One quick update Fab, I was able to build another Salas psu board by keeping R1 current limiting resistor at 2.2r 2w and now I have a proper voltage matching on both polarities of positive/negative at +/-14.61vdc with the preamp boards connected. I do not get any noise now and plays fine. No dual mono psu for now till I figure out the Salas psu issues in the other board.
I have now set the bias to 238mV (based on your suggested calculation using 4.75R resistor this comes to 50mA) with the offset on both the channels closer to 0.01mV. After an hour the heat sinks are hot but I am able to touch so I guess this is fine to run.
I will give some hours to run-in but right now it is playing via 1862 -> USSPA -> USSA5 -> Troels TQWT MKii. I will give around 50-70 hrs for the break-in before making my judgements but so far its playing nicely when I compare to my Korg or ACP.
Thanks again
I have now set the bias to 238mV (based on your suggested calculation using 4.75R resistor this comes to 50mA) with the offset on both the channels closer to 0.01mV. After an hour the heat sinks are hot but I am able to touch so I guess this is fine to run.
I will give some hours to run-in but right now it is playing via 1862 -> USSPA -> USSA5 -> Troels TQWT MKii. I will give around 50-70 hrs for the break-in before making my judgements but so far its playing nicely when I compare to my Korg or ACP.
Thanks again
One quick question as I see to still have noise issues and I think could be because of the way I have wired the input signal/ground wires from the RCA jacks to the Alps 10k pot and then from the pot to the preamp input signal/grounds.
The way I have done is per your suggest if making dual mono cut the pieces to make it mono and I did the same. So independent mono preamp boards. Currently using a single Salas psu to power both the mono channels.
Input RCA left/right grounds I have shorted on the RCA jacks side and running a Canare interconnect cable with the 2 cores for left/right with its shield to the shorted ground pins of RCA jacs. This goes to the pot input pins where I have shorted the grounds. From the pot out side I have taken individual grounds and goes to the input grounds of the preamp boards.
I am feeling the way I have grounded it is what making the noise and one of the reason for this is if I am using it via playing iPad there is no noise but if I use any of my other sources like Soekris/1862 which have proper grounds I get the noise immediately. This noise isn't there if I am using the Denoiser psu which has a common ground. The salas being independent positive/negative grounds where I am shorting it on the output side this noise issue might be creeping in.
To all other builders please let me know how do you guys have wired this preamp if using as dual mono psu or single psu for both the mono preamp boards.
thanks
The way I have done is per your suggest if making dual mono cut the pieces to make it mono and I did the same. So independent mono preamp boards. Currently using a single Salas psu to power both the mono channels.
Input RCA left/right grounds I have shorted on the RCA jacks side and running a Canare interconnect cable with the 2 cores for left/right with its shield to the shorted ground pins of RCA jacs. This goes to the pot input pins where I have shorted the grounds. From the pot out side I have taken individual grounds and goes to the input grounds of the preamp boards.
I am feeling the way I have grounded it is what making the noise and one of the reason for this is if I am using it via playing iPad there is no noise but if I use any of my other sources like Soekris/1862 which have proper grounds I get the noise immediately. This noise isn't there if I am using the Denoiser psu which has a common ground. The salas being independent positive/negative grounds where I am shorting it on the output side this noise issue might be creeping in.
To all other builders please let me know how do you guys have wired this preamp if using as dual mono psu or single psu for both the mono preamp boards.
thanks
Hi manniraj
Dual mono means one psu dedicated to only one channel
And other PSU for the other channel, thus 2 PSU required for 2 channels.
It is most probably a ground loop you are experiencing which can be worse depending on grounding scheme of PSU itself....Try disconnecting one channel source and leave only one connected to preamp to check if there is still noise (I suppose humming?). Shields connections may create loops if not done properly.
iPad has a common left and right ground.
As a general tip, either you go completely dual mono or completely share a common ground all the way between channels. One PSU for 2 channels is more tricky and I suggest the good reading of Bonsai grounding document which is quite practical for audio equipment and well illustrated ....
Ground Loops
Fab
Dual mono means one psu dedicated to only one channel
And other PSU for the other channel, thus 2 PSU required for 2 channels.
It is most probably a ground loop you are experiencing which can be worse depending on grounding scheme of PSU itself....Try disconnecting one channel source and leave only one connected to preamp to check if there is still noise (I suppose humming?). Shields connections may create loops if not done properly.
iPad has a common left and right ground.
As a general tip, either you go completely dual mono or completely share a common ground all the way between channels. One PSU for 2 channels is more tricky and I suggest the good reading of Bonsai grounding document which is quite practical for audio equipment and well illustrated ....
Ground Loops
Fab
Hi Fab
I could complete the VRDN psu boards for the USSPA and now using to power individual channels I made it completely dual mono but right now using my spare 18v 2A trafo till I get hold of another 15v 2A rcore. Now when i tested with a single VRDN powering both the channels and making the input side channel grounds shorting absolutely no hum at all.
With dual mono of VRDN psu boards I am still keeping the same but the grounds on the psu are not shorted to make it common. I have shorted the grounds from the input signal to the volume pot and then from the pot to the USSPA. I see there is a slight hiss/hum kind of sound coming from my tweeters audible from 2 feet as well. Now can you please let me know how do I wire up the grounds being dual mono right from the transformers to the psu boards to the mono preamp boards. Pic for your reference in a makeshift cabinet for the time being
thanks again for an awesome sounding preamp paired with USSA-5 and Troels, its making my music sound more lively and every bit of instrument sound is coming through so clean and clear.
I could complete the VRDN psu boards for the USSPA and now using to power individual channels
I made it completely dual mono but right now using my spare 18v 2A trafo till I get hold of another 15v 2A rcore. Now when i tested with a single VRDN powering both the channels and making the input side channel grounds shorting absolutely no hum at all.With dual mono of VRDN psu boards I am still keeping the same but the grounds on the psu are not shorted to make it common. I have shorted the grounds from the input signal to the volume pot and then from the pot to the USSPA. I see there is a slight hiss/hum kind of sound coming from my tweeters audible from 2 feet as well. Now can you please let me know how do I wire up the grounds being dual mono right from the transformers to the psu boards to the mono preamp boards. Pic for your reference in a makeshift cabinet for the time being
thanks again for an awesome sounding preamp paired with USSA-5 and Troels, its making my music sound more lively and every bit of instrument sound is coming through so clean and clear.
Hi manniraj
Your question is addressed to the audio community concerning grounding scheme.
In order to have full dual mono it must include the left and right input grounds separated as well. I also use independent ground on the pot and up to the USSPA. If you have continuity (0 ohms) when you measure resistance between left and right ground then you are not full dual mono...
So again, either full dual mono or stereo with common ground. If you are successful with a mono PSU configuration then it works.
As per your request I include a picture of one of my preamp using USSPA2 boards. It is 6 inputs with channels selectors with displays and passive/active selector....so many connections. The selector board was originally using a common ground so I use a twin bus ground instead for separated left and right ground. The KOZMO pot is also dual mono. I have the KOZMO pot case AC connected to chassis.
I am glad you like your combo USSPA/USSA-5/Troels
I had the same combo but different Troels speakers.
Fab
Your question is addressed to the audio community concerning grounding scheme.
In order to have full dual mono it must include the left and right input grounds separated as well. I also use independent ground on the pot and up to the USSPA. If you have continuity (0 ohms) when you measure resistance between left and right ground then you are not full dual mono...
So again, either full dual mono or stereo with common ground. If you are successful with a mono PSU configuration then it works.
As per your request I include a picture of one of my preamp using USSPA2 boards. It is 6 inputs with channels selectors with displays and passive/active selector....so many connections. The selector board was originally using a common ground so I use a twin bus ground instead for separated left and right ground. The KOZMO pot is also dual mono. I have the KOZMO pot case AC connected to chassis.
I am glad you like your combo USSPA/USSA-5/Troels
I had the same combo but different Troels speakers.
Fab
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Thanks Fab for the pics of your dual mono build and difficult to judge the wiring but it does look intimidating
Now coming to my build I am using a Alps Bluevelvet 10KA pot along with its small PCB board for easy wiring connections. The pcb board makes it common ground for left/right input and output side, hence there is no way to make it fully independent if using a pot for the volume. I guess its the same case even for other stereo pots. So the way you explained to make it fully separate grounds for each channel even in the dual mono configuration may not work out in a single chassis unless I use a mono volume pot (keeping a separate pot for each channel) or Khozomo type having independent grounds on the pot.
Link to the small RK27 pcb - Double Sides FR4 PCB Board Adapter Circuit Board For ALPS RK16 RK27 Volume Potentiometers Hifi Audio DIY 1PC|alps rk16|board pcbboard board - AliExpress
Thanks
Now coming to my build I am using a Alps Bluevelvet 10KA pot along with its small PCB board for easy wiring connections. The pcb board makes it common ground for left/right input and output side, hence there is no way to make it fully independent if using a pot for the volume. I guess its the same case even for other stereo pots. So the way you explained to make it fully separate grounds for each channel even in the dual mono configuration may not work out in a single chassis unless I use a mono volume pot (keeping a separate pot for each channel) or Khozomo type having independent grounds on the pot.
Link to the small RK27 pcb - Double Sides FR4 PCB Board Adapter Circuit Board For ALPS RK16 RK27 Volume Potentiometers Hifi Audio DIY 1PC|alps rk16|board pcbboard board - AliExpress
Thanks
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Thanks Vunce. I even have my brand name written on the front plateAwesome work Fab!
Showin off one of your toys in the stable
Fab
Hi manniraj
The volume pots are double mono (Alps Bluevelvet 10KA pot ). It is simply not the right pot pcb for a dual mono. I only use this pcb for non-dual mono configuration in some pre-amps. You can directly solder the wires on the pot pins for dual mono or find a dual mono pot pcb or separate left and right grounding on the reworked pot pcb with a Dremel tool for example.
Fab
The volume pots are double mono (Alps Bluevelvet 10KA pot ). It is simply not the right pot pcb for a dual mono. I only use this pcb for non-dual mono configuration in some pre-amps. You can directly solder the wires on the pot pins for dual mono or find a dual mono pot pcb or separate left and right grounding on the reworked pot pcb with a Dremel tool for example.
Fab
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Hello Fab and other guys who built this preamp, a quick question on how high the bias can be considering the 40mm height heat sinks used in the boards. Currently running at the default 238mV (based on your suggested calculation using 4.75R resistor this comes to 50mA). But seems like others are running a bit high like 100mA and overall a much better improvements
After couple of hours of playback the heat sinks on the preamp get warm to the touch and do not get hot to worry about so I presume we can increase the bias a bit to get more oomph being class A
Right now the preamp is paired with my J2 mono blocs and the combo is very pleasant and fatigue free to listen to with absolute dead silent even with ears closer to my Troels.
After couple of hours of playback the heat sinks on the preamp get warm to the touch and do not get hot to worry about so I presume we can increase the bias a bit to get more oomph being class A
Right now the preamp is paired with my J2 mono blocs and the combo is very pleasant and fatigue free to listen to with absolute dead silent even with ears closer to my Troels.
Hi manniraj
If your heatsinks are only warm you sure can increase the bias. The thermistors will compensate to prevent thermal runaway anyway. Increased current provides increased transconductance of the output transistors which is normally a good thing in that circuit. Using bigger heatsinks could push that even further …
Good luck in your trials.
Fab
If your heatsinks are only warm you sure can increase the bias. The thermistors will compensate to prevent thermal runaway anyway. Increased current provides increased transconductance of the output transistors which is normally a good thing in that circuit. Using bigger heatsinks could push that even further …
Good luck in your trials.
Fab
Message for one person
This message is for a person who contacted through my web site e-mail and requested USSPA and USSA-5 pcbs. We had several e-mail exchanges (our personal emails ) and I have ordered a batch of USSPA pcbs. However I can no more reply to him and get this message “
Your message wasn't delivered. Despite repeated attempts to deliver your message, the recipient's email system refused to accept a connection from your email system.“
So for this person, please contact me again by other means ( message on this forum) or fix this issue on your end.
Thanks
Fab
This message is for a person who contacted through my web site e-mail and requested USSPA and USSA-5 pcbs. We had several e-mail exchanges (our personal emails ) and I have ordered a batch of USSPA pcbs. However I can no more reply to him and get this message “
Your message wasn't delivered. Despite repeated attempts to deliver your message, the recipient's email system refused to accept a connection from your email system.“
So for this person, please contact me again by other means ( message on this forum) or fix this issue on your end.
Thanks
Fab
Hi Fabien, here I am, I'm Fabio, I will check my email in the next few hours, but in reality, I always contacted you through the fabaudio site, because the messages sent by my email did not reach you. I'll check if you accidentally ended up among the blocked senders. anyways, now you have my contact on diyaudio. Thanks, Fabio