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 Post subject: Re: PCB design
PostPosted: July 21st, 2020, 9:31 pm 
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Joined: February 28th, 2013, 3:31 pm
Posts: 1464
Cogito wrote:
tomp wrote:
I agree that if it is a one off situation you are probably better off using Vector board with pins than going straight to a PCB design. When I make more than one off I use Express PCB because they provide the software and have reasonable prices for small runs. Here is a link to Vector and a photo of one of the boards that Express did for me:




I will go with the PCB method. What do I need to take into consideration for the PCB?
Any recommendations on potentiometers ? I need them on each channel for level matching.

The most important thing to get right in PC bard design is that the layout and all details are correct. I did a board once and took for granted I knew the pinouts of an IC voltage regulator I had used many times. My memory must have been bad because I got the pinouts wrong. After the boards were done I had to lift one of the board traces and add a wire jumper to get the boards to work.

The nice thing about the Express PCB software is you first draw your schematic with the schematic portion of the application and then when you do the physical parts layout, it has a function that if you click on one component lead it will highlight all the other leads that connect to that first one. It makes layour much simpler.

As far as potentiometers, I don't use any in passive crossovers. Generally the power handling requirements of speaker level resistors in crossovers are too high. If you are going to do the passive crossover at line level to feed the inputs of different amps the situation is different. Generally for audio work I use plastic film pots because the noise level is low and longevity is high.

 Post subject: Re: PCB design
PostPosted: July 21st, 2020, 9:54 pm 
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Joined: July 24th, 2015, 4:17 pm
Posts: 1344
Location: Parkville, Maryland
Few months ago I bread-boarded a 3-way crossover using cheap caps and resistors from Amazon. Surprisingly, it sounded very good.

BTW, what resistors and caps do you recommend?[/quote]

You are working at line level so that gives you many choices.

My absolute favorite of all available resistors are the precision wire-wound bobbin resistors. They have extremely low self-inductance and really "step out-of-the-way" for superb sound reproduction.

Having said that -- my preference for resistors (non smaller than RN60 = 1/4-w) in descending order would be:

1. Vishay bulk metal foil
2. Dale metal film
3. Roderstein metal film
4. Corning Glass Works (CGW) metal film

I found that they serve the music best and are readily available.

My preference for capacitors in descending order would be:

1. Teflon film/foil or Teflon metalized film capacitors such as V-cap, Solen, or military surplus such as Custom, Components Research Co. (CRC), Tex-Cap and even the surplus Russian offerings.
2. Mundorf silver/gold/oil capacitors
3. V-cap OIMP metalized polypropylene/oil capacitors
3. Electronic Concepts polycarbonate capacitors
4. Custom, Components Research Co. (CRC) polycarbonate capacitors
5. Electronic Concepts polypropylene capacitors
6. WIMA MKP (polypropylene) and MKC (polycarbonate) capacitors

I have had good personal experience with all of them and they collectively serve the music. Stay away from polyester (Mylar) caps, Dayton polypropylene, and Solen polypropylene caps.


 Post subject: Re: PCB design
PostPosted: July 22nd, 2020, 9:45 am 

Joined: March 2nd, 2013, 2:43 pm
Posts: 188
Location: Potomac, MD
I might mention that in regards to circuit boards I use various grades or non at all. Epoxy-glass boards have a fair amount of dielectric absorption, even worse than that found in lower-grade (low Q) capacitors. Soooo... for power supplies I use epoxy glass. For the audio I use more exotic materials that have included Teflon and, more recently, ceramic. For my best amplifiers I use point-to-point hand wiring for the audio portions.

The dielectric absorption will not be an issue for low-impedance circuits such as speaker crossovers at the speaker-impedance level. It may or may not be an issue for line-level circuits at audio frequencies if the impedances are no higher than 10k. Above 10k I would begin to worry about it.

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