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#21 |
diyAudio Member
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All my amps have been labelled TGM as a reference to this:YouTube ..... The Great Machine
My entry into this hobby was to build myself a home theatre system. But then I got the 'bug' and couldn't stop.....
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"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig. |
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#22 |
Got Foam?
diyAudio Member
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Cool movie. Never heard of it before but like the effects.
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#23 |
diyAudio Member
Join Date: Jan 2004
Location: PKS, Finland
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Some fb on the "mysterious" P devices finally and all good points, thanks HD, SJ and J for your inputs!
I assume the advantage of using N devices in VAS is particularly favorable in a blameless type of amp using a bootstrapped VAS, whereas where the complementary type of VAS, even if SE driven, still have to charge/discharge the miller C on the passive side. FET's vs. BJT's, there the P FET often have a much higher input capacitance compared to an N FET, unfortunately many good JFET's have become unobtaniums. |
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#24 |
diyAudio Member
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Never heard of it - Forbidden Planet is one of the greatest sci fi movies of the 50's !
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig. |
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#25 |
diyAudio Member
Join Date: Sep 2001
Location: Melbourne, Australia
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The original Lender circuit was a combined creation of Borbely and Lender in Switzerland almost sixty years ago. They used two opposite gender as the VAS; one driven at base from the left leg of the LTP and the other driven at emitter from the right leg of the LTP. My approximation is almost trivial; it's more an asymmetrical current mirror with free collector taken to the next stage; in this role tethered to an emitter follower at the convenient base emitter resistor comprising a CCS.
In that sense its a modded Borbeley-Lender, but I am attracted to driving both sides of a common emitter because the additional diode relieves the drive at the base, transferring much of the drive to the emitter and this, as a hybrid common emitter/common base transistor it is very, very fast. The additional speed flattens the phase shift and pushes up the high pole. If we drop Q4, as Juma suggests, we must drive the VAS at 12mA to equal the drive capacity and in truth it's always advantage to drive an output stage at an emitter, since Zout is 26/mA, only 2R intrinsic here sinking current. A VAS collector has very high intrinsic impedance, and the base current is high; say 70uA, using a TO126 VAS, say a KSC2682 or a 2SC3423. The TO92 low parasitic KSA1845 has higher beta and running at 1.5mA the Ib is typically 7uA, unloading the LTP hugely. Again, a real compromise, somewhat an art, and this seems to perform very well with very low distortion and intrinsic THD 0.143%, H2 at -57dB - gain of 73.8dB without fb at all. This is a very good base from which to add global feedback, and the speed assures easy compensation and wide, deep sound field. Thanks for the interest. This is a thought experiment for me but if someone builds I'd be very interested in their SQ findings. HD |
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#26 |
diyAudio Member
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Lender's is a challenging circuit for me at least and has become something of a textbook writer's icon. 'Always makes me double take on it for the novelty but it actually turns up several times in commercial products and even in more recent times, among the up-market UK power amplifier designs. This one from Rega, ca. 2000
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#27 |
diyAudio Member
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upmarket ? - what's with the power stage on that, driver emitters loaded on the output ?
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig. |
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#28 |
Got Foam?
diyAudio Member
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After some more LTSpice massaging of the sims, it seems a few minor tweaks to the LTP degeneration resistors and adding the additional RC decoupling on the LTP supply as suggested by Juma is a good tip. Will implement on veroboard later tonight after getting back to lab form several days off on travel. Will report back and hopefully using different testing setup will remove the anomalous (not in sims) 5th and 9th harmonic blips.
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XRKaudio https://www.etsy.com/shop/XRKAudio |
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#29 | |
diyAudio Member
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Quote:
Regarding the driver emitters, that arrangement where the driver emitter resistors are returned to the output transistor emitter rather than the output rail, is typical of integrated Darlington devices. I imagine there was no reason it couldn't work in discrete format, when extended to a triple EF form and I'm sure its all been done in audio power amplifiers before. The Rega folk probably found that there was merit in it with this Mira model, at least. |
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#30 | ||
diyAudio Member
Join Date: Jan 2004
Location: PKS, Finland
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Quote:
![]() 3 Different Outputstage Driver Arrangements, Your Opinions! Edit: I must reply to myself and correct me on one thing, hope I get this one right. Quote:
through the feedback path can cause the passive VAS transistor to counteract the voltage development on the VAS output and therefore indirectly loading the active side. Last edited by Ultima Thule; 11th November 2017 at 10:54 PM. |
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Thread | Thread Starter | Forum | Replies | Last Post |
FS: AKSA GK-1 (EL) Preamp kit | kv2 | Swap Meet | 1 | 14th April 2017 12:04 PM |
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preamp for aksa 55 | Professor smith | AKSA | 98 | 12th February 2012 01:11 AM |
Borbely-Lender True Symmetry | steph_tsf | Solid State | 33 | 23rd August 2011 01:52 PM |
Aksa preamp? | rick57 | Solid State | 11 | 19th May 2006 10:26 PM |
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