sigh yet another newbie with questions regarding the meta42
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jalepeno

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Hello everybody! I'm Doctor Nick! (err...or something)


well i've been reading these boards here for a while now and i've been reading em over at Headwize for a very long time as well...and finally i decided to go ahead and build a headphone amp. i've spent quite a bit of time researching and getting parts but it seems like everytime i turn around a newer better option pops up...well instead of riding that train i've decided to go ahead and build it with what i've got (i doubt it would make too much of an additional difference) anyways before i start i would like to know a few little things since i'm fairly new to this whole diy thing.

first of all i'd like some advice on the powersupply. originally i had planned to run the thing of batteries...but after some thought i came to the conclusion that A) i'm not gonna be taking this thing anywhere and B) i have a very bad track record for leaving things on and draining away batteries. sooooooo i would like to obtain an external powersupply. now i have a budget of about $25-30 and i was thinking something along the lines of a 24v supply would work...but i have no idea how to tell a good walwart from a bad...and reading through past posts really hasnt shed much light on this subject. any recommendations would be very helpful

also would i still need the rail splitter with an external psu? if so i'm curious to know why? also do dual output walwarts exist? in my budget?

second question: i have is regarding the op amp. i am planning on using the AD820 does this opamp require a browndog adapter? or any other sort of adapter? again although i've looked through old posts a lot of the information on this particular issue seems a bit vague.


third question: resistors...can someone help me decide on what resistor combo is going to be the best for me? i will be using HD580s the source (for the most part) will be coming from my computer and passing through my Quad 34 preamps tape output. i dont really listen to my music too loud but i do listen to pretty much everything under the sun. see below for all other parts currently in my posession.

Tangent's Meta42 board
C1 - dont have one yet...havent decided if i should... anyone have a solid argument for or against it?
C2/C3 - i have some 220uF 16v Nichichon caps
C4 - Wima 6.8uF
C5- none
POT - Alps Blue 100kAX2
blue led
3x elantec 2001 buffers
Neutrik locking jack
rocking toggle switch
2x gold plated RCA jacks
Black Hammond Enclosure



thanks in advance for any help

~jalepeno
 
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post-170021
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jalepeno

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ok upon doing a little more research i found this Elpac linear regulated dual output supply WM072-1950-D5 +12v -12v for around $34 this would be perfect i think as it fits close enough in my budget....question in have is where do i find the DIN Jack associated with this type of powersupply? (ie part number) i found the supply itself at Allied electronics (they have 10 in stock) i figure it would be perfect for me...any thoughts?
 
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wilsonjm

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Hi,

First, about the power supply, if you want you can use the Elpac regulated 24V power supply. You would then split it to +/- 12V using the META42's normal configuration with TLE2426. This would be the easiest way. The Digikey part # for the DC jack is CP-6. Otherwise, with the +/- 12V power supply, you'll have to search for a suitable DIN jack on Digikey. Just search for "DIN". I believe the Elpac is a DIN-5 or DIN-7? Dunno, check the specs =)

If you use the +/- 12V, you DO NOT use the rail splitter. This is because you already have + and - voltages.

About the opamp, do you mean AD8620 - I haven't heard of anyone using the AD820? This is an opamp that is widely discussed. The new version of the META42 board has a SO8 pad on the board....so no adapter will be required, unless you want to be able to swap out the opamp, in which case you will need a DIP8 adapter from Browndog. BTW, if you really are using the AD820, keep in mind it is a single opamp meaning you will need two of them. But I definitely suggest using the AD8620...

You might want to go a little larger on the capacitors. There is room for some 1000uF x 4 on the board, and these will fit in the Hammond enclosure (which BTW i highly recommend). These caps aren't expensive, about $1.50 each at Digikey.

Your setup sounds good though. Check Tangent's site out (http://tangentsoft.net/audio/meta42) and go to Schematic. These are the default resistor values. I have built a META42 with both those values and the old Apheared values, for HD580/600, and i think Apheared's values sound better. Those values were something like....

Gain resistors: 330 and 4.75K
Output of opamp to buffer: 66

You do not have to use C1. It is there to protect your headphones from DC voltage, and it will only degrade sound quality. Try the amp without C1, and measure the DC voltage at the output. if it is small, then you do not need C1. I believe anything under 20mV is acceptable?

I probably messed up and gave you bad advice since it's 6am and i was just ...out all night. One other thing, make sure you buy at least double of the parts, cause you will break some
 
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HD-5000

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If you're just going to use the amp at home, maybe you should think about building a Kevin Gilmore Class A headphone amp.
 
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HD-5000

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Quote:

First, about the power supply, if you want you can use the Elpac regulated 24V power supply. You would then split it to +/- 12V using the META42's normal configuration with TLE2426. This would be the easiest way. The Digikey part # for the DC jack is CP-6. Otherwise, with the +/- 12V power supply, you'll have to search for a suitable DIN jack on Digikey. Just search for "DIN". I believe the Elpac is a DIN-5 or DIN-7? Dunno, check the specs =)


Wait, so that means that the 24V (Newark #16F126) Elpac supply has only V+?

So I only hook it up to V+ on the META42 board and V- is empty?

Does it come standard with the 2.5/5.5mm DC jack?

Thanks.
 
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slindeman

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For the global feedback I used:
R3 = 250 ohms
R4 = 1.5k ohms which sets the gain to 7.

For the local feedback I used:
R5 = 2.2k ohms
R6 = 220k ohms.

I did not use C1 caps. These settings have worked very well with HD580 and lower voltage line-outs such as my soundcard and portable units. With higher voltage line-outs such as home cd players I usually set the gain to 3 or 4.

For the other resistors I had:
R1 = 1k ohms
R2 = 100k ohms
R7 = 100 ohms

I did not use R8 or R9.

Quote:

So I only hook it up to V+ on the META42 board and V- is empty?


No, with the 24V power supply you will still have to hook up the PS ground to V-, and you'll use the rail splitter. With a +-12V power supply you omit the rail splitter as wilsonjm said.
 
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morsel

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The AD820 is a single rail to rail low power opamp with 3V/µS slew rate, 1.8MHz bandwidth, and 15mA output current, totally inappropriate for audio use.
 
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jalepeno

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Thanks for all the help!

sorry that was a typo...i meant AD8620...and actually i already have the tangent board Ver1 or whatever so i would rather build the meta42 amp just because those are the parts i have handy. does the older board that i have have space for these 1000uf caps you were talking about? if so what are their part numbers?

oh and yes it is a din 5 which i was able to find and will order along with the powersupply.

ok so on the older board i will need a browndog adapter eh? hmmm....

also i would like to build this amp before do anything more complicated and the gilmore amp just looks a little hectic. at least for my skill level.

well i'm not in any rush to start building although i would like to get something done...i have so many pieces to the puzzle...but the picture keeps changing. thanks for all the help with the resistors. as soon as i get a browndog adapter i'll at least get a breadboard amp built and then let everyone know what resistor values i liked...well if there is any interest in such a thing (i'm gonna assume there is since i myself needed this same bit of information) anyways i'm off inshallah i'll get this thing done soon...... good day to everyone


~TGAP Jalepeno
 
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wilsonjm

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The older META42 board will fit 1000uF caps, but they must be thin and tall. The height will work fine in the Hammond case, however. Check Tangent's site for the part # for the 1000uF caps.


BTW, it will depend on your source but I found a gain of 15 to work the best for me on HD600s. I also tried a gain of 10 but had to crank it too high to get the volume i wanted.
 
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andrzejpw

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Gain of 15!!!! I used a gain of 8 on mine, and my ct570 still drives it fine! What volume are you listening at????
 
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wilsonjm

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i have my knob at between 9-12 o'clock depending on the volume of what i'm listening to.

My source is a Terratec EWX24/96 sound card. The volume will depend on what I set the output of the sound card...Don't quite understand the settins, but WavePlay Analog is at -6dB, Analog Out -4.5dB and +4 dBu. I found these settings to be the best for sound.
 
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jalepeno

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Thanks once again...but i have yet another question...

i would like to order the DIP sockets that would fit on the meta board (i would also like to order the header pin SIPs or whatever they are called....question i have is what exactly do i search for? i found exactly what i'm looking for on Digikey (at least i think) but its considered Non-Stock and wont let me purchase them in small quantities (part number 11091-30841001000-ND from digikey) those are the DIP sockets...but i cant seem to find the SIP sockets/and cable adapters for them.

also i dont think i need such a high gain (15) i really dont listen to my phone's with that kind of volume. i think i'm leaning toward 10-11 range.

~TGAP Jalepeno
 
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