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Offline anilkumar_15

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Debug: Almost no amplification
« on: May 23, 2012, 08:10:57 AM »


I bought the smak WOT amplifier kit  and assembled it.  I do not see any gain. It seems the amplifier has become a unity gain amplifier  :'(

I played with impedance-change switches but it did not help at all.
Voltage check seems to be fine. All LEDs are glowing although not too bright.
I tried with it with Grado GS1000, AKG710 and couple of other headphone as well IEM but there is no luck.

Here is some changes I made in the kit because I had some components handy
1. Replaced  multiple resistor with same value but made by Vishay.
2. Replaced the 100K-pot by RK27112A00AK (ALPS). Pin connections are made as per the instruction provided in SMACK-manual. I am under the impression that original POT supplied by BH has same pin configuration as ALPS.

In resistance check , I noticed that that ground-buss is connected to aluminium plate. I am expected that it may cause the hum but should not kill the gain. This might have been caused short while stripping one of shielded cable for soldering. It is very painful to find which cable is causing it.

Please help me to debug it. Can I get diagram with voltage level mentioned for each net ?
Have you seen this issue earlier ?

Offline Paul Joppa

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Re: Debug: Almost no amplification
« Reply #1 on: May 23, 2012, 07:17:51 PM »
At the lowest impedance output (16 ohms), the voltage gain is about 0.75; the amp provides much greater current output but not voltage. At the highest impedance (128 ohms) the voltage gain is about 2.15.

These values are suitable for sources such as CD players which have a 2.0 volt peak output. Are you using a source with smaller output?
Paul Joppa

Offline anilkumar_15

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Re: Debug: Almost no amplification
« Reply #2 on: May 23, 2012, 07:20:14 PM »
I am using ipod-classic as source.

I did change the impedance but could not notice any difference .

Offline Grainger49

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Re: Debug: Almost no amplification
« Reply #3 on: May 24, 2012, 03:52:16 AM »
What PJ was saying above is that if your source, like the iPod, has a lower than standard output you will be short in gain at the lowest impedance settings.  Your problem is not the Smack but the low output of the iPod.

Offline anilkumar_15

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Re: Debug: Almost no amplification
« Reply #4 on: May 24, 2012, 04:11:32 AM »
I will try it with a CD player this weekend and I hope that Grado will be musical !!!

I do wonder that if the amplification is 0.75 then it is not an amplifier (by definition). Is there a way to improve gain without loosing bandwidth.
What do you think about using other type of tubes ?

Any suggestion for a CD player or other digital media player which can be helpful here ? HiFiman has 1.1V output for 32Ohm and 2V for 120Ohm.


Offline anilkumar_15

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Re: Debug: Almost no amplification
« Reply #5 on: May 24, 2012, 09:42:28 AM »
I did notice that when I use the amp then GS1000 sounded muddy (low frequency) . But when I connected headphone directly to ipod it sounded better. Is it related to trying to drive dynamic speaker with current instead of voltage ; or this thing happen after crossing 40 yrs of age.

Offline Paul Joppa

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Re: Debug: Almost no amplification
« Reply #6 on: May 24, 2012, 01:31:06 PM »
From the specs, it takes 0.18 volt to make 1mW into 32 ohms, which would be 98dB with the GS1000s. On the 32 ohm setting the Smack gain is about unity, so 0.18v input would do this.

98dB is pretty loud, and most devices will generate 0.18v easily. So if it is not loud enough, and muddy, then there is quite possibly something wrong somewhere.
Paul Joppa