Hybrid Amp

ashok

Member
2002-06-06 4:43 am
3RS
Hybrid with 6DJ8

I am not sure if you are talking about the 6DJ8 used as a differential input stage in a class A amp . I saw this on the web with IRF9540/540 mosfet output transistors.
I rigged up the circuit with the 6DJ8 at the input and followed by a bipolar stage using BD139/140. I also tried an IRF 9540 in the voltage gain stage position. The output stage was a Darlington
TIP142/147 combination. It seemed to be fine without any input. I then touched the input to see how it overloaded at low frequency (50Hz!). It seemed clean and then the output tr's blew.
Not dead short but gone bonkers. Nothing semed to be over heated and there was no load.

I replaced all the transistors (including the good ones) and tried again. It seems to be fine. I am now building a second stage to test it out in my hi-fi system. I already use a hybrid power amp and no preamp. I will test this circuit with the ECC82 and the 6SN7. Will measure the spectrum of the distortion to see how they compare.
Cheers.
 
Re: Hybrid with 6DJ8

ashok said:
I am not sure if you are talking about the 6DJ8 used as a differential input stage in a class A amp . I saw this on the web with IRF9540/540 mosfet output transistors.
I rigged up the circuit with the 6DJ8 at the input and followed by a bipolar stage using BD139/140. I also tried an IRF 9540 in the voltage gain stage position. The output stage was a Darlington
TIP142/147 combination. It seemed to be fine without any input. I then touched the input to see how it overloaded at low frequency (50Hz!). It seemed clean and then the output tr's blew.
Not dead short but gone bonkers. Nothing semed to be over heated and there was no load.

I replaced all the transistors (including the good ones) and tried again. It seems to be fine. I am now building a second stage to test it out in my hi-fi system. I already use a hybrid power amp and no preamp. I will test this circuit with the ECC82 and the 6SN7. Will measure the spectrum of the distortion to see how they compare.
Cheers.

HI

Can you show me the diagram?

thx
 

Lauris

Member
2004-09-29 9:25 am
kns
Problems with hybrid amp

Hello everyone, I have little problem.
I am planing to make 5.1 system amp and atleast four chanels will be by this schematics Hybrid schematics (wil be on each chanel 2xIRF540&2xIRF9540).

so now I have face with one problem, I have colect one chanel to try (with single IRF540&IRF9540) and something is wrong. With IRF540 I don't see any problems but, IRF9540 is burning. maby someone was doing something like this, or necessary and maybe can help me with this problem?

using PCB from same page with place for 3xIRF540&3xIRF9540 only mirrored.

in ECC88 place using [rus] 6N23P, somethere found that it is ECC88 analog.
 
Upupa Epops said:
To Lauris : Idiot, who designed this circuit, don't give there protection zener diode to the gates of both power mosfets. By the overload is gate broken by driving voltage and transistor is destroyed.


polite as usual.
;)
furthermore i don't see any protection zener in it

Lauris
if you cannot adjust the biasing correctly change the P3 pot to bigger
if you have it done then:
1. ensure the irf540 is doing well, i mean you have A class so the idle current should be Ipeak/2~=(32V/8ohm)/2=2A
so voltage drop on r14 must be 0.33 ohm*2A=0.66V
if it isnt replace the zener with a proper (adjustable)Vbe multiplier
2. set the pot P3 to max resistance
3. increase the pot's resitance slowly and simultanously watch the output voltage(for no input signal)-should be null
done
 
Wow! This is a hostile forum!

However, your question is interesting enough to answer. The schematic you posted has been thoroughly analyzed by The Tube Cad Journal (www.tubecad.com).

John Broskie has studied hybrid amps for years, and he has very good suggestions. Don’t be frightened by the Journal’s name: The Tube Cad Journal discusses solid-state as much as it does tubes.
 

Lauris

Member
2004-09-29 9:25 am
kns
So in this link which I post is't final version of this hybrid amp?
if so, can anyone post the final version link?

I one more, almost stupig question: that is "zener", where in schematic I can find it, best would be for example schematics with zener and where it is in that sch.


p.s. EN isn't my firs language so for now I still have problems with technical language.
 

Lauris

Member
2004-09-29 9:25 am
kns
OK I found it, and now one qestion: in first remake schematics instead R3(510om) is 2240om? where I can find exactly this? or wilbe enought 2,2Kom? and in final sch is also 2x374 & 1260 resistors, what about them? o maby I have to colect them from multiple diferent rezistors(but in this way I still Cant get exactly what I need)?
 
UltimateX86 said:
It is a simplification of my next amp

http://diyaudio.chez.tiscali.fr//6CW4simple.pdf

What do you think about this diagram ?

adjustable Vbe multiplier with same Thermal Background as output Mosfet
adjustable input and output offset
gain 30

THX

I think that long tailed pair is not necessary on the input. I would use common cathode stage with parallel connected triodes. It works much better, and drive the mosfets easily.
I made some hybrid amps, and I think that DC coupling is not good way. You have to use output relay to protect your speakers, during the heating up period.
Mosfets are not easy to drive due the large input capacitance. This is true for common source connected devices. Followers are better.

sajti
 
Upupa Epops said:
What I think ? This amp will be precious slow - if you will use ECC 88, output impedance will be app. 10 k Ohm. With input capacity of this mosfets you don't get acceptable SR, respectively distortion at high frequency will be high. Temperature sensing with this type of fets is not mandatory ( they have very favourable Tc ) ;) .

There is no ECC88
 
sajti said:


I think that long tailed pair is not necessary on the input. I would use common cathode stage with parallel connected triodes. It works much better, and drive the mosfets easily.
I made some hybrid amps, and I think that DC coupling is not good way. You have to use output relay to protect your speakers, during the heating up period.
Mosfets are not easy to drive due the large input capacitance. This is true for common source connected devices. Followers are better.

sajti

I used a differentiel in entry for this reason

http://diyaudio.chez.tiscali.fr//6CW4bipo.pdf

:att'n: it is only 1st diagram, I did not still simulate anything
 
UltimateX86 said:


I used a differentiel in entry for this reason

http://diyaudio.chez.tiscali.fr//6CW4bipo.pdf

:att'n: it is only 1st diagram, I did not still simulate anything


Ok, now I understand. I have another design which has same idea, but less output power, due it's SE class A design. It's not ready yet, I had no time to finish it.

sajti
 

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