watchnerd
Grand Contributor
I have a lot of 6922-family tubes.
Like 16 pairs, most of which are NOS. They range from cheapie modern production JJs to expensive collectible Siemens, Telefunkens, and Mullards.
When used in my Mjolnir 2 I *think* I hear a difference between some of them, which probably isn't completely unreasonable given the variations in specs and age and condition.
But the process of tube rolling is perilous because:
--It can't be blind. You have to take the tubes out and swap them.
--It's not quick. It can easily take 3-5 minutes to just physically swap the tubes (longer if they're hot).
--Time it takes tubes to warm up to full steady-state temperature
As a result, I'm thinking I need to devise a digital capture methodology, sample different tubes, and then put into a software ABX tester.
Currently thinking:
Raspberry Pi DAC -> Mjolnir 2 -> Pre-out -> Devialet line-in -> ADC -> USB out -> Audacity on Macbook
So assuming the chain is okay:
1. What protocol should I use for "tube readiness"? Should I just let them sit there for 5 min before testing? Play music for 30 min before sampling? Other?
2. Given the large number of tubes to sort through, the decision tree will be insanely complex if I have too many songs to listen through. So I'm convinced I need to pick one song. Any major problems with this?
3. Should the levels be matched? If one tube has more gain than another (quite likely) that is an attribute of the tube that could make it sound different. Should this be eliminated through normalization?
Feedback and thoughts welcome.
Like 16 pairs, most of which are NOS. They range from cheapie modern production JJs to expensive collectible Siemens, Telefunkens, and Mullards.
When used in my Mjolnir 2 I *think* I hear a difference between some of them, which probably isn't completely unreasonable given the variations in specs and age and condition.
But the process of tube rolling is perilous because:
--It can't be blind. You have to take the tubes out and swap them.
--It's not quick. It can easily take 3-5 minutes to just physically swap the tubes (longer if they're hot).
--Time it takes tubes to warm up to full steady-state temperature
As a result, I'm thinking I need to devise a digital capture methodology, sample different tubes, and then put into a software ABX tester.
Currently thinking:
Raspberry Pi DAC -> Mjolnir 2 -> Pre-out -> Devialet line-in -> ADC -> USB out -> Audacity on Macbook
So assuming the chain is okay:
1. What protocol should I use for "tube readiness"? Should I just let them sit there for 5 min before testing? Play music for 30 min before sampling? Other?
2. Given the large number of tubes to sort through, the decision tree will be insanely complex if I have too many songs to listen through. So I'm convinced I need to pick one song. Any major problems with this?
3. Should the levels be matched? If one tube has more gain than another (quite likely) that is an attribute of the tube that could make it sound different. Should this be eliminated through normalization?
Feedback and thoughts welcome.