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UTHAiM -- Just for Fun
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Old 4th August 2017, 07:42 PM   #71
Morde is offline Morde  Finland
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UTHAiM -- Just for Fun
a) I know it's originally designed by Mr. Nazar, but you had made a version of it and kindly provided the LT Spice file, so it was easy to try it.
b) At least my Nazar regs have drawn the same amount of power (~20W) from the 230 VAC mains according to my el cheapo energy consumption meter even if I had a resistor loading the regs or the UTHAiM board. I don't know if that's any indication or not? Unfortunately I don't own a scope so it's hard to verify. I've been looking for this though: https://www.google.fi/url?sa=t&rct=j...eaP2M7KyozZGPg It would be an affordable solution, if it's any good...

I just ordered a new chassis from eBay according to EUVL's hint: 2109 silver front pass chassis full Aluminum Preamplifier enclosure PSU case
It's a real PASS approved case. I hope I can scrub the logo off or then I'll have to place a sticker on top of it.
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Old 4th August 2017, 09:15 PM   #72
EUVL is offline EUVL  Europe
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> I just ordered a new chassis from eBay according to EUVL's hint

No Sir, not my hint.

I never endorse such copies that violates someone else's trademark.
The one I linked to in reply #68 is just a blank case with no logos, etc.
And it is located already in the EU, so no further import duties.


Patrick
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Old 4th August 2017, 09:36 PM   #73
Morde is offline Morde  Finland
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Yes. I meant no offence and I too am against trademark violations. Like I said, I'm going to scrub the logo off or cover it with something. My bad that I put the link here, maybe a forum admin can remove it. I was just looking for an adequately heat sinked case that requires minimum amount of machining for me because of my insufficient metal processing tools. Unfortunately I could not find one within EU for a price I can afford. At least the sinks in the enclosure match the one you tipped me of.
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Old 9th August 2017, 08:23 PM   #74
Morde is offline Morde  Finland
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Quote:
Originally Posted by EUVL View Post
I always test me amps with some simple PSU, first with a lab supply, then maybe 317/337.
If the temperature is significantly different with another regulator, then you for sure have oscillation.
And of course you will see it at the output with a scope, even with shorted inputs.


Patrick
Today I hooked up one UTHAiM board with a LM1086 based dual power supply set to +- 24V. The current draw is the same 0,23 A then with my Nazar reg. So I suppose the Nazar is not oscillating.

This time I let the circuit be on power for only max. 5 min at a time. Still the Vgs values measured from the lateral FET pins were 0,628 V (n-channel) and 1,01 V (p-channel) even at the start-up before things get hot. If this is the correct way to indirectly measure the bias then I think it's running quite high bias 180-190mA.

In any case I will repeat these measurements when I get the properly heat sinked case and see if the bias is still on the high side.
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Old 11th August 2017, 06:36 AM   #75
Morde is offline Morde  Finland
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UTHAiM -- Just for Fun
While waiting for my case to arrive I have made a simplified 3D model of it with Sketch-up. In the first picture you can see the UTHAiM boards placed on the side heat sink. I think I'm going to rotate them 90 degrees counter-clockwise in order to get the lateral FETs more in the middle of the sink. Also that way the inputs would be closer to the Alps pot and a bit further away from the trafo.


The second pic is a top side view and the third pic shows the Nazar regs placed on the other side sink.


I'm a bit worried about the input RCA connectors being so close to the trafo. Maybe I should use some trafo shield.


Any comments and improvements are welcome.
Attached Images
File Type: png UTHAiM case 3D 01.png (326.6 KB, 229 views)
File Type: png UTHAiM case 3D 02.png (168.7 KB, 212 views)
File Type: png UTHAiM case 3D 03.png (131.9 KB, 209 views)
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Old 11th August 2017, 08:32 AM   #76
EUVL is offline EUVL  Europe
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The FET will have no problems with 200mA bias.
But you can lower it by reducing the biasing resistor values.


Patrick
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Old 18th August 2017, 11:02 PM   #77
Morde is offline Morde  Finland
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UTHAiM -- Just for Fun
Good news for me at last. My UTHAiM is finally putting out some music! I had a quick and dirty test run after adjusting the output DC close to 0 V. Heatsinks are at 42 C degrees after one hour and the bias is quite high but I decided not to adjust it down since the amp seems to be working just fine. By the way, what's the expected power output @70ohm load with 180 mA bias?

Especially the Finnish band Kingston Wall - Shine On Me is sounding exceptionally good.

Still a lot of wirings and aluminum grinding to do, but I'm very happy that the amp board itself is working.
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Old 19th August 2017, 04:47 AM   #78
EUVL is offline EUVL  Europe
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Class A maximum output current at 180mA bias is >360mA.
At 70 ohm, you are voltage limited (to ~ +/-15V).
Which in turn corresponds to ~ 1.6W for sine waves.

For 16 ohm, you will be current limited at ~1W.
For 600 ohm, ~ 0.18W.


Patrick
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Old 19th August 2017, 05:01 AM   #79
EUVL is offline EUVL  Europe
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Power vs Load Impedance at 180mA bias.
Peak power at ~42 ohm.


Patrick

.
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File Type: png UTHAiM Pwr vs RL.png (16.3 KB, 181 views)
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Old 19th August 2017, 08:45 AM   #80
Morde is offline Morde  Finland
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Thanks a lot!
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