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Old 4th August 2012, 03:07 AM   #1391
spind is offline spind  Canada
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Quote:
Originally Posted by dantwomey View Post
No AS-4440's available yet. Antek does have AN-4440's though. They say,

Does anyone think the lack of EMI shielding would make a difference?

Regards,
Dan

You could maybe check SumR transformers. Supposed to be good quality. I priced some once and they seemed a bit cheaper than Plitron. More expensive than Antek, but they are in Toronto, so no border hassles. I haven't used any though.

SumR - Richard Sumner Technology

Steve.
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Old 29th August 2012, 06:23 PM   #1392
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The SIT amplifier [a la Rothacher] has undergone modifications and improvements since its introduction. The first version used light bulbs as the load resistor to the SIT device. It gave this amp an intrinsic output impedance of 11-13 Ohms; that of the light bulbs which were connected between the ouput node and V+ [or AC ground]. Rothacher replaced the light bulbs with an inductor in his second generation SIT amp. The inductor increased the gain and output power of the SIT amp. The inductor simultaneously increased the intrinsic output impedance of the amp. The third generation SIT amp was the work of many interested DIYers who used a CCS [modulated and not] to attain as high or higher intrinsic output impedance as SIT V2 per Rothacher. I like SIT V2

Clearly, the above SIT amps are phase inverting transconductance amplifiers [TCAs]. I have been experimenting with mating a Voltage Source Amp [or VSA; a Threshold S/150] with a diy TCA which is not a SIT design to make a Compound Power Amplifier. The thread by the same name is in the Pass Labs Forum. THe bottom line is: One can now experience the voice of a SIT amplifier [I prefer V2 by Rothacher for its hi output Z] as a Voltage Source Amp [instead of a TCA]. Food for thought and experimentation. Your input will be valuable and appreciated.
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Old 29th August 2012, 06:52 PM   #1393
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The nature of the SIT is that it has an intrinsically low output impedance,
so the output impedance of the amplifier is that of the SIT in parallel with
the impedance of whatever is feeding it current. Typical output Z for a SIT
is like 4 ohms or so, so if you have a 20 ohm light bulb for the current source
the output impedance will be 4*20/(4+20) = 80/24 = 3.33 ohms.

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Old 29th August 2012, 07:12 PM   #1394
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Quote:
Originally Posted by Nelson Pass View Post
The nature of the SIT is that it has an intrinsically low output impedance,
so the output impedance of the amplifier is that of the SIT in parallel with
the impedance of whatever is feeding it current. Typical output Z for a SIT
is like 4 ohms or so, so if you have a 20 ohm light bulb for the current source
the output impedance will be 4*20/(4+20) = 80/24 = 3.33 ohms.

The compound approach decreases the underlined to that of S/150 which I believe is less than 0.1 Ohm. Damping factor, voltage gain, and distortion performance of the compound become those of S/150.

Mr. Pass, the underlined is competitive with that of a 4 Ohm loudspeaker. The bolded statement says that S/150 will [may] dump [or force] some of its output current into the SIT device?. What will the impact be on the SIT device. What does it it mean? I am having a hard time understanding this. I hope that you could shed light and elaborate. Thank you.
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Old 29th August 2012, 08:00 PM   #1395
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Quote:
Originally Posted by Antoinel View Post
The inductor simultaneously increased the intrinsic output impedance of the amp.
The plate resistance of the 2SK82 is a little closer to 8 Ohms, in case you're wondering where I came up with the "around 8 Ohms" output impedance figure from the second article.
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Old 29th August 2012, 09:54 PM   #1396
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Quote:
Originally Posted by Michael Rothacher View Post
The plate resistance of the 2SK82 is a little closer to 8 Ohms, in case you're wondering where I came up with the "around 8 Ohms" output impedance figure from the second article.
Thank you for responding. The SIT amp has a unique voice. I am describing another way [in the compound approach] to use it; for whatever value this brings.
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Old 29th August 2012, 10:18 PM   #1397
Rush is offline Rush  United States
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Quote:
Originally Posted by Antoinel View Post
Thank you for responding. The SIT amp has a unique voice. I am describing another way [in the compound approach] to use it; for whatever value this brings.
Do you mean a complimentary pair version?
I have 2 pairs of 2SK82 and 2SJ28 that I am dying to make an amp with. Seems to me the only complication is a pair of power supplies for the bias. They would float off the rails and seems like an F6 approach would work.

Rush
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Old 29th August 2012, 11:36 PM   #1398
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Quote:
Originally Posted by Rush View Post
Do you mean a complimentary pair version?
I have 2 pairs of 2SK82 and 2SJ28 that I am dying to make an amp with. Seems to me the only complication is a pair of power supplies for the bias. They would float off the rails and seems like an F6 approach would work.

Rush
Rush: I am not sure about the underlined. A rough schematic from you will help. Please note that I am not using single devices but rather stand alone power amplifiers. The Compounding approach is to operate a VSA and a TCA in parallel. The VSA is a stand alone high fidelity voltage source amplifier like any power amp out there that you make or buy; be it Class A, Class AB, Class D etc. You, others and I believe any such VSA has a unique voice in a reference loudspeaker. The current output of this VSA is summed with that of a high fideliy transconcondutance amp [TCA] which also has its other unique voice. The net contribution of the currents flowing from both sources [VSA and TCA] through the same reference loudspeaker creates a duet voice. I speculated early on that such a Compound Amplifier may "model" the operation of Conceptual F6. I actually borrowed the use of an interstage transformer in this Compound Amplifier from Conceptual F6. Please visit the Thread entitled Compound Power Amplifiers in the Pass Labs Forum for more details.
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Old 2nd September 2012, 11:32 PM   #1399
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Default A potentially new application for SIT amplifier

I do not have a SIT Amp. Thus, I am not able to reduce to practice the title experiment. But, Mr. Pass, Mr. Rothacher, and Ms/Mr{s} DIYER who have a SIT may consider doing the experiment. It is an authentic new approach to operate a SIT. Please consult the attached file for the working schematic.

Objective: Marry a SIT amp with a voltage source amp [VSA] to make a Compound Power Amp [CPA].
Outcome: A CPA which has SIT attributes [power and character] and the objective performance of VSA.
Scope of Application. Broad and includes the mating of a variety of transconductance amps [TCAs] with a variety of VSAs.
Precedent I have assembled a CPA which is comprised of a THRESHOLD S/150 as VSA, and a DIY TCA made with bjts [opposed collector complementary pair for its output]. Works and sounds great via an A/D/S L-730 loudspeaker. The application works; but will it extend to include a SIT?



Procedure: It is like I used for my CPA prototype.
  • Open Switch to isolate VSA
  • Minimize the volume of potentiometer at the input of VSA.
  • Set generator at 100 Hz, and apply a low level sine signal to SIT to get a readily measurable Vo with an AC multimeter or scope.
  • Sweep the frequency of the source between 20 Hz and 200 Hz. Note the two frequencies which generate the Highest and Lowest Vo. The lowest Vo is expected to be in the range of 100-200 Hz. This corresponds or mirrors the minimum impedance of the loudspeaker.
  • Set the generator at the lowest frequency.
  • Increase the level [Ei] to VSA with potentiometer until its output [Eo] equals the value of Vo. Measure it with the same multimeter or scope.
  • Close switch A. The measured voltage at the Joint [JO] is still the same value as Vo or Eo.
  • Sweep the generator frequency between 20 Hz and 200 Hz. The output voltage at JO is expected to be constant throughout, and equal in value to that of solo VSA or SIT measured earlier at the lowest frequency.
  • This CPA is now tweaked.
  • Open switch A, and power down VSA, and SIT.
  • Change your source to a music signal, and power back up.
  • Open switch A and listen to solo SIT.
  • Close switch A and listen to CPA.
Are the voices of your loudspeakers the same or different in this A/B comparison?. Which will you like or dislike? You have a lot of fun and therapy ahead you. Enjoy.
Attached Files
File Type: pdf CompoundAmp SIT.pdf (31.3 KB, 203 views)
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Old 4th September 2012, 10:43 AM   #1400
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Mr. Rothacher. You wrote that you use Tekton Lore loudspeakers to listen to L'Amp SIT and other DIY amps. Would you have its impedance versus frequency curve or plot to share?
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