[iScream]

Hey DIY People,

I graduated from one of the big electronics tech schools about 10 years ago, but almost immediately got into computers and software so I haven't practiced what I learned. This forum has me interested in playing around with some DIY headphone stuff though. I still have my nice protoboards and a decent DMM but it looks like some of the new opamps and stuff are surface mount. How do you guys prototype with these chips? Do you have to solder to something like the Browndog adapters I've read about and use those with your protoboard?

Also, is there any reason not to build a case for an amp or DAC out of wood?

Thanks!

-Chris

 

[Garbz]

Browndog adapters are the easiest way to use SMD chips on a protoboard. Personally I prefer designing a circuit board and etching it for my prototypes.

Most people build into aluminium cases so that they can ground that case and shield against RFI. In theory this drops the noisefloor of the equipment slightly. But in practice there needs to be a lot of interference for this effect to be even slightly noticable Personally my cases are wooden and I've had no detrimental effect at all. Noise can only be heard when the equipment is at full volume (way beyond sane listening levels) and that is more likely the circuit itself at cause.

 

[iScream]

Quote:

Originally Posted by Garbz Browndog adapters are the easiest way to use SMD chips on a protoboard. Personally I prefer designing a circuit board and etching it for my prototypes.

Thanks. I'm really just looking to mock up one or two of the published designs and play around with different chips and options to see what I like. I've put about 30 seconds of thought into this but I have a vision of two amps on seperate protoboards so I can play around with both and see which I might like well enough to order a nice board and build a case.

Do you think just sticking all the components on a board will get me close enough to the performance potential of a design to listen and make a good decision?

For power during testing, would a LM317 in front of a 12V 7AH battery be clean enough? I'll have to drag out some old books to remember how to set the output voltage on the LM317, but I seem to remember them being pretty good and I'm sure I have some in the parts box. 10 years old though...

-Chris

 

[rickcr42]

Quote:

How do you guys prototype with these chips? Do you have to solder to something like the Browndog adapters I've read about and use those with your protoboard?

Universal Evaluation Boards available directly from the major chip manufacturers (i use ADI eval boards).

Quote:

Also, is there any reason not to build a case for an amp or DAC out of wood?

nope


though I would keep the AC section in a metal chassis with the safety shield ground strapped to the chassis then the actual audio circuits in the wood box.If for some reason you feel you must have some minimal shielding of the wood box there are two pretty good options :

1-thin copper sheeting on the inside
2-spray on metallic coatings

But wood along is fine in all but the most nasty of RF fields if you lay out your circuit properly and add proper RF protection filters at the input/loop/PS/and output of the circuit.

Think local circuit filters and not the overall device which by being unshielded would make little sens to add RFI protection where the signal or power supply enters or leaves the box

 

[Garbz]

rick on as slightly related case, what's your opinion of ferrite cores on signal wires. i'm thinking the cable out from my turntable where any noise would be amplified greatly, running the cable through a ferrite bead on the amp's input. Would that have any negligable effect do you think?

 

[JahJahBinks]

Quote:

Originally Posted by Garbz rick on as slightly related case, what's your opinion of ferrite cores on signal wires. i'm thinking the cable out from my turntable where any noise would be amplified greatly, running the cable through a ferrite bead on the amp's input. Would that have any negligable effect do you think?

Here's something I can pull out of my reference book.
"ferrite beads are most effective in attenuating signals above 1 MHz, and also to be effective the bead must add a significant amount of impedance to the circuit at the frequency of interest. Since the impedance of a single beat is limited to about 100Ohm, beads are most effective in low-impedance circuits as such power supplies, class C power amplifiers, resonant circuits, and SCR switching circuits. " - Ott, "Noise reduction techniques in electronic systems"

 

[rickcr42]

Quote:

rick on as slightly related case, what's your opinion of ferrite cores on signal wires. i'm thinking the cable out from my turntable where any noise would be amplified greatly, running the cable through a ferrite bead on the amp's input. Would that have any negligable effect do you think?

Depends on the gain facotrs involved.If a low gain stage or a digital device then no and I reserve the use of "iron" in a an LCR "mini-decoupling filter" to the lines feeding the power supply pins,if a X100 or X1K gain stage yes.At these gains anything that sneaks in becomes a big time problem and all measures to eliminate RFI a good thing

For lower gains (X1-X20) an input simpe RC filters are fine.

Whole system design means taking into consideration any point in the gain block where extraneous signals can enter the signal path.Those entry points are the input,the power supply terminal pins,the output AND the feedback loop.Each can be eliminated with minimal extra circuitry and when the added protection aquired is weighed against the additional cost a no braineer for me personally.

1-capacitor at the input to shunt RFI to ground before it enters the circuit (opamps are actualy very sophisticated circuits)
2-Inlne resistance or inductance (or both) combuined with the bypass capacitance to for a "Pi" filter right at the power pins
3-Inline resistance on the output.Not IN the loop as many do thinking they are just adding a resistor for output current limiting/protection but "outside" the loop for feedback loop RFI protection caused by inverse input of RFI from the output cable reflections
4-Capacitor across the feedback resistor to elminate this as an entry point.Very important

When you here an amp that is totally RFI free it may startle you and make your first thought "sounds dull" but that is the true sound of whatever it is passing through the device and the other artificia.
The reason is the RF (RADIO !) signal has audible consequences and is the reason for much added "sparkle" or "detail" but is in reality a false signal having nothing to do with the actual music and shouldbe elminated at all costs if it does not harm to the real signal,and it does not.

RFI=Radio Frequency Interference

the RF part means it is a "broadcast" through air and the "I" part means it interferes with what you are trying to achieve and that means BAD,very very bad

 

[rickcr42]

an example of extreme protection in a nasty environment (disregard the electrolytics,they are there for phantome power Dc blocking)

http://www.jensen-transformers.com/as/as058.pdf

The original RC filter is fine for most uses but as you can see there are extreme measures for extreme uses (high gain)

 

[Garbz]

oh silly me, never mind that I forgot that the capacitor on the input which loads the turntable cartridge automatically forms a low pass filter.