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Old 7th July 2011, 04:04 PM   #81
dadod is offline dadod  Croatia
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Here is a simulation with mosfet "beta enhancer". I used NDC7002N from LTspice libtary, as NTX model gives someting worst distortions:

Fourier components of V(vout)
DC component:0.0191634

Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 1.000e+03 2.192e+01 1.000e+00 -0.13 0.00
2 2.000e+03 5.169e-06 2.358e-07 85.63 85.75
3 3.000e+03 6.423e-06 2.931e-07 24.43 24.56
4 4.000e+03 4.998e-07 2.280e-08 98.30 98.43
5 5.000e+03 8.192e-07 3.737e-08 13.62 13.75
6 6.000e+03 2.665e-07 1.216e-08 79.89 80.02
7 7.000e+03 9.082e-07 4.144e-08 23.05 23.18
8 8.000e+03 2.407e-07 1.098e-08 25.16 25.29
9 9.000e+03 7.176e-07 3.274e-08 22.85 22.98
Total Harmonic Distortion: 0.000038%

Fourier components of V(vout)
DC component:0.0191534

Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 2.000e+04 2.190e+01 1.000e+00 -2.55 0.00
2 4.000e+04 3.065e-05 1.399e-06 -46.50 -43.95
3 6.000e+04 6.260e-05 2.858e-06 131.10 133.65
4 8.000e+04 1.819e-05 8.305e-07 -49.44 -46.89
5 1.000e+05 2.623e-05 1.197e-06 166.49 169.04
6 1.200e+05 1.922e-05 8.773e-07 -51.09 -48.55
7 1.400e+05 4.417e-05 2.016e-06 165.38 167.92
8 1.600e+05 1.480e-05 6.755e-07 -54.60 -52.05
9 1.800e+05 4.556e-05 2.080e-06 168.25 170.80
Total Harmonic Distortion: 0.000468%

I don't see a reason to use MOSFET here as a small BJT is good enough.
dado
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Old 7th July 2011, 05:48 PM   #82
dadod is offline dadod  Croatia
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Quote:
Originally Posted by ostripper View Post
Is that a bad thing ? Is it something that can be heard ?

(below 1 ) is the "base" thread topic amp. Not bad - a PPM amp. Besides what a bootstrap does in feeding back EMF in a local loop back to the voltage stage , a bootstrapped amp will only slightly deviate from it's current sourced "cousin" - both will simulate nearly the same and just sound slightly different.

(below 2 ) is the "harmonic killer" I was surprised at it , even. With just half the loop gain , it blows the lin amp away. So I built one (I actually just needed a subwoofer amp). Hooking it to a full range speaker convinced me it had some real possibilities. Cascodes and the reduction of the early effect DO make for better sound , the simulations (first watt - class A) show the VAS itself is nearly distortionless , even compared to the LIN circuit. In both simulations ,the higher power FFT's just show the contributed Xover distortion differences between a EF2 and 3. The VAS itself, in the cascoded version, still shows much better linearity.

Both simulations were done with Cordell defined models (no OEM supplied ones) , 4R , 3 pair-mjl 1302/4281 op @ 85ma bias.

I did the "no - no" homemodder mentioned , and ran a cascoded VAS on a EF2 (for 6 month's). It's sound was good at low levels but quite poor at higher levels. All this fooling around paid off - have you ever tried to modulate the impedance of the cascodes with a bootstrap ? The downside of this route is the ever increasing complexity (more parts)... quite the compromise.

OS
OS, do I do OLG diagram correctly(I suppose that you are talkink about LX1.1) from your sim page?? Quite low OLG. I changed 2SA1381/2SC3502 to KSA/KSC as I don't have those spice models.
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File Type: png mongrel_LX1.1.png (71.5 KB, 305 views)
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Old 7th July 2011, 05:57 PM   #83
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yes , you do.

Here they are (attached) , more realistic model's.

OS
Attached Files
File Type: txt Cordell-Models-5-11.txt (11.4 KB, 39 views)
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Old 7th July 2011, 06:31 PM   #84
jcx is online now jcx  United States
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I'm afraid if people keep coining new acronyms instead of using accepted circuit descriptions, preferably with circuit diagrams discussion will become completely indecipherable

and I encourage putting the actual img in the post post - I certainly skip over .pdf or .zip attachments unless really strongly motivated

VAS input buffer, “beta enhancer” seems unambiguous

Cascodes have a few variations that may not have good nomenclature to distinguish them

Pass, Hawksford have described the advantages of a cascode that returns the upper/”cascode” Q base current to the lower/“control” Q emitter – in the VAS this requires VAS degeneration R

http://www.essex.ac.uk/csee/research...%20cascode.pdf

Self, Cordell both use VAS degeneration – although the reason given is for current sense/clamping
Cherry has suggested the VAS degeneration has little cost but gives some stability advantage
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Old 8th July 2011, 11:10 AM   #85
dadod is offline dadod  Croatia
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Quote:
Originally Posted by ostripper View Post
yes , you do.

Here they are (attached) , more realistic model's.

OS
Simulation with ksa1381/ksc3503 models from mongrelmodels file shows drastic difference to 2sa1381/2sc3503 more realistic models. Daos that mean ksa/ksc are not reliable models?
First FFT is with 2sa/2sc models.
dado
Attached Images
File Type: jpg mongrel_LX1.1-FFT.jpg (330.3 KB, 287 views)
File Type: jpg mongrel_LX1.1-dado-FFT.jpg (318.1 KB, 273 views)
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Old 8th July 2011, 02:39 PM   #86
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Quote:
Originally Posted by ostripper View Post
Is that a bad thing ? Is it something that can be heard ?

(below 1 ) is the "base" thread topic amp. Not bad - a PPM amp. Besides what a bootstrap does in feeding back EMF in a local loop back to the voltage stage , a bootstrapped amp will only slightly deviate from it's current sourced "cousin" - both will simulate nearly the same and just sound slightly different.

(below 2 ) is the "harmonic killer" I was surprised at it , even. With just half the loop gain , it blows the lin amp away. So I built one (I actually just needed a subwoofer amp). Hooking it to a full range speaker convinced me it had some real possibilities. Cascodes and the reduction of the early effect DO make for better sound , the simulations (first watt - class A) show the VAS itself is nearly distortionless , even compared to the LIN circuit. In both simulations ,the higher power FFT's just show the contributed Xover distortion differences between a EF2 and 3. The VAS itself, in the cascoded version, still shows much better linearity.

Both simulations were done with Cordell defined models (no OEM supplied ones) , 4R , 3 pair-mjl 1302/4281 op @ 85ma bias.

I did the "no - no" homemodder mentioned , and ran a cascoded VAS on a EF2 (for 6 month's). It's sound was good at low levels but quite poor at higher levels. All this fooling around paid off - have you ever tried to modulate the impedance of the cascodes with a bootstrap ? The downside of this route is the ever increasing complexity (more parts)... quite the compromise.

OS
Os Is the second pic the performance of the Luxman clone amp ??, that looks pretty good.
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Old 8th July 2011, 02:44 PM   #87
Bigun is online now Bigun  Canada
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Quote:
Originally Posted by jcx View Post
“beta enhancer” seems unambiguous
Beta is the gradient of a curve, of input base current verses output collector-emitter current of a device. It's just a measure of the input impedance of a bipolar device and it's a curve not a scalar quantity. Why is it called a beta enhancer instead of buffered VAS ?
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Old 8th July 2011, 03:34 PM   #88
jcx is online now jcx  United States
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"buffered VAS" requires additional disambiguation - you can buffer the input or output - both discussed by Self

"Darlington VAS" has been used as a name except an objection can be made that "Darlington" is usually accepted as meaning both of the collectors are connected as a 3 terminal composite Q and strictly shouldn't be used for series discrete emitter followers

"beta enhancer" can be viewed as referring to a really simple "VAS" model - that the diff pair/mirror output current is multiplied by the (bjt) "beta" and then flows in the local compensation feedback&output Z

sometimes names just become accepted even when strict syntactical analysis makes another option more sensible


but "harmonic killer" really has no accepted meaning - apparently referring to cascode above?
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Old 8th July 2011, 03:44 PM   #89
dadod is offline dadod  Croatia
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First Watt on 4oHm load.
JFET input, TMC and TT triple.
Total Harmonic Distortion: 0.000014%
No nead for some exotic circuit.
dado
Attached Images
File Type: jpg DADO-TT-TMC-3-1_015-triple-FFT.jpg (210.5 KB, 214 views)
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Old 8th July 2011, 05:51 PM   #90
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Is this without gnf ?
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