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plaurids

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  • Interests
    Trying to be an audiophile with a tight room and a tight budget...
  • Location
    São Bernardo do Campo
  • Gender
    Male

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  • Occupation
    Adjunct Professor of Mathematics at UFABC
  • Headphones
    Stax Omega SR-007A, Stax Lambda Signature SR-407, Moondrop Blessing 2 IEM + Dunu Blanche cable, AKG K701
  • Headphone Amps
    Stax SRM-T1S
  • Sources
    RME ADI-2 DAC + iFi DC iPurifier + Oyaide Continental USB cable, Ifi Micro iDSD Black Label DAC, Fiio X7II DAP, Sony MDS-JE500 Minidisc Deck
  • Other Audio Gear
    M-Audio ProFire 610, Focusrite Scarlett 2i4 1st gen, RODE NT1 Condenser Mic

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  1. Whoa, I didn't know that, about HeadAmp being around HC... However, as for Mjölnir Audio, I don't remember seeing a Blue Hawaii implementation in the current version of spritzer's catalog...
  2. Thanks for the warning Pars, and sorry to all for the bad link, I'll delete it in my previous post. Using a pair of LSK170's for each channel would mean that pin 4 in each Q1 PCB pin layout (corresponding to the extra "substrate" lead of LSK389GR) is discarded, I suppose.
  3. Yeah, if you look at the picture of my SRM-T1S's internals (before recap and the CCS mod) in the first post of this thread, these are the eight large pink resistors R27-R30 (x2 each) on the upper left. These are 33 kOhm, 2W power rating each according to the schematic, and are the ones replaced by the CCS array if you do JimL's mod. Spares for these from a good brand (e.g. Vishay) and (say) 1% tolerance cost at e.g. Mouser from USD 0.85 to USD 3.58 each (the latter is the low-noise option, if that matters), so we're talking here about USD 7 - USD 29 in parts (plus shipping). As for the front-end FETs, if I understand correctly from the schematic, these are the pair of double N-channel 2SK389GR MOSFET's from Toshiba placed at Q1 for each channel, next to the signal input (more precisely, the volume pot). In this case, according to Mouser these are indeed discontinued, but as Kevin said above it may be possible to find them in stock (probably as NOS) elsewhere nonetheless (edit: or, as Pars suggested below, just replace each 2SK389GR with a pair of LSK170 JFETs - a matched quad costs about USD 30-35). If you ask me, it's worth a shot... maybe trying to replace the plate resistors first (since it's probably cheaper) and from there to these MOSFET's if the problem persists. @grawk silly me... I guess any e-stat must sound fantastic on the BHSE, of course (provided you can afford the latter)... However, HeadAmp doesn't seem to provide the normal bias option to buyers, only color options for the cabinet and two volume pot options. Since they build it on demand after each order is placed, is it possible to request a normal bias as well? (according to spritzer above, it's technically possible, but the point is whether HeadAmp will do it at the buyer's request or not)
  4. No idea. The SR-L407 that came together with my SRM-T1S is the oldest of my two Staxes, and never had any experience with an e-stat older than that.
  5. Your reservation in trying to rebias amp tubes yourself is understandable, especially in the case of e-stat energizers (which use even higher voltages than standard amps), but I assure you it's safe provided you're careful. In the case of the SRM-T1S, you can just adjust the voltmeter range, stick the voltmeter probes into the earspeaker pin sockets appropriate to the measurement to be made (that's the easiest and safest way) and turn the voltmeter on. This can be done with the energizer turned on without any problems. Please remember as well to get a fine plastic-tip screwdriver for adjusting the trimpots - I'd avoid getting anything made of metal close to the PCB while the energizer is on - and avoid touching the power supply caps (especially the four big ones). Finally, bear in mind that the trimpot adjustments for the SRM-T1S are usually tiny and the tubes in this circuit usually do drift quite a bit after the first rebiasing sessions. If even so you feel insecure about doing it yourself, you can ask a technician to do it.
  6. Hi sc351cobra, what spritzer meant is that you probably need to check the bias of the tubes since you've changed them - offset and balance are the adjustments to look at (by probing adequate pairs of output pins with a voltmeter) when doing that, and they're adjusted through a pair of trimpots for each channel. These are tiny and are best (and most safely) accessed using a plastic-tip screwdriver. A nice set of instructions for rebiasing the tubes on the SRM-T1(S) can be found here and here. In my case, last time the bias of the tubes was off, 3-4 rebiasing sessions with 1-hour intervals to account for tube drift was enough to get stable adjustments, but that may change depending on the tubes you're using and their age. The important part is to get stable measurements as close to zero volts as possible (at worst within a 15-volt interval around zero) without too many attempts - if it's taking too long to reach that, then the tubes have probably reached EOL and should be replaced. According to the SRM-T1S's manual, possible sources of distortion are too high a volume adjustment and a voltage drop in the power supply. However, both of these should affect both channels equally (supposing you are changing volume of both channels simultaneously at the same rate, as usual - the SRM-T1S's volume knob allows the user to change them separately, and I don't know how you're proceeding with that). Even if the power supply caps need replacement (which is something it's generally recommended to do about every 10 years or so), a bad power supply cap should also affect both channels equally if you are using a pair of good tubes with the same brand and age (preferably a matched pair for easier rebiasing). The fact that you are only getting distortion on one channel and the former gradually disappears as the power supply caps discharge after turning the unit off is really odd indeed. The problem I had above when doing the CCS mod shows that if there is a short circuit somewhere on the PCB by any reason then there may be some unreasonably high voltages on just one of the channels, which on their turn will cause distortion and may shorten the life of the tube on the said channel. If that's the case, it'll definitely show up in the bias measurements as unreasonably large voltage swings as you adjust the bias trimpots (e.g. well above 15 volts with even the slightest turn of an offset trimpot), and then you'll have to look for that on the signal path through the PCB. I wouldn't exclude it since you bought your unit used, but I think a bad tube is more likely. In any case, checking and trying to adjust the tube bias is the first step. If your problem doesn't disappear after rebiasing (supposing the latter is successful), then I'm out of ideas (unfortunately, my knowledge and experience with electronics are quite limited as well - I'm trying to help based on what I've learned so far). Hopefully, more seasoned people on the matter (like spritzer) may know better and provide a more educated answer if that's the case. Hope it helped.
  7. I see, thanks. Enough off-topicking, I suppose... Back to the CRBN: which DACs have you used with it besides the Denafrips Terminator, and which were your impressions with those (if any)?
  8. Also my impression. My SZ2 007A had this odd "boom" in the bass and a depressed response in the upper mids at stock config, problems which were both fixed with the port mod. Anyhow, the 007 is pretty hard to find here in Brazil - Edifier (who currently owns Stax) started selling Stax products officially here this year, but their prices are just insane and they haven't brought the whole Stax lineup yet (they are selling the 009S and some Lambdas). Particularly, no 007's are being sold (edit - November 11th 2021: I stand corrected - they've just started selling the SR-007 Mk II). I found mine used by chance at a great price, in retrospect it was a minor miracle. Unfortunately, it also means that I cannot just sell it and look for a better set - Brazilian custom taxes are no joke and the current USD-BRL exchange rate is not quite favorable right now, both of with make buying even an used 007 abroad beyond my current means -, so I have to make the best out of what I have. That's why I'm modding the hell out of my 007A and my SRM-T1S. With the port mod, how much up your list do they go?
  9. Ah, ok. Now, going back to my original question (duly qualified)... where would the first batch (production year 2007-2009) of SZ2 Stax SR-007A's fit in your top 5 list (if at all, possibly with the port mod)?
  10. That's what I thought, judging from my research in these forums... But maybe I wasn't clear enough in my question: which of the two SZ2 batches of SR-007A's are affected by this "bad behavior" (I do know there is an SZ3 range of serial numbers in between), and what would that "bad behavior" be? Does the port mod help? Thanks!
  11. I understand people complain particularly about its soundstage, which is indeed not very deep, but I like it - I use it connected via XLR (balanced) to my SRM-T1S. With the SR-007A it feels very intimate, as if I were standing where the microphones are. It also serves as a very good IEM source (it works great with my Moondrop Blessing 2 using Spinfit eartips and Dunu Blanche cable) when for some reason I cannot use the SR-007A (e.g. when my hair is wet). I was able to get some (admittedly minor) improvements using iFi's DC iPurifier to clean the power source and the Oyaide Continental USB cable instead of stock. I haven't tried its parametric EQ yet - haven't felt the need for it. I may get the Denafrips Ares II or the Chord Qutest in addition to the RME ADI-2 DAC in the future to get a different flavor of DAC. Wondering how these would sound with the CRBN...
  12. "Bad behavior" for which SZ2's, the old ones or the new ones? Mine's (for instance) serial number is SZ2-1636, got it used in the beginning of this year. Seller didn't buy it new either - I had to replace the headpad's elastic band since it was worn out, otherwise the unit is in fine shape. I reckon it's not very recent, but I may be mistaken... I did the port mod because the stock frequency response was somewhat wonky (bass a bit out of control, depressed upper mids), but that was before I did the CCS mod on my energizer. I've covered the Blu-tac filling the driver ports with a fine tape because it was sticking to the pads. The port mod evened out the frequency response and made the cans quite a bit more enjoyable.
  13. If you port mod an SZ2-serial number SR-007A (say), where would it fit on that list? 😁 Also, thanks for the feedback on the ECC99! Regarding sources... Have you tried it with the RME ADI-2 DAC?
  14. Good to know... Would adding ECC99 tubes to a CCS-modified Stax SRM-T1(S) (say) improve things with the CRBN at higher volumes?
  15. For the glue on the Audezes, I guess so (never had one). Isopropyl alcohol doesn't work so well on the earpad adhesive for the Stax Lambdas, though. Believe me, I tried. However, since the casing is all plastic and the earpad gluing base is so close to the drivers, it's not advisable to use anything else, so one has to make do with it anyway. A lot of patience and care is needed to remove the black gooey, tar-like glue residues without touching the drivers - the former just seem to stick everywhere on the outer case.
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