DIY Heaphone Amp help

rodgersk24 · #1 06-26-2010, 01:39 PM

Hello,

I just moved into a new apartment and have been getting complaints about playing bass with any sort of volume at all through my amp. So, I'd like to build a little headphone amp to use. In addition, I'm trying to learn how to read circuit diagrams, so I thought it'd be a fun project to work on.

Here is the diagram I'm using, it's a dual opamp headphone amp from General Guitar Gadgets. I understand almost all of the diagram but I have a few questions before I purchase parts begin and building.

1. Where on this diagram does the power come in? I plan on using a nine volt battery, but I can't figure out where the positive from the battery clip comes in.

2. I haven't purchased the opamps yet, so I don't know what they look like physically, but from what I've read I'm assuming there's more than three pins on the opamp itself. Are the only pins used in this diagram 2, 3, and 5 on the opamps? Or am I reading the diagram incorrectly?

Thanks in advance for the help, and thanks in advance for putting up with possibly dumb questions from a new circuit builder!

Best wishes,

Kyle

**B-string** · #2 06-26-2010, 02:22 PM

Here is the data sheet http://www.fairchildsemi.com/ds/NE%2FNE5532.pdf
Pin 8 positive (Vcc) pin 4 negative (Vdd).

zaubertuba · #3 06-26-2010, 03:00 PM

If this is your first build, you may want to check out the diy'r forum on Head-Fi:

http://www.head-fi.org/forum/list/6

There's a *huge* body of diy folks on that forum.

Are you married to this particular design? If not, I'd recommend a CMoy, actually, as the parts count is low (only one dual opamp), and it's *heavily* documented. Tangent has a great site devoted to it:

http://tangentsoft.net/audio/cmoy-tutorial/

Does your bass have active pickups? If not, you may need a preamp. I know some people have done practice headphone-amp builds on there as well, who may be able to point you in the right direction.

I've built a balanced a47 (basically a CMoy on serious steroids), and am gathering up parts to build a balanced JISBOS buffer.

Beware these diy threads, though. They're addictive! You too, will be assimilated...

rodgersk24 · #4 06-26-2010, 03:42 PM

Thank you both for the responses!

zauertuba, I have a SansAmp bass driver. Would this be a sufficient preamp if I ran this into a plain CMoy? If so, that would allow me to use my active basses with it, too. I am using a (older passive) MIM P bass special mainly, though.

Thanks!

synaesthesia · #5 06-26-2010, 05:27 PM

Quote:

Originally Posted by zaubertuba

..... I'd recommend a CMoy,....

+1

ahdunno · #6 06-26-2010, 07:58 PM

How about a DIY tube headphone amp?

I've been looking at this for my office and was curious if I can use it as a practice amp for fun.

Valve Class A Tube Headphone Amplifier preamp audio amp

http://cgi.ebay.com/Valve-Class-Tube...ht_5847wt_1137

Can I just use 1/4" Stereo Jack to 1/8" Stereo Mini Plug, (6.5mm to3.5mm) adapter?

I'm guessing I would need to use an active bass.

Thoughts? Comments?

-- A

BassmanPaul · #7 06-27-2010, 11:20 AM

Why go to all the trouble of building something when for around $40 you can pick up a cheap micro mixer with a headphone socket built in. It will also have a stereo channel for your MP3 player or computer.

The schematic you show is only part of the story. You also need a power supply, something to mount the components on and a case to put it in. All this will take you over that $40 mark. Don't reinvent the wheel!

Paul

**B-string** · #8 06-27-2010, 11:27 AM

Sometimes it is the pleasure of the build Paul?

rodgersk24 · #9 06-27-2010, 12:55 PM

Quote:

Originally Posted by B-string

Sometimes it is the pleasure of the build Paul?

Yep, that's exactly it! I do enjoy doing this as a hobby, but I'm trying to take the next step from building kits that tell you where everything goes to reading and understanding circuit diagrams.

Plus, if I can find any excuse to justify building something, I'll do it!

That said, I did a different diagram (I'll save the CMoy for later). Here is the new one I did. The only change I did was add a SPST switch between the positive lead on the 9V clip and where power goes into the circuit. It works, but I do have a problem:

Whenever I use it (especially on the dirty channel), I pick up radio stations. I've checked the diagram multiple times, and tested all my connections for continuity, but I'm picking up two radio stations. I'm using a metal case from Radioshack (which I don't recommend, it's not sturdy at all). Is this a flaw in the circuit, a problem with the case that required shielding, or it is my fault and I need to check my soldering?

And ahdunno, a tube practice amp would be awesome, but I had problems finding answers for the question you have. Let me know what you find, I'd like to do that as a future project!

Does anyone know if the SansAmp BDDI is a sufficient preamp to run a normal headphone amplifier?

Thanks again!

Kyle

**B-string** · #10 06-27-2010, 01:14 PM

Two questions. Are you using shielded wire at the input and S1 (only one side should be grounded on the shielded lead)? Are the cap leads as close as possible to the IC?

rodgersk24 · #11 06-27-2010, 01:39 PM

My apologies, but you'll have to define shielded wire for me. The wire I'm using is solid copper with a plastic outer shield, it's not the tiny strands twisted together. That wire is used everywhere except for two connections, but it is used for the inputs and S1.

The cap leads aren't as close as the could be, I don't think: when the cap lead is connected to a pin, it's right next to the pin. However, the other lead is usually farther away from the IC. I didn't use a standard perfboard, but instead a radioshack IC board (the exact one used in this picture.

BassmanPaul · #12 06-27-2010, 01:42 PM

IIRC, there should be a resistor from the IC + input to ground. Try a 100KΩ and shunt it with a 47pF mica cap to limit high frequency response. You should also add a resistor in series with the output jack say 220Ω to limit the power to your headphones.

Paul

rodgersk24 · #13 06-27-2010, 01:52 PM

Thanks Paul. I think I know what adding a resistor in series means, but I'll have to look up how to "shunt" a resistor.

Thanks!

**B-string** · #14 06-27-2010, 01:56 PM

Shielded wire has a small center conductor and a wrap or braided shield, then the outer jacket.. Cutting up an old "RCA" cable will work. As long as the side of the caps that go to the IC are as close to the IC pin you are good. If you are using an IC socket be sure it is good quality one (to avoid making a contact point diode in the socket). Un shielded hookup wire on a high gain circuits input is an invitation to noise and can even make a simple "detector" (hence the radio stations). Even a bad instument cable can "pickup" radio stations.

phatbass · #15 06-27-2010, 02:02 PM

Quote:

Originally Posted by rodgersk24

Does anyone know if the SansAmp BDDI is a sufficient preamp to run a normal headphone amplifier?

The later BDDI with the switchable output level (Inst/Line) has enough juice to drive a power amp, so I assume it should run a headphone amp.

BassmanPaul · #16 06-27-2010, 04:03 PM

Quote:

Originally Posted by rodgersk24

Thanks Paul. I think I know what adding a resistor in series means, but I'll have to look up how to "shunt" a resistor.

Thanks!

In this context you place the capacitor across, in parallel with, the 100K resistor.

rodgersk24 · #17 07-05-2010, 05:04 PM

Quote:

Originally Posted by B-string

Shielded wire has a small center conductor and a wrap or braided shield, then the outer jacket.. Cutting up an old "RCA" cable will work. As long as the side of the caps that go to the IC are as close to the IC pin you are good. If you are using an IC socket be sure it is good quality one (to avoid making a contact point diode in the socket). Un shielded hookup wire on a high gain circuits input is an invitation to noise and can even make a simple "detector" (hence the radio stations). Even a bad instument cable can "pickup" radio stations.

I've procured some shielded wire... what do I do with the shielding, solder it to anything or just cut it off on the stripped end?

Thanks!

Kyle

rodgersk24 · #18 07-08-2010, 07:42 PM

Also, I know one needs to be careful when working with caps that have been exposed to power. Do I need to be careful with these small caps or not? If I do, is it easy to discharge them?

Thanks!

**B-string** · #19 07-08-2010, 08:11 PM

Quote:

Originally Posted by rodgersk24

I've procured some shielded wire... what do I do with the shielding, solder it to anything or just cut it off on the stripped end?

Thanks!

Kyle

Only one end of the shield should be at ground (VDD pins 3&4)

Quote:

Originally Posted by rodgersk24

Also, I know one needs to be careful when working with caps that have been exposed to power. Do I need to be careful with these small caps or not? If I do, is it easy to discharge them?

Thanks!

The voltage is so small no worries.