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PostPosted: 10 Jul 2010, 04:28 
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Location: Duesseldorf, Germany
Hi,

Quote:
Also, would an ST Microelectronics P140NF55 (http://www.st.com/stonline/books/pdf/docs/11028.pdf) work as the Mosfet?

The 140NF55 specs don't read bad, but the IRF610 is likely better. The Miller charge, input charge and rise time speaks for
using the IRF's. They are easier to drive and should have a more suitable switching time / freq. response (taken from the documents specs).

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 17 Jul 2010, 17:13 
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Gio,

I have completed the amp!! I have a Carver C1 pre and I think in comparrison it sounds well...flatter. I am using the Grado SR80i headphones and it will blow your ears off when driven by my PC soundcard but nearly as much when using my Ipod. I would like to increase the gain some (any thoughts?) and maybe increase the heatsinks on the LM's. The amp is dead quiet with no filtering between the signal and power ground. I have tested using a 0-30V 3A bench supply. The bottom end really comes around with 18-20 volts. The layout and PCB were done through some connects in the biz. I scaled this to fit using your CD ROM idea and may even have enough room for a power supply?? Have you measured the output? It seems like it is at least 3X the output of my preamp. Thanks for your terrific information and willingness to share and help us make this design happen. I am adding a pic of the amp, though not in chasis complete.


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PostPosted: 18 Jul 2010, 20:44 
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Location: Winnipeg, CANADA
Fantastic! I love the board. Let me know if you have any extras. ;)
Do you have a layout for the pcb?

I only tried up to 20V for the supply and I thought the sound was best near 20V.

To get more gain you will need to add a voltage gain stage in front of the mosfet follower.

Can't wait to see your finished headamp.
Cheers

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PostPosted: 07 Aug 2010, 06:46 
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Location: India
hey,
hm.. so i am completely new to the world of audio diy and i suppose this is simplest amp even vs the cmoy head amp which got me frustrated a LOT!!,
so i've made amp SCH in tina and simulated and everything looks fine the only worry is that of the PSU and startup and shutdown voltage spikes.

1.) when started a spike of 2V for about 2ms is there, according to me DC spikes can damage headphones.how to fix this??
2.)i live in India and am about 16 years old so getting components and budget restrictions are quite tough so i need a good PSU for the amp.
3.)PCB is expensive to produce so a protobaord would do but my limited skill and experience means that i really cant imagine or design the schematic to a protoboard. could you help by posting some images :thumbsup:
4.)what would you suggest should be be my first steps into the world of electronics although i have complete knowledge abut all the components used but
how they work in synchrony or as a circuit is till some what difficult for me to understand so please recommended a few books..
5.)thanks :mrgreen:

P.S ive uploaded a image of the IRF510 class-A Headphone Amplifier with LM317 CCS circuit in TinaTI.
Attachment:
amp1.JPG


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PostPosted: 07 Aug 2010, 13:04 
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Hi Rohan, welcome to the forum.
IMO the CMoy with a 9v battery supply is about as simple as a DIY audio circuit can be. This build will be a bit tougher to make as it will need a quiet power supply and there are more devices. Regardless, this is also a fairly simple project.

Rohan wrote:
1.) when started a spike of 2V for about 2ms is there, according to me DC spikes can damage headphones.how to fix this??

I ended up using a manual mute switch for this.
Rohan wrote:
3.)PCB is expensive to produce so a protobaord would do but my limited skill and experience means that i really cant imagine or design the schematic to a protoboard. could you help by posting some images

The amp can easily be built on a protoboard. I used a 1.75" square protoboard from Radio Shack (part # 276-148), but just about any style of protoboard will work. Check out Photograph 2 of the DIY Class-A Mosfet Headphone Amplifier project page for some ideas.

Image

Rohan wrote:
4.)what would you suggest should be be my first steps into the world of electronics although i have complete knowledge abut all the components used but how they work in synchrony or as a circuit is till some what difficult for me to understand so please recommended a few books..

Here are some of our DIY Audio Books and Manual suggestions. "The Art of Electronics" is a good introductory book and also a long-term resource.
Cheers

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PostPosted: 07 Aug 2010, 22:39 
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Thanks Gio,
well its possible for me to design a quiet power supply using a LMXXXX series regulator with some sort of ripple rejection or basically a regulated wall supply would also do (most of them have inherent noise) so ill post a schematic quite soon, thanks a lot :mrgreen:

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PostPosted: 08 Aug 2010, 15:29 
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Yes and they work quite well. A LM317 will be well suited for the task. You can use this LM317 Voltage Regulator Calculator to come up with a suitable circuit. Also be sure to take a look at the datasheet which is also available on that pages.
Cheers

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PostPosted: 09 Aug 2010, 02:15 
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I'm thinking of building one of these and am currently sourcing for parts - i have a few questions - i've built a few kits, but nothing from scratch so they might be a bit newbish.

I can't find a suitable 5 ohm resistor for the constant current circuit. I recall that on the original design, some people ran it at higher current- so could i replace it with a 4.7 ohm resistor (which might give me parts commonality since the circuit already uses one) or a 5.1 ohm resistor (which would give me a touch more current)

I'd also like to confirm that the 680uf capacitor is electrolytic, and if its absolutely critical that it be matched with the headphones its connected to, or if anything close to the expected impedance should work fine. I'd also note i can't find mylar capasitors, but i'm told polyester is the same - is this correct? and what voltage and tolerances should i be getting?

Finally - for the heat sink assembly - i would definately need a heatsink and a thermal pad. Would i need thermal grease? I'm looking at using this kind of heatsink but i'm not sure which thermal resistance parameter off the datasheet to use

I'll be getting my parts from a single source, and locally, so once i get my 'wishlist' up, hopefully i can get cracking on this. If anyone's interested, i could probably put a parts list on dropbox and link it here - since i'll be updating it up until i buy the parts.


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PostPosted: 09 Aug 2010, 14:39 
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Hi faileas, welcome to the forum.

faileas wrote:
I can't find a suitable 5 ohm resistor for the constant current circuit. I recall that on the original design, some people ran it at higher current- so could i replace it with a 4.7 ohm resistor (which might give me parts commonality since the circuit already uses one) or a 5.1 ohm resistor (which would give me a touch more current)

I used two 10 ohms resistors in parallel which gives 5 ohms. A 4.7 or 5.1 ohm resistor will also be fine.

Quote:
I'd also like to confirm that the 680uf capacitor is electrolytic ... and what voltage and tolerances should i be getting?

Any 680uF capacitor including electrolytic is fine. For the voltage I would use about 50% more than your supply voltage. You could get by with a 16V cap and a 12V supply, but I would suggest a 25 or 35V cap.
Quote:
Finally - for the heat sink assembly - i would definately need a heatsink and a thermal pad. Would i need thermal grease?

You won;t need the grease as the devices won't be pushing a lot of current.
Cheers

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PostPosted: 20 Aug 2010, 03:44 
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hey guys,
i just got a really good circuit simulator at http://www.falstad.com/circuit/ and i simulated this amp but the gain was really below 1 so a few questions

1. What is the RMS value of an audio signal output of an IPOD or computer output.
2. At 2.26 V (2.0AC + 0.26DC offset simulation) output the RMS of the amp is about 700mV with a 32Ohm load. Can this be loud enough to drive headphones ??
3.What does the capacitor (0.1u) with the power do?

goto to this site and when the applet opens click on file then import >> select this text and paste it and click import :)


$ 1 5.0E-6 19.867427341514983 50 5.0 50
v 240 304 240 432 0 1 40.0 2.0 0.26 0.0 0.5
f 656 304 720 304 0 1.5
R 720 176 720 112 0 0 40.0 12.0 0.0 0.0 0.5
w 720 224 720 288 0
w 720 416 720 432 0
r 720 432 720 512 0 10.0
g 720 512 720 544 0
g 240 432 240 544 0
w 720 400 720 416 0
r 896 400 896 528 0 32.0
g 896 528 896 544 0
r 656 304 528 304 0 150.0
c 400 304 528 304 0 1.9999999999999998E-5 -1.8234655981637957
174 496 176 560 192 0 100000.0 0.47030000000000005 Resistance
w 560 176 640 176 0
w 640 176 720 176 0
w 720 176 720 224 0
w 528 192 528 304 0
g 496 176 432 176 0
r 384 304 384 512 0 100000.0
g 384 512 384 544 0
r 240 304 384 304 0 100.0
w 384 304 400 304 0
w 720 320 720 352 0
w 720 352 720 400 0
w 896 352 896 400 0
c 816 352 896 352 0 2.1999999999999998E-4 0.047574911611595536
w 816 352 720 352 0
c 720 176 784 176 0 1.0E-6 12.0
g 784 176 816 176 0
o 9 64 0 35 0.15625 0.00625 0 -1
o 0 64 0 35 5.0 7.8125E-4 1 -1


ps wait for the circuit to stabilize and then check the output

Thanks
RoHaN

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