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Old 10th May 2011, 04:46 AM   #1751
Art M is offline Art M  United States
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Default Secret Zobels

I thought that the series Base resistors on the Driver and Output devices were supposed to take care of any Cranky emitter follower oscillation due to inadvertent negative impedances ?

Just for backup I was considering optional RC's C to B in just the output devices as discussed by Cordell ?
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Old 10th May 2011, 07:56 AM   #1752
dadod is offline dadod  Croatia
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Quote:
Originally Posted by ostripper View Post
Cherry spoke of the BD139/140 pair. He said they oscillate at 100mhz if driven with over 10cm trace length. He recommended shorter traces and the stopper caps placed within 1cm of the driver C-B. I adhered to this with the above boards for both resistors and caps(and trace length -40-80mm). My modular design forces me to have 4-8cm between VAS OP and Vbe/driver. The Nikko and my JVC BOTH have the 22-47pf caps from B-C on the drivers and long VAS to driver/Vbe traces.

In the post above the addition of the caps prompted the suggestion of "HMC" "hybrid miller comp" . All I know is that it DOES work , even my ears tell me that.

OS
To put a capacitor between drivers base and collector(+ or - power supply) is electrically the same as put it between base and a ground(shunt compensation?). It is not Miller compensation.
dado
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Old 10th May 2011, 08:42 AM   #1753
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Originally Posted by dadod View Post
To put a capacitor between drivers base and collector(+ or - power supply) is electrically the same as put it between base and a ground(shunt compensation?). It is not Miller compensation.
dado
I didn't say it (that it was miller comp.) This was said on the Cordell book thread.

OS
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Old 10th May 2011, 04:16 PM   #1754
artu is offline artu  Chile
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Quote:
Originally Posted by dadod View Post
To put a capacitor between drivers base and collector(+ or - power supply) is electrically the same as put it between base and a ground(shunt compensation?). It is not Miller compensation.
dado
Hi Dado
Semantics ... even if the collector if fixed there is also a parametric "Miller cap." between B-C (with less "capacitance swing" than a loaded collector, but it swings), so the shunt cap. helps linearising this capacitance, and acts also as a LPF (R-C) R=Vas output impedance, it can be a "Miller-Shunt" if you want.

Cheers
Arturo
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Old 24th May 2011, 08:18 AM   #1755
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Default NEW stuff !! LX (luxman revisited)

After drooling over $30,000 luxman "space amps" , I decided to redo my already tested LX voltage board (below 1) and do the "correct" setup and pair it with a triple. I need a sub amp badly.

Not any triple ... but B. cordell's "DBT" (diamond buffer triple - below 2). He has it as just a concept in his book , but after rereading my "trouble with triples" thread , it decided to go ahead with the simulation/CAD work. This OP stage just has to compensate one Vbe , will be driven by a hefty output pair
( the drivers = njw0281/0302) , and basically be a scalable "mini arc welder".

I almost have the "DBT" layout done , once I do ... it will exist in the real world. The LX/DBT combo simulates very nicely (attached) ... in fact , the best non-tmc THD-transient performance I have seen. The PCB will have the cap multipliers , PMA's CFP bias spreader , single or dual voltage (without jumpering) capability.

All these subcircuits have been thoroughly tested both for being "idiotproof" and maximum fidelity. The whole package will be a choice of the AX,EX, or LX. The power boards will be the PB120F (EF2 - simple) and the PB150 (this DBT triple). with the triple scalability , i can just make the board longer , clone OP pairs and make a 10 device 80V rail monster that will not "droop" (or drive 2R loads).


WAIT till you see these !!! No more BS- the performance will be superior.
PS - I won't compromise and use angle mounted PCB's ... WHY ??? The pb150 driving a 4R sub with 3-5 pair NJW21193/4's needs excellent thermal conduction (direct mounting) to have the best MTBF. One could use 2 angles to adapt my board , but what is so hard about drilling 7 holes and using self tapping screws ??? (example board- below 3 ... "DBT" / 3-pair OP)

If this works well for my sub , I WILL buy a new $160 par-metal amp case , put the nikko out to the barn and have yet another amp.
OS
Attached Images
File Type: gif LX1.1.gif (37.7 KB, 622 views)
File Type: gif PB150DBT.gif (57.8 KB, 623 views)
File Type: gif PB150DBTpcb.GIF (37.9 KB, 612 views)
Attached Files
File Type: zip mongrel-LX-DBT.zip (9.3 KB, 96 views)
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Last edited by ostripper; 24th May 2011 at 08:21 AM.
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Old 24th May 2011, 08:49 AM   #1756
dadod is offline dadod  Croatia
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OS, did you check OLG, it does not look good.
dado
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Old 24th May 2011, 09:03 AM   #1757
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No , but I did now (below) . What is wrong ?? Gain Xover at 375khz w/ 87 degree margin. I did cap. load with squarewave , minimal ringing. Triple is very stable.

I already built the LX and ran it for 4 months , so I know it has no "bugs", besides having a high impedance VAS (needs a triple to really perform).

OS
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Old 24th May 2011, 11:11 AM   #1758
dadod is offline dadod  Croatia
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Hi OS, you are correct. Actually I took -20dB as 0 dB so in this respect it looks OK, but 25dB of OLG at 20kHz is it not that to low?
dado
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Old 24th May 2011, 11:54 AM   #1759
Macleod is offline Macleod  France
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...but 25dB of OLG at 20kHz is it not that to low?
It seems that the PA driver arrangement leads to a reduced VAS load and then a reduced distorsion. Thus a lower OLG may be needed to have similar DHT.

DHT is 0.002849% for 20V peak 20kHz. Quite good for no TMC.

Sure, we are waiting for the TMC version with increased OLG from OS...
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Old 24th May 2011, 12:02 PM   #1760
Macleod is offline Macleod  France
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Clipping may need some work I think. Sticking and traces of oscillations.
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