The "Are You Serious" Thread

Discussion in 'DIY (Do-It-Yourself) Discussions' started by DutchGFX, May 25, 2017.

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  1. DutchGFX
    After recently being asked to design a PCB to replicate the Jolida JD9, which sells for upwards of $500, I couldn't believe the scheme they had going. I figured it would be funny to post schematics or details of commercial products that are quite simple and are wildly overpriced compared to building your own. Of course some R&D goes into all of these, but still, are you serious???

    I'll start us off with the Jolida. It's just a cascode with a simple regulated supply

    [​IMG]
     
  2. HiGHFLYiN9
    $900 actually, and I've seen a number of hum complaints. Not much going on in that chassis :wink:

    [​IMG]

    The Gaincard and Grado RA-1 come to the top of my mind...
     
    Last edited: May 25, 2017
  3. rellik
    No prob Sahib, I think you are confusing Cascode with triode. Secondly, you are missing the input tube stage from the schematic...so alot more going on to discuss...

    BTW, whats the problem with cascode. Its hard to create a stable current for driver stage transistors. An input from a source has plenty of current but cannot correctly drive output transistors due to its distance from the driver stage. This creates a delay and increased resistance for the driver input stage.

    Especially if using bipolar transistors, their lower input impedance will create RLC high and low pass filters. Also to get the correct gain factor, some kind of voltage drop has to occur. The typical gain or beta factor for a transistor can be between 25 and 80. NPN and PNP from a bipolar series often do not have the same gain. Thus the need to create a dc offset to the drive stage signal.

    This could be accomplished using a resistor divider and a diode gate to sum in a bias voltage. The problem would still be the slew rate of the source before and after this voltage division.

    An opamp could be used but would be a non discrete stage. To get the slew rate necessary to drive a output stage transistor, you would need a bunch in paralell to support the Igd current. Opamps slow down when loaded beyond their limits but still operate ala cmoy.

    Back to the Jolida, Triode uses an input grid next to the supply rail (B+) cathode. This input gain and bias is set by the input driver stage. As the gain of tubes is similar, they can use one supply rail vs transistors dual rail plus can burn off dc offset and not worry about imbalanced current draw. The Second grid can be set to a bias voltage to help settle the grid to the anode. The filament also helps to settle the input grid to the anode.

    Pentode ties both grids to the same bias voltage and relies more on the filament to pull cathode to anode. The input is applied to one of the grids and can be seperated from the other bias grid with RLC network to define the amount of pentode.

    Basically a higher bias voltage will allow the tube to produce more gain (power) by limiting the voltage swing or "slew rate". Adding an additional bias grid will increase power but will shorten tube life due to increased material migration. More power will also make a tube become microphonic, reducing the voltage swing will limit how fast a tube becomes microphonic.

    Good sturdy tubes overdriven will often just hot spot in a circular fashion or whatever the speaker shape is. This is due to a lack of ion donor material in that location.

    I think you are confusing the discrete transistor voltage reg as cascode. This allows for less B+ caps to be used. This allows the amp to let the recorded music define the note rather than the playback location define a "downmixed" version of the note.

    This is the major reason to master music so that a strange rig can be meaningfully played back on a "standardized system". The "primarily" saturation makes the diff between a B movie or music and pro grade. AKA less of that feel of metallic taste after coming down from Crack/Cocaine and or LSD. Also microphones are wayy more sensitive than human hearing. People like to stare at their systems and not look for non existant components. All my components actually play music regardless of if they are speaker or not.
     
    Last edited: May 25, 2017
  4. DutchGFX

    I didn't design the Jolida, I'm just pointing out that it's JUST one stage, that's it. Of course there are numerous improvements that could be made, that's the point lol.
     
  5. DutchGFX
    Is that the actual inside of a Jolida? That's a scheme and a half haha. My PCB, which hopefully works lol, has all the parts for both PSU and both channels, and is just 3.5" x 4". I'll fit the whole thing in a cigar box! I'm building it for a friend so hopefully I can get rid of the hum: worst comes to worst i'll move the PSU to a separate board.
    ---------------------------------------------------------------------------------------
    If this is the actual RA-1 schematic, this is about as simple as it can possibly get. It's just a non-inverting opamp stage. I have a friend who is buddies with John Grado, so I feel kind of bad, but come on bro...
    [​IMG]
     
  6. rellik
    The preamp in HighFlyin's photo is a vintage McIntosh.

    Yes, I do also believe in 5 degrees of seperation. Most often, I just, you know am there.

    EDIT: Also, I would suggest against speaking ill of the dead. If you dont like it, I suggest you remove it.

    If you relax, things will be easier. Buy a massage couch and a force feedback automotive gaming system or something...
     
    Last edited: May 25, 2017
  7. Arty McGhee
    Grado RA1
    $25.00 kit from aliexpress
    3d printed case, sounds pretty good but
    are you serious

    001.jpg 002.jpg
     
  8. rellik
    I wonder what the input resistance is on those big red caps not series resistance but input resistance. Wow.
     
    Last edited: May 25, 2017
  9. DutchGFX
    For real, those caps def cost most than the rest combined. It is kinda nice that the pot and jacks and such all fit onto the board tho. But for real, that's like, intro to EE problem #1, no capacitors in the gain stage, just a coupling cap
     
    Delayeed likes this.
  10. rellik
    YEah, must be some pretty freggin serious source or preamp for that rig.
     
  11. kevin gilmore
    that does not look like any McIntosh I have ever seen, and I have seen and worked on every single tube McIntosh preamp ever made.
     
    DutchGFX likes this.
  12. rellik
    My understanding was that it was modded. The old tubes were prob replaced explaining the aformentioned confusion.

    BTW, Ive got one of your kit boards. Would you happen to have any remaining stock of the dynahi and its psu. Ive still got spare common substrate toshibas for the gain/dc offset circuit.
     
    Last edited: May 27, 2017
  13. HiGHFLYiN9
    Here's the front, it's the JD9 mentioned in the first post. This one was modded with some Auricaps.

    [​IMG]


    Tuibe-based McIntosh amps and pre-amps from the golden age of audio (early to mid 1960s, when Dynaco and H.H. Scott were also going strong) typically have brown turret boards with the parts lined up as such. May look like a rat's nest based on what we are used to today, but there is nothing like a vintage McIntosh.

    [​IMG]
     
    Last edited: May 27, 2017
  14. rellik
    Whoops, sorry. The transformer had me convinced it was a McIntosh.

    Must just be a British transformer...

    This coming from the man in the Titanium grey house. Yeah, the whole house is mostly Titanium. The patio lamps are Tungsten. I prefer JJ caps/Blackgates/Mundorfs and so do most audiophiles. BHC Aerovox are cool but require a bit of training and cajoling.

    The recent Audio Note Kaisei are cool also, using a California paper divider.
     
    Last edited: May 27, 2017
  15. HiGHFLYiN9
    Audiofiler caps are actually a heck of a bargain... great for power supply bypass caps. JRB @TubeCAD/Glassware uses them in a lot of his BoMs. I think the 4.7uFs you'd use in a Grado RA-1 clone would be about $2 each. Partsexpress and TubesandMore have them. Cheaper than Solens.
     

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