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Old 22nd May 2010, 02:19 PM   #1
Roushon is offline Roushon  India
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Default Phono-pre-amp+power supply pcb

A phono preamp circuit and pcb design based on Application note AN-1651
was put in analogue sources forum sometime back. Here is the almost
final version of the design together with a suitable power supply. Suggestions
are still welcome. There was a request from a forum member for the gerber
files of the pcb design. As I make pcb in home using iron-pressing method,
I am not familiar with all the parameters the CAM processor in eagle asks for.
If someone tells me about it I can process the gerber files and post them
here.

Also there was a suggestion to make a switchable subsonic filter out of the
unity gain output buffer in the premap circuit. As I still could not figure
out how to do it in the best possible way, I left it as it was before.

Regards
Roushon
Attached Images
File Type: png phono.png (81.6 KB, 1176 views)
File Type: png phono-circuit.png (31.0 KB, 1167 views)
File Type: png phono-ps.png (91.8 KB, 1127 views)
File Type: png phono-ps-circuit.png (28.5 KB, 1072 views)
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Old 22nd May 2010, 03:15 PM   #2
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Q: Why have a seperate power supply. IC1+2 are just that. You need between +/-15 to 22 VDC on your PAD1 and 2 and common.
Again about the common connections on the preamp board. I would go from component to component. On the "top" of the board you star 8 parts, on the "bottom" 10. I would daisy-chain them as much as possible. As I mentioned before: star grounds are necessary only when the ground is carrying a load.
Gerber files are generated by your PCB design program. I am not familiar with what program you use.
A sub-sonic filter is simply a capacitor at the output (PAD19) with an on/off switch across, followed by a resistor to common. The calculation of values must include the input resistance of the following amplifier
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Old 22nd May 2010, 03:42 PM   #3
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Check-out GCPrevue by GraphiCode, a free Gerber tool. I used it many years ago when my PCB design program did not have a Gerber conversion utility. E
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Old 23rd May 2010, 11:08 AM   #4
Roushon is offline Roushon  India
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Thanks for your critical look at the design.

1. The application note an-1651 does not say if the circuit needs a
regulated or unregulated supply, so I thought to be on the safe side
make a regulated one. I have seen other people making regulated supply
for this circuit in this note. I understand your point and thought about it.
In that case I can even place the power supply on the same board. This will
make whole project compact.

2. To connect all the ground end it is better for me to make the board
double sided and connect all the ground to a single point on the
component side. (There is another solution keeping it single sided, by
rotating the upper part of the board 180 degree and then placing
on the side of the lower part, but the free version of the eagle program
I am using does not allow a big board.) I will try this, then together
with the PS everythig will be on the same small board.

3. Regarding the subsonic filter do I have to add the (switchable) cap
at the output or the input of the buffer? I knew I have to add it
on the input (that is pin 5 of IC4).

Regards
Roushon.
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Old 24th May 2010, 12:12 PM   #5
Roushon is offline Roushon  India
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Default subsonic filter added

The cutoff frequency is about 18Hz of the subsonic filter.
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File Type: png phono.png (32.3 KB, 985 views)
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Old 25th May 2010, 10:18 AM   #6
Roushon is offline Roushon  India
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Default the pcb incorporating the sub-sonic filter

The PCB now contains the sub-sonic filter circuit and also differently designed
following suggestions by mickeymoose. I could place the PS also on the same
board, but as I will have the same PS for both the channel, the PS board will be
separate.

Regarding gerber file I look at the sources now.

Thanks and regards
Roushon
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File Type: png phono.png (80.4 KB, 263 views)
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Old 26th May 2010, 07:10 AM   #7
Roushon is offline Roushon  India
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Default both channel on the same board

The PCB containing both the channel is below. Also the pdf files of the actual size PCBs are
attached in case someone would like to make it in home. The red tracks indicate
jumpers.

Roushon
Attached Images
File Type: png phono-stereo.png (139.5 KB, 186 views)
Attached Files
File Type: pdf phono-double.pdf (31.5 KB, 109 views)
File Type: pdf phono.pdf (17.8 KB, 86 views)
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Old 11th November 2010, 11:35 AM   #8
Roushon is offline Roushon  India
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Default Final pcbs of the preamp and ps going to etch....

There is not much difference in the preamp pcb, but the
ps board has no regulators now.

Roushon.
Attached Images
File Type: png phono-double.png (131.7 KB, 147 views)
File Type: png phono-ps.png (44.8 KB, 150 views)
Attached Files
File Type: pdf phono-double.pdf (33.2 KB, 47 views)
File Type: pdf phono-ps.pdf (11.7 KB, 49 views)
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Old 11th November 2010, 12:54 PM   #9
Leon08 is offline Leon08  Germany
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Some time ago I also biuld some phono preamps and learned that it's difficult to make a good one.They have a high gain and because of this are very noisy and if you are unlucky hum can also be a problem.
Besides I think it's better to use a regulated power supply.
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Old 12th November 2010, 03:11 AM   #10
Roushon is offline Roushon  India
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Quote:
Originally Posted by Leon08 View Post
Some time ago I also biuld some phono preamps and learned that it's difficult to make a good one.They have a high gain and because of this are very noisy and if you are unlucky hum can also be a problem.
Besides I think it's better to use a regulated power supply.
I also thought in this way and designed a regulated power
supply (post number 1). But mickeymouse argued in
post number 2 that the top two ics are regulating the
power supply for the preamp (bottom ics). Did you make
exactly the same circuit as in the application notes? I am
eager to know as you have experienced some problem.
But not sure if you made the top part of the circuit.

Thanks and Regards
Roushon.
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