Indeed. In this case, because of the three channel design with an active ground, the specifications call for a ground to chassis connection. This all connects to a single bolt on the chassis base. There is no main ground connection on the pcb - it is intend to be grounded via the input/output. The mains ground and the amp ground are separated by a 10pF film cap to provide separation.
This is a good point! One of the reasons I went with rack mount power strips as a power supply/filter setup was it lets me control what grounds where. I use it to make sure that linked devices also share a single ground point.
Massive tangent but in general I think that the differences in how wiring is done and supply in north western Europe mean we often have less issue with electrical noise and poor quality supply, which helps too. For example, lights are on their own ring main from the central fuse box and each room (such as kitchen, or main living space) or group of smaller rooms (bathroom, bedrooms) are also isolated from one another. So the heavy things like cookers, or washing machines and so on, are on a separate circuit to the living areas. Additionally most wiring is run in metal channels embedded in solid masonry walls, adding additional emi shielding. Surface mounting of cable runs is rare. Anything built or resold in the last forty years can be reliably expected to follow this.
I get the impression that because of grid age, differences in construction methods and also the distances involved, (plus less strict rules), that it can be much more of a concern in north America?
Thatâs mostly how it works in the US for modern wiring, minus the metal channels and masonry.
My house for example has 20 distinct circuits, the 120âs run either 15 or 20A a piece and usually service 2 or possibly 3 sockets, itâs usually divided by room, so my kitchen has I think 3 distinct circuits (it might be 4) for the wall sockets, a 240V for the Oven, and the lighting circuit.
Any upgrades are a crap shoot, one, of my outside sockets is shared with one of the kitchen circuits I discovered a few years ago when torrential rain filled it with water and tripped half the GFI sockets in the kitchen.
FWIW I was running all the devices connected to my amp from the same power strip it was plugged into, and still had issues with the ground layout.
So. It has been a whole thing. First off, I sorted out the opamps. The recommended ones are now only available as SMB components - thatâs very small things for those whoe donât speak electronics!
I bought and assembled some SOIC to DIP converters:
⌠and fitted the opamps to them. The above one was my first and it was a learning experience. I did manage to strip the cover from the traces on one side and this one will be used on the ground channel. The other two went much more smoothly:
This done I was able to finish all the connections, adjust the bias variable resistors to get the correct output levels and time to test! This went well⌠ish. Once I had rewired the volume pot because changing from upside down and left to right befuddled me enough to get the bloody thing wrong. That done⌠success! And then a mosfet went POP and the top blew off. There was a short to the case and from there to ground. Bugger.
So I left it a week and then stripped all the wiring out and started over, wiser and having learnt. I finally got the wiring done, and today got to test again. No shorts, no issues with the sound, it works! Except the VU meter. I donât know what I have gotten wrong on that circuit so I will be buying a kit instead of making a (third) attempt to build my own. There is output until power is applied to the opamp and then⌠nothing. Itâs also late so I will have to think about it more,
However! The amp works. It sound good. Really nice actually. Very neutral, background is very black and feels still. Itâs not as exciting as the Whammy but that isnât what I was looking for. It pairs well with the ACA Mini and my Dali speakers. A good preamp.
Iâve still to add some text labels, which I plan to do with vinyl stickers. And to get the VU meter working but I am pleased. It was hard, a real learning experience, which is what I wanted. Fitting everything into this small chassis complicated everything massively as did my desire to include a mute switch and a headphone out with toggle. The chassis was also very hard to work with, being relatively heavy steel, and my tools were just not up to the job. Iâll be avoiding that in the future.
Love the look of it! You gotta get an old school on/off switch for it though to complete the look or perhaps an on off knob like the others on the left hand side? It looks so GOOD! Howâs it sounding on initial impressions? This does look like the most complex thing youâve put together by a good bit.
Thank you! I am so happy with how it looks, the photo washes it out a little. In reality the faceplate is a bit creamier and less grey.
I went through so many layouts for the front plate. And buttons!! What kind of on/off switch do you mean? I chose the round black one to keep the overall theme of round black things arranged around the VU meter. (I really really wish I could sort out the VU meter already).
Initial impressions are very clean, very neutral. Good bass and treble extension but they donât feel overly elevated. It feels very detailed, not particularly musical or warm but very controlled, less bassy but more detail in the bass than my other amps. There is a heightened sense of the recording space compared to other amps I have heard. It doesnât have a great sense of spaciousness or separation but the music feels very immersive, encompassing. Like you are sitting in the studio with the engineer.
I think the active ground channel is giving it a very empty blackness behind the music. Itâs subtle. I think this is why it feels like you are in a room with a band.
My over riding impression is that it sounds kind of old school. It sounds like the good hifi stacks my dad had in the 80s.
I did think about that but I had a lot of trouble finding one that fit the specs needed! In the end I went with what I could source, but I agree, it would have been cool
Those darned specs! Itâs very cool and itâs way outside my knowledge base to help in any way in getting the meter working but I agree, itâs a must. It just belongs there.
I just noticed the power switch was âupside downâ, then I remembered in the UK light switches and power switches work the other way around where down is on instead of off.
Oh wow, really? Light switches are weird things. Took me ages to get used to the continental European ones - much bigger rockers. Down is also on here. Funny how these little things seem so fixed and yet are so localised.
