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Old 4th October 2006, 10:09 AM   #61
Hurtig is offline Hurtig  Denmark
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Consider PSRR... Power Supply Rejection Ratio!

This schematic will have very poor values, resulting in hum direct from the power supply!
Onle solution is to use a regulated power supply, which isn't really great for at power amp.

For fun.... Try simulation 1 volt ripple on you supply rail. How much hum will this result in, on the output?? Remember that this hum will be there always, not depending on music volume!
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Old 5th October 2006, 02:34 AM   #62
lineup is offline lineup  Sweden
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Quote:
Originally posted by Hurtig
Consider PSRR... Power Supply Rejection Ratio!
Hurtig
we have already discussed PSRR, in this topic!
didnt you notice

Some suggestions, what can be done
to improve power supply rejection
has been implemented
... and from what have understood results has been very good!


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lineup
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Old 5th October 2006, 02:54 AM   #63
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Yes results were excellent on rejection, amplifier is very quiet now.
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Old 5th October 2006, 03:13 AM   #64
lineup is offline lineup  Sweden
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Quote:
Originally posted by jerluwoo
Yes results were excellent on rejection, amplifier is very quiet now.
jerluwoo

I'd like to make my own version of your best version of this Class A Single End amplifier
What version you would recommend I start with?
In what post number? ( this is Post #64 )

What I will do,
is try it in my Electronics Workbench MultiSim, like you did.
Then I will add my own changes.
So get a lineup special version design, using whatever knowledge I have.
( I have built many Class A amps before, preamps & poweramps )

I hope you do not mind me using your schematics.
I will link to this topic, and tell you, jerluwoo,
are
The Original Idea Designer


I will also present lineup special version of this simple class a
as project05 in my projects page:
http://lineup.awardspace.com/contents.html


credit to whom credit may belong
and regards from
lineup
http://lineup.awardspace.com/
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Old 5th October 2006, 04:40 AM   #65
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Be my guest Lineup, this is what I began posting this circuit for. As for the best version it would be a toss up. The ccs version in post 58 is the most stable as far as bias and temprature drift and still retains a very good sound. The schematic of post 46 although drifts a bit, has a much more transparent or natural sound in the high end treble for a lack of a better way to explain it. Perhaps the circuit of 46 on a very good regulated supply may be the best for sound, or the circuit 58 for the best stability with very good sound as well.

Havn't gotten around to you last suggestions to reduce heat, but be aware also that the load the vas is driving is only around 700-900 ohms so I expected to need a fair amount of current to drive it added with the load resistor going to ground causes a need for 2 times the current from the ccs.

Also the output capacitor should be figured a bit higher value for low end cut off. Not sure if it has to do with no feedback for the output but the circuit seems to like larger than normal caps for the deepest bass, but the circuit has a -3db point near 7hz also, so it may just seem that way by perception.
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Old 6th October 2006, 10:52 PM   #66
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Digging through some junk I came up with a couple 12au7 tubes and sockets, so I decided to toy with a hybrid version of this amp. Just for fun not sure that this circuit will work but a starting point anyway.
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Old 8th October 2006, 01:45 AM   #67
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So I decided to test my hybrid circuit this evening. I built a smaller unit just to test. Running it at only 15 volts it's only good for about 5 watts. But the wonderful news is that it started up and worked perfectly the first time. The sound is almost identical to its all ss counterpart. I've seen it said many times that tubes cannot push a bjt output stage but this little circuit has defied that saying. So heres the little simple thing that sounds really nice.
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Old 8th October 2006, 08:09 AM   #68
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So I went ahead and rearranged my all bjt version and reconfigured for the tube mod which is a simple switch.
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Old 8th October 2006, 08:48 AM   #69
lineup is offline lineup  Sweden
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Quote:
Originally posted by jerluwoo
Be my guest Lineup, this is what I began posting this circuit for. As for the best version it would be a toss up. The ccs version in post 58 is the most stable as far as bias and temprature drift and still retains a very good sound. The schematic of post 46 although drifts a bit, has a much more transparent or natural sound in the high end treble for a lack of a better way to explain it. Perhaps the circuit of 46 on a very good regulated supply may be the best for sound, or the circuit 58 for the best stability with very good sound as well.

Havn't gotten around to you last suggestions to reduce heat, but be aware also that the load the vas is driving is only around 700-900 ohms so I expected to need a fair amount of current to drive it added with the load resistor going to ground causes a need for 2 times the current from the ccs.

Also the output capacitor should be figured a bit higher value for low end cut off. Not sure if it has to do with no feedback for the output but the circuit seems to like larger than normal caps for the deepest bass, but the circuit has a -3db point near 7hz also, so it may just seem that way by perception.
right now control panel of my website has been down for 1 week
so no FTP uploads and new pages could be added

I will use what I call jlw-post58 schematic, and see what improvements can eventually be done.
See my attachment in this post.


About output electrolytic CAP and low corner frequency of amplifier.
Just as C1 ( 10uF ) together with R5, R6 ( 220k each ) form a high pass filter,
the output CAP together with nominal impedance of Loudspeaker
form another high pass filter.

Will let signals higher than a frequency f pass.

f, Hertz,
C, Farad
R, Ohm

f = 1/ ( 2x PI x C x R )

Input
C = 0.000010 F ( 10 uF ), R = 220k//220k = 110k
f = 1 / (2 x 3.14 x 0.00001 x 110000)
f ~ 0.145 hertz
so, if you use a better quality filmcap 1 uF, you still have rolloff freq
at like 10 x 0.145 hertz = 1.45 hertz

Output ( remember big electrolytic caps can have wide tolerances +-20% is not uncommon )
C = 0.0044 F, R = 8 Ohm
f = 1 / ( 2 x 3.14 x 0.0044 x 8 )
f ~ 4.523 hertz

If you can find high quality 1000 uF or 2200 uF you can try parallel them at output
instead of one big.

Your rolloff frequencies are already low enough, in my opinion.
Myself is often happy using like 5 hertz at inputs, and 10-15 hertz at outputs.

If there is any lack of bass it should not depend on your caps.
Now subjective impressions should go hand-in-hand with some
examining of the output signal in an OSCILLOSCOPE.
This will give a better hint, if there is something real.

lineup
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Old 8th October 2006, 09:42 AM   #70
lineup is offline lineup  Sweden
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I already see one thing
you should try to change.

This is the value of R2, 1500 ohm.
Try lower this to 100 ohm ( I would go as low as 47 ohm! )

This will add like 6 mA in this stage ( current in Q3 )

To also add 6 mA in your CCS, just add a 100 ohm resistor in parallel across R3 ( 22 ohm )
0.600 volt / 100 ohm = 0.006 ampere = 6 mA


This R2 resistor has some importance to lower distortions.
Read Rod ESP Elliott experiments while construction of his very simple class a
Death of Zen (DoZ) - A New Class-A Power Amp
Quote:
Originally posted by Rod Elliott:

Some interesting things came to light during testing, especially when I included the resistor (R6) from base to earth on Q2. With no resistor, I measured a distortion of 0.15%, and this was almost completely 2nd harmonic. There was a very noticeable degradation of the positive going slope on a 10kHz square wave, and a fairly low slew rate resulted. Adding the resistor improved this dramatically, and reduced the distortion to 0.05% - but it was now almost completely 3rd harmonic.
He started out by adding a resistor 3k3.
But if you look at his semi-final DOZ, using 2N3055
he now would use 100 ohm for this resistor
R5 in this Schematic
http://sound.westhost.com/p36-fig4.gif

Complete article, with some figures and some good things to learn and think about:
A New Class-A Power Amp - by Rod Elliott


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