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Old 15th October 2012, 10:31 PM   #1
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Default Help with circuit diagram of amplifier

Hi to all,
I am new here and if I posted to wrong place please forgive me and I want to ask moderators to move thread to right place.Thanks.

My question is :
I have 5x 2STC5949 and 5x 2STA2121 and I would like to build class A amplifier but I don`t have circuit diagram of amplifier with this transistors.
Does anybody know is there exist schematics with this transistors for class A amplifier?
If exist,how can I get this?

Thank you in advance.
Best Regards
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Old 16th October 2012, 12:28 AM   #2
CBS240 is offline CBS240  United States
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Those transistors look suitable for the job, here are the datasheets. 2STC5949, 2STA2121. It appears the DC current gain is fairly linear up to ~4A.
How much power into what impeadance do you need? Is it going to be single end or push pull class A? If you search there are many examples in this forum.
All the trouble I've ever been in started out as fun......
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Old 16th October 2012, 10:59 AM   #3
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Hi CBS240,
Thank you on fast answer.
I have this datasheets, I just need to know is those transistors suitable for class A amplifier (about 50 W at 8 ohm if its possible) and is there amplifier schematics, I cannot find any with those transistors.I do not care wil be single end or push-pull, just be to easier to make this.
Sorry on bad english.

Best Regards
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Old 16th October 2012, 11:54 AM   #4
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Higher power class A will not be any easier to make than class B/AB. Quite the contrary in fact. If you'd like 50W into 8 ohm, I'd suggest looking for a nice class B/AB design. Those transistors look suitable for outputs in just about any design so don't get hung up on finding a design specifically for those particular ones.
---Jason Kuetemann---
Power is only granted to those willing to lower themselves enough to pick it up.
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Old 16th October 2012, 03:11 PM   #5
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You have right but I don`t want to build B or AB class,just class A.It does not have to be 50W it can be 20 or 30.

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Old 23rd October 2012, 09:30 AM   #6
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I found this two circuit diagrams (this is look good for me), on this links :

Power Amplifier 40W -Class A
Power amp 60W Class A eng

What you think about this and what I must change that I can use my transistors
on one of this circuit diagrams.
Thanks in advance.

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Old 23rd October 2012, 01:01 PM   #7
AndrewT is offline AndrewT  Scotland
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for ClassAB I use a rule to determine the the maximum output power of the amplifier.

Total the Pdmax of all the output devices.
Let's say you have 5pairs of 130W devices. Total Pdmax = 1300W.

For mosFET output stage divide by 4 giving 325W
For BJT output stage divide by 5 to 6 giving 217W to 260W

For ClassA try using divide by 15 to 20 giving 65W to 86W

This seems to indicate that 5pr of 130W devices is good for about 65W of ClassA.

Does that get you started?
regards Andrew T.
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Old 23rd October 2012, 05:40 PM   #8
Mooly is offline Mooly  United Kingdom
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LightMatic, I would point you to this thread to first give you an idea of the "power" or more correctly voltage swing you might need,

A Test. How much Voltage (power) do your speakers need?

and I would without any hesitation suggest you at least consider the original design of John Linsley Hood if the requirements fit,

The Class-A Amplifier Site

You would need just the NPN output devices.
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Old 23rd October 2012, 07:40 PM   #9
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Thanks on answers.
Mr. AndrewT, I know this allready, I just need to know did I have to change other components (like resistors) if I use my transistors on one of this schematics and what you think about design of this schematics.
Mr. Mooly, I read this allready.
I am the proud owner of Cabasse Galion V,amplifier will be work on them.
Now Galion`s work on Harman Kardon HK3490 this is s**et of amp but is good tuner and connection to PC via SPDIF.
I have Dual CV-441 RC amplifier (dual mono, class A ???) on this amp left channel is death, original transistors is too expensive (Philips BDV66D and BDV67D).It will be super if I can use 2STA2121 and 2STC5949 on this Dual but what modification I need to do ?
I know that original is Darlington`s.If you want I will give to you schematics of Dual (if I can do this).
I think that Dual is not realy class A,if I have wrong,sorry, but its not too bad amplifier,Galion`s love him and they is from same year :-).
Sorry on my bad english.

Regards from Herzegovina
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Old 24th October 2012, 06:52 AM   #10
Mooly is offline Mooly  United Kingdom
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To modify the Dual to use your transistors would really be the basis of a new thread

The BDVxxxD devices are available as you say,
CHS - replacement remote controls, instruction manuals, audio & video accessories, electronic components & spare parts

I'm not sure what the significance of the "D" suffix is as B versions are widely available,

To modify the amp would be a major undertaking the big problem areas probably being the bias stability of any "diy" darlingtons. Realistically you would have to keep both channels the same too.
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