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Old 7th July 2004, 06:48 PM   #1
Fooman is offline Fooman  Finland
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Default Aleph Ono smd version

Hi,

I have made Ono once and I am still pretty happy with it. Now however I would like to make a new one and this time I'd like to make smd version. The trouble with smd components is power handling, or the lack of it.

So what components are there which needs to be non-smd? SMD resistors are usually 1/8 or 1/10W and transistors/fets around 1W.

Quick look at the schematics shows that Q7,Q8,Q18,Q19 and their source resistors might require better power handling. Maybe R42,R66,R40,R57 and Q26,Q26 also. Psu is left alone.

I was thinking about using jfets from vishay and mosfets from irf or vishay. Any opinions about them?

My old version: http://netti.nic.fi/~tfrisk/riaa.html
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Old 8th July 2004, 02:38 PM   #2
uli is offline uli  Austria
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Default IRF

I believe that the IRF 610 and 9610 exist in SMD too!

Uli

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Old 8th July 2004, 03:04 PM   #3
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Default Surface Mount ???????

Since you want a small package right. You will still need some large flim caps. Also, don't believe that the PCB should be issue in performance at the speeds we are talking about. So unless you doing some high speed stuff going surface mount will buy you any much at all.

I think you would be better going to a point to point wiring on the input high impedance elements of the design.

Good Luck
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Old 9th July 2004, 06:11 AM   #4
Fooman is offline Fooman  Finland
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I know some of those those caps have to be big and bulky. If I remember right, up to 220uF could be found in smd. What reasons I have for smd version? Shorter routes and lower parasitics and thus lower losses.

I have already made Aleph X and P1.7 with smd components included and they have been working fine. I'd like to make very compact version of Ono which would have connectors directly soldered to the pcb. PSU naturally external. I will start designing quite soon, lets find out what the results will be.
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Old 9th July 2004, 08:58 PM   #5
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Default Surface Mount

I have not seen a polypropylene capacitor that a surface mount and I would not want to use an electrolytic cap in place of a polypropylene or polystyrene. As for as the parasitic go I have built circuits that operate in the 100s MHz using standard convention parts. As for as electrolytic you can use some Black Gates or Some OSCON for surface mount. Have said that, BGs and OSCON work best on power filtering not as a small signal cap.

A consideration to make to a PCB is the type of solder mask; the best solder mask is no solder mask as the mask can have the parasitic capacitances that could effect high impedance circuits. So the only solder mask to use is a Dry Film and that run up the cost of you pcb. So you can use standard components and raise the input pins and have wire that part of the circuit point to point.
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Old 10th July 2004, 03:24 AM   #6
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Hmmmmm....I could have sworn that some of the posters on this forum testified that the BG type N non polarized electrolytics were even better or equal to polyproplyene caps. Maybe not????
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Old 10th July 2004, 10:02 AM   #7
Fooman is offline Fooman  Finland
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I am not fool enough to put electrolytics on the signal path, do not worry . I already have 10uF polyester caps and small polyester caps could be found on local store. The only mystery are those 220u caps on MC circuit, any idea what to use? Electrolytic or tantalum, polypropylene costs a fortune.

Yes, yes, big caps will keep the overall size big. But remember that there are resistors, over 50/channel so replacing them with smaller will reduce the size. This is a challenge I set to myself, nothing more specific behind all this.

What are the opinions about Vishay components? They have quite well specified double packed n-jetfs and other active components. Their noise figures are bit higher than 2SK170's but other values are better.

What it comes to p2p, I can't stand it in my own projects. It has its own advantages but I prefer good pcbs. And yes, jewilson, pcb related issues are advanced science and diy requires some compromises like using common FR4 board.
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Old 10th July 2004, 01:04 PM   #8
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Do not discount Black Gate from your design. Take a peek at this thread: Good Coupling and Decoupling Capacitors
I would use Black Gates over polyester caps anyday. Read these threads also before making up your mind: Aleph P 1.7 Question and this thread: Best choice for in/out caps Aleph p 1.7
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Old 11th July 2004, 02:15 AM   #9
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If you should use a BG for the 220uf however they don't sound good as polypropylene or polystyrene. Have said that 220uf polypropylene or huge and not all polypropylene or are created equal. To make thing a little more confusing BG's will sound better that Solen's, Wima and other low cost polypropylenes. Also the copper foil polypropylene or polystyrene get expensive.

Vishay bulk metal films SC102's are great if you want to use 1% metal film they also have very good resistors.

It come down to the parts all the parts, and if you so concerned about parasitic skip the solder mask. I am not say the solder is always bad however in can be a problem.

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