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post #16 of 76
11/11/11 at 12:33pm
Thread Starter 

Yea, I guess the OPA627s are quite pricey. Maybe I'll go with a pair of AD6810s, since some are saying they are even better.

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post #17 of 76
11/11/11 at 12:41pm


Why not just use an AD8620?

 

Quote:
Originally Posted by Pinnochio5 View Post

Yea, I guess the OPA627s are quite pricey. Maybe I'll go with a pair of AD6810s, since some are saying they are even better.



 

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post #18 of 76
11/11/11 at 12:51pm
Thread Starter 

Apparently there is an AD8610 (Single Channel) and AD8620 (dual), would it be in my best interests to buy just the AD6820 with the brown dog adapter? Is the sound quality with the AD8620 and 2 AD8610s the same?

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post #19 of 76
11/11/11 at 12:57pm
Thread Starter 

Ok, and here's another shopping list from brown dog:

Qty Item Total
1 Single-to-dual Op-AMP Adapter - DIP version (p/n 021001) $9.00
1 SO8 to 8-pin DIP Adapter (p/n 970601A) $23.00
 
     
 
     
 
Subtotal $32.00

 

The SO8 to 8-pin adapter includes the AD8620ARZ, which is why it costs $23.00.

 

So now my overall total is near $85.00.

 

I also changed to the 470uF 25V caps like CanJam suggested.


Edited by Pinnochio5 - 11/11/11 at 12:59pm
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post #20 of 76
11/11/11 at 2:51pm

 


Quote:
Originally Posted by Avro_Arrow View Post

The silicon (the guts) of an op-amp are the same regardless of the package.

 

This is true, but dissipation (the amount of waste heat the chip can get rid of) varies. DIPs usually have higher dissipations than SOICs with the exception that some SOICs have a pad on the bottom which can be soldered to the PCB which acts as a heatsink.

 

w

 

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post #21 of 76
11/11/11 at 9:55pm
Thread Starter 
Quote:
Originally Posted by Pars View Post

$23 for an opamp? As a single, it will be x2. For a Cmoy? :rofl:

 

I would stick to dual opamps, single socket for your first build. As someone else noted, if you use a dual DIP adapter to use a pair of singles, the chances of sticking this in an Altoids tin are slim and none due to height. You might want to look at the OPA2107... this seems to sound similar to the 627s, is a dual, and was always one of my favorites in a Cmoy.

 

Also, use 470uf caps instead of the 220uf you have listed. Look for some Panasonic FM, 470uf 25V (Mouser has them)

 

Go bigger on the input caps (or omit them). 0.47uf or even 1uf if you use them.

 

The pot you listed is mono, not stereo. Use the RK0971221Z05.

This pot (same one Amb and Tangent sell) has a built-in power switch, so you can omit the switch in your BOM.

 

EDIT: I see that these are ~$17... I would stick with the OPA2132 or 2134 for starters, and work your way up.


I ended up buying the input caps I already had initially listed. What will be the problem with having those ones in there? 

 

For power I stopped by Home Depot and bought two 9V Energizer rechargable batteries with a battery charger, so 18V worth of power. Will this be a good setup?

 

 

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post #22 of 76
11/14/11 at 10:20am

Input cap discussion: http://tangentsoft.net/audio/input-cap.html

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post #23 of 76
11/14/11 at 11:04am

Good Lord - an $80 CMOY - and a fair chunk of that into ridiculously expensive opamps. Grab yourself something much cheaper and definitely dual - my objective preference would be a NJM4556, based on how uniquely happy it is delivering lots of current into low impedance loads, but an OPA2134 or something would also be OK, if not as good.


Edited by Willakan - 11/14/11 at 12:46pm
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post #24 of 76
11/14/11 at 11:34am

I tried a 4556 in my CMoy before it was fitted into my O2, by far the best opamp i'd used; opa2132, ad823, opa2227 & ad8620... the 4556 drove my HD650's with great gusto and offered up greater detail than any of the opamps managed.


Edited by Paul Blythe - 11/14/11 at 11:38am
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post #25 of 76
11/15/11 at 12:37am
Thread Starter 

So based on my Cmoy's parts list. Would I need input caps? If so what kind?

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post #26 of 76
11/15/11 at 2:03am


How is the NJM4556 compared to LM4562/LME49720 (It's the same OP)? Has anyone tried both?

 

Quote:
Originally Posted by Paul Blythe View Post

I tried a 4556 in my CMoy before it was fitted into my O2, by far the best opamp i'd used; opa2132, ad823, opa2227 & ad8620... the 4556 drove my HD650's with great gusto and offered up greater detail than any of the opamps managed.



 

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post #27 of 76
11/15/11 at 2:37am

It is largely the same opamp, but with a dramatically beefed-up output stage, which makes it much better suited to driving headphones.

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post #28 of 76
11/15/11 at 12:59pm
Quote:
Originally Posted by Pinnochio5 View Post

So based on my Cmoy's parts list. Would I need input caps? If so what kind?



Read the link I posted, and you should be able to answer the question for yourself...

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post #29 of 76
11/15/11 at 3:02pm
Thread Starter 
Quote:
Originally Posted by Pars View Post



Read the link I posted, and you should be able to answer the question for yourself...

 

I did read it. He said if I want to risk damaging my headphones then I shouldn't get input caps. And he also said there's quite a bit of stuff to worry about if I do get them. But it was unclear the amount of risk the headphones may be subject to, which is what I am curious about.
 

 

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post #30 of 76
11/15/11 at 8:28pm

Yeah, if you don't mind the risk to your headphones, then leave them out (jumper them). Otherwise,

 

 

Bottom line, you end up wanting a corner frequency way below 20Hz to keep phase distortion down to a reasonable level.

RC Filter Weakness 3: Capacitor Distortions

Phase distortion is an essential part of the way capacitors work. You see it in the simulation results because even an ideal capacitor would have phase distortion.

Real capacitors have additional distortion mechanisms due to material imperfections. Film types have lower distortion than electrolytic and ceramic types. Film caps made with separate film and foil are better than those made with metalized film. Also, the dielectric film material matters: in decreasing order of preference for use in an audio signal path, the main types are polypropylene, PPS and polyester. You shouldn’t go any farther down the scale than polyester for signal path caps under any circumstances.

The better the capacitor, the bigger it tends to be, physically. The previous section also shows us that higher cap values are also better than lower values, which increases physical cap size as well. Since board space is limited, you may have to compromise on the input capacitor’s quality. If your board space limits you to a choice between a 1.0 µF metalized polyester and an 0.1 µF polypropylene, the polyester might actually be the better all-round choice.

 

Given the lack of board space, if I use input caps, they are 1.0uf or higher, assuming the 100K input resistor (R1 I believe). Most commercial gear has input caps. Many DIYers do not use them.

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