 14:45 
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Joined: 09 Mar 2017, 03:51
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Hello,

Another question:
I will add (as Dan did) another transformer for a protection circuit. Can this smaller transformer primary be connected directly in parallel with the primaries of the 500VA one ?
So to say directly at supply plug.

Knowing that I measured an input impedance of around 3ohms for the 500VA and 160 ohms for the smallest one**

Camille


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PostPosted: 28 Apr 2017, 16:35 
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Joined: 23 Feb 2017, 02:02
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Yes you can wire this smaller transformor pimary in parallel with the pimary of the 500va without any plorbems directly at a supply plug


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PostPosted: 25 Oct 2017, 01:20 
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Joined: 23 Feb 2017, 02:02
Posts: 204
Some guys questioned switchmode power supplies and can it be used. I said you can use smps for any amplifier.
However you guys may still be questioning if this is acutally for real, is Yamato lieing.

I considered SMPS for the Class A Amp I designed, it runs on +-24v and 2.5amps per channel.
Heres some photos uploaded as proof that SMPS can work.

One big advantages of SMPS, if your output transistors can take the maximum current supply of smps, example mine has max current of 6 amps and contiunous 4 amps. This means in case of a speaker short, the smps is short circuit proof. 6 amps of current with flow through outputs, if outputs withstand 6 amps then the amp will surrive. (most smps are fully short proof)
In otherwords, your amp can become blow out proof.


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PostPosted: 25 Oct 2017, 01:37 
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Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
Actually, when it comes to constant-current draw, I see no technical reasons SMPS can't be used. It's in class-AB with quickly fluctuating currents that IME, SMPS falls on its face :(
(unless a trickle-charge-then-surge-dump cap bank is used, then cost wise it's about the same as linear)

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
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PostPosted: 19 Nov 2017, 12:50 
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Joined: 16 Aug 2017, 11:16
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Hello Goodnight. The construction of the hiraga 30W was completed about two months ago and it worked perfectly, although when one of the channels was heated it activated the loudspeaker protection. I checked it, readjusted the tension, reviewed the welds and the problem continued in the same channel. Yesterday I plugged it in and cut off the speaker as soon as it was turned on, that is, when it was still cold. Today I have disassembled it and the two transistors have broken down. To check if it was of the transistors, I connected the plate to the other pair and they heated up quickly, with which I deduce that I have a problem in the plate, but for more laps that I give and compare it with the other I do not give with the problem. I use the MJL15035 and 15034 and the power are the MJL4302 and MJL4281. The rest of the circuit is identical to that of the forum with changes in resistance. Please, I would like you to give me an answer about what may be wrong on the plate now, because as I said, it has been working for two months and I cut when it got hot and not before. I use a transformer of 25-0-25, which gives a voltage of about 36V. Thanks in advance and greetings.


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PostPosted: 19 Nov 2017, 16:43 
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Joined: 16 Aug 2017, 11:16
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I have made a mistake. The excitation transistors are the MJE15034 and 15035


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PostPosted: 22 Nov 2017, 17:20 
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Joined: 23 Feb 2017, 02:02
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Check the voltage at speaker output, adjust pot untill near zero.
You had it running for two months then it failed?
It maybe that your over driving your transistors 36v and 1.65amps per transistor is allot. this is about 60w per transistor.
The junction to case thermal resistance is about 0.543478C per watt. If your transistor is 100% geniune.
This means for every 60w you disipate, the internal temp is 60*0.5434=32.60868C above heat sink temp. This is quite a bit. I can aslo imagine thermal condutivity from transistor case to heat sink is very poor.
Me using very thin mica and thermal grease(which is pretty much near the best you can get excluding direct contact), has a thermal resistance of about 0.5C/W. This means if I disipate 60w my case temp will be 60*0.5=30C above heat sin ktemps.

This means your transistor maybe overheating, I would suggest that you try putting a pair of outputs instead of using only one.
LIghtly match the output transistors and just parallel them.
My class a amp uses 3 pairs of outputs, not super class a schematic but another totally diffrent one, it works and 3 pairs share similar load. No emitter or collector resistors either.


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PostPosted: 11 Feb 2018, 02:30 
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Joined: 11 Feb 2018, 02:00
Posts: 1
Hi guys
I am new at all these electronic stuff so please bear with me.
What i can figure out is that the layout is a mono layout?
And the i would like to know what pcb is in the middle of the two out put stages.
And last question is it a must to use a toroid transformer or can i use a "normal" one with the same rating?

Thank you in advance


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