Purchasing Transistors in 2013
I tinkered a lot with audio amps in my childhood - built a couple of my own simple designs (they had major issues), and a couple of designs from Mr. Slone (they sounded great!). All of that led to a BS in electrical Engineering, then manufacturing control, and on to oilfield engineering, simulations, game design, and now back to industrial simulation :o
So here we are, and I'd love to get back into building amps, SS ones, i.e. - never tried tube amps, and since I have a little baby, probably won't for a few years. I decided to start small, and do a couple of standard designs first - and I discovered this website, which is visited by some of my heroes - awesome!
So I started doing some reading, and then more, and looking up designs and putting together a Mouser order - and BAM - turns out most devices mentioned in older books, schematics, and even the ones most discussed here (2SJ162/2SK1058 is a particularly nefarious example :D) are hard to find, out of production, and will be hard to replace in the future. Seeing that I really want to be able to fix my amps in the next 10-20 years, I need devices that are widely manufactured and sold in 2013.
Here are two ways to go about finding those devices I reckon:
1. Asking you guys - I am sure many of you do consider the issue of maintenance for your amps - or
2. going through the entire mouser catalog of largely stocked items e.g., reading all datasheets, looking for low CoB, High gain linearity (Driver), or low capacitance, well-behaved SoA (Output stage) etc. devices and hoping to get lucky!
So here goes attempt 1)
What is your all-time favourite one component, readily manufactured today and available on most suppliers for each of
a) small signal discrete BJT/JFET?
b) VAS or Driver stages?
c) Output stage BJT/MOS/HEX/FET?
Thanks for your help and guidance - glad to be here :)
The 2SJ/2SK lateral FET's you mention are available under the guise of later device types. Check out the Profusion and Exicon sites and the "ALFET" devices from SEMELAB for the latest types and design applications. These will all replace the older 2SJ/K types.
Favourite one off component... I haven't one because its no use on its own :)
As to the others, again, no favourite as such because a design has to be considered as a whole.
I do prefer Laterals as an output device though.
Thanks for the reply Mooly,
None of the Semelab/Exicon devices were available on mouser. Searched a few on digi-key too, and nothing. I am not claiming that those two sites are the end-all for components, but if something is not carried by them at all, I doubt it will be around in a decade or two.
Also, I understand that most people select devices after doing an initial design, however, it also works the other way around - if you have good well-behaved and well-documented devices, it makes the design process that much easier, that is why I am asking the question.
My question is not exactly like asking "what hand tool do you prefer?"...it is more like asking "What is your favorite hand-held multimeter brand" and I don't think it's that meaningless. I have been lurking and reading on these forums for a week, and even the great lists that people compiled were populated with hard-to find and out of production, or almost out-of production parts - hence the question :)
You mentioned that you like Lateral MOSFETSs for outputs - are there any widely produced ones these days that you prefer for a particular reason?
For a new design I would probably be looking at these,
Products -TT electronics Semelab
My last design used the 2SK/J types but I would envisage no issues using the above as replacements.
See this PM from Ian Finch about the lateral FET's:
I notice your concerns about fake parts for the MJR7 project in Sakis's current thread which I'm interested in too. It's a compelling article supporting amazing performance specifications from his own simple design topology. Whether that has much to do with sounding any good is another matter but I guess we'll find out soon enough.
Anyway, I'm just writing here rather than in Sakis's thread because I know you can buy genuine 2SK 1058/2SJ162 from Ampslab in the US.
Audio Transistors OnLine - AmpsLab
However, If you need a few sets, go to Profusion in the UK who are the owners of the EXICON trademark. The postage is expensive but at around $6 US each, not a bad price and about the lowest you'll find for lateral Mosfets. The drop-in equivalents are EXC10N20 and EXC10P20. (now shown as R suffix or reduced saturation types) The same parts, marketed by Maganatec as ALFET 08N20V and 08P20V are available through Newark but you might not like their prices, as I have to pay near $20 US ea. to their local Element 14 outlet or a local retailer.
Magnatec. ALFET Lateral MOSFETs
Both EXICON and ALFET products are made by SEMELAB in the UK. They are the same parts with different branding and numbers but they're at least as good for audio as RENESAS parts IMHO. 'Been around since Hitachi stopped making TO3 mosfets, too.
I guess you don't have issues with the 2SC3503/2SA1381 (Fairchild KSC3503/KSA1381) from Mouser or your favorite distributor and the small parts the same. I hope this is useful to you and helps get things moving.[End PM]
Personnaly, I'm more of a repairer, who is not interested in getting from .1% distortion to .02% distortion. The perfectionists on here seem to have an infinite budget, and tools to see these levels. My speakers have more distortion than that; under .5% distortion is probably fine. I can definitely hear the >1% distortion in my recapped retubed ST70.
I like MJ21193/94/95/96 for bipolar output devices for the toughness and the fact that mouser and newark seem to carry genuine ones. I like TIP41c/42c/31c/32c for TO220 drivers, although some designs require the more expensive MJE15032/33 for higher Vceo and soa.
For small signal stuff I like MPS8099/8599 for the high Vceo, but the MPSA56 is easier to get. The latter has a complement but haven't found any yet.
If you're not running speaker protection, lower voltage parts might work fine, but having spent $600 on a pair of used speakers to replace the $400 predecessors with the blown unmatchable tweeter, I insist on a capacitor between the amp and speaker, or something more complicated and competent. Bipolar amp designs use lower Vceo parts which sell well at the store, but leave one open to blowing the cone right out of the woofer in case of fault, so I won't use them without serious protection circuits. Series back to back electrolytic capacitors in the speaker line have audible distortion of their own on bipolar power supply amps, thus my interest in the single supply MJR7-4, dynakit ST120, G amp, Leak Delta 70, and the transformer coupled MacIntosh 250 and tube designs.
Thanks for the info about the Exicon brand, I didn't know they are the exact same devices.
I also ordered MJ21193/94 and TIP41c/42c a few days ago, and a bunch of MPSA56/06 which are supposed to be close enough. Glad I seem to have gotten some of it right!
I also got a bunch of 2SC5200/2SA1943 which is what I used in my own amp back in the days just for the nostalgia :P and I hope to find some new designs here that I can incorporate them into.
About your issue with speaker protection...have you looked at protecting them with relays controlled by a simple DC detection circuit. If I remember correctly I saw a circuit in Slone's book that additionaly had a capacitor charging to delay the turn-on/stop the thump. Might be worth looking into as relays are not going to affect your loading.
I don't have many favorite parts but I do keep a lot of MPS small signals on hand, 2N2222 and 2N5088 amongst others. +1 on Profusion. They seem to have very useful and inexpensive power devices and ship fast. I'm normally reluctant to source overseas, but they were great. My experiences with Digikey are that they have popular industrial high volume parts but their stock of useful audio devices and caps is less than wonderful. I buy from Mouser and often Jameco for older parts. Very often Jameco will have things nobody else still has. MCM is good for factory replacement parts but their profit seems to be made in their shipping department.
Check Digikey, they just started carrying Sanken's LAPT transistors and most of them are in stock!
Bob Cordell's web page at http://www.cordellaudio.com/book/spice_models.shtml lists a handful of devices he commonly uses in his designs. He apparently finds these devices useful enough to put personal effort into improving the manufacturers' standard SPICE models for them. These are certainly suitable substitutes for may others you may encounter in published projects.
Even though the list is only a couple years old, several of the devices are now discontinued or in the phase-out process. A few of them may have been superseded by electrically equivalent devices in more modern packages - e.g., the BC850/BC860 are SOT23 (surface mount) versions of the TO92 BC550/BC560. The list still represents a starting point for devices you may want to keep in stock on your experimenter's bench.
@Conrad: Thanks for the pointers. Jameco availability seems to be a bit random - will have to keep my eyes on that one :) I made a small order from Profusion - Let's see when I get the parts.
@hitachi_nut: Now that I know what to look out for, I might even be able to get them. Right now I am overloaded on parts, and need to get started on building a couple amps before being able to justify another purchase though. Thanks for the pointer.
@dchisholm: Wow,...I was looking for those spice model for my own simulations! ...And I ordered Bob Cordell's book from Amazon...and it was an awesome list - great link - thanks a lot. About the parts, well I doubt I will go SMD anytime soon, but some of those parts are indeed available as TH and will be included in my next order.
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