Author Topic: qrv-07 building and test  (Read 4046 times)

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Offline Jinkslynx

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qrv-07 building and test
« on: May 13, 2007, 06:54:44 PM »

   Having recently bought boards for the jsr06 qrv05 07 and 08 p-a asked me to leave my impression at his forum, so here goes.
Building this amp was quite easy, considering I had no previous experience with smd.  Lets see now, resistors and caps, no problem TPA6120. Well I simply smeared some solder paste under it and a bit on the pad, soldered the pins flipped the board over and filled the holes. Done. Well, not quite, some double checking revealed that three resistors and two caps were shorted. Seems I was a bit sloppy and smeared paste under some components. After fixing that and checking everything one more time I plugged it in. No smoke, good, signal and sound. Well, sound and sound, this amp definitely need some time, about two weeks I reckon before any serious listening. First though I had to   make some decent signal cables using supra eff-1 and some leftover rca plugs. (Plain pvc insulated copper wire will degrade/color the sound more than this amp)
So how does it sound then? Well, the good thing is that it does not color the sound in any way. It does however reduce the dynamics a bit most notably by not being silent between transients. It also seems to remove very weak sounds and amplifying slightly stronger, although not nearly as much as when it was brand new. Using this as a buffer between my cdp and amp (rated at 200k input) firms the bass up a bit and degrades the sound similar to a cheap (>500nok or so) retail signal cable, although not nearly as much as when driving my headphones. Hmm, those regulators have to work overtime due to those tiny trannies right? Causing regulator noise in the output.
Unfortunately I don't have any other headphone amp to compare it to (and even my power amp is quite a bit better despite having 30 db gain and weighing 30 kg). Ah well it was fun building, and the main reason I bought it was to get practice assembling the qrv08, which is done and playing as I write this :)

Associated equipment

Accuphase dp75-v (up sampling to 192khz and using those extra bits to adjust the volume)
Sennheiser hd 580 and 600 (hd 580 is almost eight years old)
Dynamic precision A1s
Forsmann Vss3 (replaced all caps and inductors)
Supra eff-1, Silk, Monitor audio cables

(complete overkill I guess, using 5k instead of 50k+ components this amp would probably not be the limiting factor)






Offline peranders

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Re: qrv-07 building and test
« Reply #1 on: May 13, 2007, 07:24:10 PM »
Hmm, those regulators have to work overtime due to those tiny trannies right? Causing regulator noise in the output.
Hi!

I'm glad that you have succeeded and like the outcome (more or less at least) :-D

The transformers are enough I think if you use the board as a headphone amp. If the transformers are under 60 deg C it's alright and I think 2.2 VA is enough to power headphones especially when the idle consumption is so low.

If you are having noise problems you have some kind of other problem. Do you have noise with shorted input? Maybe you signal source is generating the noise?

I was fun to see your results and I anxoius to hear what you have to say about the QRV08 be there you can't complain about the power supply and the regulators!
/Per-Anders Sjöström, owner of this forum

Homepage with my DIY hifi stuff

Offline Jinkslynx

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Re: qrv-07 building and test
« Reply #2 on: May 14, 2007, 06:43:22 PM »
Hi
Better look at those components I am testing it with again :-D
This is only a problem when driving headphones, not when using it as a preamp. I confirmed this by connecting a 2*18v 300va toroid transformer and the noise went away. Besides this is just a regulator and two op amps, I highly doubt it is possible to make so called "reference gear" using components like this.

About the qrv08, don't worry, it seems to be in another class altogether, I heard that right away with the headphones still lying on the floor :) still sounding (slightly) bright and thin though, better give it another week before saying something definitive.