As an update I have now fitted the different value resistors and installed a new 50k pot. All of the hum and signal level issues have been resolved. I'm finding the amp silent with no signal and working nicely with the 1840s. Thanks to all who helped identify and resolve the issues...
If the entire enclosure is wooden, you may have to create what I've called an intentional ground plane. Essentially you create a isolated, conductive path for ground instead of relying on the chassis. In essence, create a backplane/star ground point that you then run grounding wires to.
For example, you can simply screw a nylon standoff near the back cover near the IEC entry point and run grounding wires from the board, pot, and negatives of the incoming RCAs and inlet phono connector to that single, isolated screw, and then from there connect the .1 uf cap/diodes or diode bridge/resistor to the IEC's ground lug so that ground is isolated until needed.
This should create the lowest impedance path to ground. Just be sure that it is indeed isolated from the chassis except at the star point. You can verify this by probing around the chassis with your DVM set to continuity/diode mode.
--Tom
A grounded metal enclosure also effectively shields the insides from outside interference, allowing you to get away with things you couldn't otherwise, like using a higher resistance pot.
Agreed. The best builds I've seen (or heard) like this use the vintage wooden enclosure as a "skin" that house a metal enclosure inside. OTOH I've seen a bunch that look awesome but have grounding/noise issues just like the one we're trying to debug now. That is why I personally went with good looking, well constructed metal enclosures a long time ago.
So i built one with irf9610 and one with 9530 and they definitely sound different, with 9530/9530 pair being more 'soft'. Everything else in the build is the same. What would be the reason behind this? Gate capacitance?
Yeah. Could be as you say.
I wouldn't expect the higher transconductance of 530/9530 to cause that so maybe the opamp you're using struggles a bit with capacitive loads.
You could try other opamps that might have better driving ability.
I wouldn't expect the higher transconductance of 530/9530 to cause that so maybe the opamp you're using struggles a bit with capacitive loads.
You could try other opamps that might have better driving ability.
Is gate capacitance more relevant than the 22uf caps before the mosfets?
Also im wanting to try bjt outputs such as bd140/139 and wondering if its plug and play (as long as pinouts are correct)
Also im wanting to try bjt outputs such as bd140/139 and wondering if its plug and play (as long as pinouts are correct)
For bipolars you want to use a darlington. So BD139/140 is not appropriate.
Sanken make some nice Darlington bipolars. You might need to increase the resistance at the base eg 1k
My understanding is that capacitance in series with the gate does not affect bandwidth like the parasitic capactance from gate to drain and gate to source of the mosfet.
Sanken make some nice Darlington bipolars. You might need to increase the resistance at the base eg 1k
My understanding is that capacitance in series with the gate does not affect bandwidth like the parasitic capactance from gate to drain and gate to source of the mosfet.
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Which depth dimensions did you go with for the Galaxy 2U? I'm looking for a chassis that fits comfortably, but not with too much room to spare.
I'm getting a crackling noise when I turn the Whammy off, is this normal? There is no noise on the amp and is running great when it is on
Yes it does it with certain op amps. It's normal. If you use an OPA2107. The problem will disappear.
Thanks Gaz. Seems to be an issue with the OPA627. My LM833N doesn't have issues like that or my 2107 but I soldered the OPA627 myself
I didnt need any gain on my whammy so i took out the 1k5 resistor to ground from the - pin of the opamp, which r ne5334 in mine, and it works. Works really well and the offset is stable at .001, hehe. I even changed the feedback resistor to 150ohm and it still sounds wonderful. 😁
Should i maybe put 100kohm resistor from the negative pin to the gnd to define the impedance? What would that do?
Should i maybe put 100kohm resistor from the negative pin to the gnd to define the impedance? What would that do?
You could add the 100k resistor to try. It shouldn't do much.
Some opamps don't like to be run at unity gain, so if you experiment with other opamps just be sure they are unity gain stable. It should specify clearly on the data sheet.
Some opamps don't like to be run at unity gain, so if you experiment with other opamps just be sure they are unity gain stable. It should specify clearly on the data sheet.
Can someone explain to me the principle behind the capacitor that connects input signal ground to safety earth? I have basic electrical knowledge, but apparently not enough to figure that out. I have not seen this in other circuits, so I'm curious why it's here in this one.
I've built one of these and am now building another for a friend. My previous headphone amp was a Schiit Magni, and, well, no contest. (Headphones are Focal Elear.)
I also muck about with woodworking, so the cases are made from wood. The images below are from the first version, built from some gorgeous jotoba (aka Brazillian cherry, although it is not a kind of cherry) that I bought years ago and have been waiting to find a good use for. The finish is just polyurethane. It really is a great wood, with this deep color and great grain. The top is made from luan (stained cherry) and will probably be replaced at some point with something veneered. But I'm just learning to do veneer....
(It appears I need to stain the insides of the vents. The camera shows everything!)
As you'll see, I've left some extra room in this box in case I want to get creative with the volume control. Unfortunately, the volume control is not vertically centered on the first one. It will be on the next one. This is the tricky dimension.
The other box, which I'm building from redwood left over from another project, will be done in a few days. I'll post pictures then. I have just enough of the jatoba left for one more case, I think, so some other friend is likely to find one of these in their stocking....
How much interest is there in building cases from wood? Having built two of these now, I have a pretty good sense for what a set of plans would look like and could produce something along those lines pretty easily. But if it would just be a waste of time....
I also muck about with woodworking, so the cases are made from wood. The images below are from the first version, built from some gorgeous jotoba (aka Brazillian cherry, although it is not a kind of cherry) that I bought years ago and have been waiting to find a good use for. The finish is just polyurethane. It really is a great wood, with this deep color and great grain. The top is made from luan (stained cherry) and will probably be replaced at some point with something veneered. But I'm just learning to do veneer....
(It appears I need to stain the insides of the vents. The camera shows everything!)
As you'll see, I've left some extra room in this box in case I want to get creative with the volume control. Unfortunately, the volume control is not vertically centered on the first one. It will be on the next one. This is the tricky dimension.
The other box, which I'm building from redwood left over from another project, will be done in a few days. I'll post pictures then. I have just enough of the jatoba left for one more case, I think, so some other friend is likely to find one of these in their stocking....
How much interest is there in building cases from wood? Having built two of these now, I have a pretty good sense for what a set of plans would look like and could produce something along those lines pretty easily. But if it would just be a waste of time....