Here's my first draft of the signal chassis layout, top down view, dimensions 15.5" x 10" x 3.25". I measure all the major parts with an electronic caliper and build them all out in AutoCAD for my layouts to make sure everything will fit. Planning to put the heater regulators in the power supply chassis (there will be four of them). I'll run the outputs of those through the umbilical and have some high and low frequency decoupling at each tube's individual heater. For the B+ regulators (Maida style) will run the choke-filtered raw DC through the umbilical and then have the Maida regulators right at the input of the umbilical (red blocks). I need to design a small PCB for the remainder of the RIAA filter components that will mount in the center of the LCR chokes. Signal flow will be front-to-back: 3-pin XLR inputs (magenta blocks) > MC SUTs (green blocks) > D3a stage > LCR RIAA > E55L > RCA outs.
I feel good about this draft, came together quicker than I thought it would.
I feel good about this draft, came together quicker than I thought it would.
Yes but how do you deal with input capacitance of that tube? Running the needed high bias will create more noise in the first critical gain stage. I am thinking about using this srpp + 12au7 + 20k600 combination as the input. It makes a lot of sense to me if you can swing the additional 20k/600+the H-eql (I'd say Hashimoto iron). Not sure what the (para) means...the two triodes in a tube in parallel?
The traditional Shishido with 6dj8 uses big caps which I am not a fan of. Anyways, that's all for future planning. First I want to complete the Salas valve itch.
The FINIMET core transformer are $$$$$$. They say they are used in Phasemation products.
Wonder if this graph for the material is even real (see bottom of the linked page).
https://theaudiofeast.com/finemet-transformer
The traditional Shishido with 6dj8 uses big caps which I am not a fan of. Anyways, that's all for future planning. First I want to complete the Salas valve itch.
The FINIMET core transformer are $$$$$$. They say they are used in Phasemation products.
Wonder if this graph for the material is even real (see bottom of the linked page).
https://theaudiofeast.com/finemet-transformer
Last edited:
Equivalent noise resistance:
12AX7 1562R
D3a 150R
D3a has 30% greater Miller capacitance than 12AX7, so right source impedance planning is important for good bandwidth.
D3a is widely used as first stage of phono, rather with SUT, than MM cartridges.
BTW I use 12AX7 based MM phono ... but with 5751 tubes (lower gm, lower noise). 7025 also can be used better too.
12AX7 1562R
D3a 150R
D3a has 30% greater Miller capacitance than 12AX7, so right source impedance planning is important for good bandwidth.
D3a is widely used as first stage of phono, rather with SUT, than MM cartridges.
BTW I use 12AX7 based MM phono ... but with 5751 tubes (lower gm, lower noise). 7025 also can be used better too.
Equivalent noise resistance depends of tube mutual conductance (gm).
R(eq_noise)=2.5/gm
For example 12AX7 gm is 1.6 mA/V.
2.5/0.0016=1562 Ohms.
The SUT input phono has 47k as secondary load (which is transforming to primary as few - few ten - hundred Ohm load for MC).
The tube's Miller capacitance with this static 47k and parallel to this upscaled impedance of MC limits the bandwidth.
It's better, than with 47k.
Sometimes higher CMiller good for some MM cartridges, which is requiring paralleled capacitance to damp few ten kHz hump, but it's always needed correct measuring.
R(eq_noise)=2.5/gm
For example 12AX7 gm is 1.6 mA/V.
2.5/0.0016=1562 Ohms.
The SUT input phono has 47k as secondary load (which is transforming to primary as few - few ten - hundred Ohm load for MC).
The tube's Miller capacitance with this static 47k and parallel to this upscaled impedance of MC limits the bandwidth.
It's better, than with 47k.
Sometimes higher CMiller good for some MM cartridges, which is requiring paralleled capacitance to damp few ten kHz hump, but it's always needed correct measuring.