Listening Amplifier

[duke of earl]

Anybody out there ever build one of these like Doug has? I'd be willing to pay someone to build me one due to the fact I'm too busy and have never made one myself.

[Shrapnel]

I haven't built one either, BUT... I was thinking that if low power was good for one, perhaps build one around a LM386 and give it and adjustable gain (20-200 is the given fixed range.) Cheap, low power (can use a battery,) low part count (especially if only going for the default gain of 20,) and as portable as the enclosure (including a small decent speaker?) will allow.

Spec Sheet link's link: http://www.supplyframe.com/partsearchservlet/partnerWormhole.action?id=1066141&partnerName=DSA

[supro66]

Is this what you are looking for

http://www.bestbuy.com/site/VOX+-+AmPlug+Headphone+Amplifier/8889349.p?skuId=8889349&ci_src=14110944&ci_sku=8889349&ref=06&loc=01&id=1215216374928

[RicharD]

Any ol amp will work for the task.  It's all about the stethoscope probe.  That consists of a .1/600 cap, a 1M pot, a 1/4" male, a probe end, a gator clip, & some coax.  Some sorta little box might be nice to install the 2 components inside of but it could easily be built in a wad of electrical tape or shrink tube.

[craneclimber]

Any ol amp will work for the task.  It's all about the stethoscope probe.  That consists of a .1/600 cap, a 1M pot, a 1/4" male, a probe end, a gator clip, & some coax.  Some sorta little box might be nice to install the 2 components inside of but it could easily be built in a wad of electrical tape or shrink tube.

What do you think about fabbing a probe with short piece of pvc pipe containing the cap and pot. The shielded cable shield would go to the pot and ground lead.
Kinda like what you did with the 209A probe a while back (although there you used emt).

[RicharD]

Sure that could easily work.  My only reservation is to make sure your pot has a plastic knob.  You certainly don't want a ground in your probe hand.

[Shrapnel]

Rat shack also has this and it's got possibilities:

Cat # 227-1008 - Mini Audio Amplifier. ( http://www.radioshack.com/product/index.jsp?productId=2062620 )

(Description)
With a built in speaker, this mini audio amplifier is perfect for many acoustic projects. Also includes a microphone input and a speaker/earphone jack for added flexibility.
Use as a test amplifier or signal tracer
High-gain IC circuit
Volume control with 1/8" earphone jacks so you can adjust the volume
9V battery is readily available and reasonably priced
You'll also need
Requires 9V battery or #273-10027 AC adapter   (reported to eat batteries though)


With an adapter (it has a 1/8" input,) it could work... you're going to need a small box on the front end anyway for a HV cap (and level control,) could just set it up to plug into this.

[craneclimber]

Sure that could easily work.  My only reservation is to make sure your pot has a plastic knob.  You certainly don't want a ground in your probe hand.

Good point. I'd also go with nylon shaft to be safe.

[RicharD]

I've never actually built a stethoscope probe but I have used this method of troubleshooting using only a cap, a pair of clip leads, and the closest geetar amp on hand.