Wow, it's getting quieter and quieter. I just found a 22uF/100V cap and put it in. Previously there was a little bit of a buzz in gain mode with the pot at 50%. Buzz totally gone now. I'm not sure how they are related but apparently they were. Like when your back hurts, but you really needed a good hamstring stretch rather than work directly on the back.
Ok, if I'm going to get this anal, there is a very faint low frequency oscillation happening somewhere. It's faint, like the pitter patter of a chicken running, maybe 10Hz- very faint. Just in one channel, and only in the gain tube that is furthest away from the input jack. Not the best layout, but between the pot and the grid stopper is 15cm of wire. Thinking maybe I need to just increase that value a bit? Currently it's at 1K exactly as the original schematic.
I feel it's definitely a layout issue. Just added a bit more decoupling at the B+ to ground at that tube, and that didn't help. I also swapped tubes around to no avail.
I'm amazed at the improvement, since I first got it semi working to now. This thing got way quiet.
Ok, if I'm going to get this anal, there is a very faint low frequency oscillation happening somewhere. It's faint, like the pitter patter of a chicken running, maybe 10Hz- very faint. Just in one channel, and only in the gain tube that is furthest away from the input jack. Not the best layout, but between the pot and the grid stopper is 15cm of wire. Thinking maybe I need to just increase that value a bit? Currently it's at 1K exactly as the original schematic.
I feel it's definitely a layout issue. Just added a bit more decoupling at the B+ to ground at that tube, and that didn't help. I also swapped tubes around to no avail.
I'm amazed at the improvement, since I first got it semi working to now. This thing got way quiet.
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Since you use an AC heaters supply, DC reference lifting reduced cathode to heater leakage currents so much so, that far less hum and buzz couples between them now.
Regarding other small nuisances remaining, ok maybe it's about something to fix in the layout indeed, but exchange the tubes between their now places first. To exclude it's not about one of them being more "vocal".
Grid stoppers usually damp whines. Must be located directly on the base's grid pin with a short trimmed leg. You may up that 1K to 2.2K but if it will not prove useful for pitter patter return it to 1K because we don't want to lose some more bandwidth for nothing in the gain section. Volume pot's Zout (1/4 nominal kΩ at 1/2 signal division point) plus grid stopper always creating an RC low pass filter with the stage's Miller capacitance. Assuming negligible source equipment Zout. Else it has to be added too.
Regarding other small nuisances remaining, ok maybe it's about something to fix in the layout indeed, but exchange the tubes between their now places first. To exclude it's not about one of them being more "vocal".
Grid stoppers usually damp whines. Must be located directly on the base's grid pin with a short trimmed leg. You may up that 1K to 2.2K but if it will not prove useful for pitter patter return it to 1K because we don't want to lose some more bandwidth for nothing in the gain section. Volume pot's Zout (1/4 nominal kΩ at 1/2 signal division point) plus grid stopper always creating an RC low pass filter with the stage's Miller capacitance. Assuming negligible source equipment Zout. Else it has to be added too.
Thanks Salas and Bas, I will try a few things next week. I have already moved the tubes around, and the pitter patter does not follow the tube.
Btw, I'm also using the current production tung-sol. I tried an RCA metal can, and a JJ and those do not have that particular noise, but are more microphonic. Maybe it's something with this particular reissue then, although they generally sound pretty great.
Anyway, this is more of a tiny nuisance, not an emergency, so will take my time. Thanks for all your feedback
Btw, I'm also using the current production tung-sol. I tried an RCA metal can, and a JJ and those do not have that particular noise, but are more microphonic. Maybe it's something with this particular reissue then, although they generally sound pretty great.
Anyway, this is more of a tiny nuisance, not an emergency, so will take my time. Thanks for all your feedback
Thanks for the recommendation, I'll give them a try. There were a few consecutive pages early on with some subjective testing of various tubes, so nice to add these to the mix.
Some Measurements
Attached are some measurements I made with a Quantasylum QA400. The device has a dynamic range of 105db, so disregard anything below that. Input impedance of the unit is 100K.
QA400 not supported anymore, so had to bust out the windows 7 laptop. For some reason I couldn't get the markers to work all the time, so you'll have to eyeball some of the numbers.
One thing that surprised me just a bit was the LF rolloff was a little more than I expected. I used a higher bleeded than the schematic, so maybe I go back to the original. I lowered it because on startup/shutdown I got a lot of noise and burps. Just ordered some relays and timers, so will cure that the old fashioned way
Also, for gain mode I used the potentiometer at the input of the preamp to lower the output so as not too overload the analyzer which cannot accept more than 2V RMS in.
Attached are some measurements I made with a Quantasylum QA400. The device has a dynamic range of 105db, so disregard anything below that. Input impedance of the unit is 100K.
QA400 not supported anymore, so had to bust out the windows 7 laptop. For some reason I couldn't get the markers to work all the time, so you'll have to eyeball some of the numbers.
One thing that surprised me just a bit was the LF rolloff was a little more than I expected. I used a higher bleeded than the schematic, so maybe I go back to the original. I lowered it because on startup/shutdown I got a lot of noise and burps. Just ordered some relays and timers, so will cure that the old fashioned way
Also, for gain mode I used the potentiometer at the input of the preamp to lower the output so as not too overload the analyzer which cannot accept more than 2V RMS in.
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Nick, I just so happen to have a donor chassis with a working SSHV2 and 5k OPTs installed. Any guidance on how I could do an EL84 linestage?
Cheers,
Greg
What kind of ratio output transformers? Made for 8Ω output?
Something like this is needed: SINGLE ENDED Tube to line Output Transformer 15K/600 Ohms
Something like this is needed: SINGLE ENDED Tube to line Output Transformer 15K/600 Ohms
Another instance of the Salas 6v6. This time with 6p1p-ev. And 21st century Maida based regulator. Currently running trials in my kid's bedroom system. Slightly lower than the recommended b+340V. 305VDC. Power switch and fuse rather clumsily set up...but whatever...it works.
DC heaters. Heater elevated to around 65VDC with the 'thingy' by Morgan Jones (Was on the board so I decided to use it despite its detractors who claim it has not advantages over a voltage divider.)
DC heaters. Heater elevated to around 65VDC with the 'thingy' by Morgan Jones (Was on the board so I decided to use it despite its detractors who claim it has not advantages over a voltage divider.)
Attachments
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