technical questions - tube vs. solid state, etc

(x-posted on webervst)

calling randal, john, OTM, and others:

hi guys, giving a presentation as part of a job interview process (i was
able to choose any topic as long as it's "technical") and I'm hoping
someone has succinct answers or links to answer some of the
foolwing.

1). it is said that one reason why tubes sound "better" than transistors
is because they clip softly. why would a tube amp clip more softly than
a SS amp?

2) it is said that tube amps sound "better" because they generate even-
order rather than odd-order harmonics (when distorting). I could see
how this would be related to the above, but it seems it could also be a
mechansim of most tube circuits using minimal feedback (as feedback
lowers the amplitude of distortion spectrum, but drqaws it out in terms
of more and more harmonics...)

3) what accounts for the greater effeciency off PP topologies besides
the fact taht you can run them in class a/ab, ab, or b, and that the
power supply requirements are easier as there is complementarity
between the two sides?

any help appreciated. need to finish writing this tomorrow (Tues) for a
wednesday presentation. thanks

baald - baald {AT} auriculum {DOT} com

 

why thank you for asking, OTM

first let me tell you a little about the interview process....
1. phone interview
2. email quiz w/ technical adn brainteaser questions
3. 3 hour-long interviews (CTO, hiring manager, dept. peer)
4. 6 hour-long interviews (3 peer-level engineers form other depts, two managing engr's, one product manager)
5. the presentation yesterday

my presentation was 3 parts: how tubes work, why they disappeared (from the mainstream - hifi anyway), and why they have made a resurgence.

20 minutes into part 1 (it was the main part - about 40 minutes worth or so) the CTO interupts me and says "ok, can you just skip to the meat? i wanna hear about why they disappeared and why they are coming back". I'm convinced this was just part of his plan -- see how the candidate deals with a curveball. The rest of the presentation (30 minutes) was nothing but questions. one of which i couldn't answer (why does harmonic distortion happen - have read the reason but not retained it).

15 minutes after the presentation, they made me an offer. Best offer i've ever had in my life. I'm pretty stoked. btw - it's a software QA/test engineer position - sr/lead level.

John - i used some of your ideas, though i'm not sure i agree with all of them - mainly because i was tech mgr for a company who made a tubed preamp that passed 10kHz square waves like it wasn't even there (again, talkin hifi stuff). Great point about the OPT's role in tone shaping though.

my overall gist was that my theory is that it has more to do with simple circuits and especially low NFB in tube gear vis a vis SS gear (which is based on distortion spectra and behavior of NFB-laden circuits). but to be honest, i think there's genie in the bottle

thanks for your input John, and your interest, OTM.

 

ok. using an output transformerless amp w/ a dozen or so 6as7g's driving magnepans (purely resistive load).

just kiddin' with ya. getting a job after a year or so of being unemployed can make one crazy giddy .

 

thanks for the congrats, OTM.

unfortunately, TRS-80's were a bit before my time. well, actually, we had some in the high school computer lab, but i wasn't interested at the time. Strangely, for a while I majored in computer science in college, but switched to philosophy (which I rcvd my BA in) because i didn't think i wanted to code 8 hours a day. HAHA!!! now i enjoy coding, especially when it's MORE than 8 hours a day (as it means i'm very focused and absorbed).

i'm an analog guy at heart too (started on my first turntable when i was 16. it's still being improved upon. as it stands it's mainly made of about 50 lbs of delrin, though it may be rethought at sometime) but play mainly CDs (have a wall of records though). And will be investing in a 192/24 front end for my computer for recording. I have a friend in my hometown who makes gorgeous recordings on his 2" 16 track MCI, but I have neither the $$$, space, or inclination for tuning that he has.

and even though i'm a tube guy at heart, my stereo is based around this sweet little italian hybrid job (pathos classic one). i had a gorgeous 2a3 amp built by Don Garber (Fi electronics, brooklyn) that i was playing through tweaked altec valencias, but that was BEFORE marriage, when i had a 20 x 30 ft room for them in the barn cum loft i was living in at the time. now stuff has to have a high WAF (wife acceptance factor). she's pretty tolerant, but even the fancy-cab'd A-7's were a bit overbearing for our current place.

anyway, thanks for the thoughtful replies. I'll have to post pics of the PPP 2A3 amp for guitar i'm working on (well, not ACTIVELY, but i have drawings on paper and the iron on a chassis in my storage place and the glass in my tube boxes) if it ever gets finished. It's based on an old hammond organ amp, but has absolutely no front end - just iron, PS, and a pair of 26's driving the 2A3's. Still deciding if i want to keep it period correct and do 26 or 76 gain stages, or get "modern" and go 6SL7 hehe...

baald