Avt3k

I found some nice tutorials

 

 

 

 

 

 

 

 

 

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Hearing Aids Circuit

This low-cost, general-purpose electronic hearing aids works off 3V DC (2×1.5V battery). Transistor T1 and associated components form the audio signal preamplifier for the acoustic signals picked up by the condenser microphone and converted into corresponding electrical signals.

The medium-power amplifier section is wired around popular audio amplifier IC TDA2822M (not TDA2822). This IC, specially designed for portable low-power applications, is readily available in 8-pin mini DIP package. Here the IC is wired in bridge configuration to drive the 32-ohm general-purpose monophonic earphone.

The audio output of this hearing aid circuit is 10 to 15 mW and the quiescent current drain is below 1 mA. The circuit can be easily assembled on a veroboard. For easy assembling and maintenance, use an 8-pin DIP IC socket for TDA2822M.

 

source: http://www.electroschematics.com/1676/digital-hearing-aids-circuit/

Simple Cable TV Amplifier Circuit

 

This cable tv amplifier circuit is a rf amplifier designed to be quickly installed between two coaxial cables. Both input and output impedances are compatible with 75 Ω cables. The main amplifier si T1 transistor, T2 is working as an emitter follower. The feedback bias is determined by R3 and R4.
The total gain of this tv cable amplifier is 22dB.

Because of the high frequency limit of transistors (<= 2GHz) the tv amplifier works well up to 150 MHz. It must be housed in a metal case and the coaxial cables must de 75 Ω type. The total current consumption of this tv cable amplifier circuit is around 20mA.

 

Tv amplifier active components

T1, T2 = 2SC4308 or 2SC1324

source:  http://www.electroschematics.com/401/simple-cable-tv-amplifier/

 

DIY HiFi Orthodynamic Portable Headphones (aka Ribbon Driver Headphones)

Are you sick of cheapo portable headphones? 
Are you sick of paying $200+ for a decent set of portable cans? 
Do you like Unique Technology? 
Are you DIY?

These headphones use drivers that are Orthodynamic. To sum it up, they are very similar to electrostatic and ribbon drivers in that they are planar. However, one major difference between electrostatic and orthdynamic is that Orthodynamiccan be driven from simple headphone sockets whereas ‘Stats  need several hundred volts for bias. This makes them the best possible candidates for HiFi drivers in most headphones with some costing more than $550 a set. Unlike most headphone or normal drivers/woofers, this type actually has the voice coil printed onto the thin mylar diaphragm instead of attached to the back. This mylar piece is actually then suspended between two strong magnets with holes in them. When a signal is applied, the diaphragm will be charged to go back and forth with the sine wave. Since the diaphragm is flat, there is not peakiness and almost no delay due to “return”. Please see th diagram below for a better understanding.

 

What you will need:
- 1 Set of FAKE Audio Technica ESW9/ES7 or other 40mm driver portable headphones. (ebay, dealextreme, etc. will have many of these).
- Small Rubber Case feet ~$2 (can also use foam tape circles your gf or mom might have for scrap-booking)
- Extra Rubberized foam ~ $0.50 (you can ind similar at craft stores, just had some extra of this lying around)
- 1 Sheet of Dense Wool Felt ~$0.75 at the local craft store in the kid’s section
- 1 Sheet of looser, Soft Wool felt ~$1.25 usually found in the fabric section with the other felts on the spool
- 2 Kleenex Tissues ~ Free
- Some scotch tape for the driver fronts
- Borrowed Dremel for drilling holes in the cups
- Krylon Fusion Plastic paint in your favorite color (Rustoleam works just fine too) or whatever way you want to paint these.
- 50ft. of 28AWG black teflon coated silver plated copper stranded cable (SPC, can find on ebay as military surplus). I did my cable in an 8 conductor configuration with 2 strands for each channel going to a driver in a tight litz braid. The wire I used is 11 strand, cryo treated, 1000V Teflon, 99.99% pure silver covering 99.999% pure copper. Literally some of the best wire on earth and when done in this way, minimal skinning, thin, and very durable. Bought it as military surplus meant for fighter jets made by Alpha Wire (no on their site).
STEPS:
Unscrew the Headphones and Remove the stock Drivers. Replace them with the SFI (the front of the driver has smoother cloth).  Remove the cups and drill the holes, then sand and paint.
Once dry, place a layer of the damping foam around the edges of the cups and sides of the back of the driver baffle as seen above. This will keep the plastic in check.  Heat up some shapelock with a torch or coffee warmer, then surround the driver edges so that the driver is molded into the plate. Then place a rubber foot over the center hole of the Othrodynamic driver, this is to tame the driver and prevent bulging when in use.
Place a disc of the Dense wool against the back of the cup (black matched best for me).
Now, place the disc of the Softer Wool Felt into the back of the cup.
Here, you fold the Kleenex so that there are 4 layers of “tissue”.
Cut out the tissue to the shape of the back of the driver and cut a center hole the size of the rubber feet.
Fit all 4 layers over the back of the driver.
Screw the assembly back together and put some tape over a couple of baffle front paper covered areas to prevent air leakage.
 
Put the Ear Pads back on and Enjoy the Fun!
They will be unique, and VERY inexpensive considering how well they compare to much more expensive headphones and can still be driven with an iPod or such, but still does do best when attached to an amplifier.
source http://www.stacydevino.com/?p=18
 
You want more DIY? Check out the links on this page: http://jap.hu/electronic/