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Old 18th November 2012, 06:37 AM   #171
lineup is offline lineup  Sweden
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Quote:
Originally Posted by sakis View Post
OK ....first attempt for pcb is done
here is some detailed pictures and also large files can be downloaded from my server .
There is also detailed explanation and also someone should double check for errors
Users that also have S-Print layout 4 may also down load a complete file from my server
board size is 135X80

kind regards
sakis

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.
It may work this way.
But for latest instruction see my schematic I send to you.
Great work Sakis.
You are really clever making PCB
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Old 18th November 2012, 11:14 AM   #172
Zero D is offline Zero D  United Kingdom
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Lightbulb DC Offset etc

Hi, if this was built as a bridged Amp, from what i've read in the past anyway, it "could" solve the DC Offset issues. Also it "might" take care of turn-on/off thumps too.

Not only that, but the output power would obviously increase, assuming the same voltage rails. Alternatively, you could use lower voltage rails & still achieve Very lower distortion for the equivalent power output compared to a single Amp !

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Old 19th November 2012, 05:02 PM   #173
Struth is offline Struth  Canada
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Hi Guys

Zero D, I believe you are thinking of "balanced" amps. With the DC and AC conditions of both pathways connected, there is symmetry of behaviour but no actual guarantee of perfect DC balance despite the moniker. It is really a similar condition for bridged amps, as well.

The DC offset of one amplifier is not going to be matched by another unless a DC servo is there to set them equal In a balanced circuit, a current source with common-mode feedback can achieve this, while also assuring improved AC balance. With conventional bridged amplifiers, the DC offset correction within each amp is the assurance of little or no DC through the load.

"Balanced" PAs are all the fashion now, along with balanced interconnections. For the very high power "super" amps with "super" price tags, balanced operation is the only economical way to achieve high power with common devices. It is really just pre-bridged amplifiers with different packaging.

Single-ended drive of the speaker at least limits the DC "problem" to one circuit.

Lineup, the class-A performance numbers are awesome! People should pay attention to the low-level performance as that is where most actually listen. The high power numbers are equally as impressive and outperform most production amps and even some of the "super" amps.

Saki, is there a way to post a smaller thumb nail that can be clicked on when people want a larger image? I don't know how to do that myself as I can only make PDFs anyway. It would make loading and scrolling through the pages of the thread quicker.

Have fun
Kevin O'Connor
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Old 19th November 2012, 05:11 PM   #174
lineup is offline lineup  Sweden
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I havent heard from Sakis.
He should be doing the PCB.
But I guess he is busy.

Meanwhile I post a simplified version.
This has Complementary JFET input
and the output is MOSFET IRFP240/9240.

The distortion is a bit higher than for Normal with Triple EF output.
But this circuit is still showing not too bad numbers.
For most applications this will do very well.
.... and it is so simple!
Attached Images
File Type: jpg powerfollower29-JFETin.jpg (74.7 KB, 244 views)
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Old 19th November 2012, 05:24 PM   #175
Struth is offline Struth  Canada
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Hi Guys

The biggest problem with complimentary jfet circuits is acquiring jfets and matching them.

John Curl famously uses such input stages - complimentary jfet diff amps - in has amps since the 1970s. When he bagen, the range of jfet types was expanding. In recent times, that range has diminished to a great extent. His designs for Parasound are essentially what he has been building for decades, but with a DC servo added, more degeneration here and there to accommodate unselected parts, and other accommodations for production. His own company builds the versions of these circuits with critically selected components and he can only produce a few amps a year at mega-prices. The sim models for jfets will be ideal, reflecting a need for selection and matching for best performance - possibly even for reliable functioning.

Both Curl and Pass bemoan the hunting and hoarding required to be able to sort through and find matched sets of comp jfets. These are very useful devices but industry has generally abandoned the need for p-channels.

If there was a "p-type" tube, you could make the tube version front-end.... Likely be less accurate than the jfet one.

Have fun
Kevin O'Connor
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Old 19th November 2012, 05:34 PM   #176
lineup is offline lineup  Sweden
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Yes, you are right Struth.
Get hold on complementary JFET pair is very difficult.
One could only dream of getting a bunch of 2SJ74 preferably BL grade.

2SK170 is not that difficult to get.
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Old 19th November 2012, 08:09 PM   #177
Struth is offline Struth  Canada
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Hi Guys

Here is a partial layout, just of the diamond feedback buffer area, to show how two TO220s and two TO-92s can be held in thermal contact. Hopefully the PDF allows colour. In the layout, RED is top copper and BLU is bottom copper as is standard. I set the Q1-4 designations out to the side to make it easier to see them in case the PDF is all-black.

Between the TO-220s there is a top trace that covers a bottom trace over part of their travel. In Eagle (PCB layout software), you can turn off layers to see things more clearly.

The schemo shows R1 and R2 intact, instead of the trimpot. Also, there are base stops for Q3 and Q4.

V+ and V- are the supplies.

CS+2 is the current source that supplies the base of Q1.

CS-2 is the current source that supplies the base of Q2

Drive-pos is the signal drive to the upper EF half

Drive-neg is the signal drive to the lower EF half

Input and output are as they sound.

Have fun
Kevin O'Connor
Attached Files
File Type: pdf DFB-input-schemo.pdf (38.4 KB, 119 views)
File Type: pdf DFB-input-layout.pdf (36.7 KB, 69 views)
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Old 20th November 2012, 05:19 AM   #178
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Thanks Struth. Kevin.
I only hope that Sakis will use this way.
You have solved THE HEART of the amplifier on your PCB.
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Old 20th November 2012, 06:52 AM   #179
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ok ppl

been away with 39+fever and a terrible stomach can somebody please update me ?

Kind regards
sakis
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Old 20th November 2012, 07:34 AM   #180
lineup is offline lineup  Sweden
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Quote:
Originally Posted by sakis View Post
ok ppl

been away with 39+fever and a terrible stomach can somebody please update me ?

Kind regards
sakis
It has not happend much.
Good you are well again.
But you should study the suggestion from Struth.
In his last post: New Lineup IDEA - Power Follower/Output stage

If you have questions regarding PCB, just send me an email.
I will answer.
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