OP amp driving BDW83A/84A

[poynton]

Hi.

I have a few BDW83A/84A power Darlingtons.

Can I use a pair as outputs driven by an op-amp ?

Ultimate hi-fi not required, just a reasonable sound.

Power supply about 35-0-35 (with regulators for the opamp)
What output power can I expect into 4ohm.

Thanks.
Andy

[Kapibara]

http://www.diyaudiotr.com/islecler/t....php?metinid=6

[poynton]

Hi.

Thanks for the link.

Is the circuit up-to-date or did the comments result in some changes ?

Not what I asked for but I do have an old board I could modify.


Andy

[consort_ee_um]

Here is a sketch of a circuit I modelled but did not get around to building. The problem with it is thermal tracking of the quiescent currents. The tracking with dual schottky diodes did not work very well (in spice) so I tried an NTC thermistor which theoretically could do the job. The pot is to set the quiescent current.

[sakis]

i wonder why you post and drive other people to do a circuit that doesnt work .....

also this amp is so called the john fisher amplifier and its NOT you property to publish in a turkish forum ...

you were also TOLD AND OR ADVICED from many including me in this forum not to mess up with this amplifier since dont really working ....

if you search our post in the back about this only negative things about it .....

the last time we talked i expalin to you that i had trouble with the circuit and if you made an efford to make it work properly we would like to share your comments about it

STILL WAITING !!!!!!!!!!!

[jaycee]

The problem with using an opamp frontend is that you are limited by the supply rails of the amp, unless you configure the output stage to have some voltage gain. This has a habit of being unstable.

It's a much better idea to use a discrete front end, in this case.

[Nico Ras]

Originally posted by sakis
i apologize to the forum and i am ready to be banned if the moderators decide to

you litle mizerable thief !!!!!very nice off you to present somebody else"s work under the name of diyaudio turkye and kapibara !!!!! this is complete bull***** sheet

shame on you to behave like that .....

i presume that in this forum everybody respect other peoples work

how destroyer x will feel if i take his amp ...post it is a greek forum under my name ???????

you should remove your name from there
give the credit to the one that owns it thats john fisher
and then inform all poor guys that may be want to copy this that this amp is not working properly any way

Hi Sakis,

There it should work ok now. I did not like the diodes setting the quescient current and replaced with VBE multiplier. Also changed the VAS emitter resistor to 47 ohm which seemed to balance the current flowing in each output.

[Kapibara]

Calm down sakis, dont be mad.
Does not any body to steal John Fisher schema.
I'm only draw pcb and layout this schema, like you.
But my pcb and equipment diffrent to your pcb and equipment.
My pcb works, your pcs does not works. Thats is your problem.
Mybe it is not to much quality, but works fine, simple and cheap.
Sorry for the bad English.

[lumanauw]

Various topologies can be seen here :
http://www.angelfire.com/sd/paulkemble/sound5.html
The oldest I can see using similiar topology is 40W from 1974 RCA.
It uses resistor for feeding differential pair, PNP differential pair without degeneration, NPN VAS, bootstrapped VAS load. Output stage is can be made of darlington and quasi complementary.
30W Bailey topology also uses this bootstrap for loading VAS, but the input is singleton, not differential.

[Ipanema]

Hi Sakis,

Why do yo think that the opamp based power amp will not work?

Regards.