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PROS? High Voltage VS Low Voltage Amp
PROS? High Voltage VS Low Voltage Amp
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Old 12th September 2017, 09:30 AM   #21
DF96 is offline DF96  England
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Quote:
Originally Posted by SMY14INCH
explain why it is not Class A.
I didn't say it is not Class A. I said it is not "super class A"; no change in idle current is a sign of Class A. I don't know what "super class a" is, but I suspect it is just marketing talk.

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What I was implying with the idle current is that it dosen't need to increace right up to near clipping, for a 40v pk-pk the current through transistors required are about 2.5amps, i'm idling somewhere at 2.5amps.
That is Class A: quiescent current equal to peak signal current. Any smaller quiescent current would not be Class A. Any greater quiescent current means you have not reached clipping.

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I want to say caps do nothing but distortion, you put ac voltage through caps, theres phase shift and dilectric losses and all kinds of distrtion, a copper conductor direct input to a fet is always less lossly than a cacpacitor input.
You have clearly drunk deeply from the audiophile myth well.

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All bets are off with the length of those wires to the transistors...
No they are not and they all share the load nearly equaly. Wires are all same length
If PCB are used, then resistance from transistors to transistor varies. with wires used, all resistance can be equal and the effective resistance would be lower than on a pcb without added copper tracks
Each wire used can take in excess of 5 amps, approx 8amps no plorbem can do 10amps warm.
There is much more to amplifier design than merely avoiding overheating wires.

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Thanks for the tip, but in my point of view, then noise picked up from the wire is negible and low same with inductance.
Have you ever heard of parasitic oscillation?
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Old 12th September 2017, 12:16 PM   #22
Junm is offline Junm  Philippines
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If u don't like caps, remove them in your amp then listen to it and talk about hi-fi. ������
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Old 12th September 2017, 09:18 PM   #23
SMY14INCH is offline SMY14INCH  China
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yeah I had heard of parasitic oscillation.

also for the caps, I was only talking about input and output stages of your amp, I am saying they have very high distortion compared to a direct input with a mosfet

EDIT:from my experience, amps with capacitor couppled stages tend to have large ammounts of distortion, capacitor couppled input or amp stages with very high input impedances (80k Ohm or higher) tend to have low distortion similar to having a direct input, that is if your using quality audio capacitors.

I had built a all transistor pre amp that has zero negative feed back, both local and global. It runs on 160v dc regulated and it has very good sound quality. it is se and has a input impedance of 159k ohms and has input and output capacitors. It is also Class A and consumes approx 15watts during idle.

Have tested with very high input impedance head amp 100k ohm, with mosfet inputs no in put caps. A direct input has less sound qualty compared to buffered with pre amp.
In this case the distortion from caps are negible becasue there is less load on it. input is 159k and output load is 100k.
Pre amp sounds better because it helps isolate the amp from the input source, this means the feed back at the source can work perfectly. It also runs on high voltages so it adds little high voltage distortion controbuting to better sound, just like tube taste from valves but diffrent.

Last edited by SMY14INCH; 12th September 2017 at 09:40 PM.
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Old 13th September 2017, 03:01 PM   #24
DF96 is offline DF96  England
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Quote:
Originally Posted by SMY14INCH
also for the caps, I was only talking about input and output stages of your amp, I am saying they have very high distortion compared to a direct input with a mosfet
Correctly used capacitors have such low distortion that it is difficult to measure. "Very high distortion" is simply untrue, or indicates incompetent design. Now a MOSFET: that could have high distortion! In almost any audio circuit almost all of the distortion comes from the active devices, not the passives.

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I had built a all transistor pre amp that has zero negative feed back, both local and global. It runs on 160v dc regulated and it has very good sound quality. it is se and has a input impedance of 159k ohms and has input and output capacitors. It is also Class A and consumes approx 15watts during idle.
I find that hard to believe, unless very careful distortion cancellation has been used. Most people achieve such claims by redefining emitter degeneration as 'not feedback' when it most clearly is feedback.
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Old 13th September 2017, 05:13 PM   #25
Ultima Thule is offline Ultima Thule  Europe
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Quote:
Originally Posted by SMY14INCH View Post
I had built a all transistor pre amp that has zero negative feed back, both local and global. It runs on 160v dc regulated and it has very good sound quality.
Hi, do you have any schematics to show of the preamp which is using 160 VDC, or at least tell about what kind of transistors you are using and some more about its configuration?

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Old 14th September 2017, 03:36 AM   #26
SMY14INCH is offline SMY14INCH  China
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I used mpsa42 and mpsa92, with tip47-50 output transistors or its complementry depending on my circuit design.

Its bascially input cap into common collector directly inserted into two common emitter with emitter degenration, then directly inserted into common collector with heat sink as output then output cap.
Sorry but thats all I am willing to give away for my schematic.
I actually also designed a new version of the pre amp two nights ago and soldered a test model one night ago worked very well. However this time with a little nfb cus had designed a tube pre amp and nfb allowed for best sound quality. There is only so much emitter degeneration can do, distortion from transistor nature its self still exist, nfb will fix this.

The design is very simple but boasts very hifi quality. I had tried pre amps runs on +-36v with many transistors 25+ per channel and sound quality is less than 160v amp.
Had designed a head amp ocl with capacitor couppled input stage zero nfb, perfomred very well so decided to do a pre amp using similar topnology. It perferomed much better than expected, sound quality and test on scope was very good. Square, sine and rap wave on scope are for head amp + pre amp have excatly same output as input.

First model of zero nfb 160v pre amp had cap couppled gain stage to output stage, because output stage input resistance is not very high less than 20k ohms, sound quality suffered.
Second model omitts all caps and only have input output cap allong with circuirt redesign having better q points for transistor, most noticble is bass increace from removing cap coupple from gain to output, secondly midrange is more clear.

I do not count emitter degenration as feedback, why?
Because it dosen't feed output back into input to reduce distortion.
feeding signals back to reduce distortion can have large inpact on sound quality.
Too much feedback escpecally when you have series capacitor or inducts in the loop, sound quality will reduce. Therfore has to be just right ammount for best sound quality.
Even pure resistor feedback loop will have very small negible phase shift plorbem, the time for input signal to and output signal to hit together and feedback happen is not same time.
The output has a slight negible delay before it reaches back to input to nfb. Nothing travels in zero time, including light and sound and electircal

Last edited by SMY14INCH; 14th September 2017 at 03:50 AM.
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Old 14th September 2017, 07:49 AM   #27
AndrewT is online now AndrewT  Scotland
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Originally Posted by SMY14INCH View Post
As promised I will let you know if I modd my amp <snip>
Max unclipped output of 44Vpp (peak to peak) is exceptionally low for an amplifier fed from +-50Vdc supply rails.
I would be expecting around 37Vpk to 42Vpk ( 74Vpp to 84Vpp) on those supply rails.
Are you operating from +-24Vdc supply rails?

50W peak power is a not useful number.
25W into 8ohms makes more sense, but your +-50Vdv supply rails should be giving an unclipped low distortion maximum output exceeding 90W and maybe as high as 110W into 8ohms.
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Last edited by AndrewT; 14th September 2017 at 07:52 AM.
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Old 14th September 2017, 07:56 AM   #28
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by SMY14INCH View Post
explain why it is not Class A. <snip>
The justifications presented show that the Member knows very little about the operation of the amplifier/s he has assembled.
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Old 14th September 2017, 08:28 AM   #29
SMY14INCH is offline SMY14INCH  China
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Quote:
Originally Posted by AndrewT View Post
Max unclipped output of 44Vpp (peak to peak) is exceptionally low for an amplifier fed from +-50Vdc supply rails.
I would be expecting around 37Vpk to 42Vpk ( 74Vpp to 84Vpp) on those supply rails.
Are you operating from +-24Vdc supply rails?

50W peak power is a not useful number.
25W into 8ohms makes more sense, but your +-50Vdv supply rails should be giving an unclipped low distortion maximum output exceeding 90W and maybe as high as 110W into 8ohms.
This is running on +-24v supply to lower heat from transistor and be able to increace bias current further making Class A
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Originally Posted by AndrewT View Post
The justifications presented show that the Member knows very little about the operation of the amplifier/s he has assembled.
Thanks
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Old 14th September 2017, 09:46 AM   #30
DF96 is offline DF96  England
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Quote:
Originally Posted by SMY14INCH
I had built a all transistor pre amp that has zero negative feed back, both local and global. It runs on 160v dc regulated and it has very good sound quality. it is se and has a input impedance of 159k ohms and has input and output capacitors. It is also Class A and consumes approx 15watts during idle.
Quote:
Originally Posted by DF96
Most people achieve such claims by redefining emitter degeneration as 'not feedback' when it most clearly is feedback.
Quote:
Originally Posted by SMY14INCH
Its bascially input cap into common collector directly inserted into two common emitter with emitter degenration, then directly inserted into common collector with heat sink as output then output cap.
Sorry but thats all I am willing to give away for my schematic.
As I expected, you use massive local feedback. You are deluding yourself if you think this circuit has no feedback.

Quote:
I do not count emitter degenration as feedback, why?
Because it dosen't feed output back into input to reduce distortion.
Emitter degeneration obtains feedback from a good proxy for output current. It is thus feedback. Common collector, also known as emitter follower, uses the output voltage directly as the feedback signal. People describing feedback as 'not feedback' may be fooling themselves, and possibly trying to fool their customers or fans.
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