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Old 24th February 2012, 06:19 PM   #31
vgeorge is offline vgeorge  Greece
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With mje340 (be careful of the different pinout) and bc546 it works fine. Have not listened it it yet though.
I used mje 15030 in the beginning when I had problems. These seem too fast for this circuit.
Ray, could you advise what exactly transistor did you use?
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Old 25th February 2012, 12:46 AM   #32
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I use MJE3055 and BD937, both works fine. BD937 sounds better.
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Old 25th February 2012, 03:35 AM   #33
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This is a great little circuit !!!
I was looking for something like this.

I have now modified this circuit for a higher current and I have it doing about 9.2v peak into 2 ohms, 8.73v peak in to a 1 ohm load, and 6v peak into .5 ohm and will even do a .25 ohm load.
All in class a mode operation in a simulation using Circuitmaker 2000.

With no errors!

I was beginning to think that this was nearly impossible on a +/- 12v supply.

All I did was add 4 more pairs of output devices and juggle a few resistor values.

In this example I have the bias set at 3 amps per device so each one is dissipating 36 watts approximately half of what an MJE3055 can do.

I will try to build this some time in the near future and put it to the test.

But if any one is interested I can post the schematic at any time.
It would be very interesting to know what kind of performance this thing has and could do with the modifications.


Keep on DIYin' !!!

jer
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Old 25th February 2012, 09:40 PM   #34
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I guess I was a little over excited in my last post!

But I was thrilled to see such a low THD figure and in researching the JLH circuit I have found that what I had discovered a lot of DIYer's are already doing this! he,he

I have been looking for a way to build some Class a amplifiers for a reasonable cost and I had found that this may be the ticket vs the Nelson Pass designs.

Both seem to be very popular only I am not willing to track down and pay the price for some jfets that are out of production.

These use BJT's and I already have every thing I need to build these in my box of spare parts, and will still have great performance on the cheap.
Particularly for driving my ESL's.

I had already known of the JLH design but it wasn't until this thread that had got me hooked on the modernized versions of this design that I have found.

So far I have created a design the uses 8 pairs of output devices and is good to 1 or 2 ohms on a +/- 30V supply with little changes to the original circuit.
The design is the same and I could probably build it with new parts for around $10 for just the amps components (using the MJE3055 at $.39 each).
That is alot of amplifier for the price.


Thank You !!!

jer
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Old 7th March 2012, 02:45 AM   #35
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RE1506 is the ideal enclosure for the headphone amp. One 20W transformer, 2 board, RCA connector, ICE connectors, potentiometer, 6.35mm jack and switch can be easily fitted into it without any mod. There's still enough room for a small power board with a rectifier and 2 big caps.

dual 9V toroid transformer is also available for only $18.

Click the image to open in full size.
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Old 15th March 2012, 03:43 PM   #36
Puffin is offline Puffin  United Kingdom
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Can anyone advise the best voltage to use with 8ohm speakers? These boards are for a single rail supply only and not split rail?
What are the variable resistors for? Dc offset?
Is there a specified adjustment proceedure on start-up?
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Old 15th March 2012, 04:47 PM   #37
vgeorge is offline vgeorge  Greece
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This is a headphone, not speaker amplifier.
They work on +-12V.
One trimmer for offset an one for bias.
If you want a speaker amplifier look at the JLH class A thread. I think that siliconray offers free boards for them too.
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Old 17th August 2012, 04:47 PM   #38
RS232 is offline RS232  United Kingdom
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Hi everybdy
Managed to finnish the 2 board but I have to small issues...
First is the bias and off set are not steady, they change up and down (from +/-0.00 to +/-30-40 mV (offset) and from 150mA to 220/230ma (bias) for no reason.
The second one is, if I touch the heatsinks the offset changes +/-20mV.
All the components are the ones on the schematic, R10 is 0.47Ohms and output transistores are the 2SC2238
Power supply is +/-12V regulated.
Any Ideas ?

Ric
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Old 17th August 2012, 06:15 PM   #39
vgeorge is offline vgeorge  Greece
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Maybe oscillation, do you have a scope?
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Old 17th August 2012, 09:30 PM   #40
RS232 is offline RS232  United Kingdom
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Hi Vgeorge
Yes I have a scope
Yes it is oscillating....
Any suggestion ?
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