I built a preamp based on the circuit of the Matisse Fantasy 2 years ago. While the preamp sounds amazing, it had a soft buzz coming out from the mid high and I am able to trace it down to the Khozmo 64 steps ladder attenuator. For some reason, the body is not able to properly grounded even installed to the front plate of the amp which is aluminium. The front part of the thread and nut just won’t do. So I attached a wire and ground it from one of the screw at the back of the body(please see the third picture, the black wire). But this connection doesn’t always work. Sometimes the buzz comes back out again and I have to readjust this screw or jiggle it then the buzz will go away again and it’s dead silent. Can anyone tell me what can I do to make this buzz go away permanently or someone using this same attenuator knows a method of properly ground this attenuator? Different than their earlier product, this one does not have the ground nut nor the ground spot marking. Many thanks in advance.
Hi Jon. Thanks for your reply. Would this affect the stability of the grounding? The back panel works but just the buzz will come back for no reason and after jiggle the screw a bit it goes away again. May be I will do a test to see if the front and the back panel is connected and try the spots that your arrows pointing to. But I will have to find a screw to do this as it doesn’t come with a screw to go into there. Very frustrating, If this is a known behavior, they should release a note to the user and give the user an option of grounding.
I have measured and the front and back panels are connected. However the resistance being 3ohms. Would it be better to ground both front and back panel or just the back is enough? M3 stainless steel screws and star washers ordered.
Update: I have email Khozmo and got a response from arek, he suggested me to connect the signal GND to the GND of the 5V power supply that powered the attenuator. And bingo! The buzz that has been bothering me occasionally for the past one and a half years has gone! Anyone using this attenuator please note.
I had exactly the same problem with two preamp I built dual mono attenuators. One pair had a threaded hole that worked - I grounded that to the audio ground buss. The other pair had no such hole. I ended up wrapping a very soft wire around the large threaded mounting boss and grounding that. Silenced both of the units. Not really happy with the "cludge" aspect of the second setup but happy with the results!
When you say signal ground do you mean your signal ground for the whole preamp or just the lug on the attenuator circuit board? Maybe post a sketch?
The Signal GND of the attenuator lug to the GND side of the 5V power supply that powers the attenuator. I also wasn’t sure so I confirmed with arek before I proceeded. And after I connected the above, the buzz and soft hum has vanished. Now I don’t even have to ground the attenuator body. Although by grounding the attenuator body to the chassis works but it was not stable. The buzz came back once in a while. I think it is because the body is anodised. But the method suggested by arek seems to be stable.
Just to clarify that I have the 64 steps ladder type attenuator with remote which requires a 5VDC power supply.
Jumping in here rather than starting another thread. I just want to make sure I'm correct in my grounding. I'm adding a khozmo to an existing preamp.
Does the grounding go;
Input ground - khozmo ground - preamp input (-) ?
- khozmo ground lug to earth
Does this seem correct?
Thanks, I'm learning
Does the grounding go;
Input ground - khozmo ground - preamp input (-) ?
- khozmo ground lug to earth
Does this seem correct?
Thanks, I'm learning
Please first use the correct terms and understand (or google) what "earth" and "ground" are exactly. Then try PE and GND.
Many misunderstandings come from the habit in english speaking areas to call 2 different things by the same name and as a consequence by using their applications mixed up.
Casing/chassis is connected directly to PE for safety. GND is at the secondary side of a PSU and used as conductor in audio circuits.
Many misunderstandings come from the habit in english speaking areas to call 2 different things by the same name and as a consequence by using their applications mixed up.
Casing/chassis is connected directly to PE for safety. GND is at the secondary side of a PSU and used as conductor in audio circuits.
I've got a balanced pre from Khozmo, with the 64 step attenuators and input switch. Beautifully built, with the custom remote that is so hefty you could hammer nails in with it.
I of course took the lid off. I noted that there was a grounding wire in a particular location. I need to do some dusting and contact cleaning, so I'll take the lid off again and take a photo.
Arek was very responsive in advising on the impedance and resistor type.
Craig
I of course took the lid off. I noted that there was a grounding wire in a particular location. I need to do some dusting and contact cleaning, so I'll take the lid off again and take a photo.
Arek was very responsive in advising on the impedance and resistor type.
Craig