Good to know. I'll make a mental note of it.
Now all I've got to do is build them, lol.
Hi Kevin,
I enjoyed reading this thread and liked your design very much. As in the initial design there is no baterry bias for the second stage, it does not appear in the BOM. What kind of 1.5 V baterry do you use ? I read somewhere that different type of baterries have different impact on the sound and noise.
I shop for tubes at Gstube.com and had a positive experience in the last couple years. I ordered couple dozens of 6c3n-eb at $1.25 a piece. Just one disadvantage: it takes for ever to arrive from Russia these days. Last order took 2 months.
I appreciate your dedicated work and the fact that you are sharing your design.
Best regards,
Radu
I enjoyed reading this thread and liked your design very much. As in the initial design there is no baterry bias for the second stage, it does not appear in the BOM. What kind of 1.5 V baterry do you use ? I read somewhere that different type of baterries have different impact on the sound and noise.
I shop for tubes at Gstube.com and had a positive experience in the last couple years. I ordered couple dozens of 6c3n-eb at $1.25 a piece. Just one disadvantage: it takes for ever to arrive from Russia these days. Last order took 2 months.
I appreciate your dedicated work and the fact that you are sharing your design.
Best regards,
Radu
Hi Abszero,
For the first stage which is a cascode I would pair by transconductance with the lower tube in the cascode being the more critical of the two.
For the second stage which is a choke augmented mu follower I would pair by mu in the bottom stage, not critical in the top tube.
I have not bothered to match the tubes in mine, interestingly enough the gain match between channels is very close even so.
I would zip the files and make sure you include all of the parts in the library to insure that anyone trying to get boards made has everything required.
I would recommend checking and if necessary replacing the A123 every year as they seem to have some internal discharge mechanism and mine which were no name brand had dropped by 20% in the two years since I built the prototype. The AA dropped no more than a few mV over the same period of time. I have now installed duracells which I will monitor periodically, it could be that the super cheap A123 I purchased originally had some sort of quality issue.
For the first stage which is a cascode I would pair by transconductance with the lower tube in the cascode being the more critical of the two.
For the second stage which is a choke augmented mu follower I would pair by mu in the bottom stage, not critical in the top tube.
I have not bothered to match the tubes in mine, interestingly enough the gain match between channels is very close even so.
I would zip the files and make sure you include all of the parts in the library to insure that anyone trying to get boards made has everything required.
I would recommend checking and if necessary replacing the A123 every year as they seem to have some internal discharge mechanism and mine which were no name brand had dropped by 20% in the two years since I built the prototype. The AA dropped no more than a few mV over the same period of time. I have now installed duracells which I will monitor periodically, it could be that the super cheap A123 I purchased originally had some sort of quality issue.
Hi Kevin,
1. I am posting this first try for the stereo pcb. It definitely can be improved.
Can you look at it and see if you see any issues related to layout of the components and ground.
I was able to zip the file that is ExpressPCB generated ( has .pcb extension).
I am not sure what else one needs to view the file. Do I need to link a schematic to the pcb in order to have a library of parts?
2. I ordered the EXO001 choke from Mike. Very excited to use quality parts. Is the layout of the choke relative to the PCB critical? I assume that the plate choke is not shielded and would easily pick up any em fields in close proximity.
Thanks for the tip about the batteries.
Best,
Radu
1. I am posting this first try for the stereo pcb. It definitely can be improved.
Can you look at it and see if you see any issues related to layout of the components and ground.
I was able to zip the file that is ExpressPCB generated ( has .pcb extension).
I am not sure what else one needs to view the file. Do I need to link a schematic to the pcb in order to have a library of parts?
2. I ordered the EXO001 choke from Mike. Very excited to use quality parts. Is the layout of the choke relative to the PCB critical? I assume that the plate choke is not shielded and would easily pick up any em fields in close proximity.
Thanks for the tip about the batteries.
Best,
Radu
Hi Radu,
Can you also post as a pdf file along with the schematic version you used to generate the PCB? I've migrated to Altium for most of my projects since that is what I use at work.
You should include any parts and footprints from the library that you created, and you should zip and include the schematic with the pcb file. Anyone using the tool can link the schematic and pcb files to verify that things are as they appear.
The choke should be placed as close to the tubes as possible both from the standpoint of stability and the possibility of pick up on wiring. I would say three inches or less - the most critical connection is the plate end of the choke. The choke is very sensitive to magnetic fields which means the power supply and other generators of magnetic fields should be kept away. (about a foot from experience)
Can you also post as a pdf file along with the schematic version you used to generate the PCB? I've migrated to Altium for most of my projects since that is what I use at work.
You should include any parts and footprints from the library that you created, and you should zip and include the schematic with the pcb file. Anyone using the tool can link the schematic and pcb files to verify that things are as they appear.
The choke should be placed as close to the tubes as possible both from the standpoint of stability and the possibility of pick up on wiring. I would say three inches or less - the most critical connection is the plate end of the choke. The choke is very sensitive to magnetic fields which means the power supply and other generators of magnetic fields should be kept away. (about a foot from experience)
Muscovite PCB first draft
I have included in the zip the schematics and pcb, bill of materials. Could not figure out how to include custom library parts.
PCB is stereo, channels are mirrored and share common ground plane.
Connections are top layer colored red, but are designed as bottom (considering that print option (Express PCB) does not allow separate print for bottom layer). I am etching PCBs at home and it is easy for me to do it this way. Tube sockets will be soldered from the bottom layer side (tubes will be exposed outside of the enclosure, they'll be out half way, just enough for easy replacement).
I am planning to have this PCB, and two SSHV2's (one per channel) in one enclosure and PSU in a separate enclosure.
I have included in the zip the schematics and pcb, bill of materials. Could not figure out how to include custom library parts.
PCB is stereo, channels are mirrored and share common ground plane.
Connections are top layer colored red, but are designed as bottom (considering that print option (Express PCB) does not allow separate print for bottom layer). I am etching PCBs at home and it is easy for me to do it this way. Tube sockets will be soldered from the bottom layer side (tubes will be exposed outside of the enclosure, they'll be out half way, just enough for easy replacement).
I am planning to have this PCB, and two SSHV2's (one per channel) in one enclosure and PSU in a separate enclosure.
I think you have to turn off some layers to see the others?
The silk screen looks fine at a glance, but the traces are of interest of course.
Where do you connect the chokes in the second stage? I noticed you added some 1R resistors in the plates of both stages, these aren't strictly necessary, but not a bad idea on the second stage. Not required for determining the plate current, although they do make that easier. Note that each channel should probably have a decoupling capacitor on its 300V rail although this is not recommended with the Salas SSHV2. (I used them with no ill effects on an SSHV2 in one of my dacs.) I would have some concern about stability without them as these tubes can oscillate in the VHF region. (0.22uF low inductance film type)
The silk screen looks fine at a glance, but the traces are of interest of course.
Where do you connect the chokes in the second stage? I noticed you added some 1R resistors in the plates of both stages, these aren't strictly necessary, but not a bad idea on the second stage. Not required for determining the plate current, although they do make that easier. Note that each channel should probably have a decoupling capacitor on its 300V rail although this is not recommended with the Salas SSHV2. (I used them with no ill effects on an SSHV2 in one of my dacs.) I would have some concern about stability without them as these tubes can oscillate in the VHF region. (0.22uF low inductance film type)