I just got around to fitting my S-5 electronics stereo tube amp in a case with a wood bottom and a metal top with vent holes. The binding posts are attached to the metal top but are isolated from it. The top is something I found at a kitchen store and is teflon non-stick coated. I got a volume knob from radio shack for $3 that has ALPS stamped on it. I soldered it off the board with wires and bolted it to a hole in the metal top. With the source paused, the amp is quiet until the pot is around 1 oclock, until about 5 oclock, when it hums kind of like a guitar amp. The hum doesn't get louder, it just exists. There is no hum with the pot all the way up. Does anyone have any idea what is going on?
Is the pot's shaft connected to the amplifiers ground? It should be, unless you have the amplifiers ground and the pot shaft both referenced to earth ground.
Also, I found on my kit (it's an old revision S5 kit) the hole where the provided on the PCB to ground the pot shaft, was actually connected to the input of one of the channels instead (this causes the buzz characteristic to change when you touch the pot shaft at certain volume settings). If your board has the same error, do not use the provided hole.
Also, I found on my kit (it's an old revision S5 kit) the hole where the provided on the PCB to ground the pot shaft, was actually connected to the input of one of the channels instead (this causes the buzz characteristic to change when you touch the pot shaft at certain volume settings). If your board has the same error, do not use the provided hole.
I actually purchased this as a completed amp, and just fit it to a chassis.
Which wires should be twisted? I twisted the wires that lead to and from the power switch I supplied.
I used the advice Jeb-D gave me and changed the grounding wire from the hole it was in to a spare hole on the ground trace in the rear of the board. It worked very well, reducing the hum to little, but I still get some buzzing when the pot is almost full bore. There is also some very quiet what sounds like power AC hum that doesnt change with pot position. Is this the "AC under the caps" hum I've been reading about?
gmilitano, I actually got this amp after being inspired by your build on DIY Audio Projects. Youve got some interesting builds.
Thanks
Which wires should be twisted? I twisted the wires that lead to and from the power switch I supplied.
I used the advice Jeb-D gave me and changed the grounding wire from the hole it was in to a spare hole on the ground trace in the rear of the board. It worked very well, reducing the hum to little, but I still get some buzzing when the pot is almost full bore. There is also some very quiet what sounds like power AC hum that doesnt change with pot position. Is this the "AC under the caps" hum I've been reading about?
gmilitano, I actually got this amp after being inspired by your build on DIY Audio Projects. Youve got some interesting builds.
Thanks
This is normal for these kit's. Especially if your speakers are rated above 90dB 1W/1M. If S5 were to put in more into the power supply it would jack up the cost of the amp kit. There are ways to improve the power supply which will reduce this, if it is bothering you and you have have some cash to spend.
If the amps buzz characteristic changes with knob position, this usually indicates grounding scheme. If you can post pictures of the amp guts, it would be easier to tell what is going on. Is this happening with a source connected or no source?
Of course. Remove the pot. On the PCB holes for the pot, put jumpers from the pots input terminals to the pots output terminals. Then add a pull down resistor from the input tubes grid to ground. The value will depend on your pre-amps capabilities. 100k is the safe side, but if your pre-amp can handle a 10k load, I'd go with that.
I removed mine too. but check for grid leak voltage when a source isn't attached. Check it when the pot is at maximum setting.
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