HiFi Haven Group Project - Building The "World's Best Tube Phono Preamp"
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Haven't had a chance to make much progress. I made a new sub-chassis plate that will allow me to measure and tweak the circuit much more easily. I'm hoping to wire it up sometime this week. This is a bit of a busy week for me, so no telling how much time I'll get to devote to it.
How's yours coming along? You finalize your layout as yet?
You don't need a whole turret strip if all those lugs are ground lugs. In the front middle where your LEDs connect, string a piece of buss wire across the chassis between those two turrets. At the top of the photo, you have a turret where the ground buss lands. Between that turret and the middle of the wire going across the chassis at the front, put in another piece of buss wire.
If you use 16 or 18 AWG buss wire, it will be plenty stiff and more than strong enough to hold what's mounting to it.
If you use 16 or 18 AWG buss wire, it will be plenty stiff and more than strong enough to hold what's mounting to it.
Sure, I could do that. I have some nice tinned copper buss wire I've used before. Any thoughts on other aspects of the layout?
I'd rather have the tube sockets mounted to a metal plate with shields over them, creating a nice big ground plane. This also allows the heater wiring to sit right against the chassis plate as well which has some advantages. These big phenolic boards with 9 pin sockets and lots of turrets are totally fine for power amplifier drivers and line level preamps, but a little less than ideal for high gain circuits like this.
Going this route would allow you to orient the 9 pin sockets for the D3A tubes so that pins 4 and 5 are facing away from the incoming signal, and you could get the G1 pin much closer to the RCA jacks, possibly even with just the resistor itself between the RCA jack center pin and the G1 pin.
The LED that biases the D3A can be connected between the cathode and the center lug of the 9 pin socket, then a wire run from the center lug of the 9 pin socket to ground.
The AN 1 meg resistors are drawn going from 5687 plate to ground, which is probably not intentional. You definitely have room for the coupling caps in that layout.
Going this route would allow you to orient the 9 pin sockets for the D3A tubes so that pins 4 and 5 are facing away from the incoming signal, and you could get the G1 pin much closer to the RCA jacks, possibly even with just the resistor itself between the RCA jack center pin and the G1 pin.
The LED that biases the D3A can be connected between the cathode and the center lug of the 9 pin socket, then a wire run from the center lug of the 9 pin socket to ground.
The AN 1 meg resistors are drawn going from 5687 plate to ground, which is probably not intentional. You definitely have room for the coupling caps in that layout.
I see what you are saying.
The one Meg resistor should go from the output side of the caps not shown to ground.
I could mount the sockets directly to the top plate of the chassis and therefore accomplish much of what you suggest. Maybe even use sockets with shields in case there is more noise than I'd like.
I need to leave space for the SUT transformerd I'm planning on using so IDK about mounting the sockets that close to allow directly hooking the 47K resistor directyyo the input RCA.
I oriented the sockets how I did to allow symmetrical parts positioning and I was thinking of dropping the heater wires in from below to avoid crossing other wires as much as possible.
I'm going to work on your suggestions.
Thanks
The one Meg resistor should go from the output side of the caps not shown to ground.
I could mount the sockets directly to the top plate of the chassis and therefore accomplish much of what you suggest. Maybe even use sockets with shields in case there is more noise than I'd like.
I need to leave space for the SUT transformerd I'm planning on using so IDK about mounting the sockets that close to allow directly hooking the 47K resistor directyyo the input RCA.
I oriented the sockets how I did to allow symmetrical parts positioning and I was thinking of dropping the heater wires in from below to avoid crossing other wires as much as possible.
I'm going to work on your suggestions.
Thanks
For step-up transformers, you'll want to do a little testing with your power transformer energized and a digital volt meter set to AC millivolts hooked up to the high impedance side of the step-up transformer. There will be certain orientations that produce some magnetically coupled 60Hz noise, and it's good to know which orientations those are before committing to a layout. I damn near tanked my most recent build when I almost forgot to check that, and that was an output transformer on a headphone amp.
You will definitely want tube shields, and they need to be tied to the chassis to really do their jobs properly. The 5687s probably would work OK without them; the signal level is quite a bit higher there and they are not as susceptible to noise like a high Gm tube is.
You will definitely want tube shields, and they need to be tied to the chassis to really do their jobs properly. The 5687s probably would work OK without them; the signal level is quite a bit higher there and they are not as susceptible to noise like a high Gm tube is.
I have had several sowter SUTs and use one currently, the new ones with the OCC wire sounded better than the standard and vintage ones I have compared and I thought favourable to the lundahl ones as well. All 1:10 ratio.
I haven’t tried a Sowter or Lundahl in my system so I can’t comment on them. For a real bargain, however, I recommend the Jensen JT 44K-DX which is a 1:10 that sells for a bit more than $100 each. I used the Jensens for nearly 20 years and liked the sound very much. I compared them to several other SUTs in my system over the years including all of the Hashimotos (3,5 and 7) and preferred my lowly Jensens over each of them. There were only two exceptions—(1) an Audio Note Silver SUT (I forget the model) which had wonderful midrange transparency even though I missed the warmth of the Jensens, and (2) Intact Audio /EMIA Silver SUTs. I ended up buying a pair of EMIA copper SUTs which I like perhaps even more than the silver. However I can honestly say if I had to return to the Jensens I could live quite happily with them.
Every detail in a SUT is important. I quickly settled on a setup with Cardas RCA input jacks and hardwired output cables, I.e. no output jacks. I used a short 1/2 meter Discovery Essence cable with plugs on only one end. The other end was soldered directly to the SUT wires. I am sure there are better sounding cables that can be used in that spot but that’s what served me well for nearly all of the time I used the Jensens. At one point I added output jacks (I tried both Cardas and WBT) so I could try different output cables, but the hardwired Discovery sounded best. I am not a fan of the Discovery Essence as a regular interconnect but for some reason it sounds really nice as an output cable for the Jensen.
Every detail in a SUT is important. I quickly settled on a setup with Cardas RCA input jacks and hardwired output cables, I.e. no output jacks. I used a short 1/2 meter Discovery Essence cable with plugs on only one end. The other end was soldered directly to the SUT wires. I am sure there are better sounding cables that can be used in that spot but that’s what served me well for nearly all of the time I used the Jensens. At one point I added output jacks (I tried both Cardas and WBT) so I could try different output cables, but the hardwired Discovery sounded best. I am not a fan of the Discovery Essence as a regular interconnect but for some reason it sounds really nice as an output cable for the Jensen.
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I would move everything up closer to where the input jacks are and have the big output coupling caps at the other end of the chassis. The signal level is high at the output end, so that circuitry isn't so sensitive. The little impedance/capacitance switch board could be on the vertical walls, perhaps centered between the RCA jacks.
The ground buss looks nice, don't forget to secure it to the chassis at the input end where the ground post for your turntable will be.
The ground buss looks nice, don't forget to secure it to the chassis at the input end where the ground post for your turntable will be.
I'm sure I'm missing something but I thought the ground buss was to float in the audio chassis only connected at the negative terminal of the D3a cap negative terminal. I'll try rearranging the parts as you suggest.
You could certainly experiment with that, but if you have tonearm cables with the shield wire integrated so that it's just the shell of the RCA jacks, those will really work best if the ground post and signal ground are tied together right where all the input cabling comes in.
Before I get too far I'd like some opinions about this signal layout if possible. I'm having trouble figuring out how exactly to ground the PS B+ circuit and heater supply from the PS chassis to the signal chassis. In this I'm tying the ground from the B+ circuit directly to the first 100uf cap as @Salectric mentioned earlier. (FWIW I didn't have it this way initially - it went straight to a ground lug in the signal chassis. Not sure which way is correct). The heater supply goes to the signal chassis ground bus and then onto the filaments.
I'd also like some sort of clarification on wiring the D3A in triode if possible. I'm following the directions posted earlier about tying the anode to to the screen with 100 ohm resistor and the suppressor grid to the cathode. But I don't see what to do with the remaining pins and connections to make this triode strapped. I've got extra cathode pins and an extra grid for some reason. If I can get it figured out I'll supply a pin-out drawing for this thread for future reference.
Anyway, here's what I'get as far as PS and signal chassis thus far:
I'd also like some sort of clarification on wiring the D3A in triode if possible. I'm following the directions posted earlier about tying the anode to to the screen with 100 ohm resistor and the suppressor grid to the cathode. But I don't see what to do with the remaining pins and connections to make this triode strapped. I've got extra cathode pins and an extra grid for some reason. If I can get it figured out I'll supply a pin-out drawing for this thread for future reference.
Anyway, here's what I'get as far as PS and signal chassis thus far:
DIY Layout Creator: Software > DIY Layout Creator : DIY Fever – Building my own guitars, amps and pedals
Cathodes are pins 1 and 3 on the D3A. I guess part of the confusion on my part is having both AND having to connect both the LED and the suppressor grid to them. Pins 1 and 3 are connected within the tube. Does that mean for example I could connect the LED to pin 1 and the suppressor to pin 3 and get the same result? Or is it best to do as you say and tie 1 and 3 together externally and then tie both the suppressor and the LED to pin 1 or 3?
I see that I've got the wrong connections drawn for the D3A in my submitted drawing thus far. I'll revise once I figure it out.
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