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Old 15th February 2007, 10:57 PM   #1521
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Hello,

Quote:
Hi,
a big hum could be mis-wired primary, or shorted secondary, or shorted turn, or DC from the mains, or poor quality control from the factory.
Well, the hum went down after running the ransformer for a few seconds. After I out a piece of rubber under the torroid it went away.

Concrete:

Primary-wirering was correct.
secondary wasn't connected at all, actually I emediately checked if the scondaries are shorted-they weren't.

Remains the possibility of a shorted turn, or bad mains-voltage. The torroid was custom made by a small german company- they should have a good quality control. I still have the results of measurements they made (isolation-voltage and loadregulation).

Last thing I did was to leave the torroid on the mains, since the hum was very small. All secondary voltages were perfectly OK.

Greetings
Black

PS: These are the finished Boards for my NMOS. Tomorrow I'll start mounting the Fets and the MJEs on the heatsink Cant wait to test these Modules with my Lab-PSU
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Old 16th February 2007, 02:21 PM   #1522
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Location: Willowdale
Quote:
Originally posted by BlacK_Chicken
Hello,
PS: These are the finished Boards for my NMOS. Tomorrow I'll start mounting the Fets and the MJEs on the heatsink Cant wait to test these Modules with my Lab-PSU
Hi Black,

Nice work.

I am curious about your PSU. It looks like you have 3 different sizes of filter capacitors. One pair, the Black looking ones (no pun on your name intended) look th smallest. Did you design your PSU with 3 different size filter capacitors on purpose? If so your reason(s)? I know there is a school of though about to use different rather than the same size in the PSU, but I have yet to understand the reason(s).


Regards,

John L. Males
Willowdale, Ontario
Canada
16 February 2007 10:22

P.S. I have not had the time in almost a week to continue the forum research on the specs of the quasi amp. I had some unexpected matters arise. jlm
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P.S. My appologies in advance for any typo errors. If you cannot "decode" the typo or feel there is a typo (some typos are correctly typed spelling, but can be mix of wrong/omitted words) speak up and ask me to clarify. jlm
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Old 16th February 2007, 04:17 PM   #1523
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Default PSU....

Hello Keypunch,

In short:

No.


There was some development. At first I had 4 of these smaller 4-pin Philips "LL" caps (4700) left over from my Symasym. With these I wanted to form one commen PSU for both channels. Then I got the Possibility to get these Philips 5-pin "LL" caps (10 000). I ordered 8 of these - intended for a split PSU. But I only got 4 of them - they were out of stock. After that i went for the small ones on ebay, more for psychological than for electrical reasons. I personally dont think that 3300 more per rail make such a differnce.


Update: Today I completed one channel. Half an hour ago I wnated to test it on my bench. But on applying +-30V my Lab-PSU was shorted, the current-regulation went into action for a limited current of 100mA.


No further measurement were done, I wanted to heave a break.

I check things this eavening.

Greetings
Black
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Old 16th February 2007, 05:22 PM   #1524
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Smile it works!

Hello again,

It works perfectly....

It was a bit of solder between the TO220 pads.. the whole board is that small, really hard to solder without unwanted joints.


Plays musik nice.

DC-offset ca. 1,5mA.

Bias 60mA

Greetings
Black
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Old 16th February 2007, 10:11 PM   #1525
quasi is offline quasi  Australia
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Default Re: it works!

Quote:
Originally posted by BlacK_Chicken
Hello again,

It works perfectly....

It was a bit of solder between the TO220 pads.. the whole board is that small, really hard to solder without unwanted joints.


Plays musik nice.

DC-offset ca. 1,5mA.

Bias 60mA

Greetings
Black
Congratulations. You'll have to post some photos. I am interested to find out how quiet the amp is in terms of residual noise. Well done again

Cheers
Quasi
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Old 16th February 2007, 11:10 PM   #1526
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Default Residual noise....

Hello Quasi,

Quote:
Congratulations. You'll have to post some photos. I am interested to find out how quiet the amp is in terms of residual noise. Well done again
I dont exactly understand "residual noise"in this context. If you want to know if the NMOS200 is noisy (noise from the AMP, no RF, no music, no hum - am I right?), I dont think it is.

On the bench with all those flying leads, bad PSU (high ripple), bad grounding and no rf-shielding (because there is no metal case) AMPs are imo always noisier than the finished amp.

Today my NMOS was a bit noisy at first. I had connected the input-GND to the main-GND, not the the floating input-GND (only for testing purpose, I now I am lazy ). After input-GND was connected there was less noise. On top my testing speaker is very "noisy" (hard to explain, one reason might be the high efficency - probably up to 100dB/1 meter).

I think that this AMP is going to be dead-quiet, once its finished.

Regards,
Black
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Old 17th February 2007, 10:43 AM   #1527
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Cool Update....

Hello again,

My second channel is working now. No problems so far.

->Bias 60mA
->DC-Offset 0,8mV (!)

These figures are measured with very high quality DMMs, with high accurancy.

Supply voltage again was +-32V (I dont get more out of my Lab-PSU), The currents in the diffenrent stages match well to given currents.

One thing that might be interesting:

The bias current is not shared equally between the Mosfets , if I measure the voltaes across the paraleled 1R resistors (source-resistors) i get very different current ratings. They range from 10mA to 40mA.

But its playing music very nice.

Shamefully I have to travel to work next tuesday, therefore have to wait some weeks until I come back to finish my NMOS.

Many thanks to Quasi for publishing (and develloping) this wonderful Project!

Regars,
Black
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Old 17th February 2007, 11:01 AM   #1528
AndrewT is offline AndrewT  Scotland
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Hi,
how many pairs are you using?
How close did you match them?
What current did you select for matching?
Did you match the emitter resistor values?

Any one of those could cause at least part of your problem.

But first, insert a shorting plug in the input and disconnect all output loads then do the tests again.
An alternative to the shorting plug is a plug fitted with a ground to input resistor that matches the source resistance (Rs) of the source component (preamp)
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Old 17th February 2007, 11:14 AM   #1529
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Hi,

All measurements were done without any load and with the iunput shorted to ground. When I know everything is ok then I connect a speaker - just to have some fun, not for serious testing.

Fets werent matched at all. The only transistors I matched were the 2sc1845 at the input. The Source resistors werent matched too, but I dont think that is a problem because these are 1R/5% in paralel.

Iam running 2 Pairs of IRF640N.

I dont actually know If this really IS a problem, maybe the current sharing is better when the amp is working under normal conditions.

If I remeber correctly the current range was between 12 and 37mA on my last channel. I havent measured the singele current on the first one.

Greetings
Black
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Old 17th February 2007, 12:56 PM   #1530
AndrewT is offline AndrewT  Scotland
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Hi,
it is a problem, but you have to decide if it causes a serious enough temperature worry to make you change it.

You have 8 devices in your two channels. You can match them into 4 pairs. You can then put them together in an amp with no further worries.

Now, each of the high current (low Vgs) Fets is carrying 3 to 4 times as much current as it's high Vgs partner. This makes the FET Tc run hotter than it's partner. It may also increase the sink temperature locally around the hot device (the amount of local temperature rise depends on sink thickness).
If you stress the hot device, it is more likely to fail than the cooler device. i.e. it runs closer to it's SOAR limit. Decision time.

The resistor tolerance is MUCH closer than the errors you have measured, so they are giving a close enough indication, but if you decide to do some Vgs matching at Ib then consider doing some resistor matching as well.
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