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Hi,I recently aquired a MF-X24K DAC which I like a lot so far. I decided to change the OpAmps from the default NE5534 to BurrBrown 627AP. After making the change, the DAC hardly produced any sound. I had to turn the volume all the way up to get some sound out of the system. To make a long story short, it turns out that the +15V supply voltage on the PCB goes to pin 8 instead of 7, as it should according to the data sheet for both the NE5534 and the BB627. Pin 8 is not used for the BB627 and is the Bal/Comp pin for the NE5534. I measured the voltages after inspecting the PCB layout and sure enough there was +15V on pin 8 for all four opamps and 0V on pin 7. The -15V is where it should be. Although this kind of explains my results, it leaves me completely puzzled: what weird kind of NE5534 was in in my DAC (it said NE5534AN on the IC) and how do I correct for this? Can I safely connect pin 7 to 8? Does anyone have any experience with this?
Thanks,
Togge
Follow Ups:
If it was the other way around (putting duals instead of singles) you could kiss the digital filter or the other computer chip good bye.
Try the opa 2604 or the opa 2134 I've done a lot of work on the X-dac which is it's fore runner [?].Some of the best mods you can do are to fgive the thing a decent power supply fit some schottky diodes and fit some decent supply caps.
The RCA sockets could be easily up graded too.
Shield all the IC's in side using copper foil and star earth them.
The crystal can be damped and its probably agood idea to ground the can too but becare ful you do not overheat the crystal !
Thanks a lot for your comments. I fitted the first two OPA2134 last night and hope to lay my hands on another pair today. The DAC is fed by an X-PSU, which makes all the difference compared to the standard power supply. I plan to upgrade the power supply caps when I'm done with the OpAmps. Currently, there are 6 of them: 4x1000 uF, 35V and 2x2200 uF, 16V all of te TEAPO brand. I plan to replace them all with 2200 uF, 35V Panasonic FC which should just fit. The RCA jacks are of pretty high quality already, I think the previous owner replaced them but that's all he did to the unit. Did you experiment with replacing the small caps near the crystal with silver-mica caps? I did that once for my old NAD cd-player and it made a huge difference.
No but it could help ....the biggie is the schottky diodes, I built a Psu for mine using 150va 12 ac transformer, the benifits were across the board. I'd go for at least elna stargets for the caps. What are you using as a digital cable.if you have alook at the zerogain.com site you may get a few more ideas....look up "isotrans" or zanash to get my posts. The isotrans is a little widget that helps the X-DAC hugely, I'm currently haveing the thing investigated to see what its doing to the signal.
5534 and 627 have identical PS pins. Look for a mistake elsewhere.
You are right it is impossible, and the mistake was elsewhere: I plugged in some NE5532s and all was well again. The thing is: I'm absolutely certain it said NE5534 on the OpAmps I removed, because I checked what I had in stock to see if anything would fit in, and it turned out that I only had dual OpAmps, like the 5532, the OPA275 and the OPA2134. So I got the OPA627 to replace the 5534. So...either the OpAmps were mislabeled or I was seriously hallucinating :).Thanks everyone!
Check once agian, did it really say NE5534 in clear printing? Was it a SMD part? Maybe you hade a 34 somewhere and it was production week, or something else?
Sounds like the PCB is wired for a dual opamp. According to www.chipdocs.com, the NE5534AN is a dual opamp. Two OPA627s mounted on a browndog (www.brndog.com) single to dual adapter will make it work.
NE5334AN is a single, NE5532AN is the dual...
So much for Chip Doctors! They have it listed as a dual... Strange that his PCB is wired for a dual however.
You're right!MF may have done some 'smoke and mirrors' stuff and found a way to extract more performance from it by feeding the power in through the 'balance/compensation' pin. Other than that I'm stumped unless our friend misread what it said on the chip.
Without looking at the schematics it's hard to say but as the OPA627 needs no compensation or offset-trim components, it should be straightforward to remove any such parts and feed the +15v in where it should be going. (i.e., make sure pin 8 is no longer connected to anything before shorting it to pin 7).
Very, very strange though.... I know there's an AD chip where you can bypass its output stage by sneaking the o/p out of a compensation pin, or something like that, and then using a better buffer.
Come on experts!
Hi everyone,Thanks for responding so quickly. I agree that the power supply lines are consistent will a dual opamp package, but I don't make a habbit of misreading part specs. Unfortunately the old opamps went out with the garbage this weekend, so I can't check...
Better safe than sorry though, so I'll try to locate some dual opamps and see if I feel safe to insert them. I've checked the other pins on the sockets and no other pin carries a supply voltage.
I take that back, it does have offset trim connections... I was thinking of AD825 which doesn't...
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