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justin

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Posts posted by justin

  4. unbalanced/balanced to balanced tube input

    in Do It Yourself

    Posted · Edited by justin

    On 8/16/2023 at 1:15 PM, Satyrnine said:

    Oh hey, something I can answer! I'd give it a 6-7. My electronics experience is mainly with HV tube gear. I'm a repair tech and do custom builds, so lots of experience there. While Alum Oxide definitely IS better, we're only talking about 100v here, I don't think mica will give you any trouble. Be smart with thermal paste, as some types CAN be conductive and can cause a "bridge" if you're too generous with it. I've seen far worse than mica insulating 500+V successfully, but you should be OK. It's typically 600V insulation per mil of thickness. 

    I just realized, while working on a hand-drilled prototype, how much more likely it is for this type of thing to be problematic for a one-off or a DIY project that doesn't have CNC machined holes, pre-calculated lead bends, and things that result in the transistor lining up perfectly with the hole. Even many hand drilled/DIY projects where the transistor 'lines up' there may be force required to get it in place, a screw head going in at an angle - due to placement of the transistor, the hole drilled at an angle or both...all recipes for issues with insulators

  10. goldenreference low voltage power supply

    in Do It Yourself

    Posted

    On 3/3/2019 at 8:56 AM, kevin gilmore said:

    someone needs to check this, works as single rectifier with center tapped transformer, or a pair with dual secondaries. Up to 72vdc, perfect for GRLV

    caps are 100v rated, 1uf is 0805 size, 10uf is 2220 size

    I can certainly do a bigger version with different fets for higher currents and lower voltages. .9 x 1.1 inches

     

    syncrectifier.jpg

     

    syncrectifier.zip

    I ordered some panels of these. I’ll send a free panel if anyone is willing to build/test one once they receive it

    IMG_1344.jpeg

  15. and now for something completely different part 3

    in Do It Yourself

    Posted · Edited by justin

    38 minutes ago, bdinnev said:

    OK, a bit more testing. The previous tests I did were all with the SS jumpers in place. I have taken them off and jumped all the ZF jumpers and get some different results. 

    In ZF mode, on the board that was reading -2.5v the DC offset comes down considerably - 145mv and -81mv @ ~150mA bias. 

     

    On the other board that was measuring -500mv it still measures the same in ZF mode, however I need to adjust the 5k trim-pots a fair amount to get back to ~150mA bias - I think I saw a post a few pages back with a similar situation so will go back and read the thread again!

    measure the DC voltage to ground at every node in the circuit, and write it down on the schematic, will be very helpful

    also do you have pF caps across the feedback resistor in SS Mode?

    • Like 1

  20. kgst

    in Do It Yourself

    Posted

    On 8/9/2022 at 3:08 AM, simmconn said:

    I took the challenge again to squeeze a DIY eStat amp into a small enclosure. This time is a KGST in a Breeze Audio 2409.

    1247746267_IMG_2111(799x1024).thumb.jpg.3f328f579b57f79e7e64e67e807404d0.jpg

    I was using an Antek AS-1T350 with a separate low-profile quasi-toriod for the LV supply. The Antek was well shielded with both copper and steel bands under the wrapping, I still need to move it all the way back to reduce the hum. I'm glad I pulled the trigger and ordered the custom R-core transformer. I asked the vendor to build two identical bobbins to balance the flux, each with a 115V primary, a 350V, a 17V and a 6.3V secondaries. With the copper band on the outside, the flux leakage is so low that I couldn't pick up anything significant at 60Hz or 120Hz on the FFT.

    I have more than twenty 6S4 and 6S4As, many of which are NOS. However I had a hard time matching a second pair, and had to decide between a well matched pair that is slight noisy and one that's less well matched. The curves look all similar below 400V, but could go all over the place on the higher voltage region. The below picture is kind of an extreme case, an example that two tubes both testing good on a tube tester at 150V on the plate, may be quite different when you need them to swing up to 800V:

    1430607758_IMG_2099(1024x792).thumb.jpg.f313df42d3cf147cd3ba376dd0b68d80.jpg

    <To be continued..>

    This may not happen again..here is a never opened box of Philips ECG 6S4A tubes, USA made, delivered to a defense depot in utah (dry climate!) in 1983

    very curious to see how they match

    think the box is actually full of tubes?

    IMG_0842.jpeg

    • Like 1

  21. The ultimate DIY? A Stax SRM-T2!

    in Do It Yourself

    Posted · Edited by justin

    31 minutes ago, simmconn said:

    Hmm, I wonder what kind of noise and hum level would be when you connect like that. Unless your source is true balanced pro gear with transformer-isolated output, most DACs and preamps have ground-referenced output stage. In other word, the +/- are not using each other as the return path, but pin 1 in that XLR cable. Once you include the PE connection and the signal ground connection in your common-mode return path, noise and hum inevitably gets included in the signal coming to the amp. Remember any amp has a finite common-mode rejection.
    However the theory says, I guess at the end of the day, whatever works best in my/your system matters the most.

    I usually buy the XLR jacks with separate Pin 1 and chassis connection and then can test it with jumpers on the input board. Nelson Pass said he connects pin 1 to audio ground, though it was 15+ years ago he posted it on diyaudio. I think also people who are using XLR/RCA adapters are under the assumption Pin 1 is ground

    I can connect Pin 1 to chassis only but unless something has changed in 15 years, my experience has been that customers report fewer issues when it's connected to audio ground.

    • Like 1

  22. The ultimate DIY? A Stax SRM-T2!

    in Do It Yourself

    Posted

    20 hours ago, audiostar said:

    Exactly as I wrote above. Meanwhile Kevin uses a 10R resistor between circuit ground and PE ground (like on newer GRLVs), same as Krell. Nelson Pass uses a thermistor and the IEC recommends a real ground break circuit consisting of a HF power cap, power resistor and a rectifier (inverse parallel coupled power diodes). The idea is that this network must survive longer that it takes the mains fuse to rupture and for the arc to extinguish. This is also described on Rod Elliott pages in more detail. 

    The essence thing is to connect both PE and circuit grounds in the PSU box only at the star point and have both grounds run separately to the amp's chassis.

    Regarding pin 1 grounding which in this context plays a role as well and was asked above, here is a pic. It goes to the amps chassis and then to the PSU chassis (remember separated chassis ground wire run) and then to PE and is (in a differential amp setup) used with metal chassis basically for shielding only. 
    In order to satisfy the various environments and wildly used grounding schemes and avoid loops, there is a new series of expensive Neutrik EMC XLR connectors using a cap between the connector's shell and pin 1. Here is a good read up on this.

    The right way to use Pin1.jpg

    some of the quietest gear ends up accidentally built by people putting ground or chassis connections wherever they feel like it, even places they don't know about

    btw almost all of the audiophile type gear I've ever seen is connecting Pin 1 directly to an audio ground plane. In some cases this is even bypassing the ground break circuit

    • Like 1
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