[guest1632]

Hi all, Well, been searching through the DIY forums, and well kinda give up.

I am trying to figure out/decide which UCD amp to Build, either the 180 or 400. Now the question is how to decide on the correct transformer VA size. If to big, I read somewhere that because of all of the metal in there it won't sound as good as a smaller one. Now at the same time, if to small, I don't want the amp to sound wimpy. And then there's the other issue, to use either one or 2 transformers. I will be building my supply with a bridge and caps for each channel. The secondary voltage is not an issue.
For the UCD400, I can get Kevin's 1KVA for both channels, or say 2 smaller ones, like Avel, from Parts Express, for each channel. Hard to know, just how much interaction there is between the 2 secondaries.
My caps, I'm gonna just do it right and get some Jensens 10000 2 per side (20K MF) and be done with it. Any ideas?

Also, any ideas for a soft start to deal with the inrush of current? I don't want to spend $69 for the softstart board that Hypex sells.

Ray

[bhiggins]

I don't have any experience with the UCD modules, but

1) To handle inrush current, you can use an Inrush Current Limiter, which is specialized thermistor.  It has a high initial resistance and as it warms up, the resistance decreases to almost zero.  You should be able to find them at Digikey or Mouser.  Price will depend on resistance and current ratings, but should be under $10.

2) I've always been a fan of dual transformers to maximize channel separation.  I also prefer monoblocks to reduce speaker cable lengths.   (Additionally, 1KVA transformers kind of scare me ).

3) For capacitors, I usually end up with whatever I can find at my local surplus store or I parallel a bunch of panasonic low ESR types to get the value I want.

[JoshK]

My opinion, is if you can swing the extra money, I'd go with mono block configuration, which means seperate txs, seperate bridges, etc obviously.  I think if you are going to swing for Jensens you might as well go full monty.  Also I think it is worth the extra to go for really good bridges, like IXYS, or discrete equivalents.  This made a big difference in my UcD amps.

Some feel that dual bridges is worth while also.  I haven't tried but plan to.  I just feel that the full seperation and minimized cable lengths might even trump the Jensen caps over other more reasonably priced but high performance caps, such as Nichicon KGs or Panasonic caps.

[_scotty_]

Ray,at any given moment you can pull a very large amount of current out of a 1Kva transformer and put it into a set of pws caps that are isolated from the other channel by separate rectifier bridges. You will also have half the power supply impedance of a dual mono transformer setup with 500 watt transformers. I like your Jensen cap decision,they have always worked for me.
Scotty

[guest1632]

Ray,at any given moment you can pull a very large amount of current out of a 1Kva transformer and put it into a set of pws caps that are isolated from the other channel by separate rectifier bridges. You will also have half the power supply impedance of a dual mono transformer setup with 500 watt transformers. I like your Jensen cap decision,they have always worked for me.
Scotty

Hi Scotty,

Not following you. I'm gonna go with Jensens, 2 10000 MF per channel with maybe an icys bridge per channel. So not sure, what you are suggesting? Everybody seems to think that 2 transformers is better. I've been told there is interaction between the 2 windings, since the one wire of each secondary would share ground. At this point, I pretty much have the PS parts I have in mind, but it's the transformer stuff I'm dealing with.

Ray

Hi

[guest1632]

I don't have any experience with the UCD modules, but

1) To handle inrush current, you can use an Inrush Current Limiter, which is specialized thermistor.  It has a high initial resistance and as it warms up, the resistance decreases to almost zero.  You should be able to find them at Digikey or Mouser.  Price will depend on resistance and current ratings, but should be under $10.

2) I've always been a fan of dual transformers to maximize channel separation.  I also prefer monoblocks to reduce speake ...

[_scotty_]

Ray,wire the secondaries in parallel,you are going to pretend it is one big transformer without dual secondaries and have separate rectifiers for each channel. The rectifiers
are oneway valves that only let the current flow from the transformer to the caps.  Once the energy is in the caps the other channel can't get at it.
You will get the benefit of the 1Kva roid's low impedance and current delivery
capability which may outweigh doubling your impedance to eliminate crosstalk across the transformers core.
You should have better dynamics and bass than a power amp with separate 500watt transformers.
Scotty

[guest1632]

Ray,wire the secondaries in parallel,you are going to pretend it is one big transformer without dual secondaries and have separate rectifiers for each channel. The rectifiers
are oneway valves that only let the current flow from the transformer to the caps.  Once the energy is in the caps the other channel can't get at it.
You will get the benefit of the 1Kva roid's low impedance and current delivery
capability which may outweigh doubling your impedance to eliminate crosstalk across the transformers core ...

Hi Scotty, Now if that's the case, wouldn't I double the voltage coming off the secondary, or should I take the two ground of the secondary, and put them together, and use the two hot leads for each side of the bridge?

Ray

[_scotty_]

The wiring diagram that should come with the transformer will make it easy to figure out how to wire the tranformer's secondary windings in parallel so that the tranformer has in effect a bi-filar wound secondary instead of two separate secondary windings.  No voltage doubling will occur with the secondaries in parallel.  I don't know how many wires you may have coming off of the secondary side of the transformer. If there were six wires it could get confusing. You could have four hot leads and two ground or center tap leads. To add to the confusion the secondaries have to be parallel wired in phase with one another.  This requires refering to the diagram that comes with the transformer again to figure out what leads to connnect together.
Scotty

[guest1632]

The wiring diagram that should come with the transformer will make it easy to figure out how to wire the tranformer's secondary windings in parallel so that the tranformer has in effect a bi-filar wound secondary instead of two separate secondary windings.  No voltage doubling will occur with the secondaries in parallel.  I don't know how many wires you may have coming off of the secondary side of the transformer. If there were six wires it could get confusing. ...

Oh Brother, This kinda sounds like a pain in the butt. Is there any advantage of sharing the ground leads and hooking up each side of the secondary, like a center tapped  position.  

I plan to get Kevin's 1KVA transformer for the UCD400 module. Man, this is beginning to be a project.

Ray

[peranders]

Also, any ideas for a soft start to deal with the inrush of current? I don't want to spend $69 for the softstart board that Hypex sells.

Remember that Hypex softstarter has more features than a plain softstart.

I have a softstarter pcb for sale but there are more, see below.

http://home.swipnet.se/~w-50719/hifi/sst01
http://www.hypex.nl/docs/softstart.pdf
http://sound.westhost.com/project39.htm
http://lcaudio.com/index.php?page=12 in the middle of page
http://ampslab.com/inrush.htm

Have you seen this review of UcD400?
http://www.sjostromaudio.com/phpBB2/viewtopic.php?p=635

[guest1632]

The wiring diagram that should come with the transformer will make it easy to figure out how to wire the tranformer's secondary windings in parallel so that the tranformer has in effect a bi-filar wound secondary instead of two separate secondary windings.  No voltage doubling will occur with the secondaries in parallel.  I don't know how many wires you may have coming off of the secondary side of the transformer. If there were six wires it could get confusing. You could have four hot leads and two ground o ...

]

Hi Scotty,
hmmm, So I hook the two grounds and the two other leads of the secondary together. Ok, now because I'm going with 2 bridges and separate total of 20K MF per side, the question is do I hook up the bridges in parallel with the transformer or in series with it? 1 side going to an AC side of the bridge, the other AC side of that bridge going to an AC connector on the other side, and the other connector on that other bridge going to the "hot" wire of the transformer.

Ray

[_scotty_]

The bridges are in parallel. This two separate bridges and cap banks for each channel with only one large transformer feeding them.
Scotty

[guest1632]

The bridges are in parallel. This two separate bridges and cap banks for each channel with only one large transformer feeding them.
Scotty

Hi Scotty,

Ok, Remember this is a dual secondary, so you would have 2 wires for ground and the other side to use the term loosely "hot" Wouldn't there be a problem just hooking up the AC sides of the bridge in parallel with the now 1 big! secondary. What's the tradeoff between what you are suggesting versus the 40V shared ground/centertap idea.

Ray

[_scotty_]

Ray I am not sure I understand your question. The hook-up I had in mind would also tie the centertaps together.  You would have a total of three wires
which you would Y off from to connect the bridges. Three wires from each bridge come back to the leads from the transformer.  The ground from each cap-bank would come back to the common centertap.
Scotty

[bhiggins]

How do you determine the value needed and how do you hook them up? Series or Parallel with the line?

1) Connect in series on the secondary side before or after your rectifiers, but before your capacitors.
2) Select based on initial resistance and steady state current.  Initial resistance  is determined by peak voltage divided by maximum allowable inrush current.  Steady state current is determined by your transformer.

I had a look at the Hypex softstart module and I think it might be a better choice, because you can hardwire it into your enclosure instead of messing around with through-hole components.  Also, thermal shutdown is a nice safety feature to have and push-button start gives you a high 'gee-whiz' factor.

[guest1632]

Ray I am not sure I understand your question. The hook-up I had in mind would also tie the centertaps together.  You would have a total of three wires
which you would Y off from to connect the bridges. Three wires from each bridge come back to the leads from the transformer.  The ground from each cap-bank would come back to the common centertap.
Scotty

Hi Scotty,

Ok, so if I read your description, that's hooking up the two secondaries in series with each other. Each bridge is in parallel with each secondary lead and ground between them is common.

I thought the way you described it was to hook up both secondaries together in parallel with each other, and the bridges also in parallel with each other.

Ray

[_scotty_]

Ray, trying to describe this wiring job with words only is almost impossible.
If my last post didn't make any sense please disregard it. The centertaps are wired together as well as each hot leg of the secondary. Where there were six wires there are now three. That's three connection points to wire to bridges to.From each junction formed by tying these separate leads together you will come off with a Y to each connection
at the bridges resulting in the bridges being in parallel with one another
and the secondaries of the transformer being also wired in parallel.
Scotty

[guest1632]

Ray, trying to describe this wiring job with words only is almost impossible.
If my last post didn't make any sense please disregard it. The centertaps are wired together as well as each hot leg of the secondary. Where there were six wires there are now three. That's three connection points to wire to bridges to.From each junction formed by tying these separate leads together you will come off with a Y to each connection
at the bridges resulting in the bridges being in parallel with one another
and the secondaries of the transformer being also wired in parallel.
Scotty

Hi Scotty,

Nice to have you confused. lol. Ok, as far as I know there are only two wires from each of the 2 secondaries, making a total of 4 wires. Two being Plus and Ground, and Minus. The ground wires are The wires put together for both sides of the shared sets of secondaries.

Ray