[Bob_McBob]

What type of transformer does the Veda Audio Dynahi SA use? I know it is toroidal, and their old site just said "150VA High Quality Toroidal Transformer" with no other specifications. It is about 10cm in diameter by 4cm in height, and has no manufacturer's label or anything like that (that I can see).

I'm asking because the transformer in my Dynahi makes an annoying buzzing sound whenever the amp is turned on, and I'm hoping to be able to replace it with something quiet.

 

[jarthel]

buzzing sound is common to low quality toriods.

you can use a VOM to measure the secondary. that should at least give you some indication on the secondary voltage. as for the secondary amperage, you can install .1ohm resistor on the "+" wire of the secondary and measure voltage. using Ohm's law, you should be able to get the amperage.

you should be able to get a replacement transformer now.

ps. make sure you leave allowance on the amperage rating.

 

[Bob_McBob]

Apparently it does have specs listed on a label:

60HZ
PRI: 0-115V/RED-RED
SEC: 0-34V/WHI-BLU
SEC: 0-34V/WHI-BLU

I tried a few things like moving the transformer around, removing the metal retaining bolt (Kevin's suggestion), etc. Sometimes it will stop buzzing for a few seconds after it's turned on, but it always returns. People have suggested it may caused by knocks and bumps in transit (this amp has been owned by several people) rather than the quality of the transformer itself.

How much would it cost for me to replace the transformer with say, a Plitron of the same specs? Would it be essentially silent? This buzzing is not THAT loud, but I can hear it when I am sitting beside the amp, and it is annoying. I assume it would not be a big job to replace, as long as I get the wires right. There are four screw connections on the PSU board, and a couple of solder connections I think I could manage.

 

[jarthel]

if you don't want to measure the current load, make sure you get a "beefy" transformer

 

[Bob_McBob]

It is not that I don't WANT to measure it, I CAN'T measure it. I don't have anything beyond a multimeter here.

 

[DaKi][er]

The requirements for the transformer in a dynahi are pretty well known, 30VACx2 at 80VA is good.

For more reading, you can go here - http://headwize.com/ubb/showpage.php?fnum=3&tid=6025

 

[jarthel]

Quote:

Originally Posted by Bob_McBob It is not that I don't WANT to measure it, I CAN'T measure it. I don't have anything beyond a multimeter here.

using ohm's law, you can measure a current load.

place a .1ohm 5W resistor on the "+" of the secondary and then measure the voltage across. using ohm's law, calculate the amperage.

 

[Bob_McBob]

I know you're trying to be helpful, but like I said, I have nothing but a multimeter. I am not a DIYer, I just thought this would be an appropriate place to ask about a Dynahi.

 

[Clutz]

Quote:

Originally Posted by Bob_McBob I know you're trying to be helpful, but like I said, I have nothing but a multimeter.

You're missing jarthel's point, which is that even if you only had a voltmeter (which has more limited functionality than a multimeter) you are capable of measuring current using ohm's law: V=I*R. Using a bit o' algebra magic, we can restate Ohm's law in terms of current as: I=V/R

Assuming the resistance is 1Ohm (as per jarthels suggestion, although you'd probably need a pretty freaking beefy 1Ohm resistor - something in the range of 900 Watts, which I'm imagining doesn't actually exist), then the above equation for current simplifies down to: I=V.

Hence, any voltage measure is equal to the current running through that device.

Thus, if you place a 1 ohm resistor between the +ve and ground the secondary of your transformer and measure the voltage across it, you're also measuring it's current output capacity.

(You could also use a resistor with a higher resistance, say, 1KOhm, and then get away with using a 1 Watt resist, in which case, I=V/1000)

Additionally, I'm willing to bet that if what you have is truly a multimeter, that it is actually capable of measuuring current, or it's probably not a multimeter, and just a voltmeter (multimeter meaning it is a meter capable of measuring multiple things, voltage being one of them).

 

[Bob_McBob]

Well, the point I was trying to make is that I don't have a resistor to try his suggestion. My (incredibly ancient analog) multimer does measure current up to 300mA, which I guess is not a lot of help.

 

[jarthel]

Quote:

Originally Posted by Bob_McBob I know you're trying to be helpful, but like I said, I have nothing but a multimeter. I am not a DIYer, I just thought this would be an appropriate place to ask about a Dynahi.

you're not a DIYer and still want to mess around with AC.

good luck!

 

[DaKi][er]

Quote:

Originally Posted by Clutz You're missing jarthel's point, which is that even if you only had a voltmeter (which has more limited functionality than a multimeter) you are capable of measuring current using ohm's law: V=I*R. Using a bit o' algebra magic, we can restate Ohm's law in terms of current as: I=V/R Assuming the resistance is 1Ohm (as per jarthels suggestion, although you'd probably need a pretty freaking beefy 1Ohm resistor - something in the range of 900 Watts, which I'm imagining doesn't actually exist), then the above equation for current simplifies down to: I=V. Hence, any voltage measure is equal to the current running through that device. Thus, if you place a 1 ohm resistor between the +ve and ground the secondary of your transformer and measure the voltage across it, you're also measuring it's current output capacity. (You could also use a resistor with a higher resistance, say, 1KOhm, and then get away with using a 1 Watt resist, in which case, I=V/1000) Additionally, I'm willing to bet that if what you have is truly a multimeter, that it is actually capable of measuuring current, or it's probably not a multimeter, and just a voltmeter (multimeter meaning it is a meter capable of measuring multiple things, voltage being one of them).

You’re confusing the thread even more here, and with a lot of nonsense at that

What this basically describes is a shunt resistor, where you insert a small known resistor inline with the power supply line, measure the voltage across it and as ohms law, you get I=V/R

But Clutz, you have the wrong idea on what is a suitable shunt resistor. You want something that is going to have minimal effect on the rest of the circuit. as you know, if you put a current through a resistor you are going to have a voltage drop across it, now with our shunt in the power supply line, that is going to cut into the voltage used to supply the circuit itself, and therefore change the current draw as it is receiving less voltage now. so you have to pick a shunt resistor that is not going to have much effect at all, one with a small V drop. Using the dynahi which when working right will use about 600mA, picking the 1 ohm resistor you said first, will measure about 600mV across it (1ohm * 600mA) which while high is not going to severely effect the operation of the amp, now for power loss in the resistor, you said it would be 900W, but I think you got your formulas a bit mixed up, P = I^2*R, = 0.36w which is no problem
Now you go on to use a 1K resistor, with 600mA through that we get 600V!! Which is 10 times more that what dynahi uses - we have gone completely wrong here
A 0.1 ohm resistor would be a very suitable choice, with a voltage drop of 60mV across it @ 600mA and we can see that lover R we have the lower V we get across the resistor and less effect on the circuit we want to measure.

But after all that electrical basics, the dynahi is a well known diy project and the power requirements are pretty well given as +/-30V @ 600mA and using the power supply designed for it, 30V AC * 2 is a good AC supply for it, gives our transformer requirements of 30 * 2 * 0.6 = 36VA, we always add a bit more onto that and one of the most common values for a power transformer is 80VA so that is most recommended

 

[Bob_McBob]

Why is the current transformer higher-speced? Or is it? I would like to order a replacement transformer from Plitron, but I don't have the faintest idea what I should be buying. Please be patient with me

By the way, I am not really too concerned about working with this, since as far as I can see all that is involved is identifying wires, screwing some to the PSU board, and soldering a couple of joints. I'm fairly certain I can manage that without killing myself!

 

[Clutz]

Quote:

Originally Posted by DaKi][er Using the dynahi which when working right will use about 600mA, picking the 1 ohm resistor you said first, will measure about 600mV across it (1ohm * 600mA) which while high is not going to severely effect the operation of the amp, now for power loss in the resistor, you said it would be 900W, but I think you got your formulas a bit mixed up, P = I^2*R, = 0.36w which is no problem

Actually, that's completely different from what I was thinking. I was imaginging connecting a load resistor up to the secondary of the transformer - but not in series or parallel with anything else - just the resistor on it's own, hence the power going through the resistor would be P=V^2/R, were V=30 instead of 34, because 30^2 was easier to do in my head at the time than 34^2.

That said, I don't know why I was thinking that. I know that we needed to measure the voltage drop across a resistor in series with the amplifier, so I don't know what the hell I was thinking- but my head doesn't seem to be screwed on correctly today.

 

[DaKi][er]

Quote:

Originally Posted by Bob_McBob Why is the current transformer higher-speced? Or is it? I would like to order a replacement transformer from Plitron, but I don't have the faintest idea what I should be buying. Please be patient with me By the way, I am not really too concerned about working with this, since as far as I can see all that is involved is identifying wires, screwing some to the PSU board, and soldering a couple of joints. I'm fairly certain I can manage that without killing myself!

A transformer with dual secondaries of 30V AC each and about 80VA