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Old 15th January 2004, 03:32 PM   #1
rulezzz is offline rulezzz  Lithuania
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Default preamp

i'm not very experienced in preamp building so i want to ask i found this preamp here ,built it and realized that it is not very good quality thurthermore its output power is about 50% lower than my pc sound card(AC'97).Can somebody post link or circuit with preamp ,which quality and output power would be much higher than that preamp's.
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Old 15th January 2004, 04:58 PM   #2
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The design seems ok..............
You can increase the gain by changing R3 to e.g. 10K, which would give you 10 times amplification instead of the current 5.6 times.......
Which OpAmp did you use ??? The TL071???
Also the diodes D1, D2, D3 could be of a better and faster type
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Old 15th January 2004, 05:21 PM   #3
Praise! is offline Praise!  Australia
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Default suggestion

I have seen your link and circuit.

Since you have already bulit the pre-amp, why not up-grade it?
There are lots of room for improvment for this bad design.

The quickest way is to change the opamp. Try the pin for pin compatiable premium audio opamp such as the
Burr brown OPA604, OPA134 or the analog device AD797. I graruntee, it will be much better. Next, use batteries as power supply, like 2 SLA 12V 1.2Ah.

I am not sure if you have a good layout. It's very important as well.

If you are looking for a total change, ie build another one.
If you are interested in my suggestion, pop me a email and
I'll show you a very simple and nice sounding circuit. (Also
based on opamp)
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Old 15th January 2004, 05:27 PM   #4
sobazz is offline sobazz  Denmark
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Hmm.. never seen that biasing method before... how does it compare to the method used in the PPA headphone amp:

http://tangentsoft.net/audio/ppa/amp...schematic5.pdf
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Old 15th January 2004, 05:43 PM   #5
Praise! is offline Praise!  Australia
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1 more thought:

If you use that design to drive headphones, you will need
to increase the output stage bias current from 30mA(present)
to at least 50mA. To do this, add one more diode so that the bias
voltage increased to 2.4V. With the emitter resistors at present
of 10ohm, the bias current will be 60mA which is good enough
for most good quality hi-fi high impedance headphones. You will need to change the transistors to BC337 / BC327. You can increase the bias current to 100mA by changing the emitter resistors to 6ohm. However, don't push it too hard! Have fun


James Yung
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Old 15th January 2004, 06:30 PM   #6
rulezzz is offline rulezzz  Lithuania
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yap i'm using tl071
P.S. what tipe diodes should you recomend?
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Old 15th January 2004, 06:59 PM   #7
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You could use same BAV21....
Or go to my website under projects and take a look at my PATH preamp......
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Old 15th January 2004, 08:32 PM   #8
moamps is offline moamps  Croatia
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Quote:
Originally posted by ACD
You can increase the gain by changing R3 to e.g. 10K, which would give you 10 times amplification instead of the current 5.6 times......
Hi,

A=1+5k6/1k

Quote:
Also the diodes D1, D2, D3 could be of a better and faster type.
Why faster diodes? Those diodes are always ON.

Regards
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Old 15th January 2004, 08:45 PM   #9
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Quote:
A=1+5k6/1k
Ok! 11 times
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