[Russtafarian]

OK, I'll give this a shot.  If R=8 (speaker impedance), and V=30 (DC rail), does it work like this?

Current: I=V/R

3.75 = 30 / 8

Power: P = V x I = V x V / I = V^2/ R

Does this mean:
P = 30 x 3.75 = 112.5 or
P = 30 x 30 / 3.75 = 240 or
P = 30^2 / 8 = 112.5

I apologize for my ignorance but I'm not sure what to make of this.

Russ

[Gordy]

I came up with the same bad numbers for my 400's as you did and I can't begin to remember how we came up with 150 watts for my 54v rails so I eventually consulted my tube guru, Eddie Vaughn, who's a truely gifted tube amp designer/builder and guitar amp restorer.  He's also very adept at explaining things to newbies like myself, so I left his email to me intact.  Keep in mind that this isn't meant to be an exact calculation, just a very good estimate!  

Hi Gordy! nice to hear from ya!
 
The 3 inter-related power equations that are derived from Ohm's Law are:
 
P = EI
I = P/E
E = P/I
 
Power is Watts, I is Current in amps, and E is Voltage (Electromotive force).
 
Let's say you measure 50V across the load and 3 amps into the load. A resistive dummy load of adequate heat wattage dissipation rating, and a static frequency sinewave test tone (1 kHz is usually used) are needed for accuracy.
 
50V x 3A = 150 watts
 
If you know any two of the three variables, you can calculate the unknown variable, just like Ohm's Law. Since you know for a fact that your amp is rated at 200 watts into 8 ohms with 63V rails, you can just use P = EI to find the current it's producing. Divide 200 by 63, which is 3.17 amps. The problem here is inefficiencies and losses, and the fact that the output stage cannot swing voltages above and beyond that of the supply voltage, but the estimate will still be close. The drop in current produced will be logarithmically proportionate to the drop in rail voltage, so we can't just use our figure of 3.17 amps and multiply it by 54V and say it would be 171.2 watts. Unless the bias of the output stage has been changed so that the current is increased as well, then the current will drop along with the supply voltage.
 
So, let's forego our figure of 171.2 watts, because it was contrived under the assumption that the current remained constant, regardless of a drop in supply voltage. Although the ratio we'll calculate will be linear and not logarithmic and true to the actual device (we'd need a set of characteristic curve charts for that), it'll be quite close.
 
63 to 3.17 is a ratio of 19.8738 to 1. So, let's calculate the number for our estimated current using this ratio and our figure of 54 volts: 54/19.8738 = 2.7171 amps, which multiplied by 54 volts would be 146.7 watts.
 
You can estimate that if the bias adjustments have remained the same, your power output is approximately 150W.
 
Have a great day, Gordy!
 
Eddie :^)

[Russtafarian]

Thanks Gordy.  That's close enough for my estimate.

Russ

[ryno]

I just finished my amp from the dig and analog group buy. Everything works, but the transformer hums.
I added a soft start and RFI filter from DIY cable. The numbers coming out of the tranny and out of the power supply were correct. I grounded as per hypex, power ground connected to the RFI filter but not to the chassis. The signal ground connected to the chassis.
Any trouble shooting hints, or is it possible I got a bad tranny.  Parts express has them for $60, I'd rather not buy one if there's some other problem.
Thanks, Ryan

[JoshK]

Hi Ryan,

Is you hum mechanical or electrical?  Meaning is the noise coming from the amp itself, even when there is no sound coming from the speakers, or is the sound coming from the speakers?  

If it is mechanical then you can try tightening down the transformer bolts or adding some barrier between the tx and the chassis.

[ryno]

It's mechanical, It's dead quiet from the speakers. It makes the hum with or with out speakers or rca's hooked up. Everything is pretty tight, and I used foam pieces that came with the tranny. The amp is about 5 feet from my seat, and the noise is very noticeable.
Ryan

[JoshK]

Can you take a picture of the inside of your amp?  Try tightening the bolts a little bit harder, but if not possible, you could also try removing the foam to see if that helps.   Don't worry, there is hope to this, as you have already eliminated a lot of possibilities by knowing it is mechanical.

[samplesj]

I've just come to the conclusion that the avel transformers aren't really good quality.  Haven't others complained about them before?  My 500VA avel hums too.  I tightened it really tight to test that out, but it actually made it hum worse.  I ended up with a looser fit and a piece of cork underneath it (I've got tons of extra cork so its just what I had around).  Even now it hums too loud for such a quiet amp.  Its not as bad as other gear I've had but its otherwise extremely low noise floor makes it seem worse.  I sort of wonder if its because I run 124v from the wall most of the time.  Maybe it was just marginly speced and I'm overloading the core.

If I'm lucky my 1000VA shielded/screened plitron will be here this week .  I needed to do something to get rid of the hum and I'm now driving very power hungry 4ohm speakers so I thought I'd go ahead and get a bigger size while I was at it.  I think the UCD400s technically need like 850-900va for full dual 4ohm power don't they?

[Kevin Haskins]

I've just come to the conclusion that the avel transformers aren't really good quality.  Haven't others complained about them before?  My 500VA avel hums too.  I tightened it really tight to test that out, but it actually made it hum worse.  I ended up with a looser fit and a piece of cork underneath it (I've got tons of extra cork so its just what I had around).  Even now it hums too loud for such a quiet amp.  Its not as bad as other gear I've had but its otherwise extremely low noise floor makes it seem  ...

Before I'd blame the transformer I'd make sure you don't have any DC on the mains.   It doesn't take much to saturate a toroid.     I've had nothing but great results with the Avel units I've used.   No mechanical hum at all and they are all right on spec.   If it is humming without DC on the line I'd return it.

[samplesj]

Before I'd blame the transformer I'd make sure you don't have any DC on the mains.   It doesn't take much to saturate a toroid.     I've had nothing but great results with the Avel units I've used.   No mechanical hum at all and they are all right on spec.   If it is humming without DC on the line I'd return it.

Well, the poster that was originally asking about the Avel (a few posts up) did actually use a DC blocker (your JR RFI filter is also a DC blocker right?).  Personally I've not put a DC blocker inside this unit, but it hums even when plugged into a BPT3.5sig and also a Running Springs Audio Duke.  Because the BPT is a transformer it shouldn't be passing DC and I'm pretty sure the RSA guys claim to stop DC too.

Unfortunately we both bought ours in the group buy run by Ken so we can't really return them since we weren't the original purchasers.  I'm not really complaining about the GB though because that was an very good deal (2x UCD400s, Hypex HG power suppy, 2x Hypex cables, case, transformer for $650).  It didn't include a softstart, but I bought one from you just before the new year since I'm moving to a 1000va tx (thanks for the extra fast shipping btw).

EDIT: Maybe I shouldn't knock the whole brand after all.  I just remembered that when my amp parts first arrived I did have a decent dent in the front panel of the case from where the tx smashed into it (don't really notice it now with the faceplate on).  Maybe it got whacked hard enough to break some of the epoxy/whatever loose and the wires are rattling against each other now.

[Kevin Haskins]

Well, the poster that was originally asking about the Avel (a few posts up) did actually use a DC blocker (your JR RFI filter is also a DC blocker right?).  Personally I've not put a DC blocker inside this unit, but it hums even when plugged into a BPT3.5sig and also a Running Springs Audio Duke.  Because the BPT is a transformer it shouldn't be passing DC and I'm pretty sure the RSA guys claim to stop DC too.

Unfortunately we both bought ours in the group buy run by Ken so we can't really return them si ...

I'm sorry...  I rarely have time to read every post and I should have.   If a transformer is vibrating though there is no fix.   You just replace them.   It is either an Q/C problem in production or the unit took a hit during shipping.

[samplesj]

Yeah, I just edited my above reply because I forgot that mine had taken a whack in shipping.  I probably shouldn't have talked about the whole brand.

Has anyone ever tried redipping their txs?  Isn't that a proposed fix by some people?  I've got plenty of poly around, but I didn't like the baking in the oven part.

[JoshK]

I have two 500va Avels in my UcD 400 dual mono and they hummed a little at first, not you can only hear it if you put your ear up to the case.  I tightened them down and ran them for a bit and it lessened.  On diyaudio I have read hit and miss reports with Avel.  They seem to not have the best QC but they are much less expensive then other brands so sometimes it is worth trying.

[JoshK]

btw, if you have room, you can mount the txs on a sub board inside the chassis.  Basically take a 1/2" piece of plywood a bit larger then the transformer, mount it on standoffs from the chassis and mount the tx to the board.  The wood may absorb a lot more the electromechanical vibration and noise.

[Kevin Haskins]

btw, if you have room, you can mount the txs on a sub board inside the chassis.  Basically take a 1/2" piece of plywood a bit larger then the transformer, mount it on standoffs from the chassis and mount the tx to the board.  The wood may absorb a lot more the electromechanical vibration and noise.

My personal opinion is that any hum is too much.   I wouldn't use them if I had a problem and at this point I've not had to reject even one.    My guess is that PE shipping is causing the problems.... not Avel's Q/C.

[JoshK]

I am glad you haven't had problems.  I didn't buy mine from P/E, and they were shipped in large foam coffins about 5" all around them.   Anyway, I am not complaining for the price I paid, but many of the poorer accounts match mine in that the windings are pretty nonuniform.

[ryno]

Thanks guys, at least I feel like everything is assembled right.
Josh, I think I have a gallery set up with a couple of photos, let me know what you think.
I might wait a little to change the tranny. I left room in the amp for another power supply and a pair of modules. If I really like it I might put in a bigger tranny and turn it into a four channel.
First I'll do my own little shootout. The ucd vs a bryston 3bst, and an IRD purist vs a minimax.
Samplesj, mind if I ask what you paid for your new tranny?
Thanks again, Ryan

[JoshK]

Excellent work Ryan, looks quite good and I don't see anything wrong with your layout at all.  If you are still getting a hum try a couple of my cheats, but otherwise it means your tx isn't so hot.  You might try playing music through the amp for 30+ hours and see if it quiets down, but I am not sure if there is any plausible reason why it would.

Maybe a good time to bring up the topic of what makes a tx hum. I am not sure myself.  Is it due to the windings not being properly balanced?

[samplesj]

I finally got my new transformer installed and it is dead quiet.  So the hum I was getting out of my Avel had to be specific to that unit.

While the hum in the Avel may have been due to shipping mishap, the Plitron was shipped also and it arrived perfect.  Either way I'm not going to be buying more Avel because to me its just too much of a gamble and I'm already behind.

I also wanted to pass along a tip that may save someone else quite a bit of frustration.  The Hypex softstart switch is backward depending on how you look at it.  The switch isn't a power switch, but rather a standby switch.  

My metal bits stopped one size below what I needed to mount my pushbutton on the front (hard off on the back and soft power on the front was the idea).  Since I didn't want to make a special trip to town for a new bit I just wired it up with a wire between the switch terminals.  It wouldn't give full power out.  Finally I hooked up two junk drawer red LEDs and found that it wasn't coming out of standby.  After I found that I was able to remove the wire and found the relay clicked over and the normal LED lit fairly quickly.   I'm actually going to email a request that they add "STANDBY" in front of the switch terminalogy on their online PDF.  If I had seen that it worked that way instead I would have saved an hour or more of troubleshooting time (I'd hooked up the tx and power supply so I started troubleshooting there first).

[studley]

I am the allout assault type

I plan on doing a lot of reading today, then placing some orders in preperation for my first Audio, DIY project, wish me luck!

CornellAlum
what conclusions did you come to as regards the Hypex power supply and other options?

Regards
Ian