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Old 25th January 2013, 05:31 AM   #3831
shaan is offline shaan  India
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Use a 20k pot. One end to source, other end to ground and the slider to SSA.
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Old 25th January 2013, 05:45 AM   #3832
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Quote:
Originally Posted by shaan View Post
Use a 20k pot. One end to source, other end to ground and the slider to SSA.
I guess the previous sketch isn't nice and exact, so this attachment should be perfectly fit your description ?

Regards,
Leong
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Old 25th January 2013, 06:05 AM   #3833
shaan is offline shaan  India
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That's correct.
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Old 25th January 2013, 06:17 AM   #3834
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Ok, I know what value should I use, but is there any specify material to use ? for resistor, pot and cap.
Sometimes people say avoid mica, wirewound or something else, what should I pick, or what should I avoid ?

I have no experience buying 'better' potentiometer, what type/brand should I buy for reliable ? (no need for top-notch performance, but fairly good/worthy ones)
I only buy dirt-cheap type before, which over few month you can heard noises from adjusting.
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Old 25th January 2013, 12:07 PM   #3835
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guitar89, caps in the signal path are, indeed, critical. You can use in order of quality, and if they are available:
- Film caps with polypropylene dielectric
- Other film caps
- Tantalum caps, but they need to be polarized in such a way that DC always remain > 3V whatever the signal is negative at full excursion.
- Electrolytic caps with the same precaution but less margin (they just need to never reverse). Use Low ESR models, in a high impedance circuit. When non polarized ones are used, take a BIG margin for voltage.
Avoid any ceramic (they are ok for decoupling), as they are resonant.

To Know all, or near about cap's quality for audio:
Picking Capacitors - Walter G. Jung and Richard Marsh

For PSUs, where you need Electrolytics for big values, a good solution is to use paralleled little values instead of a big one: their parasitic resistance and inductances will be divided by their numbers, and little capacitances present less of those individually.

About Pots, they, indeed generate little distortion and noise. Less you ask current from them (Charge them with FETs,) better it is. The best choice for audio, at the moment is ALPS.
A better solution is to use a muti-position rotating switch with array of metal film resistances.
Or to use a PGA23xx circuit (my preference).

For resistors, use metal thin film ones for signal path (wirewond ones to be reserved for PSUs) . More the resistances heat, more they create distortion: take a big power margin.
This is specially important for the feedback serial resistance, because their distortion will be applied to the feedback loop, when you want a perfect mirror of output: take audiophile parts here. (the only situation where i suggest an audiophile part :-) A good solution can be parallel devices here.
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Last edited by Esperado; 25th January 2013 at 12:19 PM.
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Old 25th January 2013, 12:32 PM   #3836
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Quote:
Originally Posted by Esperado View Post
guitar89, caps in the signal path are, indeed, critical. You can use in order of quality, and if they are available:
- Film caps with polypropylene dielectric
- Other film caps
- Tantalum caps, but they need to be polarized in such a way that DC always remain > 3V whatever the signal is negative at full excursion.
- Electrolytic caps with the same precaution but less margin (they just need to never reverse). Use Low ESR models, in a high impedance circuit. When non polarized ones are used, take a BIG margin for voltage.
Avoid any ceramic (they are ok for decoupling), as they are resonant.

To Know all, or near about cap's quality for audio:
Picking Capacitors - Walter G. Jung and Richard Marsh

For PSUs, where you need Electrolytics for big values, a good solution is to use paralleled little values instead of a big one: their parasitic resistance and inductances will be divided by their numbers, and little capacitances present less of those individually.

About Pots, they, indeed generate little distortion and noise. Less you ask current from them (Charge them with FETs,) better it is. The best choice for audio, at the moment is ALPS.
A better solution is to use a muti-position rotating switch with array of metal film resistances.
Or to use a PGA23xx circuit (my preference).

For resistors, use metal thin film ones for signal path (wirewond ones to be reserved for PSUs) . More the resistances heat, more they create distortion: take a big power margin.
This is specially important for the feedback serial resistance, because their distortion will be applied to the feedback loop, when you want a perfect mirror of output: take audiophile parts here. (the only situation where i suggest an audiophile part :-) A good solution can be parallel devices here.
I have 2 of these little cute thing in stock: 100pF Capacitor
About the Potentiometer, I just oredered them before I look into this thread: Alps 20k Potentiometer
Just coincidencely brought alps ^^ although cheap ones

About the Stepped Attenuator, I would like to save cost, so means DIY, but it seems complicated for me to accomplish nicely. I prefer analog ^^ Another option I had heard is about LDR type of attenuation.
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Old 25th January 2013, 03:04 PM   #3837
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Quote:
Originally Posted by guitar89 View Post
Another option I had heard is about LDR type of attenuation.
You can forget about them: good enough parts are not available, need to be carefully matched (need a lot of samples) and, whatever , will present too much distortion, comparing to the PGA23xx.
You can find cheap Chinese of those last ones, that you can enhance to the top with few modifications, like removing electrolytic caps or little changes of ground paths:
4 Ways Stereo Remote Volume Control Motorized ALPS Potentiometer, Stand-By Board eBay Boutiques | HiAmplifier Audio Store
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Last edited by Esperado; 25th January 2013 at 03:07 PM.
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Old 25th January 2013, 03:58 PM   #3838
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hi lc,shaan

which is the correct schmatic of shaan build.
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Old 25th January 2013, 05:01 PM   #3839
shaan is offline shaan  India
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Hi coolet.

Both are correct. However, the first is more complete. So go for it.
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Old 25th January 2013, 06:13 PM   #3840
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Shaan ? What is the use of the 1MOhm to ground input ?
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