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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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Old 29th January 2013, 08:35 PM   #2671
RNMarsh is offline RNMarsh  United States
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Re making a th circuit --- sm for the input transistors is OK and the rest th. Size isnt important... meaning it doesnt have to be the absolute smallest possible size. Use "standard" part size. That way most brands will fit. Is a kit being made of pcb and parts? Or better, yet assembled pcb? If not, it doesnt matter what is in the BOM.... Susumu or otherwise.

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Old 30th January 2013, 08:04 AM   #2672
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Link to a prototype folded Kaneda-style Class-A DIP8 single opamp module, approx. 11mm x 14mm in size:

kaneda preamp

The resistors are 0603 size; all actives are SOT23, except a Rohm dual-PNP in SMT6; and the rail-to-rail bypass is a Panasonic ECHU PPS film-foil in 1210 size, mounted on the underside. All signal traces are on the component side only, allowing the possibility of a single-sided board in future revisions.

I cheated on the prototypes shown, by using a Zetex ZRA125 1.25V bandgap reference instead of the BAV99 dual-diode in the schematic - I just wanted to be sure that the first prototypes would work, i.e. produce some sound, which they did on the very first test.
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Old 31st January 2013, 12:33 AM   #2673
RNMarsh is offline RNMarsh  United States
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Excellent article on sm film resistors by Vishay.... EE Times; News and Analysis. 1/30/2013

www.eetimes.com/electronics-news/4199812/Strengths-and-weaknesses-of-common-resistor-types

Be sure to read comments section as well.

-RNM

[As I suspected, film thickness varies in thin film for reasons explained in article]

Last edited by RNMarsh; 31st January 2013 at 12:56 AM.
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Old 31st January 2013, 01:13 AM   #2674
jcx is online now jcx  United States
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Thin film resistors consist of a metallic deposition (made by vacuum deposition or sputtering process) with a 50 to 250 angstrom thickness on a ceramic substrate [recall that one angstrom (Ε) = one nanometer = 10-10 meter].
I can spot that as wrong 15 min after 3 drinks with dinner, search doesn't find CVD in the article either - are they sure they're up to date on R film tech?

Last edited by jcx; 31st January 2013 at 01:22 AM.
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Old 31st January 2013, 01:21 AM   #2675
bcarso is offline bcarso  United States
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Originally Posted by jcx View Post
I can spot that as wrong 15 min after 3 drinks with dinner
poor old Mr Angstrom-unit (and Mrs Nanometer isn't doing so well either)
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Old 31st January 2013, 01:41 AM   #2676
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A little more insight
thin film resistors versus thick film resistors how they compare
Quote:
However, the heat generated during laser trimming causes micro-cracks on a thick film resistor and therefore affects the short term and long term stability. Thin film resistors need less laser power than that needed for thick film resistor. Thin film resistors do not exhibit micro-cracking during laser trimming. Consequently thin film resistors show superior stability and noise performance.
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Old 31st January 2013, 04:35 PM   #2677
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Originally Posted by scott wurcer View Post
This is common, the output impedance rises with frequency so it looks inductive and a cap load can make it oscillate. Usually a small R like 25-50 Ohms helps. The addition of a capacitor from the output back to the inverting input provides AC feedback without "seeing" the cap load. This stuff usually helps well outside the audio band.

BTW even an open-loop emitter follower can oscillate, but that is usually 100's of MHz and not seen easily on the scopes DIY'ers often use.
Hi Scott,

The information Ive seen showed improvement for extremely low distortion levels, like around -100db.
Is that caused by oscillations?
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Old 31st January 2013, 05:48 PM   #2678
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Originally Posted by myhrrhleine View Post
Hi Scott,

The information Ive seen showed improvement for extremely low distortion levels, like around -100db.
Is that caused by oscillations?
Can't tell without a careful look at before and after, but in my experience when oscillating at a low level at several hundred MHz it is more pronunced.
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Old 31st January 2013, 06:50 PM   #2679
S.A.G. is offline S.A.G.  Italy
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Default Transistor selection

I'd like to go full SMD to avoid the somewhat complex assembly of TO92 devices in the output stage. OTOH, I'd like to retain the thermal tracking feature of the PTH configuration while driving low loads.

I've been looking for dual NPN/PNP transistors in SMD packages capable of some power dissipation and the only parts that I came up with are the NXP PBSS4041SPN:

http://www.nxp.com/documents/data_sheet/PBSS4041SPN.pdf

It seems to me that those parts are designed for (static) switching rather than linear operation. They are also comparatively slower than 2N4401 / 2N4403, for instance.

Questions for the Semiconductors Gurus:

- are those parts any suitable for the output diamond buffer?
- any similar, better, parts?

Thank you.

Giorgio
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Old 31st January 2013, 07:17 PM   #2680
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by myhrrhleine View Post
Hi Scott,

The information Ive seen showed improvement for extremely low distortion levels, like around -100db.
Is that caused by oscillations?
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