The return of the Beast

[Mr T]

The Beast gradually returns to life, thanks to Jan's generosity who replaced my melted AMP2.

The board is populated and as I now have hold of and inductance meter I checked the value of the inductors I had for playing with. Jan’s recommendations for the standard iron powder cores is to wind 29 turns of wire for 11µH, which I did and I measured 12µH, spot on ! Then I wound an MPP core for comparison, and it needed only 11 turns of wire to get the same inductance. So I will install those on my 3rd (in 3 months !) AMP2 : the lesser the resistance the better.

Before installing the board I carried out the first tests of the power supply now equipped with bleeder resistors (50W, 250 ohms) that I installed in order to gently discharge the capacitors at power off and to smooth possible fast voltage variations. The resistors are wired between positive / negative rails and the 0V center tap. Purpose of this setup is multiple : soften power up / power off transients and achieve a permanent full load to the power supply, thus eliminating possible over voltage / over current peaks when the power demand is little.

As you can see, positive and negative rails show perfect matching, 2.0mV of variation is guaranteeing an extremely quiet power block. Voltage is slightly lower than before, it was 59.0 volts in the previous (but defunct) AMP2 due to the consumption of the bleeders. This in turn will allow safer operation for the 2350 chip I guess.

Power supply returns back from 58 volts to 0.5volts within 56 seconds and does it in a perfectly symmetrical way (on my previous amp I checked once the rails after shutting off the power and there was a HUGE difference between + and - rails). Here we have the same decay curve on both rails, which the circuitry it feeds will certainly like.

Taking into account the size of the heat sink and dissipated power in the resistors heat is reasonable. Obviously, good thermal compound is interfacing the resistors with the heat sink.

This time I am taking no risk at all from a calorific point of view as I don’t want to see this again http://www.dcx2496.fr/melt.htm !

You will see on the attached pics that I tried to foresee the worst operating conditions : a BIG heat sink is glued under the chip by the means of a heat conducting kapton foil from Fischer Elektronik (Farnell order code 1211708). The heat slug of the TP2350 chip is interfaced with the board with Dow Corning 340 compound. As an additional safety measure a fan will be blowing cool air taken from the outside of the cabinet onto this heat sink. T

his 12V fan, ex from a Pentium CPU cooler is powered by an external 6.0V power supply - for lower noise - which also unmutes the amplifier by the means of a delayed relay.

I hope this third AMP2 will last forever as I am convinced it is playing amongst the best amps money can buy. I'll keep you posted after first power on, if I'm still alive of course [^]



Mr T




Some pictures

Negative rail voltage : http://www.dcx2496.fr/3rd/V_m.jpg

Positive rail voltage : http://www.dcx2496.fr/3rd/V_p.jpg

Difference : 2.0 millivolts, nice ! Note the bleeders on the heat sink. Lovely heater for the winter [8D]

Populated board : http://www.dcx2496.fr/3rd/amp2_3.jpg

Heat sink underneath the TP2350 : http://www.dcx2496.fr/3rd/amp2_3_b.jpg

Fan from an old Pentium CPU cooler : http://www.dcx2496.fr/3rd/ventilos.jpg it will be running with 6V DC for quiet operation

It'll cool the chip's belly heat sink located 10mm above it : http://www.dcx2496.fr/3rd/ventilo.jpg

The innards of the beast, ready for rebirth : http://www.dcx2496.fr/3rd/P1000444.jpg

[aleka]

I just had a look at the picture of your beast. Sure is.

Anyway noticed that the toroids on the output section have very few windings. To get the 29 turns as mentioned in the manual my windings are packed tight together for the whole circumference of the core.

Have you changed the core material? or done something different?or just relying on a multimeter to check the value. My meter won't measure that low so can't double check mine.

Just curious, that's all...

[Mr T]

Yup, I have measured it with my L-Meter and I had to unwind a few turns to get 11µH, hence the loose aspect of the windings.
The grey cores are MolyPermalloy Powder ones (MPP) from this company : http://www.mag-inc.com/
Actually I had to wind 11 turns of Litz wire to get 11µH (measured) with them.
Before trusting my meter I measured plenty of inductors of known values to be sure of the meter accuracy. and I found out that the reading was accurate by +/-2% of the displayed value

Mr T

[chris4916]

hmmm, unless I totally misunderstood, this is what Mr T explains at the very begining of his post He changed from std toroid to MPP.

Interesting... I'm currently building a Truepath and I'm just wondering whenever I should move MPP too.

Christian

[ENG]

Dear Mr. T:


I am very much interested in the bleeder you have installed. I think it should help what you are doing. Can you explain by means of scheme/circuit/drawing how you have connected the resistors : just +V-----resistor----0V------resistor -V ? 250 Ohm enough or bigger ?

Thanks in advance !

Best regards,
ENGH

[ENG]

Hi :


Just for your information, I also use different toroid material. It is called sandust and it is suppose to be more expensive then MPP, a friend suggest this material as he has no iron powder. I also measure 11 windings. My friend is measuring it with his professional meter.

Bestregards.
ENG

[Mr T]

quote:Originally posted by ENG
[br]Dear Mr. T:


I am very much interested in the bleeder you have installed. I think it should help what you are doing. Can you explain by means of scheme/circuit/drawing how you have connected the resistors : just +V-----resistor----0V------resistor -V ? 250 Ohm enough or bigger ?

Thanks in advance !

Best regards,
ENGH

Hello ENG,

Yes absolutely, you are right for the wiring.
For the sake of simplicity here's the link to the resistors I used :
http://uk.farnell.com/jsp/Passive+Co...sp?sku=9508210
You'll need quite a big heat sink as they dissipate a lot of calories [:0]

Mr T

[Reverie]

We love you Mr. T!

Thanks for all this info, will help a lot when i come to build a Truepath myself!

By the way, a few of your pic links returned a '404 page not found' error...

[audiophool]

Mt T

Suggest you wait until your wife/partner and daughter are out of home when you power up. That will alleviate your most likely cause of death!

Your classic pictures of ground zero are still ringing in my ears as I play with my new Truepath.

Re: bleeder resistors. Why are you so careful to equalize the decay between rails? Can differential decay damage the Tripath chip?

Regards,

Tim

[Mr T]

quote:Originally posted by Reverie
[br]We love you Mr. T!

Thanks for all this info, will help a lot when i come to build a Truepath myself!

By the way, a few of your pic links returned a '404 page not found' error...

Hi Reverie, good to be back [:I]

I corrected the wrong links

Mr T