Sjostrom QRV08

Discussion in 'Headphone Amplifier Measurements' started by tomchr, Dec 2, 2016.

  1. fishski13

    fishski13 Friend

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    Yes, the E-I Hahn TXs spec'd in the BOM didn't make any sense from an economical stand-point, requiring $ourcing from across the pond in the EU. I instead used quality over-sized 7VAC toroids from Amveco, easily sourced from Digikey. The BOM specs 4.5VA TXs.

    This amp would never have been built under the SWA moniker. I threw it in a repurposed scrap chassis that once housed an EHHA, and was happy that I had expected basic DVM measurements and music. I dickered about with a few duiferent pots and SAs. I once entertained building a few one-offs with P-A's permission, but got scared when I started my build.
     
    Last edited: Dec 3, 2016
  2. fishski13

    fishski13 Friend

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    I was partial to Switchcraft TRS phone jacks and had one in the parts bin. The Neutrik RCAs were already mounted. IIRC, I only had to drill 4 holes to get the QRV-08 to mount and play music into a chassis originally drilled out for an EHHA.
     
  3. Armaegis

    Armaegis Friend

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    Oh man, so many random projects that started this way just because I needed to use up crap that I had lying around.



    .... although lately it's been less DIY and more kitchen.
     
  4. Armaegis

    Armaegis Friend

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  5. tomchr

    tomchr MOT - Neurochrome

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    Transformers are a pain in the bee-hind that way. That was one of the motivations behind my SMPS-86. International mains in, ±24 V out. The HP-1 takes international mains voltage (85-264 VAC) in as well.

    Tom
     
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  6. tomchr

    tomchr MOT - Neurochrome

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    The output impedance measures 80 mΩ, so that's not what limits the output current.

    Tom
     
  7. ultrabike

    ultrabike Measurbator - Admin

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    I see your point about the 1/f noise. Indeed I would blame the input impedance + AC coupling cap, and yes 1 Meg is quite large. It may get worse on high gain.

    LOL! I don't think it will, even if it was a bit higher than that. To me it just means low impedance cans may use this headphone amp with little interaction.
     
    Last edited: Dec 7, 2016
  8. tomchr

    tomchr MOT - Neurochrome

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    You'd have to get up to 11 Ω before you could no longer drive 1 A into a short circuit with an 11 V (peak) swing. So yeah, 80 mΩ is fine.

    I had an email exchange with P-A Sjöström about the output current. I was not able to get a satisfactory answer to my question about why the amp won't deliver the 1.0 A specified. He mumbled something about cheap transistors and the PCB being an early rev, which don't explain anything. He mentions in the circuit description that the drivers for the output transistors run at 2.4 mA, so I bet the real reason is that the output transistors run out of base current drive once they get close to saturation. That's a design oversight. Oops.
    The amp will probably deliver 1 A into a short circuit, but that's not very practical or relevant for headphone use.

    Tom
     
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  9. ultrabike

    ultrabike Measurbator - Admin

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    One of the most difficult headphone loads I know is the HE6 which I think is sort of a resistive 53 ohm load:

    http://www.innerfidelity.com/images/HiFiMANHE6.pdf

    To get this thing to 90 dB SPL it needs about 19 mA (if I did my math correctly). That said, more current drive capability probably means it can deliver lower current drive more cleanly (other considerations aside). Who knows.

    To get the amp to spec, do you see any simple mod (resistor change or so) that would get it to crank up?

    Not asking to solve his design, but if its somewhat obvious it might be a kool data point. "Cheap transistors and the PCB" don't make sense to me either. Ideally, P-A should come up with some sort of a ECO equivalent or so (if possible).
     
    Last edited: Dec 7, 2016
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  10. ultrabike

    ultrabike Measurbator - Admin

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    LOL! Meh... Don't do it. It's P-A's responsibility obviously.

    BTW, again, great review, and great comments. Dunno about others, but I certainly appreciate it.
     
    Last edited: Dec 7, 2016
  11. Armaegis

    Armaegis Friend

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    I did run my HE-6 with the QRV08 when it was on my desk next to the HP-1. Both did an adequate job pushing to loud levels, though the HP-1 was certainly more up to the task. I wouldn't say either of these would be the definitive amp for the HE-6, but I'm one of those nutjobs drinking the koolaid from the speaker camp fountain.
     
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  12. Poleepkwa

    Poleepkwa Friend

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    Great read and educational. Much appreciated. There seems to be surprisingly little measurements of headphone amps available from a reliable source. Tyll started some amp measurement database, but that seemed to be on hold indefinitely . The O2 measurements and impressions will be interesting. I remember Tyll found it measured well, but preferring the worse measuring Apex Butte to it for listening.
     
  13. tomchr

    tomchr MOT - Neurochrome

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    No. It's likely a complete redesign to get the amp to deliver 1.0 A. At least, that's how I would approach it, assuming 1.0 A is actually needed.

    I don't think there is a need for 1 A of output current in a headphone amp. 5 W into 50 Ω is 450 mA (peak). I'm not concerned that the QRV08 is only able to deliver 120 mA. I am somewhat miffed that it took me less than five minutes to find a spec that the amp doesn't meet. Not only does it not meet spec, it's off by 10x. You don't need fancy equipment to find this spec violation. All you need is a load resistor, signal generator, and AC voltmeter .... or a circuit simulator.

    Tom
     
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  14. Psalmanazar

    Psalmanazar Non Voting Friend

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    I heard @HitmanFluffy's loaner at his place today. This QVC-08 is hot garbage. It is incredibly compressed. All the instruments close to each other in sound manifest as one uniform block of volume. There is no dynamics, there is no extension on either end. There is no grain due to the smoothed chifi rolled sound of cornstarch and high fructose cornsyrup making a sticky sauce for the anime soundtracks for those with chronically low testosterone. This is shit. This amp gets smoked by the Magni 2. This is so underpowered and dead inside, I feel like this is the amplification equivalent of having relations with a half-eaten, refrigerated jar of mayonnaise compared to actual sex with a human being. If I owned this amp I would take it down to the range and blow it up with grenades as practice for when the Chinese invade the American heartland of Varginia.
     
    Last edited: Dec 12, 2016
  15. OJneg

    OJneg The Most Insufferable

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    There's a reason 3 senior pirates deferred from publicly commenting on this so called "amplifier" that is supposed to produce "music" ;););)
     
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  16. BMF Flyer

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    I finished my QRV-08, today. I don't know about what others are hearing but my ears are happy. I like this amp and it sounds good with HD-650, as well as some orthos.

    Like fishski13, I spent a lot of time verifying measurements of each component before and after installing them. This saved me from a world of pain trying to troubleshoot after the fact. I found 3 or 4 errors "in the moment."

    fishski13's BOM guide was a Real life saver! ...thanks for the help.

    Looks like I need to do some studying about uploading URL photos. I tried to link a photo from my google drive account but it didn't work.

    Right clicking didn't work for me.

    Here's a link to googledrive:
    https://drive.google.com/file/d/0B5ZWXtWdNv9UTTUzaVlsZ2NCU2s/view?usp=sharing

    [​IMG]
     
    Last edited: Dec 31, 2016
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  17. anetode

    anetode Moderator

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    [​IMG]

    You can usually right click on the image to open it in a new tab or get the source. Congrats on the neat clean build!
     
  18. BMF Flyer

    BMF Flyer Acquaintance

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    Thanks for the help...still studying ;-)
     
  19. Armaegis

    Armaegis Friend

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    I'll help ya out...

    [​IMG]

    [​IMG]
     
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  20. anetode

    anetode Moderator

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    Are you f'ing kidding me, my post didn't turn out either. So much for those two computer science courses ten years ago...
     

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