Upgrading OPA2604 in a Fubar II USB DAC

[Veniogenesis]

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

[stephensank]

I think the OPA2134 is a better sounding dual opamp than the OPA2604. Some think the expensive OPA627 is better, but is only available single channel, but adapters are available to mount two 627's in an 8pin dual position. I like the 2134 best, personally.

[alcoholic]

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.

[MatchASM]

Originally posted by Veniogenesis
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.)

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.

[Veniogenesis]

Originally posted by alcoholic
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.

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!

Originally posted by MatchASM
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.

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!

[MatchASM]

Originally posted by Veniogenesis
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?

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 ).

[colonelkernel8]

AD8620?

[Veniogenesis]

Originally posted by MatchASM
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 ).

Can the MKT capacitor be of any size? Or are there values I should shoot for?

Thanks!

[MatchASM]

Originally posted by Veniogenesis
Can the MKT capacitor be of any size? Or are there values I should shoot for?

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.

[Veniogenesis]

Thanks MatchASM.

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. Any guesse?

Thanks!