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mwl168

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Posts posted by mwl168

  5. Technical Assistance/Advice Thread

    in Do It Yourself

    Posted · Edited by mwl168

    Thanks MLA and Kevin for your help.

    I got the player up and running yesterday first using the variac to slowly ramp-up. Later tested it without the variac and, fingers crossed, it's working fine so far. 

    The device in question is a Marantz SA-1 SACD/CD player which uses linear power supply based on what I can see in the service manual. 

    To expand on a long story made short, it powered up but was unresponsive when I first took it out of the box. After consulting with the service manual I dissembled the unit and found a blown fuse inside. Instead of the factory spec'ed 1A/250V slow-blow fuse, whoever last serviced the unit put in a fast-blow 2A/250V fuse. Which likely explains why it's blown upon turn-on. I replaced it with a proper slow-blow 1A/250V fuse. This is when I posted my question thinking I should play it safe given the age of the unit and suspecting why the last person serviced it put in an out-of-spec fuse.

    By the way, this thing is beautifully built like a tank and getting to the fuses take some work. A few photos from the web and of the exact unit.  

    It's wonderful sounding especially with the SACD.

     

     

    sa-1(2).jpeg

    SA-1 internal.JPG

    SA-1 internal 2.JPG

    sa-1.jpeg

    • Like 4

  6. Technical Assistance/Advice Thread

    in Do It Yourself

    Posted · Edited by mwl168

    Need advice about safely powering up an all-transistor CD player that has not been powered up for many years. .

    I have a Marantz SACD/CD player that has been sitting in its box for many years. Is it a good idea to use my variac, like the one in the picture below.  to gradually power it up? 

    If so, what's the proper process? 

    Thanks in advance.

     

     

     

     

    Screenshot 2023-11-27 at 2.57.25 PM.png

  11. and now for something completely different part 3

    in Do It Yourself

    Posted

    16 hours ago, Satyrnine said:

    Swapped all 15030/31’s and the bias issue is solved! Behaving nicely. I tested all the removed transistors with a cheap ebay tester and none tested “bad” but I realize thats a limited test. Thanks for the help all. I can finally try this beast in balanced mode!

    Still waiting on tube input boards from Dukei who had spares. Also need to wrap up dc connector details and order chassis yet. 

    Assuming all the removed transistors are indeed all good, this leads me to wonder if the original issue was caused by cold-soldering?

  12. i'm on a roll... the kgsshv

    in Do It Yourself

    Posted

    Nothing seems out of ordinary to me based on your description. If the offset trim pots are responding but you cannot get the offset to 0V, most likely you just need to trim the value of the resistors in series with the trim pots. 

    I am going by memory without seeing the schematic but this information is in this thread somewhere.
     

    • Thanks 1

  18. KGSSHV Carbon Build Thread

    in Do It Yourself

    Posted

    So I did indeed install 150K and 200K chain for the bias resistors of the C2M1000170D when I first built my Carbon.

    Today I replaced the 200K with a 150K, I had also dialed the bias back to 18mA and disengaged the servo. Then took a few measurements  after letting the amp warmed up. Now the PZTA42 Vce is around 13.7V, voltage drop of the 20K R is 25.4V and the Vgs of the C2M1000170D is around 3.3V. 

    And I did not blow up the amp. 

    • Like 4

  20. KGSSHV Carbon Build Thread

    in Do It Yourself

    Posted

    Thanks MLA. That was what I was thinking too. Then I don't understand why Simmconn was worried about exceeding the C2M1000170D's max Vgs rating?

    Here is an interesting thing - I went back to my PM's and could not find anything that discussed this mod to the 175K+175K bias resistor chain. However, I came across an early correspondent with Kevin about my plan to use 200K+150K instead (values I  had on hand at the time). Now I wonder if the one that looks like a 100K may be in fact a 200K. It's hard to tell visually. 

    I can desolder the resistor in question and measure it. But part of me, the lazy part, is thinking if all is well why not leave it along? Maybe between the +/- 406VDC rails and the 20mA bias current somehow puts the PZTA42 Vce in the desired region?    

  21. KGSSHV Carbon Build Thread

    in Do It Yourself

    Posted

    On 3/24/2022 at 7:08 PM, simmconn said:

     

    On 3/22/2022 at 3:41 PM, simmconn said:

    In a previous post I mentioned the less-than-ideal performance when Carbon is powered by a ±400V supply, and I suspected that the lower Vce on the PZTA42 is the culprit. Now it's been proven. The PZTA42 being a high voltage transistor, has a non-linear region at low Vce, as the slanted curves you can see on the upper left side. With 407V on the negative rail, the transistors on my board works at Vce=8.4V and Ic=20mA, right around the knee. The global negative feedback would have a hard time correcting that non-linearity. It also explains why some people prefer setting the Carbon at a lower current when powered with ±400V supply, as it also improves the linearity of the PZTA42, albeit to a lesser degree.

    PZTA42_annotated.thumb.jpg.c5907f341f31fd69bd85d8a0428b8c68.jpg

    I guess Kevin chose the high voltage PZTA42 to deal with the power-on transients. I have a quick and dirty fix. Just bias the SiC MOSFET a little higher to give the PZTA42 more headroom. The SiC MOSFETs are biased by two 175k and an 20k at the gate. Reducing either 175k or increasing the 20k would do. The goal is to move the PZTA42 operating point to the right, well into the constant-current region (parallel lines).  I would use Vce=14 to 15V. Pushing it even higher would increase the power dissipation on the PZTA42, eat into the max output voltage swing and have diminishing return. What I did was to put a 260k resistor in parallel with one of the 175k resistors. YMMV because it has to do with the operating point of the PZTA42 in your circuit, the Vgs(th) of your SiC MOSFET, etc.

    After the quick fix, one of the channels now measures as good as with the ±450V supply. We can see that the max output voltage is slightly less compared to with ±450V supply. The difference is subtle with the log scale, though.

    259404259_A-A_THDN_VS_AMPL_biasfixed_400V_RCH.PNG.8c0257f1e46b4bc5235ef1a90b123a98.PNG

    Now I'm continue to work on the other channel and see if I can find something else.

     

     

    Today I decided to make this mod to my Carbon I built in 2015 and parallel a resistor to one of the 175K to raise the Vce of the PZTA42. My Carbon is running on +/-406VDC rails and 20mA bias.

    To my surprise, instead of the 175K + 175K bias resistor chain, I had already replaced them with 150K + 100K at some point. As such, I measured Vce  = 10V for PZTA42 and 21.8V drop across the 20K resistor. According to the graph above, this should put the PZTA42 in its linear operating region. Some wise man must have suggested this mod to me (I suspect SorenB) very early on. 

    However, I measured Vgs  of the C2M1000170D to be only 3.2V. Based on how I understand simmconn's posts, I was expecting 20V or higher. What gives?     

     

     

    IMG_0744.jpeg

    • Like 1

  23. KGSSHV Carbon Build Thread

    in Do It Yourself

    Posted

    9 hours ago, Pars said:

    Fired the first board up after rechecking all connections, and wiring the inputs to ground. I'm getting full voltage (806 Vdc) from O+ to O-. Nothing exploded or seems to be getting hot, though I didn't leave it on very long. Both LEDs are lit evenly on the board. All pots were centered when I built it, and other than the current source pots, which I had adjusted using Soren's method to ~17mA, haven't been touched yet. I know I've seen this problem in the thread somewhere, off to find it.

    IIRC, I encountered a similar “issue” when I was adjusting my Blue Hawaii first time I powered it up. As Kevin already said, it turned out my offset pot was way off range. Once I got the offset adjusted to within reasonable range, the balance started to fall in place as well.

    I need to find the schematic but sometimes it’s necessary to change the resistor value that’s in series with the offset pot to be able to adjust the offset to 0V.

    Good luck!

  24. The problem with the Woo Audio 3ES

    in Headphone Amplification

    Posted · Edited by mwl168

    @spritzer: You are correct - re: the two hand-drawn schematic; first one says “3ES pre-amp section”, second one says “3ES electrostatic headphone amp section” on top and “same for 4 channels” at bottom, the script in the rectangle in the schematic says “3ES amp module”.

    According to the OP, the pre-amp section is “ tube-input and tube-output”, headphone amp section is “transistors”.

  25. goldenreference high voltage power supply (GRHV)

    in Do It Yourself

    Posted

    18 hours ago, BadgerMcBadger said:

    that was super helpful, thanks. i bought some ksc5026m off aliexpress but i couldnt find a transistor tester at the electronics store so i bought some BU2508AF as a replacment . if the ksc fail, could there be any harm done to the rest of the circuit?

    I would be very wary of buying hard to get parts from aliexpress. In these high voltage applications, a fake part that breaks down can easily cause catastrophic and expensive failure.

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