Pass Discrete Opamp in DIP-8 Package

[jacco vermeulen]

JRC or NJR co.

 

[jean-paul]

I think you mean Harris who made class A opamps a long time ago. Good sounding too at that time. But IMO class A alone is not a guarantee for good sound. I heard class AB opamps that were better.

JRC/NJR make cheap silicon that sounds mediocre (to stay on the positive note). Never heard a real good product of them while the audio world seems to like their NJM4580, probably because of the price. That NJM4580 can be replaced by LME49860 with guaranteed good results....

 

[riktw]

after seeing this topic i couldn't resist turning this in a DIP8 opamp:
Discrete Operational Amplifier

as its fully class A making it with smaller transistors limits the output current even worse.
I got a 7mA bias, so 1.5mA output is about the max, but it works, has the same pinout as an 741 and it was fun.
sorry about the soldering skills, had a bad day
http://img844.imageshack.us/img844/4522/dsc02197xc.jpg
http://img191.imageshack.us/img191/8581/dsc02199dl.jpg
resistors are 0603 and i used NXP BC857's, 2 transistors in a small sot666 package.

 

[EUVL]

Very well done.

Patrick

 

[EUVL]

Seems that dual BC857 is no longer available in SOT666.
Possibly PMP4201V / PMP5201V, with the advantage of hfe & Vbe match ?

10p cap in 0603 is available at DK :
Digi-Key - 478-4448-1-ND (Manufacturer - 06035J100GBSTR)

I might well give it a try.


Patrick

 

[Jenyok]

I am looking for discrete op amp in germanium transistors.
.

 

[jps1964]

Hello Patrick,

here the BF862 version.

Is the LSK489 a good candidate for version 1? I´m starting with layouting and I will try to put all on the top side to simplify the heatsink design.

Or is today another simple discrete OPAMP available for DIY? I want to use it for the DSC1 DSD-DAC redesign.

Jean-Paul

 

[Jenyok]

Hello Patrick,

here the BF862 version.

Is the LSK489 a good candidate for version 1? I´m starting with layouting and I will try to put all on the top side to simplify the heatsink design.

Or is today another simple discrete OPAMP available for DIY? I want to use it for the DSC1 DSD-DAC redesign.

Jean-Paul

.
Please, show us a circuit of BF862 ?
.

 

[EUVL]

If I have to do it again today, I would use 2SK209 / 2SK2145 instead.
BF862 has high gate leakage when Vds is >5V.

I still have no solution for the P-channel device, and also for the DC drift.
I would have gone for a LSJ74, but then they do not have them in SOT23.
Maybe you can try J175, but they are rather noisy.


Patrick

 

[jps1964]

Hello Patrick,

first stage with 1x 2SK2145 grade Y with 5.6mA bias (CRD and 1.1k)?

Second stage with 1x ZVP3306F with 10mA bias (CRD)?

Third stage with 2SK2145 grade BL with 10mA bias?

Jean-Paul

 

[EUVL]

2SK2145 has no matching guarantee, though they track thermally better than 2x 2SK209.
Also the package can dissipate half the heat of a 2SK209.

For the first stage, the current is determined by the CRD, so the Idss of the JFET pair does not matter.

Perhaps it is worth trying J175 for 2nd stage.
Third stage current is a load / thermal consideration.
You can also make a CRD with 2SK209 using a suitable source resistor.


Patrick

 

[wengtech]

hello...
i am building one with J309 as input
and IRF9610 as output
current arrange with resistors

with 15vdc rails, measured dc offset (output to ground) is 7,5vdc
is that normal? how to make it zero?

thanks.

 

[Zen Mod]

certainly easier when looking at schematic

 

[wengtech]

Hello ZM
This is the schematic I build.
Output DC is -7.5v

Thanks.

 

[Zen Mod]

you need feedback loop to maintain output offset

so , post complete schematic

if you have that , vary R2 (increase it ) to get 0 on output

 

[wengtech]

Do you mean Rd and Rc have to be there?
And about R2, can I use trimpot?

 

[Zen Mod]

yes and yes

 

[wengtech]

yes and yes

I see...
Oke I'll try it.
Thanks zm.

 

[EUVL]

Connecting -IN to Gnd helps.


Patrick

 

[wengtech]

Connecting -IN to Gnd helps.


Patrick

I only changed the R2 with 10K trimpot and it works immediately null the DC out.
And it sound much better than my previous opamp.
So i am not doing the other thing for now.

Thanks.