Thanks both. The sad truth is that I was using the lead lengths as a guide but still managed to botch it. Good news is that I've recovered, finished the amp, and am now thoroughly enjoying listening as I write this!
Will try and sort this later, although I suspect the issues are more around the levels themselves. Here's some info regarding the levels that are feeding into the Whammy -
Front end = Denon DL-160 with 1.6mV output (Possibly nearer 2mV)
Phono Amp = Modded Rotel RQ970 which increases the gain in MM mode to X100 and in MC mode to X1100
Potentiometer in Whammy = Alps 100K
Headphones being driven - Shure SRH1840 65 ohms impedance.
I'm using the MM mode in the phono amp but the volume levels are too high when volume level is on 0. It's listenable and sounds quite good but definitely needs to be reduced.
Is anyone able to identify where the issue lies?
Here's an in the box pic. A littl emessy and I am yet to connect the signal ground to the IEC earth via a capacitor (in the post...) which should resolve the hum.
To clarify, the amp is working fine but the volume levels are too high and there's a fair amount of volume being generated when the potentiometer is turned right down. That's why I wondered if it's a gain issue?
Double check that the input caps underneath the PCB are connected to the correct pads, and not to other pins of the volume pot
The 2.2uF caps in C1 and C5 are connecting to the cetral 2 pads of the potentiometer which are the signal out pads I believe so correct.
My hunch is there’s an issue with the turntable setup instead. It’s a bit tricky getting grounding issues solved on turntables.
The truntable is grounded on the chassis of the phono amp. I'm not so concerned abou the low level hum as I am expecting this to be resolved when the signal ground is attached to the IEC earth via the cap.
What is the output of your source?
1V rms, 2V rms, 3V rms
Here are the stats of my source :
Front end = Denon DL-160 with 1.6mV output (Possibly nearer 2mV)
Phono Amp = Modded Rotel RQ970 which increases the gain in MM mode to X100 and in MC mode to X1100
Potentiometer in Whammy = Alps 100K
Headphones being driven - Shure SRH1840 65 ohms impedance.
I'm using the MM mode in the phono amp but the volume levels are too high when volume level is on 0. It's listenable and sounds quite good but definitely needs to be reduced.
1V rms, 2V rms, 3V rms
Here are the stats of my source :
Front end = Denon DL-160 with 1.6mV output (Possibly nearer 2mV)
Phono Amp = Modded Rotel RQ970 which increases the gain in MM mode to X100 and in MC mode to X1100
Potentiometer in Whammy = Alps 100K
Headphones being driven - Shure SRH1840 65 ohms impedance.
I'm using the MM mode in the phono amp but the volume levels are too high when volume level is on 0. It's listenable and sounds quite good but definitely needs to be reduced.
I found this.
https://d24z4d3zypmncx.cloudfront.net/Pubs/SRH1840/SRH1840_Spec_Sheet.pdf
It says 96dB per milliwatt
You only need around 2 milliwatts
P= v^2/R
0.002 = V^2/65
v= (0.002*65)^0.5
V=0.36 V rms
MM
1.6mV x 100 = 160mV
6 to 9 dB of gain is plenty.
Maybe reduce the gain in the feedback loop.
https://d24z4d3zypmncx.cloudfront.net/Pubs/SRH1840/SRH1840_Spec_Sheet.pdf
It says 96dB per milliwatt
You only need around 2 milliwatts
P= v^2/R
0.002 = V^2/65
v= (0.002*65)^0.5
V=0.36 V rms
MM
1.6mV x 100 = 160mV
6 to 9 dB of gain is plenty.
Maybe reduce the gain in the feedback loop.
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P= v^2/R
0.002 = V^2/65
v= (0.002*65)^0.5
V=0.36 V rms
MM
1.6mV x 100 = 160mV
6 to 9 dB is plenty.
Maybe reduce the gain in the feedback loop.
Scratching my head at those equations. How do I reduce the gain in the feedback loop? Looks like there are a few options in the schematic to adjust the gain at various points....
0.002 = V^2/65
v= (0.002*65)^0.5
V=0.36 V rms
MM
1.6mV x 100 = 160mV
6 to 9 dB is plenty.
Maybe reduce the gain in the feedback loop.
Scratching my head at those equations. How do I reduce the gain in the feedback loop? Looks like there are a few options in the schematic to adjust the gain at various points....
R8/R12
R4/R1
Taken from schematic on the first page
You could try 3K for both R8, R12, R4, R1
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That's what I thought. It's an Alps 100K and is wired onto the board as seen (no wires crossed over). I assume the Alps are all configure the same (input-outpt-ground). Have checked and the connections seem to be fine. The only thing not yet in place is that the singal ground is not yet connected to the IEC erath via the capacitor. That surely shouldn't compromise the potentiometer though?