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Old 28th July 2010, 08:56 AM   #1
lineup is offline lineup  Sweden
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Default 8 Watt Hifi with few parts

Hello.

This amplifier is designed to not consume too much power
eventhough the output runs in True Class A.
Using 2 power transistors you will get 20 Watt across each.
The maximal output is around 8 Watt RMS
with very low distortion. (~0.003%)

Actually this amplifier is a spring off from my explorations into Pass ZEN amplifier.
But he uses no opamp to handle the feedback loop.
He takes the feedback right back to the MOSFET gate.
Original ZEN Amp from 1994: http://www.passdiy.com/pdf/zenamp.pdf

Using an opamp will be another cake.
Now we can begin talking real Hifi.
Here is the simplified diagram of my idea.
I post a detailed schematic later.

Regards Lineup
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Old 1st August 2010, 03:18 PM   #2
anti is offline anti  Slovakia
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Hey, this looks interesting!

An idea: how about using a JLH output stage (with mosfets)?
Perhaps this could become the "ultimate" JLH ...

With "precision-enough" opamp, I think that it would have a very low DC-offset in case of symmetric supply as well.

(sorry to hijack)

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Old 1st August 2010, 05:36 PM   #3
tadiam1 is offline tadiam1  Argentina
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Default re

The last year duild an proto of this amp.Work well.but my circuit have an small signal transistor in the second fet.
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Old 27th October 2012, 11:56 AM   #4
lineup is offline lineup  Sweden
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Quote:
Originally Posted by tadiam1 View Post
The last year duild an proto of this amp.Work well.but my circuit have an small signal transistor in the second fet.
Interesting to hear about.
Somebody has the same idea as I have.
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Old 27th October 2012, 01:29 PM   #5
AndrewT is offline AndrewT  Scotland
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composite opamp & follower.
But you have not read Jung.
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Old 27th October 2012, 07:32 PM   #6
lineup is offline lineup  Sweden
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Quote:
Originally Posted by AndrewT View Post
composite opamp & follower.
But you have not read Jung.
No, I havent Andrew.
Thanks for posting.

I have made a working design in SPICE.
It took me some hours
With a power supply of 30 Volt
it is possible to squeeze out more than 11 Watt RMS into 8 Ohm.
Class A.
As you can see from my picture here
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Old 28th October 2012, 02:51 AM   #7
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Curious why you chose r6 to be 330 ohm. The datasheet for the opa134 shows 2k as optimum and 600 as minimum load for acceptable performance.
By the way, have you looked at Nelson's recent amp camp amp, a nice looking little circuit.

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Old 28th October 2012, 07:25 AM   #8
superR is offline superR  Netherlands
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I don't know why, but something draws me to this design. The sheer simplicity without the MiFi of a Pass amplifier. According to the OPA134 sheet, the opamp can do +/-35mA. Is the 14.7 mA the max driving current?
And what would be changed in the design if instead of a mosfet a transistor was used and what would be the (dis)advantage of that?
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Old 28th October 2012, 08:47 AM   #9
superR is offline superR  Netherlands
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I am not so sure about the harmonics. Next to that, the BD140 model I had was not performing nicely so I used a different PNP, which seems to work better. (just randomly picked)
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Old 28th October 2012, 08:53 AM   #10
lineup is offline lineup  Sweden
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Quote:
Originally Posted by jerluwoo View Post
Curious why you chose r6 to be 330 ohm. The datasheet for the opa134 shows 2k as optimum and 600 as minimum load for acceptable performance.
By the way, have you looked at Nelson's recent amp camp amp, a nice looking little circuit.
Quote:
Originally Posted by superR View Post
I don't know why, but something draws me to this design. The sheer simplicity without the MiFi of a Pass amplifier. According to the OPA134 sheet, the opamp can do +/-35mA. Is the 14.7 mA the max driving current?
And what would be changed in the design if instead of a mosfet a transistor was used and what would be the (dis)advantage of that?
I wanted like 15-20 mA across the MOSFET gate.
I settled for 15 mA not to make the opamp work too hard.
I think it is possible to use 220 Ohm, but I also think 15 mA and 330 Ohm is enough to drive the big MOSFET alright.

In this case the output of MOSFET will probably swing 15mA, +/-5 mA. This is something OP134 can easily do. OPamp output will work totally in Class A

I have not followed what Nelson Pass has done recently. I want to look into that. There is always something to learn from him.
You have any link to his latest 'amp camp amp' ?
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