I'm building a new preamp which will be all tube based and include a MM phono stage and perhaps an on-board SUT for MC. Planing all P-to-P wiring except maybe PS. Tubes are:
Phono: 6922 & 12AX7 (w tube shields)
Line: 2x 6SN7
First questions: build on top of a Hammond (10x17) steel box, or inside one?
Second: Toroidal or EI PT?
Thanks
Phono: 6922 & 12AX7 (w tube shields)
Line: 2x 6SN7
First questions: build on top of a Hammond (10x17) steel box, or inside one?
Second: Toroidal or EI PT?
Thanks
I always build on top personally.
Toroidal looks more modern and will surely have less flux leakage so hum wouldn't be an issue... Antek has several that would work for you as does Triad if you can use ~320 volts (VPT230 series) and don't mind using a separate heater transformer (VPT12 series).
I've never needed tube shields but if you have them, why not use them, right? Obviously place the power supply on one end and the inputs on the other unless you want it to be symmetrical, then put the PSU in the middle back, inputs on one side, outputs on the other.
Also, I would use the aluminum chassis instead of the steel. It's not ferromagnetic, it's easier to work, and it's a better conductor (I use the chassis for DC return).
Do you have schematics in mind yet?
Toroidal looks more modern and will surely have less flux leakage so hum wouldn't be an issue... Antek has several that would work for you as does Triad if you can use ~320 volts (VPT230 series) and don't mind using a separate heater transformer (VPT12 series).
I've never needed tube shields but if you have them, why not use them, right? Obviously place the power supply on one end and the inputs on the other unless you want it to be symmetrical, then put the PSU in the middle back, inputs on one side, outputs on the other.
Also, I would use the aluminum chassis instead of the steel. It's not ferromagnetic, it's easier to work, and it's a better conductor (I use the chassis for DC return).
Do you have schematics in mind yet?
Building inside is rather difficult, especially with a box like that where you can't take the side panels off. You'll also trap a fair amount of heat inside the box.
As far as transformers go, I would suggest EI all the way. If you want to make things really quiet, have a 240V transformer wound and double all the secondary voltages you need, then run it at 120V.
As far as transformers go, I would suggest EI all the way. If you want to make things really quiet, have a 240V transformer wound and double all the secondary voltages you need, then run it at 120V.
Thanks for the responses. I think I'll build on top of the box. I don't mind an EI transformer, but as Kodabmx suggests, a toroidal will have less flux leakage. That being said, I'm kind of thinking potted like the Hammond 370CAXP, though it's $240! Not only does potted look nice, but it may help with shielding.
Design is the next thing. I'm thinking of using the Audio Innovations P2 (updated to use 6922) phono schematic. I've used this before and it sounds great. I have ordered a Maida Regulator for it - lower noise floor would be good. Line stage - not made up my mind except to use 6SN7, likely in a voltage amp to cathode follower style, or a CCDA style. Always open to other ideas. One of my goals is to reduce the number of "boxes" on my audio rack - and the number of RCA connections along the way. Today I have a MC feeding a SUT, going to a phono stage, going to the preamp. I'd like to get the SUT and phono stage in the preamp and be able to eliminate some cables, boxes and connections.
Design is the next thing. I'm thinking of using the Audio Innovations P2 (updated to use 6922) phono schematic. I've used this before and it sounds great. I have ordered a Maida Regulator for it - lower noise floor would be good. Line stage - not made up my mind except to use 6SN7, likely in a voltage amp to cathode follower style, or a CCDA style. Always open to other ideas. One of my goals is to reduce the number of "boxes" on my audio rack - and the number of RCA connections along the way. Today I have a MC feeding a SUT, going to a phono stage, going to the preamp. I'd like to get the SUT and phono stage in the preamp and be able to eliminate some cables, boxes and connections.
To play devil's advocate for a bit but I prefer separates that gives you the ability to mix and match phono, linestage, etc. SO many times in DIY I have said "this is my final ... stage" 😛
Just throwing out my opinion. As far as building, I build on top as I like to see the tubes. I always use shielded sockets on phono whether I use the shield or not. Torroids are fine and you can mount them on top and then cover them with a smaller Hammond box by screwing it on from the inside of the main enclosure. Take a look at the MAD EAR+ for examples of that.
For phono, check out the BigBottle MM/MC group buy. I admit I am partial as I did the PCB layout but the sound is incredible! I have been listening for the past week or so and it is VERY quiet and very dynamic stage. MC trumps MM performance however so if you have an MM cartridge there may be better options. But it is still better than an EAR MM in my opinion.
LOVE 6SN7 linestages! I have build Thorsten's parallel 6SN7 line stage which sounds great! Also did an octal Aikido but WAY too much gain for my system. Next up is a simple 6SN7 voltage gain stage with adjustable gain ... parts should be here this week yet.
Good luck with the build and keep us posted on progress!
Just throwing out my opinion. As far as building, I build on top as I like to see the tubes. I always use shielded sockets on phono whether I use the shield or not. Torroids are fine and you can mount them on top and then cover them with a smaller Hammond box by screwing it on from the inside of the main enclosure. Take a look at the MAD EAR+ for examples of that.
For phono, check out the BigBottle MM/MC group buy. I admit I am partial as I did the PCB layout but the sound is incredible! I have been listening for the past week or so and it is VERY quiet and very dynamic stage. MC trumps MM performance however so if you have an MM cartridge there may be better options. But it is still better than an EAR MM in my opinion.
LOVE 6SN7 linestages! I have build Thorsten's parallel 6SN7 line stage which sounds great! Also did an octal Aikido but WAY too much gain for my system. Next up is a simple 6SN7 voltage gain stage with adjustable gain ... parts should be here this week yet.
Good luck with the build and keep us posted on progress!
Okay a quick update... I remembered that some time ago I built a rather robust preamp power supply so I could do a two-chassis set up. It's in great shape and so I think I'll use that with an umbilical to the actual preamp chassis. Originally I made it because I wanted to play with two Heathkit preamps that need power from the amp chassis.
I ordered a Front Panel today. So the main chassis will have the line stage, the phono stage, the SUT, the regulator, and of course the controls. The chassis will have a ton of extra room, but that's never a bad thing. The one thing I'm not happy about is how light-weight it will be. Maybe I should think about adding some damping or weight of some kind?
I ordered a Front Panel today. So the main chassis will have the line stage, the phono stage, the SUT, the regulator, and of course the controls. The chassis will have a ton of extra room, but that's never a bad thing. The one thing I'm not happy about is how light-weight it will be. Maybe I should think about adding some damping or weight of some kind?