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Old 22nd June 2006, 06:15 PM   #21
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Quote:
Originally posted by theAnonymous1


The AMP1-B is not a bridged amp, both channels share a common ground.
Agreed, i think i was a bit confused thinking about the t-amp.
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Old 24th June 2006, 12:28 AM   #22
BWRX is offline BWRX  United States
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Ok, I played around with that first design and realized it wasn't very good at all. I played around some more in SwCAD before I had to go back to work, but since then I've come up with what I think could be a decent design. It's more complicated, but it is symmetric with a BJT driving stage and FETs at the output. If it works, I'd like to dub it the SLPUCD - symmetric, low-power UCD. When I have time tomorrow I'll work on figuring out some values for the driver stage and maybe try to tackle the feedback values too. I'm still a little confused as to what values would be a good starting point for the feedback components.

Please don't hesitate to post any tips, feedback, or suggestions about the circuit (whether you know what you're talking about or not! ).

I used the LT1818 opamp because it can source and sink up to 40mA of current, has a high slew rate, and can work off of split supply rails. If anyone knows of a good dedicated comparator that can handle a split supply, have a rail to rail that can source and sink current please let me know. Most of the LT ones advertise split supply and rail to rail, but the output only goes from ground to + supply... at least it does in SwCAD.

Almost forgot, these are the supply voltages:
V+=12V
V-=-12V
Vdd=5V
Vee=-5V
The 5V rails can easily be derived from the 12V rails or have their own isolated supply (the best option as the current draw should be very low).
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Old 24th June 2006, 06:51 PM   #23
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If you want to use a P channel, You could try a source follower arrangment for kicks. Also I believe you can simplify this somewhat by AC coupling the comparator to the drivers.
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Old 25th June 2006, 02:38 AM   #24
mirlo is offline mirlo  United States
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A thought:

I think you would get much cleaner and faster switching by not using BJTs that get driven into saturation as MOSFET drivers.

Maybe you could use emitter followers instead, or if you need to swing the gates rail to rail use CMOS gates to drive the FETs.
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Old 1st July 2006, 12:22 AM   #25
BWRX is offline BWRX  United States
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You both have valid points, thanks for the input. I have since read more into MOSFET driving schemes and have come up with a revised circuit. The driver part of the circuit simulates ok, but I can't seem to get the feedback values right to obtain a high switching frequency with the output filter (L=30uH, C=0.68uF) and load values (32ohm) I'm using. I'll post some part values later along with the SwCAD file so anyone can fiddle with it too.
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Old 1st July 2006, 05:27 AM   #26
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Naw this there's a few other options like source follower or better yet dual n channel that puts far less transistors in the signal path. AC couple or go dual N channel with good level shifters.
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Old 1st July 2006, 05:55 PM   #27
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Default Low power right?

We are talking low power right? Why all the complication with the output? As suggested earlier a 4420 as the output stage would be more than adequate. This could be powered with split rails but may require a means of level shifting for the input signal. http://download.siliconexpert.com/pd...er/mic4420.pdf
The only thing that bothers me would be if the amp didnít oscillate properly the output would be full rail and would destroy any phones connected to it. Since we are talking high freq at the output a small cap could be used to couple the output into the filter, 1uf film? This would give the DC protection we need and also insure no offset.
This implementation would be good for several watts of power so could be tested with small speakers. Various input schemes could be tried including the suggested lm319. 2 chips and a few small parts implementation looks very good and would be very friendly to battery portability.
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Old 1st July 2006, 07:54 PM   #28
Tim__x is offline Tim__x  Canada
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Quote:
Since we are talking high freq at the output a small cap could be used to couple the output into the filter, 1uf film?
Sorry, but it's not just a high frequency. It's a high frequency modulated by a much lower frequency. The cap will need to be as large as it would in a conventional amp (A, AB, B).

BRWX.
What's your goal for this amplifier. Why class-d, what advantages do you think it has for a headphone amplifier.
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Old 1st July 2006, 08:05 PM   #29
Pano is offline Pano  United States
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Quote:
Originally posted by Tim__x
Why class-d, what advantages do you think it has for a headphone amplifier.
The idea is to see if a class-d amp built for headphones has all the detail and fidelity that the class is known for with speakers.

My guess is that at these low powers class-d will not sound as good as a good, simple class-a or a/b amp.
But let's see if Brian can prove me wrong!
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Old 1st July 2006, 08:20 PM   #30
mourip is offline mourip  United States
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Quote:
Originally posted by BWRX
Has anyone tried a pair of headphones with their Hypex UCD modules? I'd be interested in hearing the results of such a test.
I built a UCD180-AD amp specifically to power my AKG K1000 headphones after having such good luck with my Audiodigit 2020 amp. The Audiodigit was powered by SLA batteries. It was absolutely silent and had amazing detail.

The UCD is better. It has a much more relaxed upper end, way better bass, and there is no comparison in complex choral or orchestral passages. Of course the UCD costs 4 times what the Tripath 2020 did to build and has 180 watts instead of 8.

I tried my Sennheiser HD650's with both amps and was disappointed but mainly because the K1000s are so much better sounding to begin with.

AKG K1000s with the UCD are the best sound I have gotten so far as a primarily headphone user. My front end is "PC Audio" (Foobar and iTunes) to Scott Nixon USB DAC to Sowter TVA to Hypex UCD180-AD.

I have the T-amp for sale on EBAY right now and am keeping the UCD.

Hope this helps...
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