"ST151" 100W amplifier

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D5 and D6 are nothing special...

Rod Elliott has a nice text about it here: http://sound.westhost.com/vi.htm

Some amplifier circuits show diodes connected between the output and the +ve and -ve power rails - these are shown in grey in Figure 1. The purpose of these should now be obvious - they will "catch" the spikes generated under the conditions Phil has explained. These will (hopefully) prevent the destruction of output transistors by shunting the excess voltage and current back into the power supply which simply absorbs the energy. The diodes prevent the amplifier's output voltage from ever exceeding the supply by more than 0.65 volt or so, and therefore prevent reverse biasing of the transistors under fault conditions.
 
Sixtec, thanks man!!
Sounds great the amp!
I used one old supply, trafo 24V and 4700uf per rail, 70W rms is enough loud!! Heatsink is small, i will get another.
The bias setup, the dc oscillate around 10mv, (8mv, 10mv, 9mv, 11mv), is right???
doubt: another amps need a inductor before connect the speaker, in this amp is needed?
I´m glad with this amp!
Thank you Sixtek!!!

p.s : Excuse me for the wrong english!! iuahiua
 

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Hi Dedepc,

I'm happy to hear that your amplifier runs fine.
Small sltering of bias current (8-11mV on the 0.33 Ohm) is not problem. Anyway I hadn't observed that.

doubt: another amps need a inductor before connect the speaker, in this amp is needed?

No, the ST151 is stable without Thiel-network (Thiel network = paralel 1-5uH inductor and 1-20 Ohm).

Aguantesoda,

Rule of thumb.
 
Questions.......

Sixtek, a good one. Simple and easily built. However, I need to ask some questions as I am more of a builder rather than a designer.

a) Is it possible to use 0.25W resistors instead of 0.5W resistors as specified? I have a large stock of 0.25W resistors.

b) How can I remove the protection circuit? Can I just remove T10 and T14 and their associated components? Reason is I am planning to operate the amp with higher voltages with the changes in (c) and (d).

c) It seems that there is insufficient drive to the final output transistors from the BD139/140 drivers. What will be the output if high beta/gain transistors are used, for example the Toshiba 2SA1943/C5200?

d) Can higher voltages be used if the Toshiba transistors are used? Any changes to the circuit's front end?

Comments are welcomed. Thanks.
 
BC547, BC557 alternatives?

Thank you for your post.

I don't have BC547 and BC557.

Instead, I have

- 2N3904, 2N3906
- 2N2222, 2N2907
- BC337, BC327
- 2SC1815, 2SA1015

If I can use instead of BC547, BC557 which pair is the best alternative?

Or could you recommend some other pairs?
 
Hey dude! Very nice work!

I totally understand what u said about "No audiophile modifications". I am already making my first amp(actually it's a Bass Guitar amp) and I was trying to understand all those fancy things on the Super Amps around here, but I didn't (and still don't) have the knowledge to that.

I'm glad to this very simple, but nice, work done. When I finish my project I'll try to do this.

Obs: Believe what the brazilian guy said... Good parts is very diffucult to find, and if U find it... thank God if u can afford it! So we use Hitano elet-caps, generic polyester-caps and pots, standard transformers...
 
I have some questions, Sixtec.

I'm preparing to make ST151.
After checking your latest schematic and placing diagrams,

http://sixtek.uw.hu/st151_krajz.pdf
http://sixtek.uw.hu/st151_beult.pdf

I cannot make clear 2 things.

1. C5(3.3u) polarity
It's polarity in the two files above are different.
I guess the placing diagram is wrong.

2. P1(1k VR)
The connections of the 3 legs of P5 are somewhat
different between the 2 diagrams.

If the files have some mistake, could you please
correct them and upload again?
 
Hi,

Thx for the feedback!

1., C5's polarity is OK on the schematic but wrong on the placing diagram

2., I'm going to modify the schamtic by P1 trimmpot.

OK, I will correct errors and upload the files again!

Thanks a lot!

PS.: I think you are the member who wrote me a mail. Sorry, I'm not planning to translate the text to english :(
 
Hi dear Cantabile,

I would but now I haven't got the enough time and energy. My english is not the best and that translation would be many-many hours for me...
But maybe. I thinking about that...

On the margin of course I can give any technical support by ST151!

Bye,
 
+- 50V ST151

Hi Sixtek

I want to build this amp since it is simple and easy to build. I am sure the sound is good and the amp is stable. I have two +-47V DC toroidal transformers that I can use. Can I power this amp from this supply??? What changes do I need to make for this amp to work from this supply's???? The Pot in your final PCB seem to be wrong. Can you fix this and upload the new PCB please???

Thanks for this design.
macd:) :) :)
 
Welcome Macd,

Pot is OK both on PCB and schema, but the wiring is not the same. The ampilfier built with that PCB and placing is 100% workable.
Of course when I have some time I will correct the schematic - that's the wrong not the PCB.

+/-47V-DC is too high for the semiconductors Vceo ratings and SOA.
So you'll need to use MJE340/MJE350's instead of BD139/BD140's, change BC547/BC557 to BC546/BC556, and use 2SC5200/2SA1943 or MJ15003/MJ15004 as output transistors - then you'll get about 150W on 4Ohm and 100W on 8Ohm.
If these 2SC/2SA or MJ parts arent available there then keep the BD249C/250C-TIP35C/36C outputs but be sure to use ONLY 8Ohm speaker. Then you'll get 100W-RMS on 8Ohm.

Good luck,
Keep informing us with your ST151-project!:)
 
+-50V version of "ST151"

Hi Sixtek

Got your reply. Thanks. I am going to do the following changes:

T1,T2,T5,T10 - BC546
T3,T11 - MJE350
T4 - BD139 (unchanged)
T6,T7 - MJE340
T8,T9 - 2SC5200
T12,T13 - 2SA1943
T14 - BC556

All other resistors and caps will stay the same. I kept T4 unchanced. Is this okey????

Will make the board today and built the amp and test is. Will give feedback.

macd;) ;) ;)
 
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