Power amp under development

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#2,841
Hi Maci.Laci

This is truly a marvelous looking stereo amplier, congratulations.

Are the zeners directly on the FET gate or are they before R24 & R26. I ask this beacuse if the zener on the positive side of the amp ever turned on, it will likely destroy T9. If the zener is directly on the gate you should increase R24 & R26 to 100 ohms to give the zener half a chance of doing its job.

So its a problem choice, the zener will provide a degree of over current protection, but will need some current limiting via a series resistance.

Cheers
Quasi

PS. Ahem.... it would be nice to see some builds from other constructors
 
#2,842
Quasi, the fuse placement in the Nmos amps (except the 400 which looks right) may cause a chain reaction destruction when the fuses blow. The drivers will try to drive the output on their own possibly punching through the gates of the output transistors and smoking their emitter resistors. If the gates of the outputs short or are zener protected the driver transistors will probably blow up too. The connection in the Nmos400 with drivers connected after fuses looks right but I suggest you add something to current limit the VAS too, for example clamping diodes or a zener between its base and the positive rail. As it is now the only thing limiting the VAS current when the output is unpowered and/or shorted is the current gain of the VAS and tail current of the input stage.

I've seen an amp blow up its drivers, VAS transistor and set some resistors on fire because of a bad connection on an output transistor emitter resistor - quite similar to having your rail fuses open in this design. One driver shorted as it tried to drive the output by itself and the non-current-limited VAS blew up trying to pull on the base of the shorted transistor. The resistors that burned were driver base resistors and VAS emitter resistor IIRC.
 
#2,844
Putting the input stages after the fuse has one drawback I can see - if the positive rail fuse blows the output will go to the negative rail. The connection used in the Nmos400 looks fine, adding a clamp for the VAS base should make the VAS stage protected from blown fuses and blown output stage/drivers.
 
#2,845
I was looking for an amp to power my subwoofer. I have seen from previous posts that the nmos350 amp would be suitable for that.

I have not built any amp before. Would this amp be difficult to build if it is a first time build ? Will just following the schematics exactly allow a sucessful build ?

Thankz.
 
#2,846
Hi, I'm up to build a couple of those amps for bridge operation. But I've encountered some issue. Amp didn't work properly with buffer, there is strong offset of input signal after buffer or inverter stage. It's on the picture. What's the case? I can't figure it out. How to fix it? Really want to bridge them 🙂
 

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#2,847
Buzzy said:
I was looking for an amp to power my subwoofer. I have seen from previous posts that the nmos350 amp would be suitable for that.

I have not built any amp before. Would this amp be difficult to build if it is a first time build ? Will just following the schematics exactly allow a sucessful build ?

Thankz.
Click to expand...


This should not be your first electronics project. It can be your first amp project but you should have successfully completed other electronic projects of medium complexity. It might pay you to practice with a chip-amp first and get the feel of building a complete amp with power supplies, mains wiring etc.

Cheers
Q
 
#2,848
niroborn said:
Hi, I'm up to build a couple of those amps for bridge operation. But I've encountered some issue. Amp didn't work properly with buffer, there is strong offset of input signal after buffer or inverter stage. It's on the picture. What's the case? I can't figure it out. How to fix it? Really want to bridge them 🙂
Click to expand...


Hmm...I don;t know what the problem is. Is there a DC offset being created on the base of the power amps input transistor?

Can anyone else help?

Cheers
Q
 
#2,849
Quasi in Phuket

Hi Folks,

I will be away for about 7 days attending a conference in Phuket -Thailand. Please don't feel sorry for me, I had it coming. Of course if any fellow DIY'ers happen to be in Phuket over the next week send me an email and I'll give you some details. There will not be any posts from me during this time.

Try not to burn yourselves with your soldering irons and I'll try not to burn myself in the sun.

Cheers
Q
 
#2,850
Re: Quasi in Phuket

quasi said:
Hi Folks,

I will be away for about 7 days attending a conference in Phuket -Thailand. Please don't feel sorry for me, I had it coming. Of course if any fellow DIY'ers happen to be in Phuket over the next week send me an email and I'll give you some details. There will not be any posts from me during this time.

Try not to burn yourselves with your soldering irons and I'll try not to burn myself in the sun.

Cheers
Q
Click to expand...
Quasi, do take some time out from the beach to attend the conference

😀
Have a good trip, cheers
Hari
 
#2,853
Maci.laci your amp looks so neat and compact.


I intend to use IRFP240 for the output instead of the irfp450. I have seen that Quasi has mentioned that irfp240 can be used in previous posts. Would I need to make any changes to the nmos350 circuit to use irfp240 ? Or can I just follow the schematic w/o changes ?

Thankz.
 
#2,856
Hi,
one could have one timer/delay circuit controlling one relay shorting out one resistor, but feeding multiple transformers.
But, better would be one timer controlling dual relays, shorting dual resistors so that each transformer has the correctly selected series resistor.
 
#2,857
Hi Andrew,

Tks, that would mean a relay added parallel to the existing one with its associated seriial resistors, right? And what about the diode? Do we have to have an extra one (or will it hurts to add one ?)

Tks
 

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