OPA548 pcb layout - for your enjoyment

pinkmouse · 30th April 2003, 11:54 PM

Hi Folks

Well, I have been busy building 10 channels of OPA548 gainclone for a friend over the past week or so, and as I had to make so many I made a single sided pcb layout to make it easier!

So, for all those that are interested the PCB layout is below, scale is based on 1" squares, so it should by easy to rescale to whatever output you want. The circuit is based on Thorsten's new ideas, and is not minimal! As I live in an area of huge RF interference from two of the biggest TV/Radio transmitters in the UK, I have given up on the minimal designs, but if you wish you could just use wire links instead of some components. You may also need to slightly adapt the design depending on the size of your components.

The circuit layout is completely hum free and stable, with no oscillations I can detect on my 5meg scope.

Note, the E/S pin(9) is snipped off the IC before installation!

Have fun

carlosfm · 2nd May 2003, 11:53 AM

Al,
At least with an LM3875 I had around -10mv of DC offset with that 18k resistor.
I changed it with a 50k multi-turn pot, and now I have between 0.0 and 0.1 mv DC offset.

Beautiful.

pinkmouse · 2nd May 2003, 12:13 PM

Hi Carlos

The dc offset on all my amps was around +8 to +10mV. Your idea of using the multiturn pot is a good one, I may give it a try at some point.

These amps were configured as two 5 ways for a friends 2 HT setups, one in his lounge and one in his bedroom to replace the mixture of cheap amps he was using. They were all built in 2U rack cases, and were nothing to look at really, which is why I took no photos.

I was also playing with my stereo OPA548 the other day, that I modded to the same circuit for testing, and got some interesting results when I fed it square waves, I may post these photos later in a different thread for others to look at and discuss.

carlosfm · 2nd May 2003, 12:55 PM

Just try it, Al.
You won't need to modify the circuit board.
It's not very important actualy the value of the DC offset (8 to 10 mv is fine).
But on a stereo amp it's good to have both channels with exactly the same value.
Differences kill soundstage.

popes · 15th May 2003, 12:40 AM

i remove input capacitor
and i'll try 3 parallel bridge 548 gainclone.
this PCB use for bridge mode.

popes · 15th May 2003, 12:44 AM

3 parallel PCB

pinkmouse · 15th May 2003, 07:45 AM

Hi Popes

Looking good! Certainly much quicker and more economical to home etch

The only problem you will have is with the Earths. The three up board will definately need the ground plane splitting so you have one per amp, and you may need to split the signal earths to make a star ground as I did on my version. The only way to find out is to build one!

Good luck

carlosfm · 15th May 2003, 04:42 PM

Yes, after building one you may find you need to fine-tune the circuit.
The way to go first is doing it in breadboard, like I did.

popes · 18th May 2003, 03:58 AM

i'm aready make 548clone
here is my..

inverted
R=caddok 10K and IRC 200K
C=10uF MKP

power supply is two single output SMPS 20V 5AMP.

popes · 18th May 2003, 03:59 AM

there is no....Hummmmmm

2nd May 2003, 11:53 AM	#2
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	multi-turn pot Al, At least with an LM3875 I had around -10mv of DC offset with that 18k resistor. I changed it with a 50k multi-turn pot, and now I have between 0.0 and 0.1 mv DC offset. Beautiful.

2nd May 2003, 12:13 PM	#3
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Hi Carlos The dc offset on all my amps was around +8 to +10mV. Your idea of using the multiturn pot is a good one, I may give it a try at some point. These amps were configured as two 5 ways for a friends 2 HT setups, one in his lounge and one in his bedroom to replace the mixture of cheap amps he was using. They were all built in 2U rack cases, and were nothing to look at really, which is why I took no photos. I was also playing with my stereo OPA548 the other day, that I modded to the same circuit for testing, and got some interesting results when I fed it square waves, I may post these photos later in a different thread for others to look at and discuss. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

15th May 2003, 07:45 AM	#7
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Hi Popes Looking good! Certainly much quicker and more economical to home etch The only problem you will have is with the Earths. The three up board will definately need the ground plane splitting so you have one per amp, and you may need to split the signal earths to make a star ground as I did on my version. The only way to find out is to build one! Good luck __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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2nd May 2003, 12:55 PM	#4
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	Just try it, Al. You won't need to modify the circuit board. It's not very important actualy the value of the DC offset (8 to 10 mv is fine). But on a stereo amp it's good to have both channels with exactly the same value. Differences kill soundstage.

15th May 2003, 04:42 PM	#8
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	Yes, after building one you may find you need to fine-tune the circuit. The way to go first is doing it in breadboard, like I did.

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