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Old 6th January 2004, 03:56 AM   #11
Felix is offline Felix  Hong Kong
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Default Re: Re: My First Gainclone have background noise

Quote:
Originally posted by peranders

Could you take a picture of the solderside too?

The copper wire is the power and signal ground . They met at the bridge of capacitors . Do you think that it will be a problem on the layout ?
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Old 6th January 2004, 08:19 AM   #12
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Looking at the downside, where do you connect the power ground from the single(?) transformer? have you tried to test one channel at the time? As we have pointed out earlier you must or at least ought to, add 10-100 nF close to the power pins. One from V+ to ground and one from V- to ground, close to the IC. Try to implement the "star ground concept"
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Old 7th January 2004, 08:21 AM   #13
Felix is offline Felix  Hong Kong
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I hooked up one channel after another . Both channels have background noise. I will get some .1uF box cap for power rails and hope it will solve the problem . I am not sure if I understand 'ground star concept '. I am going to make a PCB that connect all ground to one point . Is this correct ?
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Old 7th January 2004, 02:52 PM   #14
macboy is offline macboy  Canada
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Yes, that is exactly what a star ground is.
Remove the bridge to the left of the 100n capacitor (near "Out"), and remove the bridge under the 470R resistor. These both have the possibility of creating a ground loop; the grounds should connect only at the star, not at any other point.
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Old 7th January 2004, 03:39 PM   #15
GregGC is offline GregGC  Canada
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Quote:
Originally posted by Felix
I hooked up one channel after another . Both channels have background noise. I will get some .1uF box cap for power rails and hope it will solve the problem . I am not sure if I understand 'ground star concept '. I am going to make a PCB that connect all ground to one point . Is this correct ?

The wiring is wrong. What are the input resistors for?
Hope that's not the way you wired the hissing amps.

Keep in mind that there always some noise level in an amp.
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Old 7th January 2004, 04:26 PM   #16
Felix is offline Felix  Hong Kong
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Quote:
Originally posted by GregGC


The wiring is wrong. What are the input resistors for?
Hope that's not the way you wired the hissing amps.

Keep in mind that there always some noise level in an amp.

Opps ! It seemed I have done somthing pretty wrong . Okay. Let's try again

Greg, I copied your schematic , but omitted 50K pot as I do not need it for power amp . There are resistor of 680Ohm and 470P ceramic capacitor at input . Should I omit them as well ? Can you suggest a schematic for power amp without volume pot .

Macboy, thanks for pointing out the ground route . It is very useful .

Thanks everybody for your support . You are so friendly .
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Old 7th January 2004, 04:51 PM   #17
Nuuk is offline Nuuk  United Kingdom
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This just confirms for me that in the case of a simple circuit like the Gainclone, there is less possibility of getting it wrong with hard wiring!
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Old 7th January 2004, 06:26 PM   #18
GregGC is offline GregGC  Canada
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Quote:
Originally posted by Felix



Opps ! It seemed I have done somthing pretty wrong . Okay. Let's try again

Greg, I copied your schematic , but omitted 50K pot as I do not need it for power amp . There are resistor of 680Ohm and 470P ceramic capacitor at input . Should I omit them as well ? Can you suggest a schematic for power amp without volume pot .

Macboy, thanks for pointing out the ground route . It is very useful .

Thanks everybody for your support . You are so friendly .
Depends a lot on what kind of preamp you have.

1. The gain of the GC you need?
The best to be between 20 and 30. In the setup below I used 22 (10k/220k NFB resistors R6/R4). You can use diferent res values here: 1k/22k 2k/47k; 4.7k/100k, 6.8k/150k. Pic the lowest res values with reasonable DC offset at the output. I think 10k/220k should be the optimum, but if you want to go with lower noise level, try the other ones too (4.7k/100k), though I don't think you'll get any less noise.

2. Does your preamp have a DC present at the output?
Measure with the DC voltmeter. If you build it and you know you have a cap at the output of the preamp, then don't use the input cap (4.7uF in my case).

3. HF noise.
If your GC has a separate case from the preamp I would add the input RC (in my sch. it's 15k/47pF in your case should be 680/470pF) just in case the the interconnects pickup some RF. The RC network should be as close as possible to the RCA, so that it kills the RF before it enters the housing of the GC.
If the housing of the preamp and the GC are the same one, then ommit the 680/470pF.

I'm posting 3 dif sch. for each case.
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Old 7th January 2004, 06:27 PM   #19
GregGC is offline GregGC  Canada
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Old 7th January 2004, 06:28 PM   #20
GregGC is offline GregGC  Canada
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