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Old 6th September 2008, 03:14 PM   #1
kmj is offline kmj  Sweden
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Default A little story about my favourite SOAP

A while ago a friend started to play aroud with Eagle and producing ideas for different board with the thought to make some project suitable for beginners and thus being easy to builld, no exotic parts (if you don't want to) and tested. "Fine" I thought, you play around whith that. Just don't drag me into the design because I had lost the interest at that point. So, I saw some posts but didn't pay them that much attention. Instead I produced a casing to house three of my five completed projects, the BOZ by Nelson Pass, Peter Daniels DAC and a Bugle RIAA from Hagtech. The casing got completed and I was/am very satisfied with it but my three main parts didn't like being moved from their other casings so they started to humm and buzz or just shut down, as in the DACs case.

So. The friend posted me a PCB for one of the projects, a OP-based Preamp designaded SOAP (Simple OpAmp Pre) and I put it in one of my drawers since I didn't feel like building anything. But I got fed up with chasing humm so I checked my partsbin and saw that I had all components needed for the SOAP and last night I started out by just soldering some resistors in place. One thing led to another and this morning all components where placed and soldered. Some parts where missing but the could be found in the pre I was using at the moment. So I decided to remove it and place the SOAP there instead and do some light testing. And thats where I am now.

I guess that I should post some pictures now that I have rambled on for this long. Here is one of the plain board, it measures approx 50x100mm (thats roughly 2x4 inch)
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Old 6th September 2008, 03:18 PM   #2
kmj is offline kmj  Sweden
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The board consists of a PSUpart an preamplifierpart. Here is another picture with the PSU populated. It's not that good since I was a bit tired and thus not to steady of hand.
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Old 6th September 2008, 03:24 PM   #3
kmj is offline kmj  Sweden
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I wanted to have a transformer placed on the board but since it didn't come with that possibility I sawed out a piece of board, soldered the transformer and a fuseholder to it and screwed it to the SOAP-board. The result isn't that esteticly pleasing but it works for me. I placed a pair of cylidrical caps on the output but didn't like the way it looked so I later removed them (black-yellow in the picture).
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Old 6th September 2008, 08:25 PM   #4
zei is offline zei  Sweden
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Thanx kmj !

It looks great, Could we get a picture of your chassi installation as well ?

Thanx

/JZ
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Old 6th September 2008, 10:15 PM   #5
kmj is offline kmj  Sweden
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yep, more pictures and rambling to come. Got other things to do first thou.

(for those who missed it, the above poster it the friend mentioned in the earlier posts)
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Old 7th September 2008, 06:43 AM   #6
kmj is offline kmj  Sweden
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So, then I placed it in the casing and this is how it looks now. At the start I planned to have tre different transformers at one place and due to the larger BOZ that was the only way. Now with this smaller pre-amp I will move some things around and shorten a lot of wires.
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Old 7th September 2008, 06:45 AM   #7
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last one with lid on.
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Old 7th September 2008, 08:13 AM   #8
kmj is offline kmj  Sweden
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Well, there seems to be a lack of intrest but lets round it up anyway.

The pros and Cons

Cons: Some minor point regarding layout. None of these poses any problem at all, they are just minor things.
*If the length of JP3 that connects the earth of the PSU and that of the amp is shortened then you can use a piece of the cut of legs of a diode or similar instead of i wire.
*By changing place of the input and output caps it will be easier to switch OP if you want to.
*I want an onboard transformer

Pros:
*The price! Compared to my BOZ (which I build REALLY cheap) I built the entire SOAP for less than what I payed for only the PSU-caps of the BOZ.
*Physicly small.
*Easy to build. Read, place, solder and you're done.
*No fuzz, no humm, no cracking.
*Dead quiet background and good bass and sound in general.


Ok, it is not as good as my BOZ, it lacks some of the midrange compared to it so the music feels a bit more alive with the BOZ, I do however like the bass more in the SOAP, I can't put my finger on it but I feel that there are a bit more detail and punch in it. I will stick with the SOAP since I find it a good sounding Pre-amp which fits my system and tast in music.

My system is as follows.
Sources:
Pro-ject 6.9 turntable w. Benz micro E2 gold pickup
Advanced acoustic MCD-203 CD-player

Pre-amp
SOAP
Hagtechs Bugle RIAA

Poweramp
Greg Balls GB150 (aka the SKA, simple killer amp)

Speakers
Troels Gravesens C17 HES.
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Old 7th September 2008, 10:47 AM   #9
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Quote:
Originally posted by kmj


Ok, it is not as good as my BOZ, it lacks some of the midrange

For more midrange,have you tried a small cap between the supply pins (+ to -).100nF is a good starting point.

What op amp are you using ?
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Old 7th September 2008, 12:00 PM   #10
kmj is offline kmj  Sweden
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I'm using OP2134 and I have 100nF between each rail and ground but not directly between the rails. Perhaps I sound try to add one there too?

Oh, straight at the pins or can the cap be placed a bit away from the pins?
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