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Very unusual old quasi complementary design... which sounded great at the time.
Very unusual old quasi complementary design... which sounded great at the time.
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Old 24th April 2010, 05:08 PM   #11
Mooly is offline Mooly  United Kingdom
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Very unusual old quasi complementary design... which sounded great at the time.
Default You are spot on Ian

A 3BP1, and running at around 800 volts I seem to remember. Zener stabilised HT.
I got the proper case for it, but made all my own boards to the designs in the mag. It used point to point wiring on the main X and Y amps on a large ground plane PCB. 6mhz bandwidth... it was great. I had just started college at the time... radio and TV course

The Europa... clip on heatsinks for the drivers and VAS. The VBE multiplier was a flat pack to mount next to the outputs on the chassis. At the time of course I was much less sure of my abilities and substituting and tweaking. I remember the dreaded preamp and realising it sounded better with the inputs reduced in level, but then it wasn't quite loud enough, so I tried rigging a 741 as a simple x3 or whatever gain stage. It was weeks later I came to understand that altering the feedback on the main could alter the gain... and that you could actually calculate such things.
Things moved on quickly after that... learning learning all the time, at work (TV engineer) and at play.
Built a Radford ZD22 and HD250... some JLH's... and still didn't fully understand grounding... they always had residual hum.
And I'm still learning now and the amps are silent now... no hum.
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Old 24th April 2010, 08:28 PM   #12
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by Ian Finch View Post
Hi Mooly, Steph may be right about the circuit of the inverting input. It certainly doesn't seem warranted there. If it comes from a schematic, there may be an error there. It would not be the first time draughting and PCB designs disagreed.

best regards
Quite often in those days PCB's were tape on a clear sheet.

These days with error checking there shouldnt be any differences between schematic and PCB. My CAD package has an integrity checker.
I also found I could use the forward annotator to look for errors too.
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Old 24th April 2010, 09:17 PM   #13
Ian Finch is offline Ian Finch  Australia
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I recall the LM381N and LM381AN turning up in a locally published edition of National Semi's Linear applications databook 1971. No, I hardly understood a word of the details then either!
I assume you did eventually get the 381 to behave but I'll bet that there were DC offset problems arising from coupling electros and whatnot. Was it really the only source of amplification in the preamp? If so it probably followed National's AN64 pretty closely as this has a complete MM RIAA, vol, and Baxandall tone control circuit. It would have been quite a feat to get that to also accomodate a further MC gain stage and line buffer. Optimally, the 381 suits input impedances of the order of only 200 ohms and there must have been an additional line level discrete or single rail biased opamp in the Europa somewhere.
We draw a little closer?
best regards
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Old 24th April 2010, 09:28 PM   #14
steph_tsf is offline steph_tsf  Belgium
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Quote:
Originally Posted by Ian Finch View Post
I recall the LM381N and LM381AN turning up in a locally published edition of National Semi's Linear applications databook 1971. Was it really the only source of amplification in the preamp? If so it probably followed National's AN-64 pretty closely.
Unfortunately, I dumped all my databooks years ago and the AN-64 is not available on National Semi website. Can you help me locating a .pdf version of National Semi AN-64 and other LM381 LM387 related stuff, apart from their datasheets ?
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Old 24th April 2010, 11:23 PM   #15
Ian Finch is offline Ian Finch  Australia
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steph, you are right about National Semi and old data. 'Been there and got angry too!
http//www.datasheetarchive.com/ (sorry the active link keeps reverting to site description) Try this and enter "National Semiconductor AN-64" in the search window. The 2 PDFs you want are right there-no sweat! (4 pages of LM381 + 6 pages for 387) This seems a bit short since there are 12 A5 pages in the book. Come back if not enough.
regards
Ian
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Last edited by Ian Finch; 24th April 2010 at 11:32 PM. Reason: correct website link
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Old 25th April 2010, 02:47 AM   #16
steph_tsf is offline steph_tsf  Belgium
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Quote:
Originally Posted by Ian Finch View Post
steph, you are right about National Semi and old data. The 2 PDFs you want are right there-no sweat! (4 pages of LM381 + 6 pages for 387) This seems a bit short since there are 12 A5 pages in the book. Come back if not enough.
Hello Ian, I'm afraid, those are the datasheets. I have them since long. Actually, the search engine spotted "see AN-64" in the datasheet texts instead of delivering the actual AN-64 file. I still don't remember if the National Semi applications engineers were able to get the LM381 LM387 properly working as a non-inverting buffer at line level (say +6dBm). An active Baxandall is an inverting amp, with no common mode on the differential pair, so I can imagine the LM381 LM387 in an active Baxandall now. But what about the unity gain non-inverting buffer ? And what about a multiband equalizer using gyrators for synthezising inductors ? I think this is precisely there, that the LM381 LM387 acquired some bad reputation. Throw them in the circuit, and you get assymetric clipping and glitches, like they have hiccups, if working close to a 0dBm level. They were so good, high gain, fast and low noise with low THD and good output driveability, but they were unable to cope with the simplest, low gain, less demanding applications ! What a waste ! Regards, Steph

Last edited by steph_tsf; 25th April 2010 at 02:53 AM.
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Old 25th April 2010, 06:09 AM   #17
Mooly is offline Mooly  United Kingdom
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Very unusual old quasi complementary design... which sounded great at the time.
Quote:
Originally Posted by Ian Finch View Post
I recall the LM381N and LM381AN turning up in a locally published edition of National Semi's Linear applications databook 1971. No, I hardly understood a word of the details then either!
I assume you did eventually get the 381 to behave but I'll bet that there were DC offset problems arising from coupling electros and whatnot. Was it really the only source of amplification in the preamp? If so it probably followed National's AN64 pretty closely as this has a complete MM RIAA, vol, and Baxandall tone control circuit. It would have been quite a feat to get that to also accomodate a further MC gain stage and line buffer. Optimally, the 381 suits input impedances of the order of only 200 ohms and there must have been an additional line level discrete or single rail biased opamp in the Europa somewhere.
We draw a little closer?
best regards
Hi Ian,
No I never did get the LM381 to behave at all.
Yes, it really was the only source of gain in the preamp... I remember it all so clearly. There was no other active circuitry, discrete or opamp
The PCB accomodated a bank of push buttons to configiure the LM381 for all the different inputs, RIAA, tape head, Tuner etc etc.
I bet if I looked again they were all DIN spec inputs around 100 mv sensitivity. The preamp had a single BFY51 and zener/resistor supply of around 24 volts (again all from memory)... a pity it let the whole side down.

I might start a new thread asking if anyone remembers or has details of this amp.
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Old 25th April 2010, 11:05 AM   #18
Ian Finch is offline Ian Finch  Australia
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Thats a good idea, Mooly.

Steph, I'm sorry about the lead. In my haste I assumed 'that the circuits were from the AN but not so. I will try to get my neighbor to assist with getting some "details" from my 1986 Notes to you via email. I think I need a direct address though.

That Europa must have been a "culpable" design! Line levels would have been way down and noisy unless you switched the whole RIAA bias network out and reconfigured as Steph is saying to give the gain for the controls to function. That's not impossible but surely another OPAMP would have made things much cleaner. Did it ever sound ok on just phono? It might seem that your 741 x 3 stage was not misguided, just awkward with the single rail.
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Old 25th April 2010, 11:30 AM   #19
Mooly is offline Mooly  United Kingdom
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Very unusual old quasi complementary design... which sounded great at the time.
I only used tape and tuner at the time lol... no turntable, so I don't know.

Have put a new thread up asking... slim chance I suppose.
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Old 16th August 2012, 07:33 AM   #20
tiefbassuebertr is offline tiefbassuebertr  Germany
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Quote:
Originally Posted by Mooly View Post
This amplifier appeared in Practical Wireless in 1978 ? and was designed by a B.C. Toms ? It went under the name of the "Europa" and the power amp I have drawn in outline from memory... the preamp was awful, used an LM381AN that was spectacularly bad on all fronts.

I built this at the time, the first "proper" amp I made from scratch and always remember the wonderful musical sound it seemed to have (without the preamp). It was AC coupled and ran on a 56 volt rail.

Aside from it being a quasi design look at the input stage and the darlington arrangement on the "inverting" input to the amp. At the time I didn't think it particularly odd, but of course it is. I have never seen this done before, the "balance" of the stage must be awful, but how would that arrangement affect the distribution of harmonics etc. It sounded good though.
The main advantage here is the fact, that I can choise higher values for the NFB resistors and thus a smaller value for the capacitor. This means, it is more realistic to replace the present electrolytic version against a foil version, because the needed space is still sufficient (only helpful in amp versions, where the supply voltage is symmetric and thus the electrolytic capacitor actually must be an unipolar version).

Last edited by tiefbassuebertr; 16th August 2012 at 07:36 AM.
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