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OnAudio 8th September 2012 09:49 PM

1DIFFQC amplifier
The Schematic, BOM can be found here

OnAudio 8th September 2012 09:52 PM

There have been requests to try out different darlingtons and this is fine. Among those suggested are MJH11018/20/22 and MJH6284 among others.

Struth 10th September 2012 11:08 PM

Hi Guys

Integrated Darlington packages are only ever used when cost overrides performance and reliability - so only for budget amps like guitar amps and cheapo stereos.

Use a discrete Darlington circuit and cross-connect the bases of the output BJTs with a single R for faster response. Yes, it is five parts instead of two but it is more reliable and performs better. The bias reg should be affixed to the drivers on their own little heatsink. Only the outputs should be on the main heat sink, otherwise you run into problems similar to having the integrated Darlingtons.

For outputs use TO-3P or TO-247 devices. For drivers use TO-220 types.

Have fun

OnAudio 11th September 2012 02:49 AM

Thank you for the input Struth. This research amplifier will most likely allow us to explore more about our perceptions about darlingtons, PSRR, quasi complementary, T.H.D. and a few other parameters.

There are a group of audio researchers working hard at it right now (they are putting themselves out there for us) i.e. WSJ, Kindhornman, Evette, Dagwood and many more.

As we await for feedback from them. You can read a surprising result here : PauloPT 1DIFFQC

There has to be a balance between what the meters measure and what the ears perceive. Sound perception and its dissonance with measurements is a broad area of research.

OnAudio 12th September 2012 06:32 AM

The Bom has been updated to reflect the alternative output transistors

Kindhornman 12th September 2012 07:24 AM

I just caught this thread. I am about to stuff all the capacitors, all the resistors and diodes are in and I see that you are talking about changing the output transistors. What has you going in this direction, is this just another possibility or has something changed in your thinking?
I'll have to look and see what is going on.


OnAudio 12th September 2012 08:10 PM

Hi Kindhornman,

Looking forward to your review :) . Some members requested to use the alternative devices :) .

kind regards,


Kindhornman 13th September 2012 12:35 AM

Okay Harrison,
Is the reason that these people want to use a different device because of noise differences or is there just some preferences for one output device over another? I haven't compared the BOM to the original yet to see what changes you have posted. Is it only the output devices or are there also other changes to optimize these output transistors? I am building the amplifier with standoffs so I could potentially change the output devices without have to De-solder the devices. I will watch and see what is going on closely.


OnAudio 13th September 2012 01:25 AM

Thanks Kindhornman. Some members already had stock of these output devices :) there was no need to buy the TIP142.

This will be an opportunity to find out the superiority between the darlingtons. ;).

evette 13th September 2012 02:34 AM

Yes I Have them all. Evette

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