Started researching a good line stage to match these 1625 power amps. After a lot of reading, stumbled on the low mu approach. The more I read, the more it made sense. So, found this design by Thomas Meyer, which I found intriguing. Was initially going with a 12B4, but I love the sound from octal tubes, so went with Mr. Meyer's design.
The parts cost forced me to re-consider this project. However, after a talk with my friends at Heyboer, found out they could make the iron for a reasonable price.
Since I wanted this to come out great, enlisted my buddy to build it. He is much better at this type of work than I am. My skills are OK, but nothing like his. Since he was intrigued with the design, he happily accepted the job.
The only real change made was using a Khomozo stepped attenuator connect to the input vs. the transformer volume control on the output. Used a slightly beefier power transformer, DC'ed all the tubes, and went with 6DE4 damper tubes.
This preamp sounds better than anything I've ever heard. It's shocking just how good it sounds.
The parts cost forced me to re-consider this project. However, after a talk with my friends at Heyboer, found out they could make the iron for a reasonable price.
Since I wanted this to come out great, enlisted my buddy to build it. He is much better at this type of work than I am. My skills are OK, but nothing like his. Since he was intrigued with the design, he happily accepted the job.
The only real change made was using a Khomozo stepped attenuator connect to the input vs. the transformer volume control on the output. Used a slightly beefier power transformer, DC'ed all the tubes, and went with 6DE4 damper tubes.
This preamp sounds better than anything I've ever heard. It's shocking just how good it sounds.
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Absolutely. The only choke not made by Heyboer are the ones on the 1625 power amps. All the iron on the preamp, and the power and output iron were made by Heyboer. Outstanding quality.
I'm sure about their quality, I have a small pair of trannies made by Heyboer. Congratulations on both, they look very nice and clean. Good work!
I like the 6AH4 too. Built a small 1W power amp using the 6AH4 in a DRD configuration with 6J5 driver tube. Sounds much better than what it deserves. The 6CK4 is the 6AH4's bigger brother. In addition, the 6BX7 is very close to two 6AH4's in one octal bottle.
The Stax Headphone Amp boffin over on the headphone website pushes the 6CK4 as a replacement for the 6CG7/6FQ7 in their amps. Too much rework to achieve for that project.
I went with this approach because I liked the design. Thomas Meyer is one smart guy, and it's pretty easy to make it sound right. All the iron in the power supply and the output makes it one very low noise and clean sounding preamp. I would put this up against any commercial product.
The 6CK4 is not as linear as the 6AH4 or triodes in the 6BX7. I would never consider the 6CK4 as a replacement for the 6CG7/6FQ7 - they are nothing alike.
Hi!
Great that the 6AH4 works out so well for you. For those interested here is a link to my post about this circuit:
VinylSavor: Making of a 6AH4 line stage: circuit
And the assembly of the preamp:
VinylSavor: Making of a 6AH4 Line Stage: Assembly
And here an implementation of that circuit with separate PSU chassis:
http://vinylsavor.blogspot.de/2012/05/modular-preamplifier-part-10-6ah4.html
Best regards
Thomas
Great that the 6AH4 works out so well for you. For those interested here is a link to my post about this circuit:
VinylSavor: Making of a 6AH4 line stage: circuit
And the assembly of the preamp:
VinylSavor: Making of a 6AH4 Line Stage: Assembly
And here an implementation of that circuit with separate PSU chassis:
http://vinylsavor.blogspot.de/2012/05/modular-preamplifier-part-10-6ah4.html
Best regards
Thomas
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Thank You, Thomas, for your work and support with tube audio. Lots of great information on your blog.
Here is a picture of the power amps I'm using with the 6AH4 preamp. The combination sounds outstanding. The 6AH4 preamp makes the power amps sound a lot better than they did before. Amazing upgrade.
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What changes are needed for more gain?
I assume with the above circuit the gain would be in the range of 3-6 db?
If one wanted to run a phono source and needed gain of about 12 or more, would it still be feasible to use this circuit by simply removing the step-down plus a few other adjustments? (and I'll assume the TVC would be gone since the plate resistance would increase to around 1800 ohms from 200) or would different pre-amplifier be better suited for phono.
Cheers & thanks for posting
FM
I assume with the above circuit the gain would be in the range of 3-6 db?
If one wanted to run a phono source and needed gain of about 12 or more, would it still be feasible to use this circuit by simply removing the step-down plus a few other adjustments? (and I'll assume the TVC would be gone since the plate resistance would increase to around 1800 ohms from 200) or would different pre-amplifier be better suited for phono.
Cheers & thanks for posting
FM
Hi!
Sure you can do that. It would turn it into a different preamp. It twas purposely designed to drive a low impedance TVC and to have low gain since most systems have way too much.
You could use this circuit instead:
VinylSavor: The Octal Line Preamplifier, Part 1 : Signal Section
This can also be used with the 6AH4
Or if you want to keep the transformer coupled theme, use a tube with more gain, for example the 6J5. Then use the line section of these full function preamp:
VinylSavor: The Octal Preamplifier Mk1
Best regards
Thomas
Sure you can do that. It would turn it into a different preamp. It twas purposely designed to drive a low impedance TVC and to have low gain since most systems have way too much.
You could use this circuit instead:
VinylSavor: The Octal Line Preamplifier, Part 1 : Signal Section
This can also be used with the 6AH4
Or if you want to keep the transformer coupled theme, use a tube with more gain, for example the 6J5. Then use the line section of these full function preamp:
VinylSavor: The Octal Preamplifier Mk1
Best regards
Thomas
Personally, I wouldn't modify Thomas's design for the 6AH4. The only modification to the 6AH4 design with my project was to move a stepped attenuator to the front end of the circuit, DC filament the tubes, and use a 6DE4 damper tube. It sounds so good, wouldn't dream of changing anything. 😎 It's perfect for the application with the 1625 power amps.
The suggestion from Thomas to use his Octal preamp or Octal Line Stage is the way to proceed.
Good Luck!
The suggestion from Thomas to use his Octal preamp or Octal Line Stage is the way to proceed.
Good Luck!
Hello Redwingnine,
The 6ah4 is very intriguing. I would live to build it one day. Does your 1625 amps have enough gain on their own..like they can be driven from a linesource directly? Im asking as I have a pp 6l6 amp which has already high gain but sounds really good with a pre. I need a low gain pre for them so im building a 6v6 cathode follower pre.
Ty
The 6ah4 is very intriguing. I would live to build it one day. Does your 1625 amps have enough gain on their own..like they can be driven from a linesource directly? Im asking as I have a pp 6l6 amp which has already high gain but sounds really good with a pre. I need a low gain pre for them so im building a 6v6 cathode follower pre.
Ty
Hi Redwingnine,
Sorry to revive a >1 yr old thread. But it sounds interesting, and I have a few questions for you:
- How did you generate the DC for the heaters? Three-legged regulators ICs or did you go LCLC like Thomas Mayer did in several of his higher-level preamps? I ask this because I have trouble achieving 6,3v the LCLC way: too much fiddling with voltage drop capacitors that dissipate a lot of energy (hence expensive)
- Did you try the design without the 30uF Ultrapath capacitor? I wonder what his contribution is to the overall sound signature and performance?
Thanks!
Maxime
Sorry to revive a >1 yr old thread. But it sounds interesting, and I have a few questions for you:
- How did you generate the DC for the heaters? Three-legged regulators ICs or did you go LCLC like Thomas Mayer did in several of his higher-level preamps? I ask this because I have trouble achieving 6,3v the LCLC way: too much fiddling with voltage drop capacitors that dissipate a lot of energy (hence expensive)
- Did you try the design without the 30uF Ultrapath capacitor? I wonder what his contribution is to the overall sound signature and performance?
Thanks!
Maxime
Hi!
No need for DC heaters with the 6AH4. And especially LCLC for an indirectly heated tube would be total waste. AC is fine.
Thomas
No need for DC heaters with the 6AH4. And especially LCLC for an indirectly heated tube would be total waste. AC is fine.
Thomas
Old thread revival but this pre might be just what I need. I'm fairly beginner but have built a preamp from scratch recently and didnt struggle so I can pull this off haha.........I think
If anyone has the voltages for PSU and different points in the circuit that would be really helpful? I'd like to use the TX and chokes I already have as much as possible as that would keep cost down.
Luckily I already have some Slagle Autoformers.
If anyone has the voltages for PSU and different points in the circuit that would be really helpful? I'd like to use the TX and chokes I already have as much as possible as that would keep cost down.
Luckily I already have some Slagle Autoformers.
I guess all I would really like to know is what b+ I should be aiming for.
My current preamp is CLCLC at 430v b+
I can muck around on PSUD2 to work it out if I have a target
My current preamp is CLCLC at 430v b+
I can muck around on PSUD2 to work it out if I have a target
Have you contacted Thomas? He would know - simple question.
He hasn't supported his older DIY activities for a while to make way for new projects, but he may respond.
The data suggests 250v a-k, -23v and 30mA. That would give a cathode resistor of 767R at 3W.
What you have is 1K so not too far off. In view of the LL1692A it's not over 25mA and at 25mA the bias is -25v. That would figure with 250v a-k and give you 1K. It would certainly work.
That would give you 275v on the anode. Reckon 700R DCR for the LL1692A so add 20v and the B+ is 295v.
Your target is probably around 300v B+. This looks about right. Just using a bit of deduction here from the circuit.
He hasn't supported his older DIY activities for a while to make way for new projects, but he may respond.
The data suggests 250v a-k, -23v and 30mA. That would give a cathode resistor of 767R at 3W.
What you have is 1K so not too far off. In view of the LL1692A it's not over 25mA and at 25mA the bias is -25v. That would figure with 250v a-k and give you 1K. It would certainly work.
That would give you 275v on the anode. Reckon 700R DCR for the LL1692A so add 20v and the B+ is 295v.
Your target is probably around 300v B+. This looks about right. Just using a bit of deduction here from the circuit.
@andyjevans thank you for your response 🙂
I’ve sent a msg to Thomas so we’ll see.
I’ll see if I can make my current tx/choke set work as it’s good quality from AE Europe.
Now to do some learning in PSUD2
I’ve sent a msg to Thomas so we’ll see.
I’ll see if I can make my current tx/choke set work as it’s good quality from AE Europe.
Now to do some learning in PSUD2