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Old 13th July 2012, 06:30 PM   #1
Puffin is offline Puffin  United Kingdom
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Default De-Lite strange problem

I still have the hum as mentioned in the previous thread I started.

Can anyone comment on this :-

The light bulbs dim when a source is connected to the input. I can get output from an MP3 player and it sounds very nice (apart from the hum)
But when I put a passive pre-amp in betweenmsource and de-lite the light bulbs go out and I get no sound.

I am wondering whether R4 (1 ohm resistor) Is causing problems. I am using a wirewound 3W. I think that NP used the same 1ohm resistor as he used in the power supply and as this has to dissipate about 20W.

The 3W resistor gets quite hot, but has not failed. I have some high power alu cased 1ohm resistors. Is it likely that the 3W is not man enough for the circuit?
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Old 13th July 2012, 06:35 PM   #2
Zen Mod is offline Zen Mod  Serbia
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I didn't search and I can't remember previous thread

please , post exact schmtc you use , and some pictures

my crystal ball is muddy these days

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Old 13th July 2012, 07:09 PM   #3
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Improved De-Lite schematic


Click the image to open in full size.

R4 is the 3W resistor I mentioned above.
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Old 13th July 2012, 07:14 PM   #4
Zen Mod is offline Zen Mod  Serbia
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pics
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Old 13th July 2012, 07:30 PM   #5
Puffin is offline Puffin  United Kingdom
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Nothing to show in pics. I have built the thing as per the schematic.

This may help?

Version 2

The first effort works, but with the high distortion, it's hard not to want to monkey with it. After you have basked in the glow of accomplishment and light bulbs for a while, perhaps you will feel ready for a little more effort.

In this case, that means a couple more parts. Placing a power resistor on the Source of the Mosfet will lower the gain and distortion. After a little testing, I settled on a 1 ohm power resistor, as seen in the schematic of Figure 5. Frugal guy that I am, I used the same resistor as in the power supply.
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Old 13th July 2012, 07:33 PM   #6
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by Puffin View Post
Nothing to show in pics. I have built the thing as per the schematic.

......
well - something is obviously wrong ;

either some part , or your implementation

I can't be sure what's the culprit , without proper information
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Old 13th July 2012, 08:07 PM   #7
Puffin is offline Puffin  United Kingdom
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Ok Zen mod. I can post pics, but I did this before about 2 years ago, but no one had any idea about the problem I had then i.e that it didn't work, light bulbs did not light. I was using the IXYS 6N Fets.

I have now rebuilt the modules using IXYS 20N Fets and have some success as outlined in my first post.

I have had someone check the modules and they agree that all parts are connected as on the schematic.

The light bulbs used are 300W 130v.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.
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Old 13th July 2012, 08:21 PM   #8
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Quote:
Originally Posted by Puffin View Post
I still have the hum as mentioned in the previous thread I started.

Can anyone comment on this :-

The light bulbs dim when a source is connected to the input. I can get output from an MP3 player and it sounds very nice (apart from the hum)
But when I put a passive pre-amp in betweenmsource and de-lite the light bulbs go out and I get no sound.

I am wondering whether R4 (1 ohm resistor) Is causing problems. I am using a wirewound 3W. I think that NP used the same 1ohm resistor as he used in the power supply and as this has to dissipate about 20W.

The 3W resistor gets quite hot, but has not failed. I have some high power alu cased 1ohm resistors. Is it likely that the 3W is not man enough for the circuit?
It depends at what voltage the amp is connected , but I think 3W for R4 is too low . I still use 30W for example .

For the hum , if they are 2 separated power supply arrangement , it should be seen how the ground are connected . It is better ( imo ) to connect the 2 channels together at the output of the amp . A bad ground "scheme" could produce hum .

For the fact that the amp dim when connectin a source , check the input capacitor also .


s

Edit : For a decent s/n ratio I needed 150.000 uF / channel . 96dB speakers , it is dead quiet .

Last edited by stefanobilliani; 13th July 2012 at 08:24 PM. Reason: adding information
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Old 13th July 2012, 08:27 PM   #9
Puffin is offline Puffin  United Kingdom
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Voltage is 80v as per diagram 5.

Something is pulling the voltage down?

What you normally get when you hold a phono input lead is a hum through the speaker. I get no noise at all?

Last edited by Puffin; 13th July 2012 at 08:29 PM.
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Old 13th July 2012, 08:28 PM   #10
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Quote:
Originally Posted by Puffin View Post
Voltage is 80v as per diagram 5.
And what is the actual voltage across R4?
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