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Pars

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Pars last won the day on June 5

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About Pars

  • Birthday 05/16/1954

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  • Location
    Chicago
  • Occupation
    engineer (telecom mktg)
  • Hobbies
    golf, music, cycling
  • Headphones
    Modded Fostex T50RP, Hifiman HE4XX
  • Headphone Amps
    DynaFET, Gilmore dynamic (headamp v2 PCB), Dynahi, SS Dynalo full size
  • Sources
    Rotel RCD-855 modified (clocking, discrete output stage) � Rotel RCD-991 THS4031 I/V, AD8599 buffers
  • Other Audio Gear
    Classe CP50 preamp, Odyssey Stratos poweramp, Von Schweikert VR4 Gen.II speakers

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  1. I think that 10M90S is for the bias voltage. I assume it doesn't get that hot, but don't know the actual reason for the on board heatsink instead of sinking it to the main heatsink/bracket. It does look like there is sufficient board real estate available to have done that instead. EDIT: Kevin beat me to it while typing; go with his explanation.
  2. You could try replacing the opamp. Maybe something is wrong with that servo? Your other headphone amps could very well be ac coupled (cap on the input), so would not be effected by dc offset on the source. Is the dc offset you mention with a DAC connected and powered up? You might take a look at that.
  3. I use JFETs, which to me sound markedly superior to bipolars in the front end. I'm not so sure your problem lies with the front end. Is the scratchiness there noise there without changing volume, etc.? What are you using for a volume pot? Does the source feeding this have any dc offset present? As a dc coupled amp, it will not like that, and will amplify any dc offset present on the input.
  4. In the US, NAC has the LSK389B in the TO71 for $7.12 ea.
  5. The reference voltage of 10V comes from the Linear Technology LT1021DCN8-10#PBF. You normally won't need to measure this unless you have problems with the output voltage. You don't need to worry about transistor or diode matching on these. If you like, use 0.1% low tempco resistors for the R7-R10. You will get acceptable +/- voltage tightness with 1% resistors, particularly if you match those. No. Just use the specified Wimas with the 220uf Panasonic electrolytics and you will be good. Do not buy that cap from Partsconnexion and ignore all the audiophool bullshit. I never test these loaded, and I don't think you need a variac, particularly if you pay attention when building (right part in right place, etc.). I've never used a variac with a GRLV even though I have one. Just make sure you have your desired +/- 20V before connecting an amp board, and you should be fine. DItto.
  6. Happy Birthday!
  7. James, all: Nice writeup BTW. Correct me if I'm wrong, but I believe you can use a dual secondary transformer as a CT simply by tieing the two secondaries together? http://engineering.electrical-equipment.org/wp-content/uploads/2013/07/Dual-Voltage-Transformers-1.jpg All of the GRLVs that I have built use dual secondary transformers and dual bridges, and I don't foresee a reason to use the single bridge for one.
  8. Kevin retired from Northwestern Univ. (the .edu links) a few years ago, so those links are no longer valid. The Stax thread will provide google drive links to the board files and other documents. For a Dynalo, you will want +/-20V for the GRLV. There are BOMs for the GRLV posted in the thread. Sorry, but we don't provide build guides, etc. here. Going thru both the Dynalo and the Golden Reference LV threads should provide you with all you need to know. Build the GRLV first, and test it unloaded to make sure it is performing properly. Pretty easy build. And I would stay out of the and now for something completely different part 3" thread for now. The Dynalo is a very good amp. Not sure what phones you are intending this for, but the CFP 2/3 is a very good amp.
  9. No, they won't work correctly backwards, as it basically flips the N's and P's, and those will be in backwards as well (emitters/collectors). Barring having a "1" marking, the pad for pin 1 should be square vs. round for the others. From what I recall, putting a similar JFET module in backwards resulted in nasty DC offset. I never tried to see if any sound came through or not. The seller of diyaudio of these does provide genuine devices. Also, it should be noted that a similar adapter for dual JFETs (2SJ109/2SK389) will not work for bipolars (SA1349/SC3381) as the pinouts are different, even though they use the same device package. Yours are marked for the bipolars, so should be good. Is the distortion in both channels?
  10. Did you remove or re-install these after bringing the amp out of storage? From your pic above, pin 1 doesn't seem to be clearly marked, so the potential for putting these in backwards is there. Also, have you tried it with the THAT340s?
  11. You could always use something like the Pi2AES that SBAF seems to recommend.
  12. Good NOS (heh) 6922s are probably rare as hell anymore. When I used to have a tube preamp (Counterpoint SA5.1) 10 years ago, I had a pair of Amperex PQ white label 6922s in it, which I really liked. The EH 6922 gold pins are quite good. If you can manage to find some vintage, you will pay out the nose for them, and possibly get ripped off. Some seemingly decent recommendations for dealers here: https://www.thegearpage.net/board/index.php?threads/online-tube-dealer-sticky.1197164/
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