Hello DIYr’s-
I’m new to building amps and I’m looking for some help on a slight hum/buzz issue I’m having with my new VTA SP14 Khozmo build from Tubes4hifi. We can take a step back and I’ll give as much info as possible about me. A few weeks back I built a pair of M125 mono block amps from Tubes4hifi/Bob Latino. They are dead quiet, transparent, open and clean. I was using my Bluesound Node 2 as my preamp to stream music. Love them! I was so impressed how they sounded I wanted to compliment them with a Tube preamp therefore opting to build the VTA SP14 from Tubes4hifi. I opted to upgrade the standard SP14 to the Khozmo design which incorporates a digital display and remote control. I also upgraded the output caps to the Muldorf’s and went with the NOS Sylvania tubes.
The project went very well. It is completed and it sounds really nice except for the issue I’m now getting an annoying buzzy/hum coming through my speakers. I’ve been working back and forth with Roy from Tubes4hifi and I’ve tried different things including powering everything into the same power strip (which I hate) but for the sake of testing did and because my voltages were on the high side, I changed the HV tap on the tformer per Roy from the 280vac tap to 260vac. The buzzy/hum persist. I have attached some pics of the SP14 builds along with the mono blocks. Looking for any suggestions from some of the experts out here. This thread is in no way to bash this product or seller. The seller Roy has been very helpful to this point.
I have $1500 into this project but this preamp is also boasted to compete in the big arena’s $4k-$6k price range. That is why I’m trying to get it right to be able to use it to its capabilities. Thank you in advance.
I’m new to building amps and I’m looking for some help on a slight hum/buzz issue I’m having with my new VTA SP14 Khozmo build from Tubes4hifi. We can take a step back and I’ll give as much info as possible about me. A few weeks back I built a pair of M125 mono block amps from Tubes4hifi/Bob Latino. They are dead quiet, transparent, open and clean. I was using my Bluesound Node 2 as my preamp to stream music. Love them! I was so impressed how they sounded I wanted to compliment them with a Tube preamp therefore opting to build the VTA SP14 from Tubes4hifi. I opted to upgrade the standard SP14 to the Khozmo design which incorporates a digital display and remote control. I also upgraded the output caps to the Muldorf’s and went with the NOS Sylvania tubes.
The project went very well. It is completed and it sounds really nice except for the issue I’m now getting an annoying buzzy/hum coming through my speakers. I’ve been working back and forth with Roy from Tubes4hifi and I’ve tried different things including powering everything into the same power strip (which I hate) but for the sake of testing did and because my voltages were on the high side, I changed the HV tap on the tformer per Roy from the 280vac tap to 260vac. The buzzy/hum persist. I have attached some pics of the SP14 builds along with the mono blocks. Looking for any suggestions from some of the experts out here. This thread is in no way to bash this product or seller. The seller Roy has been very helpful to this point.
I have $1500 into this project but this preamp is also boasted to compete in the big arena’s $4k-$6k price range. That is why I’m trying to get it right to be able to use it to its capabilities. Thank you in advance.
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I cannot enlarge the images. I built the SP14 with a Khozmo but it's just manual and no display. Yours sounds interesting. I had no hum troubles and I currently use mine with a Pass F4. Vey good sound.
Have you searched on here for good signal earth wiring practice? Perhaps if you could sort the photos out we could take a look.
By the way I use 12SN7 - cheaper than the 6V item.
Have you searched on here for good signal earth wiring practice? Perhaps if you could sort the photos out we could take a look.
By the way I use 12SN7 - cheaper than the 6V item.
Hope you solved your problem.
I had terrible buzzy hum with VTA built M-125's.
I use a passive LC1 I designed.
I solved it. Full instructions ieLogical VTA M-125
I had terrible buzzy hum with VTA built M-125's.
I use a passive LC1 I designed.
I solved it. Full instructions ieLogical VTA M-125
@luvrockin Did you ever find the hum cause? Interesting to spot your post via google as it reminded me of what a builder told me just a week ago. For the sake of some qualification this builder who is in Tx and sells his builds online and there is one review out there for his initial preamp offering .. Brown Audio Labs. In discussing a potential build for me he mentioned that he had a hum issue when using the Khozmo and if I recall correctly it was creating a ground loop (hum) because of it grounding to the through hole in the chassis. My only qualm like a few others is there is just no info online about BAL to be found. There is the Absolute Sound review which is very positive of his preamp but nowhere else any info regarding anything about it. Im considering going for an SP14 myself and was going to upgrade to the Khozmo remote stepped. I would be ordering one assembled. Certainly would mention this to Roy and if he has run into this issue with Khozmo.
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"The Khozmo attenuator is not the issue. It does not ground the audio ground to the chassis, though there is a lug on the Khozmo that is an earth in case you mount the attenuator in a piece of non conductive material like plastic or wood.[/QUOTE]"
that sure is interesting -- Im going to check with BAL on this. We had been discussing a build and trying to decide how I could have a stepped installed and the Khozmo came up but also his line stage has a phono onboard which is nice but there would not be enough volts left over from other uses in the preamp (2 trannies) to supply at least 12v for the stepped. Apparently a Khozmo worked in his design although of course the hum issue of which he said was from metal to metal contact creating ground loop.
Im going to follow up with him to see what he thinks. Although not sure he wants to do my custom build anymore because it got a bit tedious re/doing stepped. Goldpoint or Dact apparently would need more volts and another p.s. would be required according to him . Of course Im the last person that can explain this stuff. I really dont know squat --(my camp amp sits in the garage waiting to be built) just piecing together what bare facts im gathering.
that sure is interesting -- Im going to check with BAL on this. We had been discussing a build and trying to decide how I could have a stepped installed and the Khozmo came up but also his line stage has a phono onboard which is nice but there would not be enough volts left over from other uses in the preamp (2 trannies) to supply at least 12v for the stepped. Apparently a Khozmo worked in his design although of course the hum issue of which he said was from metal to metal contact creating ground loop.
Im going to follow up with him to see what he thinks. Although not sure he wants to do my custom build anymore because it got a bit tedious re/doing stepped. Goldpoint or Dact apparently would need more volts and another p.s. would be required according to him . Of course Im the last person that can explain this stuff. I really dont know squat --(my camp amp sits in the garage waiting to be built) just piecing together what bare facts im gathering.
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although too late now, I am wondering if your issue was a ground loop issue and not so much related to the preamp, since the new owner seems to be very happy with them!
A ground loop hum/buzz can be easily misdiagnosed by a novice as a preamp/amp hum issue. Ground loops are usually external to the piece, but can also be an issue with the internal ground wiring of a preamp or amp.
It is not always easy to try and solve a ground loop issue, they can be a real pita!
There is no doubt it was a ground loop issue. But I tried that preamp on 4 different systems in different rooms in the same house and everyone of them had the issue. It wasn’t very loud but I heard it every time I turned it on. I just got fed up with it because I wasn’t going to start reinventing the wheel in my electrical panel for the house lol
As another just suggested. Ground loop.. This is exactly what the builder of Brown Labs Audio said. Ground loop but occurring for some reason where metal meets metal on the chassis for Khozmo volume control shaft . Now I would like to think that this builder checked out what was going on and apparently when Khozmo was removed everything was ok .. Maybe it was something in his topology design that created the GL . I have a message out to him and curious what he will say.
Hello I am having the same problem , hum and buzz , can hear about 3 ft. Away from my omega 3 xrs speakers , both channels ! Even though there is noise the sound is excellent!!! I also have the Benchmark media DAC3 preamp and AHB2 amp this equipment is “DEAD” quiet!!! I heard so much about the 6sn7 preamps . This sp14 could turn out to be a shelf ornament, frustrating !
Lot's of theory in this link but I'm wondering if people suffering ground loops have more than one signal ground to protective earth connection. If not then there is a ground lift
circuit which should help - look for 15.10: Ground Lift
http://www.valvewizard.co.uk/Grounding.pdf
I remember when I built my SP14 I did have more than one signal earth comming from the pcb initially.
circuit which should help - look for 15.10: Ground Lift
http://www.valvewizard.co.uk/Grounding.pdf
I remember when I built my SP14 I did have more than one signal earth comming from the pcb initially.
The Devil is in the Details
I don't have an SP-14, but I just looked at the online image.
http://www.tubes4hifi.com/SP14-266.jpg
Two things that are wrong are the transformer orientation and the 0vA buss joining the panel RCA connectors.
It appears one half of the high voltage line is adjacent to one of the heater lines. The High Voltage line should be twist up to the point the enter the PCB. ALL A/C lines should be well twisted. The aforementioned Valve Wizard article should be followed explicitly.
0vA - ZERO Volts Audio - should be one point.
The transformers appear to be HT and heater. They should be oriented so Line is as far away as possible from output. Twist ratio is inadequate. Heater winding polarity should match between channels.
See http://192.168.1.160/Audio/VTA_M-125.php#Polarity for more info on transformer and heater polarity.
There should be no direct connection between 0vA and chassis.
Rod Elliott has a very good page on Earthing and Ground Loops Earthing (Grounding) Your Hi-Fi - Tricks and Techniques in particular.
I don't have an SP-14, but I just looked at the online image.
http://www.tubes4hifi.com/SP14-266.jpg
Two things that are wrong are the transformer orientation and the 0vA buss joining the panel RCA connectors.
It appears one half of the high voltage line is adjacent to one of the heater lines. The High Voltage line should be twist up to the point the enter the PCB. ALL A/C lines should be well twisted. The aforementioned Valve Wizard article should be followed explicitly.
0vA - ZERO Volts Audio - should be one point.
The transformers appear to be HT and heater. They should be oriented so Line is as far away as possible from output. Twist ratio is inadequate. Heater winding polarity should match between channels.
See http://192.168.1.160/Audio/VTA_M-125.php#Polarity for more info on transformer and heater polarity.
There should be no direct connection between 0vA and chassis.
Rod Elliott has a very good page on Earthing and Ground Loops Earthing (Grounding) Your Hi-Fi - Tricks and Techniques in particular.
There is an internal grounding of the attenuator to the case of the Khozmo, I did a line stage build for a customer, and had the same ground loop issue, I’ve never grounded my preamp stages to the volume pot, tried to contact them with no response! I connected one of my motorized ALpS to the unit and sounded great with ZERO hum!!
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