Discrete Opamp Open Design

[flg]

Originally Posted by bcarso

I compliment those who use "complement"...

Thank you, and thank you

[fitzfish]

Brad,

Originally Posted by bcarso

...of the Toshiba dual N device, the 2SK2145, which is apparently a two-chip dual using 2SK117 devices

Yes, same die as the 2SK209 single in sot 23 also.

The 2SK880 single in a SC-70 (100mw max pdis) is also the same die... which is available from Mouser in BL.

Dave

[scott wurcer]

Originally Posted by dadod

This is my simulation with no transistor selection, just took it from LTspice librery, exept jfets.
I moved the compensation cap and distortion halved.
dado

Can't see the lines on the schematic.

[EUVL]

> They sent samples of all grades and more than one lot was represented, so it looks like there is progress.

Didn't they give samples away at one of the Audio meetings (Burning Amp) in the US a year or two ago ?
If there were samples then what kept them from volume production, one hesistates to ask ?


Patrick

[scott wurcer]

The LSK389's would probably be OK in the first circuit even at +-24V supplies, at least worth a look. Having a very hard time finding high breakdown JFET's, for instance the J74 is only 25V.

[scott wurcer]

Originally Posted by EUVL

> They sent samples of all grades and more than one lot was represented, so it looks like there is progress.

Didn't they give samples away at one of the Audio meetings (Burning Amp) in the US a year or two ago ?
If there were samples then what kept them from volume production, one hesistates to ask ?


Patrick

Yes, I got no answer. All samples until this batch had the same date codes and I worry that they need to sell at least more than we buy to make it worthwhile.

[EUVL]

I cascode 2SK170 with J111 and 2SJ74 with J174.
Works quite well. But still only 30V.

To go higher one needs to use BJT or MOSFET cascode, I am afraid.
Makes things too complicated.


Patrick

[staccatiss]

Scott,

I entered your design into Microcap 10 Pro. Used 20 dB gain (2k21 and 221R). Exchanged some of the BJTs into 2SA1360/SC3423, and changed some values to get the currents I wanted to have. Used one of the 250R resistors to null DC offset.

OL gain is ~100 dB and F-3dB = 330 Hz.

THD20k into 600 ohms and at 3Vrms output voltage = 0,0006%.
SNR is 107 dB rel. 1Vrms, 20-20kHz, flat.

I have attached some nice THD vs Freq, THD vs Vout, THD+noise vs Vout sweeps.

BTW, what does R22 (50R) in your schematic do?



/S

Originally Posted by scott wurcer

One last one for today, the fully complimentary version. If SK170/SJ74 FET's are used high source impedances are not recommended.

[dadod]

Originally Posted by scott wurcer

Can't see the lines on the schematic.

Better?

[scott wurcer]

Originally Posted by EUVL

I cascode 2SK170 with J111 and 2SJ74 with J174.
Works quite well. But still only 30V.

To go higher one needs to use BJT or MOSFET cascode, I am afraid.
Makes things too complicated.

Patrick

The J111 looks good here. This is a problem, un-cascoded the distortion is degraded a bit with even a 10k source. Not that big a deal, I am measureing at extremes 20V at 20k. At normal line levels the effect is small. Will need a little more work.

Dick, did you measure yours with a 50k volume control?