DIY Headphone Amplifier

[PJPro]

The problem I've been having is distortion. If I take the amp out on my Beresford, or the headphone out on an iPod, there is no distortion at all. If I take the lineout from the Beresford I get really quite bad distortion.

The recommended fix was to reduce the gain produced by the amp by increasing the resistor going to ground on the ouput side of the op-amp from 2.55K to 10K. This reduces the gain to 2. The thought was that the op-amp was clipping. Unfortunately, this fix has made matters worse!

The next step was to measure the draw of the amp. This turned out to be much higher than expected, indicating oscilation as the probable cause. The recommended fix is to decouple the op-amp from the power supply using 0.1uF ceramic resistors. Hopefully, I am going to be able to get a couple of these from Maplins and apply the fix today.

The Headwize thread (see link above) has all the details. When I finally get things sorted, I'll post the revised schematic detailing all the changes made from the original design.

 

[PJPro]

For those of you who have been following this thread with a view to perhaps have a go yourself, I've got some good news. The fix has worked!!!

Listening to the amp right now. As my first electronics project and an amplifier which has been crafted by my own hands, I'm having more than a little difficulty being entirely objective. It's absolutely fabulous! Control, poise, detail, transparency and a whole host of other adjectives I often read in the magazine but don't really understand. It's got it all. Graham Slee...who's he?

Err, I do have one or two ideas how I can get a bit of objectivity into the procedings....but more on that later.

I will update the thread with the final schematic, costings and lessons learnt (which haven't been covered already) in due course.

 

[Olli1324]

A noticeable/worthy improvement over the Beresford?

 

[PJPro]

Here is the final schematic.

You'll notice the two 0.1uF capacitors on the power leads going into the op-amp (the triangle in the left channel schematic). These are the "fix". They go from the power pins on the op-amp to the virtual ground provided by the power supply and prevent the oscillation which was the cause of all my problems.

You'll also notice the 10K resistor going to the virtual ground (at the bottom of the schematic for the left channel). It's this resistor which you can tweak to increase or reduce the gain produced by the amp. The higher the resistance provided by this resistor in relation to the resistor in the feedback loop the lower the gain.

 

[PJPro]

Olli1324:A noticeable/worthy improvement over the Beresford?
Hmmmm. A noticeable improvement? Yes, I think so. A worthy improvement? Difficult to assess at the moment as I don't know what it's cost me.

To be honest, the fact that I've produced something that works at all is pretty satisfying. Not only that, it opens up possibilities for more ambitious undertakings. For example, the M3 by amb (another headwize poster). Here's one someone made earlier.

There is also a companion power supply. Vanman, here we come!

So, as a basic tutorial and introduction to DIY audio, this basic project is priceless.

 

[PJPro]

OK. Here are these costs for the components. These include import tax for the US sourced components and delivery for the protoboard. I did not have to pay delivery for the US stuff as I my order was over £50.

Again, please scroll down to get to the table. I don't know why this whitespace gets introduced. All looks fine in the Preview tab.

ID
Description
Qty
Mouser Part #
T2 Retail Part #
Maplin Part #
Cost (£)

C1
470 æF 35V electrolytic capacitor, radial leads
1
647-UVR1V471MPD

£0.27

C2
0.47 æF 50-plus volt full-size film capacitor
2
75-715P200V0.47

£4.09

RLED
10 KO 1/4W metal film resistor
1
71-RN55D-F-10K

£0.06

D1
Power indicator LED, red diffused, 3mm
1
859-LTL-1CHE

£0.08

R1
4.7 KO 1/4W metal film resistor
2
71-RN55D-F-4.75K

£0.12

R2
100 KO 1/4W metal film resistor
2
71-RN55D-F-100K

£0.12

R3
10 KO 1/4W metal film resistor, gain 2
2
71-RN55D-F-10K

£0.12

R4
10 KO 1/4W metal film resistor
2
71-RN55D-F-10K

£0.12

OPA
Dual op-amp OPA2132PA
1
595-OPA2132PA

£3.89

OPA
DIP-8 IC sockets, gold contacts
1
575-113308

£0.45

IN/OUT
Phone Jacks 3.5MM STEREO JACK
2
502-35RAPC4BH3

£2.24

POT
Volume control, Alps 10K (RK097)
1
688-RK0971221Z05

£2.02

POT
Volume knob (aluminium, black anodized & silver)
1
450-7015

£1.84

RS
TLE2426IP Rail Splitter
1
595-TLE2426IP

£0.94

C3
1uF 50-plus volts electrolytic capacitor
1
647-UMJ1H010MDL

£0.27

C4
0.1uF 35-plus volts ceramic capacitor
1
140-50U5-104M-RC

BX03D*
£0.22

CASE
Plastic Enclosures 2.75X4.94X.94 BK
1
635-H-659V-B

£5.83

BOARD
Protoboard
1

2760150

£1.90

Total

£24.46

The above does not include the consumables, e.g. solder, hookup wire, isopropanol, etc, or the tools e.g soldering iron, helping hands, wire cutters, etc. I will update this post to include those details later.

Without these additional costs, the amp is looking like extremely good value for money. I did get some of the components cheaper due to the number of spares I bought......just in case I messed it up!. In fact, I have enough for at least another complete amp.

 

[Olli1324]

Considering I have access to all the extras needed for building the amp, this does look good value.ÿ

Of course, now that I have started building ProAc Response 2.5 clones, I won't be able to build this amp until the new year, but I am adding it to my list of projects.

ÿThanks for taking the time to give such a detailed development history of your attempt; it will be very useful for me, and I am sure, many others.ÿ

 

[chebby]

Wish I had known about Mouser a few days ago.

Could have saved a few quid on my OPA2107AP. (Bought mine from RS Components.)

Never mind. I only needed one so no great loss.

 

[PJPro]

It would have cost you £12 in postage unless you spent more than £50.

What was the posatge from RS? I was going to use them but they didn't stock all of the components I needed.

 

[chebby]

The whole package (OPA2107 + VAT + delivery) was almost £20, so delivery was cheaper than from Mouser (and it arrived within 24 hours)

 

[Anonymous]

PJPro:Olli1324:A noticeable/worthy improvement over the Beresford? Hmmmm. A noticeable improvement? Yes, I think so. A worthy improvement? Difficult to assess at the moment as I don't know what it's cost me. To be honest, the fact that I've produced something that works at all is pretty satisfying. Not only that, it opens up possibilities for more ambitious undertakings. For example, the M3 by amb (another headwize poster). Here's one someone made earlier.

There is also a companion power supply. Vanman, here we come! So, as a basic tutorial and introduction to DIY audio, this basic project is priceless.

I had a M^3 before, it is an amazing amplifier!! I'm so regret that I sold mine.

 

[Olli1324]

Cankin:
I had a M^3 before, it is anÿamazing amplifier!! I'm so regret that I sold mine.

Is it a relatively straight forward build? What kind of price is one looking at all in? My biggest problem would probably be the PCB... Any ideas on how I would resolve that?ÿ

 

[PJPro]

The PCB for the M3 is available from the amb labs online store here at $21 each. The PCB for the companion power supply, the s11, is also available at $10 each.

Hope that helps.

 

[Olli1324]

Nice site... I'll bookmark that and add it to my list of DIY projects (after speakers (currently underway) and the cmoy as a basis for reminding myself of my basic electronics skills).

ÿAt least this is cheaper than buying manufactured stuff!

 

[Anonymous]

@PJPro thanks for this overview, it seems approachable as a task and your notes have turned it into something that seems reasonable to undertake.

I noticed the gamma1 today tooÿhttp://www.amb.org/audio/gamma1/ a portable usb and spdif DAC

Seems like a tempting box to make too.

Now to finish that book and then figure out schematics...ÿ

 

[PJPro]

Looks like there's some pretty fearsome soldering to do on the DAC project!

 

[Anonymous]

yes at least a dozen surface mount elements, how hard are they to work with?

I think you used a socket mount for the cmoy?

Does the look of that fill you with the fear or look like a nice challenge?ÿ

 

[Anonymous]

performance soldering of ÿ28 pin surface mount

http://uk.youtube.com/watch?v=Bq7fXcAMRcQÿ

AÿSSOP-28, which is the same package as the WolfsonÿWM8740 in the DacMagic

ÿ

 

[Olli1324]

One more thing about the cmoy... PJPro, are you planning on keeping the spares, or do you want to get rid of them?ÿ

 

[PJPro]

Well, I'm considering selling a "one off" complete kit on ebay as I have enough for at least one additional amp.

 

[Olli1324]

Ah that sounds good. Have you thought of a rough price?ÿ

 

[PJPro]

I don't want to bring the mods down on my head, so can't discuss things like cost. The kit will include all components, solder, hookup wire to complete the job. So a bit more than the BoM early on in this thread.

I'll setup an account on ebay (PJPro if it is available) sometime over xmas. I'll bump this thread when the parts are available.

 

[Olli1324]

Sounds good, I'll keep my eye on this thread then.

ÿ

Cheersÿ

 

[PJPro]

My ebay name is pj_pro

 

[PJPro]

zzgavin:
yes at least a dozen surface mount elements, how hard are they to work with?

Don't know as I haven't done one. More difficult I would think.

zzgavin: I think you used a socket mount for the cmoy?

Yes, I did...but this DIP08 socket was still a through board component

zzgavin:
Does the look of that fill you with the fear or look like a nice challenge?

Fear mostly. I'd hate to get so far through completing it and then not be able to finish due to soldering incompetance.