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Old 26th February 2018, 07:38 PM   #291
Antoinel is offline Antoinel  United States
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DEF Amp
Default Another application of a power amp using DEF wired in common gate configuration

I will post a "listening application" for this amp in the thread entitled DIY the device of US Patent 4,899,387 which is found in the current forum.

The salient features of this amp are shown in the attached schematic:

1. Detailed values are shown for resistors, capacitors, and idle operating conditions.
2. The series resistor string which generates Vgs for the FETS, starts at Vout [center of the two ~+/-36 V PSUs] and terminates at a separate regulated PSU [-21 V]. Current flowing through this resistor string is ~1 mA. This biasing arrangements minimizes DC offset at Vout with some help from the 5K pot DC offset adjuster.
3. A dual voice coil [DVC] subwoofer is the load to the overall power amp [OPA]. OPA is a voltage source amp [VSA] which drives DEF common gate amp [DEFcg].
4. VSA drives voice coil #1 of subwoofer to common. VSA is also connected directly to voice coil #2; but it does not actually drive it like it drives voice coil #1; because
5. DEFcg drives voice coil #2 exclusively because it is a current bootstrap which prevents/blocks VSA from independently driving voice coil #2.
6. Voice coils #1 and #2 are wired in phase [note the phase dots on the coils].
8. Another OPA was also wired by using BJTs only instead of DEF FETs in a similar DEFcg-like circuit.
7. Both OPAs are stable and sound excellent in the final listening application.

The subwoofer and VSA will be described in my upcoming post in the thread DIY the device of US Patent 4,899,387.

Best
Anton
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Old 10th March 2018, 09:27 PM   #292
Antoinel is offline Antoinel  United States
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Default Versatile [fresh] applications of DEF and DEF-like amps

I am a bit uneasy [yet apologetic] using DEF-like circuits in this DEF thread. But I'm thankful to Mr. Pass and the moderators for allowing this. The attached circuit is DEF-like. I have it in LTSPICE to model the equivalent [and genuine] DEF circuit. It runs without a problem in LTSPICE. Its components are already in LTSPICE; meaning I do not have to import parameters for the FETs which I frankly find complicated. But I'll learn to do this from the thread of DIYer Mooly.

The DEF-like and the genuine DEF prototype amps of the attached schematic have been assembled and are fully operational. Here is an explanation of the schematic and its versatility of application:

1. The input [Vin] can either be from a Power Follower [Voltage gain =1] and/or from Standing Waves in a cubic listening room. That's versatility!

2. The loads which are inside the schematic are the two voice coils [L1 and L2 each = 0.5 mH plus 8 Ohms] of a hypothetical dual voice coil [DVC] subwoofer.

3. Note the encircled components. This applies to the physical amp. Open the mechanical switch to disconnect the power follower at Vin. Disconnect the 25 Ohm resistor at Vout. Disconnect the Zobel [10 Ohm in series with 0.1uF] at Vin.

4. Slowly increase the PSU's voltage of the power rails. I use a Variac for the PSU, and practice this with every circuit change I am describing below and/or as a matter prudence.

5. This DEF-like and genuine DEF amps oscillate at even a +/-2-3 Vdc power rails. Not good!

6. The oscillation happens when L1 and L2 are wired as indicated [phase dots opposing each other]. And when L1 is wired the other way relative to L2.

7. Closing the switch silences the oscillations which happen as described in point #6. Good; but not enough!

8. Next open the switch to disconnect the power buffer which has a low output impedance [~0 Ohms]. Add the Zobel at Vin and the 25 Ohm resistor at Vout. They silence the oscillations which emanated in the circuits of point#6.

9. The value of this 25 Ohm resistor was the important contributor to quieting oscillations. It has an upper limit. It was determined by starting with low values and increasing it to the point where oscillations began to set in [as in point #6] at full PSU voltage rails.

10 The oscillations in the circuits of point #6 were a consequence of "too much voltage gain" in the actual amps/actual DVC subwoofer used.

I now have the following two great [amp-subwoofer combination] systems to experiment with and application test. Their application and subjective performance will appear in the thread "DIY the device of US Patent 4,899,387".

1. The DEF-like power amp/DVC subwoofer which uses Standing Waves [SAs] only for generating its input source signal Vin. The DVC subwoofer is in a corner of the listening room where SAs are found. SAs are intentionally generated by listening to another sound system [#2 below] in the same room. SAs push in and pull out the cone of the DVC subwoofer which essentially acts as a microphone. Thus, the motion of both coils [attached to the woofer's cone] in the magnetic field of the magnet generates the source signal Vin. Will this system absorb standing waves which are offensive?. TBD.

2 The genuine DEF power amp/another DVC subwoofer with a a Power Follower as the music signal source Vin. The second DVC subwoofer [and satellite] sit in a second corner [same wall] of the listening room. Will the cone of this DVC subwoofer independently also act as microphone towards SAs in its corner too?

I owe this thread the schematic of the Power Follower. A voltage gain of 1 for this power follower is all that was needed to drive the DEFcg proto amp. The output of a SONY CD player was the input to the power follower. DEFcg and DEFcg-like amps have a high voltage and a high power gains. Run the attached LTSPICE to confirm

To be continued..
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Old 12th March 2018, 08:08 PM   #293
Antoinel is offline Antoinel  United States
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The schematic on the left is for the Power Follower [Buffer] which I mentioned in the previous post. N-channel mosfet IRFP140N [actual] is in the feedback loop of [OPA134]. The load to this mosfet is LM317T which is wired as a constant current source idling at 300 mA.

I need to emphasize several points in the second attached schematic. It shows two DEF-like circuits in it. Note the title of each:

1. The title to the left schematic says its amp uses Positive Feedback. Because the two voice coils [encircled] of the Dual Voice Coil [DVC] subwoofer [load] are wired as shown. The electrical currents which flow through them are in phase.

2. The title to the right schematic is DEF-like Amp using Negative Feedback. Because the two voice coils [encircled] of the same DVC subwoofer load are alternatively wired as shown. The electrical currents which flow through them are out of phase.

3. Both circuits oscillate in the absence of the Power Follower [Buffer] as I mentioned in the previous post. The high impedance of each voice coil at the resonance frequency is a suspected culprit. Because circuit gain becomes high especially for the [left-side] coil loading the common base [gate] amp; which is a current source. I prefer the genuine DEF and the DEF-like prototype amps which use Positive Feedback only. Each has a clean sound from top to bottom, and will not oscillate in application. Most likely because a part of their operation conforms and/or is like that of the device taught by Mr. Pass in his US Patent 4,899,387.

4. I will add further details about these amps in their application thread " DIY the device of US Patent 4,899,387".
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File Type: png DEFcgLikeRoomAcoustic1.png (48.8 KB, 490 views)
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Old 8th May 2018, 10:35 PM   #294
Antoinel is offline Antoinel  United States
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Default FYI: Re-emphasizing the value of Post # 284

I just posted the attached schematic in the Thread by DIYer DieterK which is entitled "Paralleling a tube-amp with a class d amp? of the Tubes / Valves Forum.

The prototype amp option is feasible and trustworthy. It works very well because it is based on the US Patent 4,107,619 by Nelson S. Pass. It may suit DieterK's diy need. It also sounds great too.

I do not have a vacuum tube voltage source amp [VT-VSA]. So I substituted instead a Class aP prototype amp for now. It is transformer-coupled to the loudspeaker like that of a classical Class AB push-pull VT-VSA. The transformer component was important and needed to confirm the broad versatility of this suggested approach.

Notes:

1. See the recent last two posts #213 & 214 of the Thread "Class aP amplification" [This Forum] for the schematic and works of the prototype amp which I used.

2. The Constant Current inventive component of US 4,107,619 was apparent by measurement [on the scope]. It was manifested as a ~tenfold decrease in the current processed/used by the gain FETs [UJN1208K]; meaning due to bootstrapping by DEF as compared with the same Class aP amp operating without it or solo....to the same sound level by the loudspeaker. Further cascoding [of UJN1208K] refined/elevated the status of the "hybrid" amp to that taught in US 4,107,619.

Best
Anton
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Last edited by Antoinel; 8th May 2018 at 10:38 PM.
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Old 13th May 2018, 09:03 PM   #295
Antoinel is offline Antoinel  United States
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Default New DEF schematic and application thereof

The attached is a simplified schematic for a bench prototype. I am listening to it. It shows the following:

1. Two secondary windings [L1 and L2] of the audio output power transformer [OPT; TRIAD VPT24-4170] are embedded in the DEF amp.. The two secondaries are wired in series. Note their relative phase which enables positive feedback in DEF.

2. The audio OPT is separately driven by a Class aP amp. It can also be the OPT of a classical push-pull Class AB vacuum tube amp. Or other..

3. Secondary #1 simultaneously drives loudspeaker #1 [ADS L730] and the DEF FETs. This loudspeaker sits in the right corner of the listening room.

4. Secondary #2 drives loudspeaker #2 [ADS L730]. Additional current from the joined drains of the DEF FETs also flow through both, and enables the induction of positive feedback in the secondary #1. This second loudspeaker sits in the left corner of the same room wall.

5. This is a mono amplifier. I am using loudspeaker #2 to get more sound pressure because there's power output from secondary #2 of OPT and DEF.

6. The DEF circuit has two feedback loops which are essential. The joined sources of the DEF FETs are the "non-inverting" port; because they operate in common gate configuration. They enable an in-phase current to flow through the FETs and the secondary #2 to induce positive feedback . The joined gates of the DEF FETs are the " phase inverting" port; because the FETs are operating in common source configuration.

7. One must balance the extent of the resultant positive and negative feedback; otherwise the system will spontaneously sing.


What is the value of the resultant sound system [aka the application?]

1. The bass is enormous; deep and articulate. No need for a sub-woofer.

2. What standing waves [SWs]? The loudspeakers' woofers simultaneously play music and wipe out SWs in the corners; because of a net positive feedback in the DEF amp as taught in the Pass US patent 4,899,387.

3. I sit smack in the middle of the sound room. The wall that I face and the loudspeakers is illuminated [a term used by S. Linkwitz] with a clean and detailed sound across the audio spectrum. It can only emphasize the absence or high attenuation of SWs/ room-induced resonances. I do not hear any sound filth from the room!

This system has high value. The resultant solution is a nexus of uncluttered loudspeaker placement, bass enhancement and the cancellation or attenuation of SWs in one package. It sounds superb.

I'll post the full schematic.

N.B. Negative feedback from Vout to the joined gates of the DEF FETs is believed to convert their pentode-like characteristics to that of triode-like VFETs. Meaning they are simulated SITs, and operate accordingly. Another vector to add to the vectors of the corner-placement nexus.

Best

Anton
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Old 15th May 2018, 06:32 PM   #296
Antoinel is offline Antoinel  United States
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The complete schematic of the sound system is attached. Please note the color codes of the audio output transformer [OPT; TRIAD] and the following:

1. It is a must to balance the extent of positive relative to negative feedback in the DEF circuit so as to prevent oscillation. And to possibly maximize this ratio [fine tune it] for an optimal cancellation of standing waves in the room corners.

2. The extent of negative feedback from Vout [@ the center of +/-36 V PSU] to the joined gates of the DEF FETs is determined by the value of R4 found at the bottom right of the schematic. Values of R4 lower than the shown [3.7 K] will decrease the extent of negative feedback. The value of R4 will need fine tuning.

3. Overall negative feedback from the secondary#1 winding of [OPT] at the joined sources of the FETs is normally used and sent to the front-end of the vacuum tube amp. It is adopted in the like prototype Class aP amp.

4. The power which is inherently induced in the secondary#2 winding [exactly like that in secondary #1 of OPT] bucks or bootstraps the power [VA] released by DEF. Thus the shown 0.6 A idle bias of each FET in DEF is probably too rich.

5. It follows from [point #4] that DEF adds more in-phase power to secondary#2 winding to induce positive feedback in secondary#1. It is clear that this positive feedback which is internal to DEF is also exported to the front end of the vacuum tube amp in the form of overall negative feedback.

I'll fine tune further the balance of positive/negative feedback. I will post a commentary in the Thread "DIY the device of US Patent 4,899,387" of the Pass Labs Forum. This sound system is a favorable solution or answer to my quest therein.

Best

Anton
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Old 30th May 2018, 10:08 PM   #297
Antoinel is offline Antoinel  United States
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Default Another likable sound system..

The attached schematic is for a mono sound system which I am listening to. Its principal components are:

1. A TRIAD power transformer depicted on the left side of the schematic. It has two [independent] 115 Vac primaries and two [independent] 12 Vac secondaries. A primary is connected in parallel and in-phase with one secondary to generate Coil #1. Ditto for the other primary and secondary to make Coil #2. Both coils are then connected in series as shown and implanted in the power amp using DEF FETs. Note their relative phase [dots]. TRIAD imbibes the "system" with positive feedback.

2. A DEF-style power amp [old faithful] which was posted several times to-date. The right-side of the FETs is their biasing scheme to include the important use of overall negative feedback; from Vout to their gates c/o [R12 +R13]. This resultant DEF amp practices a combination of positive and negative feedback; which is important for stability against oscillation mostly influenced by the positive feedback from the transformer.

3. Your choice voltage source amp [VSA]which drives the joined sources of the DEF FETs.

4. A loudspeaker [ADS L-730] load across Coil #2. It can sit anywhere in the listening room including and preferably in one of its corners.

Please note the encircled voltages on the schematic; namely Vout, Vload, Vnoise, and V[-]fdbk which are the analysis points of the system. I used a 150 Hz signal to drive Vin of VSA, an 8 Ohm resistor load across Coil #2 and measured the said voltage values with an AC multimeter. The extent of overall negative feedback to DEF; meaning V[-]fdbk was decreased by decreasing the value of [R12 +R13] relative to R6. V[-]fdbk was the variable which essentially changed the system's ratio of positive to negative feedback.

I'll post a follow up to detail more techno -nuances to this great sounding system.

Best

Anton
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Old 30th May 2018, 11:59 PM   #298
Nelson Pass is offline Nelson Pass  United States
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You really need to be awarded some kind of prize for all your efforts.

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Old 31st May 2018, 12:05 AM   #299
poseidonsvoice is offline poseidonsvoice  United States
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Indeed he does! Talk about Research and Development!

Best,
Anand.
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Old 31st May 2018, 12:28 AM   #300
Antoinel is offline Antoinel  United States
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Quote:
Originally Posted by Nelson Pass View Post
You really need to be awarded some kind of prize for all your efforts.

Thank you Mr. Pass and nycavsr2000 for your favorable comments. They are a great and a complete award. It is mostly fun, entertainment and to hopefully advance the quality of the music listening experience.

Best

Anton
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