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Old 13th April 2011, 07:20 PM   #1491
gethin is offline gethin  Canada
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Originally Posted by Commited View Post
Guys,
I've just received this board and hooked it up to a 27v SMPS set to 28v. I have a hiss going through my speakers as soon as the power is switched on which doesn't seem right. Any ideas/suggestions? Have I got a duff board?
Do you hear the relays click on a second after you apply power? Or is the hiss immediate? Do you have the STA510A version?
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Old 13th April 2011, 07:58 PM   #1492
v-bro is offline v-bro  Netherlands
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Quote:
Originally Posted by Commited View Post
Guys,
I've just received this board and hooked it up to a 27v SMPS set to 28v. I have a hiss going through my speakers as soon as the power is switched on which doesn't seem right. Any ideas/suggestions? Have I got a duff board?
How does it go with the inputs shorted?

What kind of power supply are you using?
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Old 13th April 2011, 08:01 PM   #1493
v-bro is offline v-bro  Netherlands
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Originally Posted by gethin View Post
With the STA510A chip 36v is OK. So says hifimediy and their website.

STA505 is even 36V capable, even TP2050 is, when it is implemented well..

Just not on any Sure electronics board.... it'll fry up....

These oldest and most standard chips both have an absolute max. of 40V.
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Old 14th April 2011, 12:12 AM   #1494
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Quote:
Originally Posted by gethin View Post
Do you hear the relays click on a second after you apply power? Or is the hiss immediate? Do you have the STA510A version?
I bought the T2 TK2050 board v2.1 with 4700cap for SMPS power. The hiss occurs as soon as the relays click on which is about a second after the power is switched on.

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Originally Posted by v-bro View Post
How does it go with the inputs shorted?
What kind of power supply are you using?
I'm using a 27v SMPS power supply made by B&G. It was brand new and untested previously. Shorting the inputs makes no difference, neither does disconnecting the input cable all together.

Here's a picture of how it's all connected:
Click the image to open in full size.

I'm going to try and get it onto battery power if I can find one suitable.
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Old 14th April 2011, 05:10 AM   #1495
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Ok I just tried my 19v laptop power supply on the amp and the hiss was there also. I'm starting to think that this has to be the board that's faulty as there isn't any steel chassis etc to cause distortion. Do I need to ground the board? From the other pictures I've seen, it doesn't appear to have been done by other people.. All help greatly received - I really want to start enjoying some music!!
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Old 14th April 2011, 05:19 AM   #1496
gethin is offline gethin  Canada
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There is also the DC offset you have to tweak, put a meter across the speaker outputs and get it as close to 0mV as possible by tweaking the blue pots on the amp board.

I doubt that a wonky DC offset would cause that much hissing but it's worth checking. I would connect a ground to that SMPS that you pictured for safety. There is a signal ground plane on the amp pcb if I understand, not sure if leaving the AC ground disconnected on the smps would play a part in the hissing. I mounted my amp board on plastic isolators.

Do the LED's light up on the amp board at all?

Laptop bricks can be sketchy. Try and find two 12v batteries and wire them in series to get a nice clean 24v.

Last edited by gethin; 14th April 2011 at 05:23 AM. Reason: details
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Old 14th April 2011, 06:43 AM   #1497
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Hi gethin,
Thanks for the reply. I'll try and find 2 12v batteries, but I'm living in a new country with few tools never mind old batteries lieing around!

Thanks for the tip re the DC offsets - I have approx .4mV on each side now when I put the multimeter across the + & - of each channel. When I compare both + and both -, I have 18mV.

I just found a 3 core cable with plug attached, so I'm going to swap out that and see if it makes any difference.

Both LEDs light up and it makes music but the hiss can be heard easily 2.5m away from the speakers so it's pretty loud.
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Old 14th April 2011, 07:05 AM   #1498
v-bro is offline v-bro  Netherlands
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DC offset has nothing to do with it.

Neither does earthing the PS.

These amps run silent on almost any dirty PS. Ok, there are quality differences, a nice stiff well regulated voltage tightens up the bass a bit, but noise...?? No....

This amp is no good, probably some 100nF ceramic cap is failing on you, or there could be a defective diode (notorious white noise generators when faulty)

How sensitive are your speakers by the way?
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Old 14th April 2011, 07:22 AM   #1499
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Thanks for the reply which confirms my worst thoughts...

The speakers are CSS EL70, not the most efficient in the world @ 86dB.

Anyway to test the items or is it time to just ship the amp back (not what I want to do).

Mark
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Old 14th April 2011, 09:42 AM   #1500
v-bro is offline v-bro  Netherlands
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You can do a few probes with a scope perhaps, other tests are useless unless you know what values to expect and/or have a good working specimen next to it....

I'm afraid I'd have to tell you bad news again....
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