Upgrading OPA2604 in a Fubar II USB DAC

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Veniogenesis

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Joined 2007
#1
Hi everyone,

I've realized that I don't seem have enough money right now to buy a new DAC or build a new one, so I thought I might try tweaking the inexpensive Firestone Fubar II USB DAC I already have. It uses a OPA2604AP for the gain stage apparently. What can I upgrade that chip to? (Possibly two separate chips in parallel since the OPA2604AP is a two channel chip from what I understand.)

I can't tell if there are any other chips or parts that I can upgrade. I've included hi-resolution images (Large filesize!) of the board below.

Thanks so much!
Cheers,
Venio

http://www.veniogenesis.com/audio/fubar/IMG_0645.jpg
http://www.veniogenesis.com/audio/fubar/IMG_0646.jpg
http://www.veniogenesis.com/audio/fubar/IMG_0649.jpg
 
#3
Are there any capacitors on the other side of the PCB for the OPA2604AP? I really hope so. If not, adding some polypropylene of silver mica capacitors over it's power lines will help.
I think posting a pic of the back side of the PCB would really help.
 
#4
Veniogenesis said:
I've realized that I don't seem have enough money right now to buy a new DAC or build a new one, so I thought I might try tweaking the inexpensive Firestone Fubar II USB DAC I already have. It uses a OPA2604AP for the gain stage apparently. What can I upgrade that chip to? (Possibly two separate chips in parallel since the OPA2604AP is a two channel chip from what I understand.)
Click to expand...


You could always try the LM4562 (or the single version LME49710). The LM4562 is miles ahead of the OPA2604 in terms of sound quality, if bypassed properly with an MKT cap.
 
#5
Re: Re: Upgrading OPA2604 in a Fubar II USB DAC

alcoholic said:
Are there any capacitors on the other side of the PCB for the OPA2604AP? I really hope so. If not, adding some polypropylene of silver mica capacitors over it's power lines will help.
I think posting a pic of the back side of the PCB would really help.
Click to expand...
Unfortunately I don't think there are any capacitors on the bottom side of the PCB. I'm not sure though; I'll take some photographs once I get home. Thanks!
MatchASM said:
You could always try the LM4562 (or the single version LME49710). The LM4562 is miles ahead of the OPA2604 in terms of sound quality, if bypassed properly with an MKT cap.
Click to expand...
The LM4562 looks like a great choice. (It's dual channel too and inexpensive. Nice.) Are two LME49710's on a BrownDog adapter better than a single LM4562 though?

As a complete DIY newbie, I'll ask a stupid question: What do you mean by bypassing properly with a MKT cap?

Thanks so much for the help!
 
#6
Re: Re: Re: Upgrading OPA2604 in a Fubar II USB DAC

Veniogenesis said:
The LM4562 looks like a great choice. (It's dual channel too and inexpensive. Nice.) Are two LME49710's on a BrownDog adapter better than a single LM4562 though?

As a complete DIY newbie, I'll ask a stupid question: What do you mean by bypassing properly with a MKT cap?
Click to expand...


I'm not sure if the single version is any better than the dual version; I haven't tried the single version yet.

BTW, bypassing such an Op-Amp means connecting one end of the capacitor to the amp's V+ and the other end to the V- pin. Preferably really close to the chip (of course without frying the thing with the soldering iron 😉 ).
 
#8
Re: Re: Re: Re: Upgrading OPA2604 in a Fubar II USB DAC

MatchASM said:
BTW, bypassing such an Op-Amp means connecting one end of the capacitor to the amp's V+ and the other end to the V- pin. Preferably really close to the chip (of course without frying the thing with the soldering iron 😉 ).
Click to expand...
Can the MKT capacitor be of any size? Or are there values I should shoot for?

Thanks!
 
#9
Re: Re: Re: Re: Re: Upgrading OPA2604 in a Fubar II USB DAC

Veniogenesis said:
Can the MKT capacitor be of any size? Or are there values I should shoot for?
Click to expand...


Bigger = Better.

There are lots of different opinions on when it stops making sense to add capacitance. Personally I have used 1.5uF Philips and 2.2uF Wima caps to great effect, but a friend of mine's headphone amp performs fine with about 150nF (which is a practically small format).

I'd shoot for anything between 470nF and 4.7uF, whatever's easily available.
 
#11
Veniogenesis said:
I was also wondering about that other chip next to the OPA2604 in my first photograph. It says JRC 5021G or something, but I don't know what that does.
Click to expand...


JRC stands for Japan Radio Corporation. They make rather horrible-sounding op-amps, so my first guess is that it is one. You don't happen to have a schematic?
 
#14
Re: Re: Re: Re: Upgrading OPA2604 in a Fubar II USB DAC

MatchASM said:

BTW, bypassing such an Op-Amp means connecting one end of the capacitor to the amp's V+ and the other end to the V- pin. Preferably really close to the chip (of course without frying the thing with the soldering iron 😉 ).
Click to expand...


Bypassing from V+ to V- will be good. The best solution is actuallly to bypass +V to ground, and -V to ground.
In audio, you may get by with a V+ to V- bypass, but if the goal is to stablize the supply while its output delivers current to ground, then the bypasses really should be to ground.

btw, you can do a bypass V+ to V-, and add a bypass from either V+ or V- to ground. This accomplishes the same thing.
Short, as in bypass length is also important. If things are tough to do tightly, then by all means do a bypass V+ to V- first (tightly), and as close and short as you can a cap to ground. (since this is audio, the current to ground should be low frequency, the bypass to ground is not as important.)

Good Luck and Best Wishes.

p.s. I wouldn't bother with dual singles. The LM4562 has great crosstalk specs.
 
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