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FCUPS versions, other info

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Posted on July 14, 2013 at 13:22:23
zarniwoop
Audiophile

Posts: 579
Location: NY
Joined: November 28, 2002
Hey all,

I'm an original diyhifisupply fan since getting an ella kit in 2002! I love the transformation of products over the years into some amazing and well designed stuff. (OT, but my one hesitation is that the current price structure may prevent people starting out, like I was in 2002, from entering this amazing world of tube diy)

I have a first version (stamped 2008) FCUPS module that I am planning to use in a power amp project soon. I have 2 versions of the manual, 1b and the one on the site currently, v2.1. I was just curious what changes were made between the 2 board versions. Were there any problems/issues that were fixed on the second one that I should be aware of? I noticed that the first manual says the max. current w/o external caps is 130mA, and the v2.1 manual says the max is 100mA. Another post here mentions a mosfet being repeatedly damaged, but the cause of this was not made clear. Is there any protection feature from over current/voltage?

I'm also curious about expected output voltages from this unit when using the onboard SS rectification. The manual states that the circuit tracks the "lowest point" in the rectified voltage. Perhaps I should do some reading on these gyrator circuits and it will become clear. Does it behave somewhere between a cap. input and a choke input conventional supply? In the examples section, one circuit has a input of 300VAC and obtains a 365V B+ while another has a 250VAC input and obtains 260V B+. I understand this is related to current draw, but I am unclear what, if any, other parameters I can adjust to compensate.

Just some thoughts before I dive in, there is very little information on people diy'ing with this psu. I will report back here soon with my results for anyone else that may be interested.

cheers

 

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RE: FCUPS versions, other info, posted on July 15, 2013 at 14:03:20
Thorsten
Manufacturer

Posts: 4161
Location: Somewhere nice on planet dirt
Joined: September 25, 1999
Hi,

The design is simple.

First, the output is not fully short circuit proof.

It normally survives a probe slip, but a permanent hard short on the output and full voltage on the input will fry it crisply, with Mosfets and several other components dying.

Second, the "track low point" simply means that the circuit will always drop out as little voltage as possible.

Drawing too much current without a bigger input cap may again create too much heat.

The 2008 versions had a "bug" in the negative supply. I cannot remember which particular connection triggered it, but I seem to remember it was with centre tapped transformers.

Otherwise it is normally quite solid. It just does not like to have a permanent short on the output, which may happen with mis-wiring.

Ciao T

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?

 

RE: FCUPS versions, other info, posted on July 15, 2013 at 19:10:19
zarniwoop
Audiophile

Posts: 579
Location: NY
Joined: November 28, 2002
Thanks Thorsten,

"The 2008 versions had a "bug" in the negative supply. I cannot remember which particular connection triggered it, but I seem to remember it was with centre tapped transformers."

I think I discovered this "bug", and its quite a serious one! I am indeed using a center tapped transformer, wiring the center tap to the FCUPS CT terminal. I slowly brought up voltage on a variac (15K load on B+ output) and didn't immediately notice problems until i got up to 300VDC output, at which point I heard arcing sounds and shut it off. I, luckily, probed the film caps and found one w/ 850VDC across it. Probe slipped and I got a nice bang as the cap discharged. I'm glad I was cautious and didn't pick up the board with my hand.

Obviously, these should not be at this voltage! Since no schematic is available, I tried tracing some of the circuit board components and fitting it to the general layout as shown in the manual... Seems like it was one of the negative bias filter caps. I've since read your comment, and noticed there is the addition of a bias voltage (virtual)center tap connection on the newer boards. So I'm guessing this bug was addressed in these changes. I'm a little pissed off that nobody thought to mention anywhere that this "bug" exists on the version 1 boards. Lots of people use center tapped transformers. Is there a FIX for this that would be possible while keeping the bugged board? My plan right now is to just remove the connections to the negative bias rectifier if I can manage that with the pcb, as my transformer has a bias tap anyway.

Anyone with these older version boards, please take note and be cautious.

 

RE: FCUPS versions, other info, posted on July 15, 2013 at 23:26:00
Thorsten
Manufacturer

Posts: 4161
Location: Somewhere nice on planet dirt
Joined: September 25, 1999
Hi,

Do you want to use the negative voltage?

If so, do you have a lower voltage tap available?

Otherwise you need to de-solder two diodes, I need to look if I have the details somewhere.

E-Mail me directly, I should have the schematic for the older version.

Ciao T

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?

 

RE: FCUPS versions, other info, posted on July 17, 2013 at 19:37:43
zarniwoop
Audiophile

Posts: 579
Location: NY
Joined: November 28, 2002
If its just the negative bias supply that's buggered up I can make do. My transformer has a 50V tap.

The C- output appears to be derived from a neg. FW rectifier (2 diodes in series), then a zener/emitter-follower, with those 2 10uF 630V film caps between each stage. So, if I can just desolder those rectifier diodes I should be okay, correct?

Hopefully, I didn't fry any other bits. It did appear to be giving stable B+ supply.





 

RE: FCUPS versions, other info, posted on July 17, 2013 at 20:26:38
Thorsten
Manufacturer

Posts: 4161
Location: Somewhere nice on planet dirt
Joined: September 25, 1999
Hi,

The Bias come from a voltage doubler, that was needed for the use of a single, non centre tapped winding.

So there are some other parts that need removing. Please e-mail me.

Ciao T

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?

 

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