Hi,
I ordered the kit without the chassis, as I wanted to build my own - plus I wanted to try to save some $$$’s
I’m getting a LOT of noise out of this…
All the voltages are as they should be.
B+ is 276vdc
H+/H- is 6.13 and 5.87
Voltage drops from 313 to 276 across D13 (both sides…)
6.43vac on heater from transformer
I have checked, double and triple checked the wires from all RCA inputs/outputs. The ground bus and all the connections to that, the ground to the circuit board from the bus. I’ve gone over the input selector, and all the wires coming and going from that. All the connections from the selector, through to the gain and volume controls. The output from the volume to the board, and ground wire are as outlined in the instructions.
I did not install the tape switch, and ran the wires straight from selector to the gain pots.
There are two things I changed as far as the power supply goes. I used an old school toggle switch in place of the power switch that came with the kit. And I accidentally reversed the red and black primaries to the transformers from a hot/neutral perspective. But I don’t think the transformers care about hot/neutral?
The noise is the same regardless of gain/volume settings. It’s the same in both channels. It gradually comes up in volume as the unit powers up. As soon as it’s powered off, it disappears but music keeps playing until it fades away.
The noise is the same, albeit with different volumes, if I run it into my DIY Hiraga Super 30 Class A SS amp, or my DIYAudio VFet SE SS amp.
Thank you for taking the time to read through this, any help would be greatly appreciated!
P
This is the noise as it presents at the speaker…
I ordered the kit without the chassis, as I wanted to build my own - plus I wanted to try to save some $$$’s
I’m getting a LOT of noise out of this…
All the voltages are as they should be.
B+ is 276vdc
H+/H- is 6.13 and 5.87
Voltage drops from 313 to 276 across D13 (both sides…)
6.43vac on heater from transformer
I have checked, double and triple checked the wires from all RCA inputs/outputs. The ground bus and all the connections to that, the ground to the circuit board from the bus. I’ve gone over the input selector, and all the wires coming and going from that. All the connections from the selector, through to the gain and volume controls. The output from the volume to the board, and ground wire are as outlined in the instructions.
I did not install the tape switch, and ran the wires straight from selector to the gain pots.
There are two things I changed as far as the power supply goes. I used an old school toggle switch in place of the power switch that came with the kit. And I accidentally reversed the red and black primaries to the transformers from a hot/neutral perspective. But I don’t think the transformers care about hot/neutral?
The noise is the same regardless of gain/volume settings. It’s the same in both channels. It gradually comes up in volume as the unit powers up. As soon as it’s powered off, it disappears but music keeps playing until it fades away.
The noise is the same, albeit with different volumes, if I run it into my DIY Hiraga Super 30 Class A SS amp, or my DIYAudio VFet SE SS amp.
Thank you for taking the time to read through this, any help would be greatly appreciated!
P
This is the noise as it presents at the speaker…
I built a scratch SP14 with the board only. It was challenging to get quiet. A few possibilities:
1) Did you get a manual? The grounding scheme for the input and pot connections is tricky and you have to follow the instructions exactly. The board is prone to ground loops. Too many ground connections and it will hum.
2) The value of R10 is critical, especially in relation to the B+. If you don't get it just right, there's no PS noise cancellation. Some people put a 100K pot in that position and adjust for minimum noise.
3) Raise C39 to 1uF. This is the bypass for the filament voltage divider. A friend suggested this and it was the last piece of the puzzle for my build.
4) Try a different 6X5GT. Some have heater-cathode leakage, which will inject hum into the preamp.
5) Try swapping around different 6SN7s. Some are noisier than others.
Nice looking build, though!
1) Did you get a manual? The grounding scheme for the input and pot connections is tricky and you have to follow the instructions exactly. The board is prone to ground loops. Too many ground connections and it will hum.
2) The value of R10 is critical, especially in relation to the B+. If you don't get it just right, there's no PS noise cancellation. Some people put a 100K pot in that position and adjust for minimum noise.
3) Raise C39 to 1uF. This is the bypass for the filament voltage divider. A friend suggested this and it was the last piece of the puzzle for my build.
4) Try a different 6X5GT. Some have heater-cathode leakage, which will inject hum into the preamp.
5) Try swapping around different 6SN7s. Some are noisier than others.
Nice looking build, though!
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Thank you.
Good point. The only metal plate connect to ground, is the rear panel…
I’ll run wires to the top and front plate and see how that helps!
Hi,
Thanks!
1) Got the manual, and was super diligent in following the grounding protocol for the amp! It’s grounded via the earth/transformers, all the grounds from the rca are bussed together and are grounded to the board via a single wire as per instructions as is the volume pot/gain pots.
2) R10 is the supplied 80.6k resistor
3) I will check if I happen to have a 1.0uf here for C39 to try
4) I bought 2 NOS Sylvania 6X5GT’s for the build from TheTubeStore. They both sound the same…. I may have another, untested one kicking around I can try.
5) The 6SN7’s are from my stash that I use as drivers for my Cary SLI-50…. I realize being used as drivers is different than being used as preamp/buffer tubes, but they are free of noise in that. I have tried switching them around, but noise remains
P
Hi,
Thanks!
1) Got the manual, and was super diligent in following the grounding protocol for the amp! It’s grounded via the earth/transformers, all the grounds from the rca are bussed together and are grounded to the board via a single wire as per instructions as is the volume pot/gain pots.
2) R10 is the supplied 80.6k resistor
3) I will check if I happen to have a 1.0uf here for C39 to try
4) I bought 2 NOS Sylvania 6X5GT’s for the build from TheTubeStore. They both sound the same…. I may have another, untested one kicking around I can try.
5) The 6SN7’s are from my stash that I use as drivers for my Cary SLI-50…. I realize being used as drivers is different than being used as preamp/buffer tubes, but they are free of noise in that. I have tried switching them around, but noise remains
P
Yes, R10 is 80.6K, but again, depending on the B+, the value of that resistor can affect the hum cancellation. It's a very delicate balance.
Do you have the circuit grounded to AC earth? You might try a cheater plug and see if that helps.
It looks to me as though your input and output connections on the PCB are not using the ground eyelets. That's not what my instructions say. Mine show positive and ground (shield) connected to the board, with ground lifted at the jacks and the pots except for Left Out ground to the jack commons and pot ground to Right input ground. I'd check the manual again.
Possibly the way you have the signal cables connected now is creating a big ground loop for the input and output signals, or a ground that is circling the entire board including the PS.
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There is a bus wire on the rca in/out. All the grounds of the rca are connected to that. All the wires shields, are also connected to the bus. There is a single wire that connects that bus to the board at one of the eyelets next to the output caps.
The gain pot grounds are connected to volume pot ground, which is connected via a single wire to the ground at the signal input on the board.
The earth ground is connected to the transformer ground, and now connected to the too and front panels also. The earth ground is connected to the ground eyelet where the HV and 6v heater is connected to the board.
The gain pot grounds are connected to volume pot ground, which is connected via a single wire to the ground at the signal input on the board.
The earth ground is connected to the transformer ground, and now connected to the too and front panels also. The earth ground is connected to the ground eyelet where the HV and 6v heater is connected to the board.
