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Old 17th November 2012, 01:27 PM   #21
yd1cvj is offline yd1cvj  Indonesia
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Quote:
Originally Posted by Jay View Post
To balance the two inputs, the FB resistor (at -in) will usually be equal to the other resistor (at +in). The resistor at +in is connected to ground. The higher the resistance, the better the noise floor, as can be seen in simulators.

Beside lifting the input impedance, it is often mentioned in "Design Example" of a chip datasheet to use such a high resistance (usually mentioned as 100k) to lower output offset.

I have tested many resistance and the offset differences are not big. Even the lowest offset was not the best sound to my ears.

But with FB resistance as high as 100k you can get away with 4u7 MKP in the FB path. May be it is audible if compared with low quality electrolytic? (mine was BG, so no worse)
Hi Jay,
I'm not expert in electronis just hobby. The 4u7 MKP , is it input capasitor ?
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Old 17th November 2012, 01:51 PM   #22
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by yd1cvj View Post
Hi Jay,
I'm not expert in electronis just hobby. The 4u7 MKP , is it input capasitor ?
It is to replace the 22uF on the feedback loop in your diagram. The lowest frequency you can get is a factor of RC (of the feedback 100K {or 8k2} and 22uF). The bigger the R, the lower you can use the C.

100k is very high, so you can use smaller C, around 4u7 based on calculation on the datasheet (attached). Too low than that, bass will never reach 20Hz, but slightly lower is okay, often will give better sound when the speaker doesn't have the ability to produce as low as 20Hz.

If you use MKP WIMA or Philips, 4u7 is about 3cm. But you don't need higher than 5V for the capacitor so if you can find capacitor with low voltage rating, even if the capacitance is big, the size is also small.

Sanyo OSCON (or other computer grade caps) for example, has many caps rated at 10v.
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Last edited by Jay; 17th November 2012 at 01:58 PM.
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Old 17th November 2012, 09:26 PM   #23
yd1cvj is offline yd1cvj  Indonesia
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Thank you for explanation. I'm thinking to find better quality capasitor, now the 22uF I use Elna silmic II.
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Old 17th November 2012, 11:58 PM   #24
Jay is offline Jay  Indonesia
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I think Silmic is already very good. May be even sound better than MKP (just a wild guess).

With 22uF you can use lower resistances for feedback. Datasheet example shows 20k/1k/22uF. I like lower feedback resistance value.
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Old 18th November 2012, 09:03 AM   #25
bcmbob is offline bcmbob  United States
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Very interesting. Reminds me a lot of the BrianGT with a twist. They would be great (easy removal from PCB) as a test rig for LM3886 chips. Are they available somewhere?
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Old 30th August 2013, 06:07 PM   #26
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These boards are available from KOBA Electronics in Singapore in Chinatown area. Can find info on the location here Koba Electronics
you can get a complete 2 channel kit for S$35 ... I have 4 of them for an 8 Ch setup to drive my LS521's
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Old 23rd November 2013, 10:38 AM   #27
yd1cvj is offline yd1cvj  Indonesia
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@wizadofoz,
I visited above link , but only find Gold Capacitor for sale. Other categories is empty.
Thank you for info. This pcb is designed for BTL am I right ? But I will use as stereo.
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Old 23rd November 2013, 11:43 AM   #28
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The link was for the company address...they don't really have a web site for a store/purchases

it can be used BTL as RCA or balanced input or stereo with 2 RCA inputs. I use 4 of them in the stereo mode, but I have also used in BTL mode as both balanced and rya input options.

you could also check out this place as they have single modules that can be used also in BTL with multiple boards.

http://www.jlmaudio.com/shop/ but site is down at this time I checked...normally its up and Joe ships internationally too as complete kits or just boards.

the build log is here JLM AUDIO • View topic - JLM 60Watt Power AMP Kit which oddly is up

Click the image to open in full size.
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Old 23rd November 2013, 01:23 PM   #29
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I have attached a PDF of the schematic for this board with the various options to build as described in my other post. This is the same board the original post refers to...ie not the JLM Audio version.
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Old 24th November 2013, 08:00 AM   #30
AndrewT is offline AndrewT  Scotland
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Balanced connection
Pin1 is labeled incorrectly as pin2 and it is shown connected to the audio ground.
It Must NOT be connected to audio ground.

Pin1 goes to Chassis.
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