The CCS are available right here:
K & K Audio - Lundahl Transformers, audio DIY kits and more
I used the Large Cascode CCS with heat sink for the VR tubes and the Compact Cascode CCS for the 26 tubes. The schematic is just the usual one for a CCS made from depletion mode MOSFETs (see picture below) except K&K uses 910R resistors instead of 1K, and there isn't a resistor on the input.
Attachments
Normal out. It gives better power supply rejection than the mu out, and I achieve low output impedance by using an output transformer.
If you are looking for an active load solution, it may be worth checking out the thread on the DiyHifiSupply DHT OTL Linestage
It is a 2A3 or 45 linestage pre, with a "Super MU" active load, made up of an IXCP10M45S based CSS with a 6AS7 above it.
Best of luck.
It is a 2A3 or 45 linestage pre, with a "Super MU" active load, made up of an IXCP10M45S based CSS with a 6AS7 above it.
Best of luck.
The schematic is not mine to share, but if you check out the DiyHifiSupply site and get hold of the Tram 2 manual, and the CCS Manual, I am sure it would be possible to piece it together.
btw it appears to use the MU out for low impedance drive
Just a caveat to the FR measurements - these were made with my laptop sound card, which has a 5K input impedance. In the real world with most amps the LF extension should be better due to higher input impedance, so the differences between the two transformers might not be as important.
Hey Andy,
Recognize your Aluminum plates and volume control in the pictures?
I've been tweaking and listening and I have found that the 26 sounds better at 7mA than at 6mA, and that the Cunningham globes sound better than the STs I've tried (RCA and Sylvania).
At 6mA I thought the 2C22 held an edge over the 26 in terms of liveliness and "jump factor" especially on rock and blues. At 7mA the 26 catches up to the 2C22 in that area. On female vocals like Etta James the 26 at 7mA is smoother and more spacious (3-D) than the 2C22, just plain better. Image focus may be just a hair tighter with the 2C22, however. Now keep in mind that I'm using the best of the best parafeed caps in the 2C22 preamp (Duelund CAST) versus the pretty good Duelund Alexander in the 26 - I may have to do a switch at some point and try the 26 with the CAST caps.
In the meantime, I have an order in for another output transformer to match the primary inductance of the 200H one. I'm not sure how much difference that will make but I'm obsessive that way. Given that the preamp is feeding into a 50k+ input impedance in real life and not the 5k of my sound card it may be a moot point.
So in summary, the 2C22 is a great preamp tube (I'm running it at 15mA, 175V with SiC Schottky diode bias to 3.4V). So far the 26 has impressed me and I'm still experimenting with it; I think I'll end up using the 2C22 preamp as a phonostage only (it has one built in) and complete the 26 build as an accompanying linestage. That's today's plan, anyway.
.
Recognize your Aluminum plates and volume control in the pictures?
I've been tweaking and listening and I have found that the 26 sounds better at 7mA than at 6mA, and that the Cunningham globes sound better than the STs I've tried (RCA and Sylvania).
At 6mA I thought the 2C22 held an edge over the 26 in terms of liveliness and "jump factor" especially on rock and blues. At 7mA the 26 catches up to the 2C22 in that area. On female vocals like Etta James the 26 at 7mA is smoother and more spacious (3-D) than the 2C22, just plain better. Image focus may be just a hair tighter with the 2C22, however. Now keep in mind that I'm using the best of the best parafeed caps in the 2C22 preamp (Duelund CAST) versus the pretty good Duelund Alexander in the 26 - I may have to do a switch at some point and try the 26 with the CAST caps.
In the meantime, I have an order in for another output transformer to match the primary inductance of the 200H one. I'm not sure how much difference that will make but I'm obsessive that way. Given that the preamp is feeding into a 50k+ input impedance in real life and not the 5k of my sound card it may be a moot point.
So in summary, the 2C22 is a great preamp tube (I'm running it at 15mA, 175V with SiC Schottky diode bias to 3.4V). So far the 26 has impressed me and I'm still experimenting with it; I think I'll end up using the 2C22 preamp as a phonostage only (it has one built in) and complete the 26 build as an accompanying linestage. That's today's plan, anyway.
.
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FWIW. Further update - extended listening session with the wife last night. She told me in no uncertain terms - "Don't mess this preamp up when you box it! It sounds perfect." She prefers the 26 pre over the 2C22. She thinks it sounds fuller and more real - she thinks the 2C22 has too much treble energy.
The 2c22 may be nice, but a different topic. The #26 has been shown to have excellent linearity.
I have a question, still at a deadlock on a design decision. I will be using a stepdown permalloy output transformer (parafeed) its a custom design from ElectraPrint but very sensitive picking up hum from the mains transformers. Really all opt at preamp levels pick up EMI (60 hz hum) from the B+ transformers, so I always use a separate chassis to separate the OPT's from any main transformers (need to especially with sensitive Grado's.)
But I haven't done a DHT build like this and adding the coleman regulators really adds complexity to a 2-case build.
It looks like with the SSHV2, we can have a larger distance between the regulator board and the amp section which helps. But the coleman regs still need to be in the amp chassis.
Is it OK to have the prefiltered supply to the coleman regs in the amp chassis share the same umbilical cord as the prefiltered B+ ?
My goal is one umilical cord. Has anyone found a means to do this with sub -90dB hum ?
I have a question, still at a deadlock on a design decision. I will be using a stepdown permalloy output transformer (parafeed) its a custom design from ElectraPrint but very sensitive picking up hum from the mains transformers. Really all opt at preamp levels pick up EMI (60 hz hum) from the B+ transformers, so I always use a separate chassis to separate the OPT's from any main transformers (need to especially with sensitive Grado's.)
But I haven't done a DHT build like this and adding the coleman regulators really adds complexity to a 2-case build.
It looks like with the SSHV2, we can have a larger distance between the regulator board and the amp section which helps. But the coleman regs still need to be in the amp chassis.
Is it OK to have the prefiltered supply to the coleman regs in the amp chassis share the same umbilical cord as the prefiltered B+ ?
My goal is one umilical cord. Has anyone found a means to do this with sub -90dB hum ?
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I use a speakon for the B+ and a 4 pin XLR for the filaments. One reason for keeping these separate is that you may want to put in chokes for filament bias before the Coleman reg if you are really seeking the ultimate. Chokes - I have big 280mH ones - can be heard up to two or three feet from a sensitive plate choke like the 156C. The B+ can be closer, especially if it's a toroid (not the ultimate....).
The quick-and-dirty way of doing a PSU is a couple of 9+9v toroids back to back - filament supplies out of the first one and then 9v back to 230v for the B+. That can be done with one umbilical, but not with filament chokes unless it's further away. The filament supply once choke filtered is actually almost pure DC. Just needs a couple of Hammond 159ZC - cheap and available.
Andy
The quick-and-dirty way of doing a PSU is a couple of 9+9v toroids back to back - filament supplies out of the first one and then 9v back to 230v for the B+. That can be done with one umbilical, but not with filament chokes unless it's further away. The filament supply once choke filtered is actually almost pure DC. Just needs a couple of Hammond 159ZC - cheap and available.
Andy
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After a bit more running in, I can now say with certainty that the 26 preamp is superior to the 2C22. It's fuller, more spacious, has better tone, even better clarity. I'm listening to Lee Morgan's Lee-Way right now and it sounds incredible. I'm hooked!
Next step is to build/buy a chassis. I'm seriously considering going the Bent Audio TAP DIY route, with Slagleformer volume controls. They are reputed to sound excellent, especially at low levels, will give me +7 dB of gain for those low level recordings, and a remote control so I never have to leave the couch. Not at all inexpensive, however...
On a side note, the Duelund Alexander caps are an excellent value IMO. They give you true copper foil PIO in a much less expensive form than their VSF or CAST; especially good when PCX runs a 30% off sale! After a few days of run-in they have really opened up in sound.
Next step is to build/buy a chassis. I'm seriously considering going the Bent Audio TAP DIY route, with Slagleformer volume controls. They are reputed to sound excellent, especially at low levels, will give me +7 dB of gain for those low level recordings, and a remote control so I never have to leave the couch. Not at all inexpensive, however...
On a side note, the Duelund Alexander caps are an excellent value IMO. They give you true copper foil PIO in a much less expensive form than their VSF or CAST; especially good when PCX runs a 30% off sale! After a few days of run-in they have really opened up in sound.