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DIY amp and pre recommendations (probably DiyAudio/Pass)

Discussion in 'd.i.y.' started by booja30, Feb 17, 2020.

  1. davidjt

    davidjt pfm Member

    There are several (six?) links on the diyAudio psu board - more than enough, so the (insulated) guage you are using for the rest of your power wiring will be fine. The photos just show what that builder happened to have available.

    The store sells Keratherm insulators, but they are pricey and an unnoticed burr on the heatsink has been known to puncture them, causing a short. Some MOSFETs survived this.....The ceramic version from AliExpress with a dab of heatsink compound works for me.

    Most of the BoMs on diyA include Mouser and/or Digikey part numbers in the final column. Substituting parts that are out of stock is a pita, but carefully matching specs will ensure that everything works and fits the pcb.

    A soldering station is useful - minimum heat for sensitive components and more for the psu groundplane, big caps and hardware (although different bits with a 15W and a 25W iron would suffice - a decent station is just easier. Don't go for the cheapest chinese version as bits last about ten minutes and are unobtainable.) For cleaning the tips a metal pot scourer works better for me than the little damp sponge.

    A variac is overkill - search diyA or youTube for the 'old school' lightbulb test set-up. I keep meaning to put one together myself.

    A couple of digital multimeters with croc-clip leads make testing and bias-setting easier, as do a pcb-holder and/or a 'hands-free' device. Some non-essentials just make things simpler. (For the M2 a nut-spinner is a necessity - trying to use pliers on the daughter-boards is a mug's game. Trust me.)

    Final tip: All resistors get hot and 'power' resistors very hot: when mounting any 1-3W resistor use a matchstick or similar to raise it off the board surface while soldering. Mount rectifier diodes the same way or higher. Don't ask me how much difference this makes but peace of mind is always worth having.
    booja30 likes this.
  2. booja30

    booja30 pfm Member

    @davidjt, thanks for all the info!

    I can definitely make the light bulb setup so I'll give that a shot (finding the incandescent bulbs may be the challenging part!).

    I have a decent multimeter with multiple lead types (probe, gator, hook) so that's done.

    I enjoy designing and 3D printing things including tools/jigs so I'll probably end up making a little tool for bending resistor leads and maybe a PCB holder.
  3. booja30

    booja30 pfm Member

    Our trip across northern Spain has been cut short so I'm getting ready to order some boards/cases/parts (yay).

    The BOMs pretty well cover the items needed to populate the various boards (F5, PSU, soft start, speaker protection) but I haven't found a good source of info for selecting wire for connecting things up. I'm planning to use a mix of blade connectors, pcb terminal blocks, etc.

    What gauge/type is recommended, for example, for connecting the PSU boards to the amp boards? Amp boards to speaker out? Phono inputs to amp boards? This seems to be a gap in the available information, or its hidden well in the 100s of pages of build threads on DiyAudio.
  4. CarrotMan

    CarrotMan pfm Member

    The probably because it is a bit of a mine-field of subjective opinions :D FWIW, what I normally use is:

    - Signal wiring: 22-24 awg silver-plated copper with teflon insulation. Not so much because of the silver, but mostly because the teflon insulation withstands soldering much better than PVC.
    - Loudspeaker wiring: 1.0 - 1.5 mm2 copper or silver-plated copper. Again, silver might give you a nice audiophile feeling in you soul, but actually I am more focused on PFTE insulation because it withstands heat.
    - Power wiring: 0.5 - 1.5 mm copper depending on current levels, usually "regular" installation-type wire with PVC installation. Flexible silicone insulation is easier to work with though and it's more heat resistant for soldering, but I tend to not solder power connections and use terminals/connectors instead.

    As a rule of thumb I try to only have one soldered connection per wire so that disassembly becomes easier. That normally means a screw-terminal, crimp-terminal or spade connector on the board and then a soldered connection on the terminal side. If that's not possible that's fine, but some swearing normally ensues when trying to test something and/or disassembling it to fix problems :)
    booja30 likes this.
  5. booja30

    booja30 pfm Member

    Perfect, thanks so much for taking the time to write that up. I think I will go for Teflon/silicone as much as possible to have more forgiveness. And I'll probably be buying redundant connector types while I'm at it to see what works best for my build.

    I'm on an 8 hour train ride at the moment so I've got lots of time to put together shopping carts.

  6. davidjt

    davidjt pfm Member

    When you get to the preamp, my favorite at the moment is the 'Whammy', although (whisper) I've just done a lash-up of the Korg Nu-tube on the bench and that sounds pretty good, too. :)
    brumjam and booja30 like this.
  7. Marra

    Marra pfm Member

    Don't let Jezz hear you saying that.
  8. sq225917

    sq225917 Bit of this, bit of that

    I might remember this wrong but I'm sure back in the day Nelson said the nutube wasnt hifi and that hed just build the pre for shits and giggles and make it available.

    If you want a low noise, low distortion pre build the putzeys balanced pre
  9. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    That's how I see it yes. He wanted to offer a pre using this device, as a novelty, a "first", in spite of it being the worst valve ever made.
    The worst triode valve available from China, after being left on for 3 years, would still completely thrash the "Nutube" in every way!
  10. sq225917

    sq225917 Bit of this, bit of that

    Yeh, I'm sure that was what he said, 'novelty' sums it up nicely
  11. booja30

    booja30 pfm Member

    I already posted a new thread about my F5 build that's been done for a week or two now.

    My next step is to build a preamp, and I''ve decided to wait for the next group buy of the Salas DCG3/DCSTB boards. I was going to do a Mezmerize B1 but there's no gain (may or may not be an issue with my setup), but even worse, it requires 10 JFETs (4 matched), and DiyAudioStore said I would just need to buy 2 matched quads and a matched pair, which would be $90! So, yeah, I'm waiting for the DCG3.

    But in the mean time, I am looking for something else to build and I'm considering the M2X since it looks fun, and since some of you already recommended the M2. I was also considering F6, F4, Aleph J, etc. but the M2X seems to offer the most tinkering for your buck. I'll add more info as I make progress.

    Thanks again everyone for the recommendations!
  12. sq225917

    sq225917 Bit of this, bit of that

    What fets and what idss range?
  13. booja30

    booja30 pfm Member

    The originals were Toshiba JFETs, which are long gone and extremely rare, but the modern remakes are Linear Systems LSK170. The 4 signal path ones are grade B (IDSS 6.0-12.0) and matched to +/-0.1mA. The 6 power supply ones are the same part but have no matching requirement. But DiyAudioStore only sells matched sets (I even asked and they said to just buy all matched sets).

    Anyway, I don't want to waste a prescious commodity on a project that might not even be a good fit for my system, so I'm waiting for the DCG3.

    I am a little suspicious of the parts I bought for my F5 though. DiyAudioStore sells parts kits for the F5 which is what I used, along with their matched JFETs and MOSFETs. The build guide said I should be able to achieve 0mV on the speaker output while having nearly identical voltages on the big resistors (e.g. +550mV and -550mV). On one channel I got close -- 0mV at the output with +551mV and -549mV. But on the other channel it was more like +558mV and -542mV. I checked the output resistors and they were all very close, so who knows what other component accounts for this. I got mixed opinions on whether this was worth chasing down. But if I do wind up with another set of JFETs (e.g. for M2X build) I might try swapping some of these and re-biasing the amp to see if they affect the voltage spreads.

    It's a lot of fiddling about but I have plenty of time right now.
  14. sq225917

    sq225917 Bit of this, bit of that

    I have a bunch of genuine toshiba 2sk170 bl grade, about 30 in total, I should have no problem matching a quad out of them at 0.1mv. Let me know.
  15. booja30

    booja30 pfm Member

    That's a very generous offer, but you should really be selling them for $$$$ (or ££££) on DiyAudio forums! :)

    I still don't think I'm going to build the Mezmerize B1 because I might be disappointed with not having enough volume, and it's kind of wasteful using 10 of these rare JFETs!

    My F5 build uses a 'matched quad' of 2x LSK170 and 2x LSJ74 (both B grade, so equivalent to Toshiba Bl). I don't know how the matching works in that case. Are the 170s matched to each other (and likewise 74s)? Or is are 170s matched to 74s? Forgive my lack of knowledge -- I am reading up more on audio circuits and components after the fact...

    If you have stockpiles of LSK170s and LSJ74 equivalents I'd love to buy some of them from you. If I build a M2X with the Ishikawa buffer daughter board (the original) it would be awesome to try the JFETs it was intended for. The M2X has multiple buffer daughter boards and IIUC the Ishikawa is the 'favorite' but the beloved Toshiba JFETs supplies dried up.
  16. sq225917

    sq225917 Bit of this, bit of that

    I only have 2sk170, bought for for paradise phonostage builds. Though I do know a certain cantankerous geordie with original j74s...

    2sk170 are still out there in small numbers, ignore all chinese sellers and the 9 out of 10 of those that remain that look like wronguns and it's possible to hit lucky. I got this batch from france at about £4 each.
  17. 337alant

    337alant Negatively Biased

    I have just started building the Salas DCSTB/DCG3 boards, finished the power supply and it works fine 17.14V from both channels
    Will continue with the DCG3 tomorrow if I get time ?
    I have ordered 2 x 18-0-18V transformers and the transistors will be bolted to the right hand heat sink

    [​IMG]IMG_2952 by Alan Towell, on Flickr

    laverda and booja30 like this.
  18. Yank

    Yank Bulbous Also Tapered

    There's always the Arkless valve line preamp:

  19. Chops54

    Chops54 pfm Member

    +1 for the Arkless valve phono stage.
  20. Yank

    Yank Bulbous Also Tapered

    There's a published phono stage too? I missed that one.

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