Explendid amplifier designed by Michael Bittner, our MikeB

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caglarm

Member
Joined 2011
Hi Chris,

I start to this project for build high power supply (+-65 volt) symasym amplifier.I didnt need more power,only for high speet,more dynamic,very low output empedance..

I attacthed my original pcb picture..You can see 36v zener diod and 2 2n5551 transistor.2sk170 working in 36v range.

Working very well means; yes, it sounds good.I connected singnal generator input and connect to osciloscope output (wiht 8 ohm resistif load).
10hz to 100khz gain is ultra linear..good squarewave response.

I haven't spectrum analyzer,i cant measure more detailed..
İf you want,i can give you all document.
116.jpg
 
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anatech

anatech

Administrator
Joined 2004
Paid Member
Hi caglarm,
You should post whatever you are comfortable with. I think there would be a lot of interest from various members. I have never seen that take on this basic amplifier, so I find it interesting too. If someone else builds one, maybe they can take measurements. One thing for sure, the Symasym basic amplifier sounded very good. I built some. So I'm not terribly surprised to hear you say that yours sounds good too.

-Chris
 
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caglarm

Member
Joined 2011
When i make first prototype pcb (only 1 per mos,1st pdf file),i use driver transistor.I try some combination.Then i remove driver transistor..sound is more natural.squarewave response is better.I make second pcb without driver and 5 per mosfets.I use this amplifier long time.
BUT,i can say best result transistor out ver.Only one per and high power transistor.(mjl4281-4302)

IMG_0045.JPG
 
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AndrewT

R.I.P.
Joined 2004
smartx21 said:
What?
Click to expand...
It appears he has picked the BJTs outline that have the same pin out so that the jFETs fit the PCB. And then labelled them so that you see what to use.
He has used very low value source degeneration resistors indicating that he realises that these jFETs don't work optimally with the much higher values used by BJTs.
And these 22r are big enough to allow the Builder to check that the jFETs are truly balanced currents.
expect ~30.0mVdc across the degen resistors
and ~1000mVdc across the drain loads. and ~400 to 450mVdc across the CM degen.
 
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Mace Horny

Mace Horny

Member
Joined 2016
I have a problem with my built. I have on one monoamp across the fuses 3,7V instead of 1,5V how it's described in the manual and on the other only 0,5V. All the LED's are working except the Status LED in the SPK Protection Section. I measured all Resistors they are correct. I insulated all screws. Has anyone a solution of this ? Ask if you need more information

Kind Regards
 
Mace Horny

Mace Horny

Member
Joined 2016
AndrewT said:
Have you turned the output bias ON?

Turn the output bias right down till it goes OFF.
Then check voltages around the amplifier to prove that it is assembled correctly.
Click to expand...

Well, I found the fault but I don't know what I can do now. I have a transistor Socket for Q1 and Q2 (Input differentials) to change Transistors fast to hear the differences in Sound. If I put a matched pair of BC550C in it the Amp doesn't work anymore (I can hear the click from the relais in the SPK protection without inserted BC550C's). Do I need other Transistors like 2N5551 ? In the User Manual there is described you can use BC550C... I'am confused now ...

BTW: without the input transistors the Voltage on the Fuse Sockets is around 0,3V and ALL LED's work ...
 
Mace Horny

Mace Horny

Member
Joined 2016
Mace Horny said:
Well, I found the fault but I don't know what I can do now. I have a transistor Socket for Q1 and Q2 (Input differentials) to change Transistors fast to hear the differences in Sound. If I put a matched pair of BC550C in it the Amp doesn't work anymore (I can hear the click from the relais in the SPK protection without inserted BC550C's). Do I need other Transistors like 2N5551 ? In the User Manual there is described you can use BC550C... I'am confused now ...

BTW: without the input transistors the Voltage on the Fuse Sockets is around 0,3V and ALL LED's work ...
Click to expand...

The Transistor Q5 gets hot after seconds as well ...
 
anatech

anatech

Administrator
Joined 2004
Paid Member
Q5 and Q6 should run at the same temperature, and not hot.

Have you decided to use BJTs instead of J-FETs? Otherwise the BC550C should work fine in that circuit. What are your supply voltages? If you can't find real 2SK170 transistors, try J202 transistors. Much lower transconductance than the 2SK170, but real parts will trump fake parts every time. For BJTs I was using 2SC1775A or 2SC2240s, but the BC550C are low noise, high gain parts that should work great.

Matching J-FETs is straight forward using information from Nelson Pass or Walter Jung. The BJTs need to be matched using a jig (J-FETs use a jig too where you match Vp and Idss) for beta. Vbe isn't important, but will match closely as a side effect of close beta matching from the same batch of transistors. Buying them on tape from the factory (cut tape option from a proper distributor) will insure that.

-Chris
 
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Dirk83

Member
Joined 2017
Importance of Hfe?

Hi,
seeing these suggestions on transistors I would like to throw in a question: How important is Hfe?
I have obtained Philips NOS 2n5401 and 2n5551. Couldn't find 2N5401 from Fairchild or Onsemi. The old Philips are quite a bit lower in Hfe compared to some newer equivalents from Diotec Semi or Taiwan Semi sold here (30-50%).
The Philips are very nice by appearance and despite quite a variance in Hfe I could match (<0.5% @2mA) good pairs but I am still wondering if high Hfe is important?

Would appreciate if someone could help and explain qhat a difference in Hfe could result in.
 
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