Thanks Ivanlukic. When I get back from vac next week I will start doing some sims and finalize the circuit.
I am thinking it would be very easy to cascode the buffer FET and get much lower distortion and increased PSRR.
I think there are 3/board correct? I need 6 pieces per stereo set, thanks.
PMI wrote "For comparison, I also tested two pair of original Fairchild 1381E/3503E, which tested quite close around hfe~192 and 185, respectively..."
I was lucky I bought a few of each E type about 2 years ago after Ovidiu (Syn08) warned they were going obsolete. My stock is unfortunately running low.
These devices may be available in SOT223 format from some manufacturers. I will have to do a search.
Whatever, we will have to find a decent pair of complementary TIS/VAS transistors for the future. The other alternative is to use the lower gain grades, but always cascode them, but that's a bit messy.
I am surprised you are struggling with the opto triac - I got them from Mouser IIRC and they were not shown as obsolete.
I was lucky I bought a few of each E type about 2 years ago after Ovidiu (Syn08) warned they were going obsolete. My stock is unfortunately running low.
These devices may be available in SOT223 format from some manufacturers. I will have to do a search.
Whatever, we will have to find a decent pair of complementary TIS/VAS transistors for the future. The other alternative is to use the lower gain grades, but always cascode them, but that's a bit messy.
I am surprised you are struggling with the opto triac - I got them from Mouser IIRC and they were not shown as obsolete.
I am not, they are available in the US, from Mouser no problem. Not so easily available elsewhere apparently, or from Farnell, for example.
A lot depends on how important parameters like Cob are in this case, something I do not have the knowledge to pass judgement on. I am not too impressed with the linearity of some of the alternatives, that part at least I do understand...
There was a discussion in the PeeCeeBee thread, and some testing done by Jason (JKuetemann) Examples:
http://www.diyaudio.com/forums/solid-state/231662-peeceebee-70.html#post3537454
http://www.diyaudio.com/forums/solid-state/231662-peeceebee-95.html#post3564420
PMI, Bonsai please PM me your address and I will send you some of the 556C
Thanks to Project16, here's where I got them
http://mixelec.fr/article-86978-transistors-pnp-traversants-bc556c.html
Thanks
Do
Thanks to Project16, here's where I got them
http://mixelec.fr/article-86978-transistors-pnp-traversants-bc556c.html
Thanks
Do
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I see they are Diodes Inc products.
I am ok - I will install the 546B and 556B but thanks for the offer!
Pinnocchio
Your optos (2) are already secured, I have them (from Newark) at home. I have also installed one of mine so far on one NX pcb.
But to continue my build I need precise parameter (hfe, vbe?) target for all transistors including matching % please.
To get both low cob and high HFE parameters for replacement transistors in same to126 package might prove difficult but if we use 2 different types like one for VAS (low cob) and one other for the driver(high HFE) that could be a compromise...
For Q8/q10 they see less than 20v in the NX amp thus one can use bc557c/bc547c since they are still both available. The level shifter stage (Q9/Q11) can use bc556b/bc546b. On my side I still use 557/547 for all 4 input transistors sine I use +/- 40 vdc power supply.
Thanks
Fab
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There is great alternative for VAS:
2SA1538/2SC3953 (ultra low Cob, 120V, 200mA, 400MHz)
These are also, like 2SA1381/2SC3503 pair, for use in High Def CRT Display, only Ft is much higher, and they are also in isolated case (Micaless)!
There should be KSA/KSC versions of Sanyo originals. May be it is possible to find them in US?
There are some Sanyo datasheets that come up in searches, yes.
2SA1538/2SC3953 do not come up.
Is it possible to use Cyrus trick for the future designs: configure output stage as triples and use small signal transistor for VAS. They used ROHM 2SA1038/2SC2389. It seems that it is much easier to find ultra low cob/high Ft small signal transisitor than higher power TO126 transisitor suitable for VAS. If output is configured as triple current demands are relaxed of the VAS transistors and output stage distortion is lowered. But that's just my conjecture, I'm not EE. The only real problem with output triples is stability.
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Alternative parts
PDTA115ET215, NXP Semiconductor, one of the resistor biased SMD transistors in the over-current circuit, is not available as a stocked part on cut tape (i.e., in small quantity), at least not from Mouser or Newark.
CM05ED680, C7, 68pF 500V Silver Mica, is Military grade, and fairly pricey. Not sure why this is needed in that spec, or even Silver Mica. There is a cheaper industrial grade alternative, and obviously, regular film caps are less expensive. Perhaps I am missing something here (?)
example: Wima FKP2O100681
PDTA115ET215, NXP Semiconductor, one of the resistor biased SMD transistors in the over-current circuit, is not available as a stocked part on cut tape (i.e., in small quantity), at least not from Mouser or Newark.
CM05ED680, C7, 68pF 500V Silver Mica, is Military grade, and fairly pricey. Not sure why this is needed in that spec, or even Silver Mica. There is a cheaper industrial grade alternative, and obviously, regular film caps are less expensive. Perhaps I am missing something here (?)
example: Wima FKP2O100681
A lot depends on how important parameters like Cob are in this case, something I do not have the knowledge to pass judgement on. I am not too impressed with the linearity of some of the alternatives, that part at least I do understand...
There was a discussion in the PeeCeeBee thread, and some testing done by Jason (JKuetemann) Examples:
http://www.diyaudio.com/forums/solid-state/231662-peeceebee-70.html#post3537454
http://www.diyaudio.com/forums/solid-state/231662-peeceebee-95.html#post3564420
The devices mentioned in those posts are not suited to vas duty. They are designed as drivers or predrivers in outputstages. One would be at a great disadvantage if they were to be used in a vas stage.
Pete, great alternative would be multilayer ceramic NP0. Since these caps are used to ensure stability ceramic multilayer is even better than film and foil caps. I can buy multilayer ceramic NP0 from my source but I have to buy 100pcs. Fortunately, they are cheap even in 100pcs quantity. The only problem with my source is delivery time which is 30days.
This seems like perfect candidate MLCC, 68pF, 200V, 5%, COG (NP0), CHEAP!:
Mouser part no
http://uk.mouser.com/Passive-Compon...tors-MLCC-Leaded/_/N-4gzxj?P=1z0wpt0Z1yzt48a# 80-C315C680J2G-TR
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