Recent Posts

31

Projects, Designs, and Technical Stuff / Re: Vacuum Fluorescent Display Driver

« Last post by bostonman on Today at 12:45:57 am »

The G lines are equally confusing. This is with a frozen 5MHz (5.0000000000) on the screen.

The data on the analyzer lines that are not labeled weren’t connected. For some reason they are picking up stray signals and showing on the captures.

32

Projects, Designs, and Technical Stuff / Designing a volume & power switch for an old McIntosh Preamp

« Last post by neevo on Today at 12:42:02 am »

Hello everyone! I have over the past few years been restoring a beautiful McIntosh C20 Tube Prepamplifier. These date back to the 1950-60's and are a glorious bit of kit. My restoration is now complete and I had to make a few parts along the way as these things are no longer supported by McIntosh for a lot of items (understandably so given the age). I documented the whole build process for anyone who is interested on a popular Audio forum.

My latest project is to build a replacement volume and power switch as these are known to go bad on a few vintage McIntosh machines and are also no longer supported. There are reproduction parts available which I have in my C20 (and its working fine), but they are supposed to be all over the place in terms of quality... so I am looking to make a better version that also has the option of being rebuildable if required and also tunable to dial it in perfectly.

The original C20 volume potentiometer has 4 wafers (audio) and a rotating switch all in the same assembly:



The repeated use of the switch is what seems to kill these pots, plus the balance between all the 4 wafers is not even that good

My design uses 4 stepped attenuators but where I am getting stuck is the switch mechanism and thats where I need some help:





I am keen to get rid of the mechanical switch if possible as I think I can get more control from a low voltage wiper and activate something like a relay or Triac. I could use a microswitch, but I find them a pain to set the trigger point and given the stepped attenuators ativate in 10 degree increments, I really want to activate the switch on the first 1 or 2 steps. So my thoughts were to use a voltage divider network to trigger a triac, all using the 120v line voltage on the original switch:



When I simulated this, it looked like it would work but I am not 100% sure and keen to have some experts help me understand to make sure its effective + SAFE! Ideally I would like to put this all on a PCB on the end of my design which also would need to allow for the 120v and 35w of power the C20 uses. The simulator showed only 740mv and 70 uA on the switch, which in concept seems like it will work. But I cannot be 100% sure I haven't used the simulator wrong or made some basic errors.

Hoping to get some guidance here.

33

Power/Renewable Energy/EV's / Re: Dual Complementary Rectifier PSU

« Last post by David Hess on Today at 12:38:37 am »

Lets say i need 1.3A from +15V to common 0V, 50mA from -15V to common 0V, and 150mA symmetrical load on+15V/-15V

Just going by my intuition:

1.30/2+0.05/2+0.15=0.65+0.025+0.075=0.75 Amps

However the power factor for a diode-capacitor filter is only about 0.65, so the actual RMS current will be 0.75/0.65=1.15 amps.  This comes about because the capacitor input is only drawing current in pulses during the peaks of the line cycle.

34

Power/Renewable Energy/EV's / Why are all Vicor PI3 modules suddenly out of stock or obsolete?

« Last post by quince on Today at 12:33:37 am »

https://www.digikey.com/en/products/filter/power-management-pmic/voltage-regulators-dc-dc-switching-regulators/739?s=N4IgjCBcoLQdIDGUBmBDANgZwKYBoQB7KAbXDAAYAmEAXQF9Gg

Only 8 of 65 MPNs are available. Over 40 are suddenly obsolete. My company got zero notification of the obsolescence of these modules despite buying thousands from various distributors over the past few years. What happened?

35

Repair / Re: Rigol DP712 Output Shorted; Fuse? / I Screwed Up

« Last post by zanfar on Today at 12:30:09 am »

I had time today to open the power supply. Once open, there was a clear smell of smoke.

The first image is of the battery connection, as requested. The only changes have been to disconnect the positive (red) lead from the power supply and connect the DMM to verify the battery voltage (11.467VDC). The PCB was scavenged from a cheap charger, and the terminals are (from right-to-left in the image): B+/B3+ (Red), B2/B2+ (Green), B1/B1+ (Blue), T1 (White), B-/B1- (Black). If it's not clear, the leads are connected to B+ and B-.
The second image is of the power supply operating in the failed state. Again, the only changes were to disconnect the outputs.

The third image has what I now think is (at least part of) the problem. I assume the goal will be to replace the TO-220 component, which I believe to be a Diodes, Inc. S12M15-600B (https://www.diodes.com/assets/Datasheets/S12M15600B_LS.pdf)

Are there any other places I should double-check? Are there any caveats to desoldering and replacing this part? I am a moderately skilled solderer and have a quality station available.

Thanks again for you time.

36

FPGA / Re: If Lattice iCE40UltraPlus has DDR primitives like ODDR in Xilinx?

« Last post by Shell Albert on Today at 12:29:32 am »

it's a quite brilliant idea, sir.  thanks for your reply.
my colleague, the hardware engineer dude created troubles, haha, but for us, we solve troubles.
if I force DDR SPI working in SDR SPI, I only concern about the data on rising edge, and ignore the falling edge, that needs a little trick. 

37

Projects, Designs, and Technical Stuff / Re: PC74hct4046ap Replacement

« Last post by dj_holmes on Today at 12:27:25 am »

Thank you for the feedback. Its in a very delicate location. Even a 1% improvement could potentially result in 25% better sound. I am already using the best regulator and caps and resistors but I have not altere the design in anyway. Its over 30 years old. Is there nothing that can be tweaked or slot in improvement?

As the description says its 11.2XXMhz which gets spilt into half from the other chip and appears to feedback into the 4060.  My skills are not great but am willing to do some experiementing if theer are any suggestions. Thanks

38

Metrology / Re: ADR1001 - Ovenized Voltage Reference System

« Last post by bastl_r on Today at 12:23:39 am »

Finer lithography 0.18u mentioned change "Analog Devices Beaverton OR, USA (ADBN) as an alternate Wafer Fab site to TSMC" I guess ADI has some token fab ability in America. Maxim was also hit with the acquisition and new stupid business model.

This reminds me of my employer (automotive industry) where the management team consists almost exclusively of business people who believe that everything can be bought in the desired quality at the cheapest prices.
In addition, they overlook the fact that they are continually giving up core competencies that will never come back because the knowledge is gone over time and would have to be bought back at great expense.
Fortunately, I only have just under two years left...
But our children will suffer from these bad decisions!

39

RF, Microwave, Ham Radio / Re: WSJT-X on Pi

« Last post by metrologist on Today at 12:23:25 am »

I started over and installed the 64-bit os and it worked. Also, Logitech headset works so that will be the interface to the old rig. Thanks

40

Projects, Designs, and Technical Stuff / Re: How is a motor run capacitor sized?

« Last post by aroby on Today at 12:21:47 am »

Size is the issue, there's not much space in the housing.  I found it surprising that the capacitors are a) very hard to find and b) extremely expensive, but I guess the two go together.