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Nuforce STA200 Goldmund vs Chinese Design
Nuforce STA200 Goldmund vs Chinese Design
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Old 30th July 2018, 09:12 PM   #1
glennconti is offline glennconti
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Default Nuforce STA200 Goldmund vs Chinese Design

So, I own a Nuforce STA200 stereo amplifier and in a week or so I will be in possession of Chinese designed stereo amplifier. I am happy with the Nuforce but took a flyer on this Chinese no-name rig. I love the looks of the Chinese rig and some of the design claims have me interested too. The claims of the Chinese rig:

1) Class A amp for the first 20 watts then Class AB from 20 watts to 200 watts.

2) Dual Mono design (two transformers etc..)

3) Current feedback design (not voltage feedback)

4) Omron relays to protect the speakers

5) ELNA Audio capacitors

6) 16 pairs of Toshiba 2SC5200/2SA1943 Transistors

The Nuforce STA200 is not a Dual Mono and it is a Class AB 80 watts per channel 8 Ohms. I have more money than brains so I am going to audition both and keep the one I like best taking a loss on one. The Nuforce was $500 delivered and the Chinese was $700 delivered

From what you can tell from these pictures, did I make a total mistake on the Chinese amp purchase or was the Chinese amp a reasonable upgrade over the Nuforce?

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Old 30th July 2018, 11:19 PM   #2
CaptainSniffy is offline CaptainSniffy  United States
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That is a lovely looking chassis. Please post your impressions once you've had a chance to compare!
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Old 31st July 2018, 01:02 PM   #3
glennconti is offline glennconti
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Hi All... Thanks @CaptainSniffy for your comment. I will post my impressions when the Chinese amp arrives. I may even do a video if I get energetic.

However, can no one pass an opinion on this Chinese amp design? Please chime in positive or negative. I want your honest opinions. I am not thin-skinned. I want the truth. Thank you.
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Old 31st July 2018, 02:27 PM   #4
nfsgame is offline nfsgame
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A little more heatsinking on the chinese amp wouldn't hurt if it really should do the 20 watts in class-a... Also the rectifiers are without any heatsinking - usually a no-go in class-a-amps cause the current flowing through the PSU is constantly at a high level and the recs will heat up rapidly. Especially the cap near by them wouldn't like it much.
I'm a little bit skeptical by nature about if the semis (and the caps...) are genuine.
Nevertheless I'm excited what your experience will be.
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Old 31st July 2018, 03:52 PM   #5
glennconti is offline glennconti
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Thanks so much @nfsgame. That's just what I was looking for! I can, based on your observations, fashion "slip on" heat sinks made from copper sheeting to the rectifiers (insulating the bottom edge with electrical tape if need be). Also, I can place heat shielding (adhesive backed from the performance auto parts store) between the rectifiers and the first cap. And finally, I can add if needed small super quiet fans on either side of the amplifier chassis. I will only do this if, after measuring the temperature of the heat sink fins during operation. Any suggestions on the max temperature I should let the heat sink cooling fins get... anyone?

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Old 31st July 2018, 04:09 PM   #6
nfsgame is offline nfsgame
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At 65C-70C at the heatsink near by the outputs some amplifiers will shut the unit down. Keep in mind that the outputs will already be derated in their SOA. A short thump-rule is that you'll have to keep your hand on the heatsink for at least 3-5 seconds. If you feel too much pain before the time has expired then the heatsink is too small for the heat it'll have to dissipate.
If you need insulators between rectifiers and coppersheet depends on the model of diode used. Some got the cathode/anode electrically connected to the baseplate, some not. If you clamp two diodes with connected baseplate on a conductive piece of something then .
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Old 31st July 2018, 04:48 PM   #7
glennconti is offline glennconti
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Thanks again @nfsgame! So, if the temperature is too high, I would be willing to sacrifice some of the power in the Class A section of each channel. This would require surgery! I could selectively remove transistor pairs until the temperature started dropping to an acceptable level? For example.... (please see red X's)... Too radical????

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Old 1st August 2018, 05:48 AM   #8
nfsgame is offline nfsgame
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Not just radical - it doesn't make sense. You'll lower the area the outputs are able to transfer the heat to the heatsink. So maybe the heatsink temperature would be lower, but as voltage on the rails, bias and load-current would be equal as before, the heat at the outputs would be the same. Just less spread over the output devices. So each output device will get hotter. Also the ability to drive low impedances is limited then (->SOA).
You perhaps could lower the bias to lower the heating of the output devices. But for sure you'll have to watch the distortion with an oscilloscope and waveform generator.
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Old 1st August 2018, 01:02 PM   #9
glennconti is offline glennconti
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@nfsgame Thank you again for your comments and observations. I got the idea for removing some of the transistors on the A60+ from another schematic I found of a simpler lower power version of the A60+ that was called the A60. The A60 is supposedly 60 watts (per channel) and has 4 transistor pairs but looks identical to the A60+ in every other regard (from what I can tell). Based on your suggestions more cooling is probably the best option instead of surgery on the circuit if I have a heat problem.

Now I am considering the design for the fabrication of the rectifier heat sinks from the copper sheeting. Thanks again for your warning of potential shorts caused by the conductivity of the heat sink if not properly placed and secured.
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Old 1st August 2018, 08:45 PM   #10
glennconti is offline glennconti
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Click the image to open in full size.

So, I just ordered the stuff I need to fabricate the rectifier heat sinks from Amazon. About $30 which included a temperature gun for me to accurately determine the before heat sink and after heat sink thermal readings for various places on the amplifier PCB. I can also see if the heat shielding that I put between the rectifiers and the caps has a positive effect on the caps. Also, I will post the heat sink design here when I come up with it. This is for anyone who also gets this Chinese designed amp and wants to follow in my foot steps doing these improvements that have been suggested by nfsgame.
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