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Old 24th November 2012, 07:37 PM   #221
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@alex mm, look next image:
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Old 25th November 2012, 03:04 AM   #222
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Hi Bensen, what small signal transistors are you using , and which circuit have you tried ? ( referring to your pcb picture).
Thanks.

Oh oh ! Just realised that board could be something else !
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Old 25th November 2012, 07:54 AM   #223
Bensen is offline Bensen  Belgium
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Indeed, Ashok,

My amp had nothing to do with this theath.
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Old 25th November 2012, 10:44 AM   #224
alex mm is offline alex mm  Europe
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Default PCB rev 4.1

It was a long night , work , but something was created ,PCB rev 4.1 with all in line output transistors . Bensen thanks for hint (good loocking boards too),thanks, also ,for 3 smileys from tinitus . donpetru , distance it's only0.5 mm , I know too close ,I will change footprint .... As promised PCB rev 4.1 attached Let's see comments , it's not late to make some changes.

Alex.
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File Type: jpg PCB WAHAB REV 4.1.jpg (1.11 MB, 222 views)

Last edited by alex mm; 25th November 2012 at 11:14 AM.
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Old 25th November 2012, 10:50 AM   #225
AndrewT is online now AndrewT  Scotland
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You have gone back to the split power rails with enormous separation between Audio Ground, Power Ground, -ve supply, +ve supply, Spkr Out, Spkr Return.
These and the HF decoupling must all be kept very compact to minimise EMI.

And move that big coil off board.
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Old 25th November 2012, 10:56 AM   #226
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by tinitus View Post
try look at placing power rails and ground from the board middle(connectors at front edge)
might help to try figure power lines and ground like forming a big T, or like a tree with branches

may need jumpers, but would be perfectly ok
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Old 25th November 2012, 12:54 PM   #227
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I modified some components in the latest version of the amplifier and used vertical MOSFET transistors. In practice, for reasons of reliability, the number of final power transistors will be higher (three pairs are enough). The results are quite remarkable.

If someone wants, I can make a PCB in the next week and after that is need to do some tests. By the way, which is the user wants to do this tests? Anyone!

I chose this version constructive because parts are easier to find and are cheap.

I do not know if the name DWG amplifier is the best but if you have another idea please let me know. For example, initial "DWG" come from:

Donpetru Wahab Gaborbela

I hope you enjoy this version of the amplifier.
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Last edited by donpetru; 25th November 2012 at 01:01 PM.
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Old 25th November 2012, 01:45 PM   #228
tinitus is offline tinitus  Europe
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[QUOTE=donpetru;3255671]
If someone wants......QUOTE]

repectfully waiting for Alex to finish his work
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Old 25th November 2012, 07:28 PM   #229
wahab is offline wahab  Algeria
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Quote:
Originally Posted by donpetru View Post
I modified some components in the latest version of the amplifier and used vertical MOSFET transistors. In practice, for reasons of reliability, the number of final power transistors will be higher (three pairs are enough). The results are quite remarkable.
Nice to have a low cost variant but beware that THD will be increased
with Hexfets , although it is mainly second harmonic that increase by 6dB.

In your schematic , power dissipation of a VAS branch is reduced
thanks to a 10K resistor , wich is a solution used in many such designs.

The drawback is that at power on the said VAS branch will need
to wait for the supply voltage to reach a higher value before being fully
fonctionnal , that s why i didnt retain this solution.
Rather , a transistor as voltage shifter , as in the mod below ,will be more efficient since it wont limit the VAS current at low voltages.

Quote:
Originally Posted by alex mm View Post
It was a long night , work , but something was created ,PCB rev 4.1 with all in line output transistors . Bensen thanks for hint (good loocking boards too),thanks, also ,for 3 smileys from tinitus . donpetru , distance it's only0.5 mm , I know too close ,I will change footprint .... As promised PCB rev 4.1 attached Let's see comments , it's not late to make some changes.

Alex.
Great work Alex , this is the most DIY friendly of the lot for mechanical implementation...

A few points that will help in this PCB design and in future ones since
you have skills in this domain.

The Jfets inverting input track is very well done as it s extremely
short , a point that is important for any high feedback amp as this one.

Q7 has lot of room to eventualy use a bigger heatspreader , a good point
since this transistor has the higher dissipation of all TO126.


The compensation network is the single most critical part for stability and as such the compensation network from base of Q6 --> C2 --> C3 -->Q8 base must be as short as possible in any amplifier but particularly on those using cascoded VAS where this loop will be active at frequencies exceding 100Mhz.

Whenever other parts of a PCB can have less importance , this one should be designed as a VHF circuit.


In principle any output inductance should be parraleled with a resistor ,
1R in the case of this amp , but i wouldnt recommend putting this network
on PCBs as compacts as this one.


Q9 need no heatsink as it is used as diode and has low VCE , all the dissipation in this branch of the VAS is devoted to Q7 and in fact this transistor is the one that keeps me wondering , so i propose to have its dissipation shared with an added transistor , as is done in nearby designs such as Symassym but with an elegant solution to bias this transistor using the meddle point of the two 33K resistors that bias the zener references and wich is exactly at the desired potential , close to 0V.

Below is the modded schematic. with the additions cercled in blue.

If one choose to not implement the transistor all he has to do is to put a strap between its Collector/Emitter holes.
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File Type: gif HITACHI FFET MOD5.5 SCH.gif (21.1 KB, 182 views)
File Type: jpg PCB WAHAB REV 4.1.jpg (491.9 KB, 187 views)
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Old 26th November 2012, 11:46 AM   #230
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@wahab, in the last diagram you posted would be better to be connected to GND the base pin Q20 transistor. It's better that way.

I attach in the next few days own version of this amplifier with PCB. It will be a surprise.
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