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Old 19th March 2005, 07:10 AM   #161
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Default Ten thousand apologies;

The last schematic posted is slightly incorrect. R16 & R19 have been inserted. They exist on the PCB layout.

Again 10,000 apologies.

Cheers
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Old 19th March 2005, 08:23 AM   #162
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Why is not used in this final connection higher positive voltage at VAS ? In this case clipping will be not symetrical.
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Old 19th March 2005, 09:28 AM   #163
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Quote:
Originally posted by Upupa Epops
Why is not used in this final connection higher positive voltage at VAS ? In this case clipping will be not symetrical.
My attempts at running a higher voltage on the positive side driver stage caused too many problems. I was able to achieve symmetry on the negative side by inserting R21 (100 ohms).

I have posted another circuit that achieves symmetrical clipping using a higher positive rail for the drivers in the thread "Another quasi-complimentary design". This topology should allow the output to swing very close to the positive & negative output rail.

If you decide to follow that thread I will be able to report back in a few weeks how that works.

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Old 19th March 2005, 09:39 AM   #164
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Which many problems ? You need only one small serial made transformer ( cca 3 - 5 VA ) with 6 - 7 V secondary, one bridge 1 A rectifier, one elyt 1000 M / 16 V and connect this PS in series with positive rail. That's all, any problems.
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Old 19th March 2005, 12:05 PM   #165
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Quote:
Originally posted by Upupa Epops
Which many problems ? You need only one small serial made transformer ( cca 3 - 5 VA ) with 6 - 7 V secondary, one bridge 1 A rectifier, one elyt 1000 M / 16 V and connect this PS in series with positive rail. That's all, any problems.

Configuring the power supply isn't the problem. When I splt the positive rail and fed the driver stage with a higher voltage the amplifier did not work very well. Whilst I gained greater positive voltage I lost a lot of negative rail swing and the clipping went wierd. This was covered in some detail early in this thread and no-one seemed to know a way around it.

Let me assure you I spent many hours trying to solve this problem. The answer was not as simple as applying a higher postive voltage, changes to the topology were required as well, plus I wanted to finish the amp. If you have any ideas about what these changes could be I would be very interested, but let me also assure you it is more than just feeding a higher positive rail to the input and driver stages. If you do have the answer I would be delighted if you could draw it on the schematic and post it back. Sometimes people are blind to simple answers and maybe I've just missed an obvious solution.

I did however re-design most of it and came up with the topology I have posted in the other thread. This does apply the approach you mentioned but you'll see that the topology is very different.

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Old 19th March 2005, 12:08 PM   #166
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Default Re: Ten thousand apologies;

Quote:
Originally posted by quasi
The last schematic posted is slightly incorrect. R16 & R19 have been inserted. They exist on the PCB layout.

Again 10,000 apologies.

Cheers

Ummm ...here it is.
Attached Files
File Type: pdf nchan mos 350 1v4 schematic.pdf (40.7 KB, 3432 views)
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Old 19th March 2005, 12:15 PM   #167
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Solution is easy : make the same on both rails . Look at attach, this is my mosfet amp. I'm using there quite the same solution and problems not exist.
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File Type: gif dpa386se_sch.gif (60.3 KB, 4849 views)
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Old 19th March 2005, 12:37 PM   #168
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Quote:
Originally posted by Upupa Epops
Solution is easy : make the same on both rails . Look at attach, this is my mosfet amp. I'm using there quite the same solution and problems not exist.

The cct you posted is for a complimentary amp not a quasi-complimentary amp. I cannot run a seperate rail for the negative side because in my cct R22 (220 ohm) must be tied to the same negative rail as the source of the negative rail FETs. This is because the gate voltage on R22 is referenced from the negative rail. If I split this rail I lose the reference. This was covered near the beginning of this thread.

In your cct the negative voltage drive is taken from the emmitter of Q25 as it should be when driving a P-channel device, mine is taken from the collector of T10.


Cheers
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Old 19th March 2005, 01:05 PM   #169
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OK, you have thruth. But some notices to your connection. When I was trying my connection, I discowered, that voltage on VAS can't be much higher than rail voltage ( I was trying it with adjustable supply ). Optimal value is cca 5 - 7 V DC and if is used higher, amp is less stabil at clipping. It was probably your problem too, if this voltage was 10 V , which is showed at first schematic. Set up it at 5 - 7 volts and you will see that all is more better on both polarity. Second notice : is neccessary ( ! ) use protection zener diodes, 'cos by high overload or by output shorting you break up GS and mosfets will be destroy !
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Old 8th July 2005, 02:14 AM   #170
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Default Feedback?

The amp described has been in service now since April 05 without any problems at all.

I know that some others have been built by readers of this forum and I would be very interested in receiving feedback from anyone who has built it.

Specific feedback would be welcome about;
- layout and circuit improvements
- setting up (idle current stability etc.)
- power supply and wiring
- measured power outputs
- slow turn on and protection ccts
- chassis and heatsinks used
- FET mounting and temperature sensing
- applications i.e. sub amp, PA etc.
- any failures

I would be grateful for any feedback and any pictures of your versions.

Thanks and cheers
Quasi
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