Noobie help

[Guest starushz]

Hi guys! I'm interested in making my own headphone amp and im intending to use the schematics Cmoy. Are the parts readily aviable in SLT? also whats the differnece between the OPA2134 and OPA134??

Also do you think a buffered virtual grd is important??

Since there is 2 channel i must amplify each channel separetly rite?

 

[heady 0]

Hi, I got my opamps (OPA2134PA) from Federal in SLT and the other components from other shops. Why not just get cheap resistors etc and do one first just for the experience. And then go back and source for better components (eg 1% resistors and polypropylene caps) to build the one you want to keep.

 

The OPA2134PA is a dual opamp and so it can amplify both Left and Right channel on the same chip.

 

[Guest starushz]

Thanks heady for the quick reply. Yah trying out with cheapo components first. Dnt mine me asking wats the difference between the cmoy amp and the '47' amp?sonically that is. Cause my source is a pcdp and im using koss portapro. I dont want to amplify the bass too much. Just want to tighten the bass up and maybe improve up the mids and highs?

[bpribadi 0]

Hi Starushz,

 

CMoy is the basic Non-Inverting configuration for an Op-Amp. So how good it is will be depend on the Op-Amp. Good power supply design, like design with buffer on the ground, will help to improve the sound performance.

 

A47 is Non-Inverting with additional buffer on the output to increase the output current. But personally I don't really like A47 because of a few reason:

 

1. Output resistors is necessary to minimize current flowing between the two outputs (output of the amplifier, and output of the buffer). These resistors will increase the output impedance. The ideal output impedance is 0 ohm, so high output impedance is not good, as it will reduce the damping factor, especially for low impedance headphone.

 

2. The buffer is not in parallel nor series. Means that the ouput of the buffer will have slight delay compare to the output of the amplifying op-amp, this will cause phase different.

 

So to my opinion, CMoy is better, if you use good op-amp with sufficient output current for the headphone. But for simple CMoy, remember to use JFET input op-amp such as OPA2134 to avoid output voltage offset.

 

There are other designs, but for first timer, I suggest to build a CMoy. I prefer to use the good components at the first time, because you want to be impressed with what you have made And to change cheapo components to a good one will waste more money and time. They are not so expensive anyway

 

Happy DIY But be carefull, it's gonna be addictive, especially for me

[Guest starushz]

Thanks bpribadi for the informative post. BTW when u guys do the circuit do you all use normal copper wire or higher end audio cables? Cause i think lousy wire will cut of the high frequencies rite?

[bpribadi 0]

Hi Starhushz,

 

Well, for low current audio signal, the effect is very minimum, so I normally use cooper wire for internal jumpering. CAT5 cable is good and cheap, I found that it sounds good. For cables, use OFC with shield (coaxial).

 

For high current such as speaker cable, then you need good cable to make them sound good.

 

Bram

[jasonhanjk 0]

Just use normal tinned wire. Cmoy is for beginner, when you go up the ladder then consider the expensive silver wire.

[Guest starushz]

Hi guys,

 

1.Do u all use electrolytic caps for the power supply and polypropylene for audio input or do you all use polypropylene all the way?

2. Does increasing the cap value in the audio or power supply affect the end result?

3. How much does a piece of polyproylene cap cost?

4. The i/p jack's ground is connected to the amp's ground rite?

 

Thanks in advance!

[heady 0]

This is what I understand and what I do:

1. Film caps sound much better than electrolytic caps so film caps are normally use for the audio input.

2. Film caps comes in much smaller capacities than electrolytic so are not so suitable for the larger values required for power supply. However most amps do use a combination of both for the power supply.

3. Polypropylene is preferred over polyester film as they have better sound.

4. The polypropylene caps I buy from SLT are from $1 to $2.50 each. I don't bargain so you may get to pay less.

5. If you are making a CMOY, then the audio input jack's ground is connected to the volume pot and then from that to the virtual ground of the amp. Other amps may have different ways of connecting the input ground to the virtual ground plus a ground driver.

[bpribadi 0]

I normally use Solen Caps for audio signal. They sound good and the price is reasonable. But they are a little bit bigger because they only available in high voltage.

 

You can buy them in Well Audio (Burlington Sq). The 0.47 uF cost SGD 2.4 (just as an example)

 

http://www.solen.ca/pics/polycaps.jpg

 

http://www.solen.ca/caps/mkp.htm

 

http://www.solen.ca/caps/mkp2.htm

Edited August 6, 2004 by bpribadi

[heady 0]

bpribadi, thanks for the tip re: polypropylene caps. Just a little more expensive than the plain normal polypropylene. But they look gigantic.

 

[Guest starushz]

Wished i read ur reply this morning...went to SLT to get polyprolyene caps. When i ask the ppl there if they have polyprolyene caps they just say all there go look urself. Best....took so long to find one....exactly like heady's blue capacitor. Hahah....anyway can anyone tell me how to tell the different between a polyster and polyprolyene cap?

Thanks....

[heady 0]

starushz,

Fact is, most of the shop people don't know the difference either. That's my experience. You need to do a little research on the web with the brand and see how they label their caps. For RIFA/EVOX which is what I used, their polypropylene caps are blue. Polycarbonate is yellow and polyester is grey. It's not easy to get the polypropylene caps in SLT. I was just there this evening, looking for caps for a crossfeed, could not find what I wanted.

 

If you have to space to accomodate the Solen caps which bpribadi recommended, go for it, the brand is reputed to be good for their audio qualities.

 

[Guest starushz]

yah true..i think i know more about the electronics part then them. By the way heady, how much have u spent on the parts??haha. I think I'm sinking deeper into the hole. The urge to getbetter parts after my current project is slowly crawling up on me. I was also at SLT today...hahah..maybe i saw u...

[Mackie 0]

If you have to space to accomodate the Solen caps which bpribadi recommended, go for it, the brand is reputed to be good for their audio qualities.

 

U might like to know Dynaudio Acoustic speakers employ Solen caps on their crossover boards.