[Serow]

I just finished my first amp, and thought that I might as well post some pictures. I also put in some links to non-headphone-related pics I took.

My father's Kawasaki Nomad and my 1983 Honda Magna V45 (15000 miles!)
http://www3.sk.sympatico.ca/sampc/AMP6.JPG

My dad leaving for Sturgis a few weeks ago, a 2000 mile round trip.
http://www3.sk.sympatico.ca/sampc/AMP7.JPG

New toy - damn I love this thing!
http://www3.sk.sympatico.ca/sampc/amp9.jpg

What happens when your new toy decides that you're trying to destroy it on the trail (six stitches):
http://www3.sk.sympatico.ca/sampc/AMP8.JPG
Picture from madformountainbiking.com

 

[Serow]

Some specs:

Apheared 47 mod on the stock cmoy. Currently using OPA2134, but I also have some OPA2228 and LM6172 to experiment with. There are 0.1 uF ceramic power supply decoupling caps at all power pins. The power supply uses a BUF634 as the virtual ground driver. The power supply caps are 4 Philips 220 uF bypassed with 0.1 uF polypropelene Panasonics. The amp is DC coupled and uses a shunted volume pot. Power comes from 16AA alkaline batteries. Offsets are both less than 2 mA even without a input capacitor.

It sounds extremely good to me, with the 2134 chips providing a warm midrange that take away some of the harshness of the SR-80 upper mids.

Thanks to everyone for their help and advice, especially cmoy, Apheared and ppl.

P.S. You know you are a geek when your calculator costs more than any of your headphones.

 

[divie23]

Serow, what is the purpose of bypassing the power supply caps with polypropylene panasonic caps?? I'm building a new amp and am looking to pick new ideas/tips for my forthcoming project so your help would be highly appreciated!

Thanks

 

[thomas]

Quote:

P.S. You know you are a geek when your calculator costs more than any of your headphones.

nope, you know you're a geek when your headphones costs more than everything else you own, combined

but it is quite geeky so "show off" your calculator

Very nice amp, i like your use of the virtual ground driver and bypass caps... many diy'selvers seem to overlook those...

I've never tried using a shunted volume control; does it result in a large improvement in the sound?

Also, is there really that much improvement without the input cap's. Wouldn't it be a good idea to leave those in, as any DC on the inputs would quickly fry your cans...

 

[ppl]

Serow: the Sony CD player looks just like my old Sony i had Prior to Getting my SL-SW860. I left the Sony outside and it rained That Night and The Sony Never worked again. I starts to spin the Disc then says NO Disc. If I lift the Lid and push a Pencil into the Hole that has the switch for the Lid so as to see the Laser it dose light. Humm, Strange.

 

[Serow]

Thanks for the replies. Divie23, the reason for the 0.1 uF caps is to improve the high frequency response of the power supply caps. Fairly large electrolytic caps like these are not known for their speed. Thomas, I found that the improvement offered by the shunted volume pot was small but definitely noticealble. As far as the input caps go, I tested the DC offset with both of my sources while the circuit was on a breadboard and found that it was very low in all cases. Besides, I find an improvement in the bass resolution without the input caps.

Eric

 

[divie23]

Serow, is the value for the polypropylene 0.1uF cap critical? Or is it a case where bigger is better??

Thanks

 

[gerG]

I thought that you had built it into an HP 48G, and it was still functional!

Now that would be an alpha-geek toy!

 

[Serow]

Divie, I have heard that it is recommended to bypass electrolytics with film caps that are one hundreth the value of the lytics. In my case, I used 2 220 uF caps per rail, so I should have used film caps that were larger, but these would tend to be too big to fit into a portable case.

Greg, I have a friend at university who has the case and innards from a dead HP

. I have used my HP to control the Winamp player on my PC using the interface cable. It works really well - the song information such as artist, song, album and elapsed time appear on the HP screen!

 

[thomas]

cool!

did you need a propritary interface/software, or is there an easy way to do that? THat would be awesome, especially if it was wireless... (but i don't have/need a graphing calculator, so buying one for a remote control is kinda wasteful

)

 

[Serow]

The method I use is not wireless. I have a program installed on the calculator, a plug-in for Winamp and a cable from the HP to the serial port on my pc. I'm not sure that you could make it wireless very easily. The hp has an infrared port, and people make infrared receivers that allow you to control your computer using an infrared remote. After that, how are your programming skills?

 

[eric343]

Hmm, can your HP beat my TI-89?

 

[Serow]

Alright, back to our regularly scheduled headphone diy discussions...

 

[eric343]

LOL :-D I take that as a "no"..

 

[thomas]

My programming skills suck, I was decent in C/pascal for DOS programming, but that's about where i stopped

I'm pretty good at electronics though, so it would probably be easier for me to work with the serial port and existing programs, and design a transmitter part to go inbetween... I recently built a digital RF transmitter that could work with your calculator... the main transmitter is a 2 bit parallel transmitter, which i converted to 16 bits parallel with a bit of glue logic. And it wouldn't be too hard to convert it to a parallel RS-232 interface...

The kit iteslf was 20 bucks, and is way better for a remote control because you don't have to have the line-of sight with infrared transmitter... But i'm not sure if the transmitter can handle fast datarates (then again, how much data needs to be sent by a remote control)....

ah well, i don't think i'm going to buy that calculator anytime soon, so its probably useless for me... But if you are intersted in building one yourself, i can send you more info about that stuff...