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PostPosted: 11 Nov 2018, 06:08 
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This thing is just crazy absolutley beond all expectations I had, sounds so good currently I think is better than my class a solid state amp with 2 stage op amp. Though no direct and serious comparisons done yet.

The orignal sound luster is something I would throw in the bin.

It also deserves a heaphone jack connecting directly to 4r tap.
Fairly low noise I'd say very low for a amp like this. Also absolutley blown away from the sound driving 8r phones. I always wanted to hear valve only head amp as comparison to my solid state ones and here we go


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PostPosted: 15 Nov 2018, 21:44 
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Yungman wrote:
I don't think you can conclude that. Big transistor has higher input capacitance, it depends on your driver stage. As I said, you keep talking, but no schematic. From my understanding, you don't use emitter follower as output. If you use common emitter output stage, larger transistor means larger miller caps and load the driver a lot more. If you are using common emitter, that's bad idea as a starter. Nobody use common emitter output stage other than nelson Pass using common source. It's just very inferior.

But, it's your amp, just get some other transistors.


Not sure if you ever annalised super class a but its a common emitter output stage with the common emitter as a szlkai pair with big output transistors.

I'm not gonna mention much more about emitter and collector resistorless output stages nor gonna upload photos since I don't want plagiarism of my design


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PostPosted: 16 Nov 2018, 00:21 
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Joined: 26 Dec 2016, 03:46
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Location: Bayarea
You know this is just a jean hiraga design that most people looked at already. It's is kind of similar idea with the CFP output stage design. There are short coming that it's not optimize to parallel more output stages to get higher power. And it's not optimized to run as class AB. With this kind of feedback design, frequency response suffers. Hiraga is a good simple circuit for low power amp. And being class A, you don't have to worry about crossover distortion. This really limit the design flexibility.

I consider emitter follower output stage is the most optimized design for higher power amps. It might not be as simple, but it's the best for frequency response. I am not interested in low power amps, as I said, when you have low voltage, everything is a lot easier.

You really cannot talk distortion by looking at the output sine wave!!! When you see the distortion on the scope, it's really really really high!!! Get a distortion analyzer like a spectrum analyzer type to run FFT before you talk whether the design is good or not. I am designing amps as low as 0.002% at 20KHz at over 60W output with my small amp, over 100W with the bigger one. This is a different world!!! All the amps I design even the first one I showed the schematic always produce perfect looking sine wave until it start clipping.


BTW, the layout of the Hiraga amp looks really bad, all the long signal traces. Whoever layout this had no idea what he/she's doing.


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PostPosted: 16 Nov 2018, 02:24 
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Can you do a demo of what your 24khz looks like with the sine wave zoomed close up on the scope so I can compare with mine ? Also with 8r load


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PostPosted: 16 Nov 2018, 02:43 
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Joined: 26 Dec 2016, 03:46
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Location: Bayarea
I do it in a day or two, the amp is not on the bench. Here is the picture of my second amp

Attachment:
OPS6 integrated amp.JPG


Attachment:
Dual monoblock.JPG


I decided to make all my amps integrated AVS amps that can receive from 3 sources and output the video to the tv. It is a dual monoblock, that is it's literally two separate amps in one chassis. Each channel has it's own power transformer, own filtering caps and everything. It has a single motorized remote volume control and a selector switch on the front panel. I have a switch that can bypass the buffer opamp that buffer the volume pot to drive the power amp. So I can have an option to have a total passive preamp. I have two pairs of speaker outputs so I can do bi-wire to the speakers.


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PostPosted: 16 Nov 2018, 02:53 
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Looks kind of the same as old one but its the schematic that matters which I can't see.
Looks pretty good


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PostPosted: 16 Nov 2018, 03:23 
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Joined: 26 Dec 2016, 03:46
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Location: Bayarea
OK, I use my test amp on a separate heatsink to do the test instead of the amp. It's the same as in my amp. This is 24KHz, 70Vpp into 4ohm load. That is 153Wrms output into 4ohm. The scope is 10V/div.

Attachment:
OPS6 24KHz 70Vpp 4ohm.JPG


This is 2V before clipping as I use 40V power supply. My load consists of like 20 3W resistor, one of them glow if I leave it on too long.

Distortion is already very high on the FFT at 0.02% mostly 3rd harmonic. but you cannot see it in the picture. If I reduce to 60Vpp, it's going to be 0.004% on this amp at 20KHz. You need a real analyzer to characterize the amps. They have relatively cheap ones. The one I use is QuanAsylum QA401, $430USD. You cannot do without this if you are serious in amp design. Scope is for bringing the amp up and troubleshooting. Once the amp is working, the scope is literally useless.

Also, most signal generator have very high distortion, my Wavetech gives a pointy sine wave. I have to use the QA401 to generate the sine wave. The picture that you show on the tube amp, you can see a kink on one edge of the sine wave, you must have over 1% THD already.


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Last edited by Yungman on 16 Nov 2018, 03:51, edited 7 times in total.

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PostPosted: 16 Nov 2018, 03:24 
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Joined: 26 Dec 2016, 03:46
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ILoveHiFi wrote:
Looks kind of the same as old one but its the schematic that matters which I can't see.
Looks pretty good


No, A lot more, this is an integrated AVS amp, extra power supply and remote motorized volume control.


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PostPosted: 16 Nov 2018, 05:50 
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Joined: 23 Feb 2017, 02:02
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Yeah that looks very clean, I think I really need to have a direct comparison between the standard output stage and emitter collector resistorless stage again both listening and testing.

The digiital signal generator I have generates very clean waves from exprence other than sharp rise some overshoot on square otherwise is very nice. The square wave also rise very fast


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PostPosted: 16 Nov 2018, 13:34 
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Joined: 26 Dec 2016, 03:46
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Location: Bayarea
Now, I am not saying EF is superior in ALL cases. If you use one or two pairs of output transistors, EF is not better. Hiraga and CFP has gain in the stage, they are good for single or even 2 pairs. BUT when comes to high end amps ( I assume you shoot for high end stuffs, not just an amp), multiple output pairs is a MUST. I don't even look at any amp design with less than 5 pairs of output transistors. That's when EF shines. Particular 3EF like what I have. I use 9 pairs. Krell use more than 10 pairs in the big ones.

Forget signal generator, you'll be lucky to get 0.1% or better. You really need the distortion analyzer. I only have experience on the QA401, there are other PC based stuffs, I have no idea how good they are, I can only speak for QA401. You really need it. It generate it's own signal.

You asked for 24KHz, I took that picture last night, here is the 100KHz 72Vpp into 4ohm or 162W.
Attachment:
OPS6 100KHz 72Vpp 4ohm.JPG


Here is the 200KHz 72Vpp
Attachment:
OPS6 200KHz 72Vpp 4ohm.JPG


They still look good with naked eyes. EF stage is the fastest, no double about it. There is a good reason 99% of the amps use EF output. Don't assume the engineers don't know what they are doing. They know how to design the best amps. As I said, people really look into this. Look at Onkyo amps, the few I looked surprised me. It's not their knowledge that limit the quality, it's marketing and $$$. The huge market is on cheap receiver or AVS units. It's the money they have to cheapen their design, not their knowledge. Marketing drives design, this is the sad truth. You know how much it cost me per amp I design and built? For integrated amp, it's about $900USD just for the parts!!!! Of cause if they build in large quantity, parts can be like half price. But still labor of building it. I have a slave labor that don't charge and work hard.........ME!!!

Those CFP or Hiraga output pairs have gain, thereby frequency response is low and good luck in paralleling them. Doug Self and Bob Cordell all talked about different output designs, Cordell talked about CFP is not good to parallel as crossover distortion is not being lowered after 2 pairs.

Hiraga is a cute little circuit, but you don't see people use it in commercial amps. You never see 60W or higher Hiraga design, it's limited to class A. That tells you a lot already. It's a little circuit for hobbyist to play with.


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