Power amp under development

Upupa Epops said:
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.

Cheers
 
Upupa Epops said:
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. :cool:


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.

Cheers
 
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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Upupa Epops said:
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
 
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 !
 
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
 
Hi

I was looking for a 100-150 watt amp, and found this forum, and I'm ready to build my amp :D

just curious... the final schematic would be the 1.4 and the pcb would be 1.3?

Don't know if it'll make a difference if I use a standar E-I transformer (the only one i have around, rewind needed :xeye: )

anyone has tried it as a sub amp? i want to put a crossover and drive a 15 inch woofer, while my old AKAI 2850 drives 2 12 inch and piezo horns (sometimes i do parties and stuff :clown: )

Beautiful design, quasi, hope to have a nice amp soon...
 
LuigiDJ said:
Hi

I was looking for a 100-150 watt amp, and found this forum, and I'm ready to build my amp :D

just curious... the final schematic would be the 1.4 and the pcb would be 1.3?

Don't know if it'll make a difference if I use a standar E-I transformer (the only one i have around, rewind needed :xeye: )

anyone has tried it as a sub amp? i want to put a crossover and drive a 15 inch woofer, while my old AKAI 2850 drives 2 12 inch and piezo horns (sometimes i do parties and stuff :clown: )

Beautiful design, quasi, hope to have a nice amp soon...


That is correct, the final schematic is 1v4 and the PCB is 1v3. An E-I transformer should be fine if it is the only one you have. Good luck with the rewind.

The amp should be fine for any application from sub woofer to hi-fi to PA.

Cheers & good luck.
 
Almost done with it !

Hi, it took me a little longer longer than I though, but it's almost finished (at least one channel).
I have some questions, if anyone can help:
1. How do i set up the idle current and what current would be ok?

2. How do i mount T8 on the main heatsink and as close as posible to
the output FETs? (as it states on the schematic) :confused:

3. R35 (10 ohms in series with 0.1u cap) has to be 5 watts or it could be 1 watt? (it's like 1 watt on the amps i've seen)

4. I used BD139 and BD140 instead of MJE340 and 350, they are lower voltage than the MJEs, but i'll use +/- 62 volts dc, and i think they'll stand it, any comments? :att'n:

Thanks for any info, it's very valuable and always welcome
 
1. Measure the voltage across the MOSFET source resistors. 50-100mA should be OK. For a sub amp use the lower current.

2. Use flying leads on the transistor.

3. Use 1W or 2W if that's all you have, but in extreme circumstances it may smoke it. Don't use a wirewound type though as they are too inductive, so you may be limited to 2W (I can't find more than 2W in non-wirewound).

4. They will blow up as you are exceeding their Vce rating. Check the datasheet ;)
 
IT'S ALIVE !!!

I just finished it and right now i'm listening it!
It sounds very nice and powerful, nice bass and highs on a full range speaker, later i'll build the low pass filter.

I changed the bd139 and 140 for the mje's (thanks richie00boy), and used the 5 watt resistor (wirewound, couldn't find non-wirewound), but couldn't measure the idle current. does it have to be measured with or without a load connected? i just test for dc offset on the output and connected an old speaker (in case it blows out :bigeyes: )

how do i see if all the mosfets are working? do i measure the voltage on the source resistor too? if so, all are working...

i'll begin to build the other channel and the case, (another month work), i can post photos if someone is interested.

Thanks Quasi for this project, and everybody for your contributions ;)
 
Re: IT'S ALIVE !!!

LuigiDJ said:
I just finished it and right now i'm listening it!
It sounds very nice and powerful, nice bass and highs on a full range speaker, later i'll build the low pass filter.

I changed the bd139 and 140 for the mje's (thanks richie00boy), and used the 5 watt resistor (wirewound, couldn't find non-wirewound), but couldn't measure the idle current. does it have to be measured with or without a load connected? i just test for dc offset on the output and connected an old speaker (in case it blows out :bigeyes: )

how do i see if all the mosfets are working? do i measure the voltage on the source resistor too? if so, all are working...

i'll begin to build the other channel and the case, (another month work), i can post photos if someone is interested.

Thanks Quasi for this project, and everybody for your contributions ;)


Great news that your amp is working and that you are happy with it.

Good also to see that Richie00boy has helped you along the way.

I soldered T8 under the board so that it would slip into a tight hole drilled in the heatsink when the board was mounted.

You can test if each FET is working by measuring the voltage across the source resistors while a small signal is fed through the amp. You should get a voltage reading across all the source resistors.

Yes please post some pictures of your work. I would be very interested to see them.

Anyway happy listening.

Cheers
 
I have a question related to this amplifier.

I'm not sure what value sould i use for the surce resistors. On the schematic they are 0R47 and on the PCB they are 0R33.

And what is the influence of those resistor on the quality of sound. I know they provide some negative feedback to the output stage and they have an influence on the efficiency of the amplifier, due to the voltage drop across them and relatively high currents that flows thru them.



thanks guys
 
thanks quasi,


if those resistors don't have any 'visible' influence on the quality of sound I prefer to use 0R47 for current sharing reason...

Yesterday I got the pcb's, so starting from monday I will build the beast... I hope to have-it working at the end of next week ...

cheers
 
Power fets

Hi Quasi ...

good project.

I ordering part to make my AMP.
i use your project for my HOme Theater SUBWoofer.

i have 2 question.
1- can i use IRFP 240 on the output stage ?
here is very dificult to find irfp450 but i have lots os irfp240 in my work.

2- Can i put more fets on the output do use this project in 2hom load ?

Thanks for help and sorry for my bad english hehehe
When i complete the amp i send photos