Hi
Were you taking the o/p from the the gyrator o/p or from the mu follower o/p ? The mu follower o/p
Impedance should be less than 40R. I have driven my hd800,s direct off the mu follower o/p succesfully with my 2p29l . However it measures and sounds better with a 4:1 step down in parafeed.
By the way I think 6.8uf is far too small to drive a 300R load more like 100uf.
Were you taking the o/p from the the gyrator o/p or from the mu follower o/p ? The mu follower o/p
Impedance should be less than 40R. I have driven my hd800,s direct off the mu follower o/p succesfully with my 2p29l . However it measures and sounds better with a 4:1 step down in parafeed.
By the way I think 6.8uf is far too small to drive a 300R load more like 100uf.
Headphone Sensitivity / Power Requirements Compared | Headphone Reviews and Discussion - Head-Fi.org
Power required to reach 120db:
HD600 - 199 mW - 26 ma - 7.74v rms
#26 at working operating point: 5-6mA
... just physics...
But 120db is ear shattering . 5-6 ma will give something between 100 and 110db which
will still be moderately loud. Depends on how loud you like it.
will still be moderately loud. Depends on how loud you like it.
Circuit from #4780
Somehow never noticed this before: the regulator output is decoupled from the load which allows for a reasonably large cap to be used.
My main gripe with vacuum regulator tubes has always been the severe subjective lack of bass and this circuit probably solves this. I would go for an even larger cap.
What do people who have built it think of the bass?
Somehow never noticed this before: the regulator output is decoupled from the load which allows for a reasonably large cap to be used.
My main gripe with vacuum regulator tubes has always been the severe subjective lack of bass and this circuit probably solves this. I would go for an even larger cap.
What do people who have built it think of the bass?
I guess the worse problem is the output impedance because sounds enough high to listen properly. I believe it's the main reason but I will try lytic cap 220uF or 330uF, what polarity must be connected to the headphones?
I measured the frequency response into a 340 ohm load with a variety of coupling caps. The result tallies with Ale,s calculation of o/p impedance of his mu follower.
When I tried the direct o/p I used a 100uf/500V Kemet DC Link polypropylene not an electrolytic. If I did I would connect the positive to the follower o/p. This value of cap gave a -3db point of 5hz with the roll off beginning at 30hz. I chose this as my hd800 (and my hd600,s) have a bit of a rolled off bass and I didnt want to to make it worse with an earlier bass roll off.
I quite liked the result with the direct drive but with the parafeed 4:1 step down I can use a 2.2uf cap
(Mundorf) which is probably of better quality and I think I prefer it. It measures better distortion wise anyway.
Of course Im using a 2P29L at 18ma which is probably better for direct drive. The 26 might work better with parafeed. I can wind my own tx,s but suitable tx,s shouldnt be that expensive.
When I tried the direct o/p I used a 100uf/500V Kemet DC Link polypropylene not an electrolytic. If I did I would connect the positive to the follower o/p. This value of cap gave a -3db point of 5hz with the roll off beginning at 30hz. I chose this as my hd800 (and my hd600,s) have a bit of a rolled off bass and I didnt want to to make it worse with an earlier bass roll off.
I quite liked the result with the direct drive but with the parafeed 4:1 step down I can use a 2.2uf cap
(Mundorf) which is probably of better quality and I think I prefer it. It measures better distortion wise anyway.
Of course Im using a 2P29L at 18ma which is probably better for direct drive. The 26 might work better with parafeed. I can wind my own tx,s but suitable tx,s shouldnt be that expensive.
I didn't asked to measure frequency response. Did you measured the output impedance?
N.B. I use Ale's gyrator not follower.
N.B. I use Ale's gyrator not follower.
I recall reading the gyrator have low output impedance Merlin.
I too have the boards build but haven't the time to link them all up to test.
The follower is just a buffer to add current drive capability.
Cheers
I too have the boards build but haven't the time to link them all up to test.
The follower is just a buffer to add current drive capability.
Cheers
With 6.8uF (simulation):
1kHz: 105R
100Hz: 254R
20Hz: 1.15k
#26 at low anode current, even with enough low output impedance gyrator is only a good preamp, not suitable to drive headphone.
Choose 20-30mA anode current capability tube (as 5687) for this game.
Bela I have it: 5687 triode, opt 15k/600R loaded 15mA each triode sounds wonderful but not DHT.
replace that power supply with a cap multiplier transistor to get an extra 60v to the triode.
change 10 ohm to 15 or 20 if the plate dissapation is to high. the 5.8 to 1 tranny should be ideal now.
I am using KSC3503 for 2 6922 triodes, hum is below the noise s/n 106db.
change 10 ohm to 15 or 20 if the plate dissapation is to high. the 5.8 to 1 tranny should be ideal now.
I am using KSC3503 for 2 6922 triodes, hum is below the noise s/n 106db.
The fact that you have tube equipment, which contains ..kOhm:600R transformer does not mean that it is suitable to drive headphone.
I attached the 801a, Noguchi 24k:600 (FM-24k-600) preamp schematic, which is DHT, has enough low output impedance, but NOT designed (I was the perpetrator 😛) as headphone amp!
High Ri tubes (as 801 and #26 too) very badly tolerate variable (tend to lower than calculated) load impedance.
Instead of its choose lower Ri tubes for driving headphones.
Attachments
Hi All,
For those of you who have successfully been able to run their 26 preamp with exposed tubes:
Do you have any tips you can share?
I can get the pre to be quiet if I completely shield the tubes. But the globe (balloon) versions are so nice looking. It would be nice to have them on display.
Best regards,
John
For those of you who have successfully been able to run their 26 preamp with exposed tubes:
Do you have any tips you can share?
I can get the pre to be quiet if I completely shield the tubes. But the globe (balloon) versions are so nice looking. It would be nice to have them on display.
Best regards,
John
John suspended platform is the way to go.
https://www.jacmusic.com/sockets/Images/Dampers/damper-11.mp4
Not necessary to buy to Jac Music, it's only the image for reference.
https://www.jacmusic.com/sockets/Images/Dampers/damper-11.mp4
Not necessary to buy to Jac Music, it's only the image for reference.
Last edited:
Hi Merlin el Mago,
Thanks for the tip. I currently have them mounted on rubber isolation stand-offs like your picture. (I am actually working on trying to improve this a little by making a mass-loaded platform that will be suspended.)
I don't think my trouble is microphony. It seems to be related to electrical/magnetic fields.
If I put a temporary cowling of heavy aluminum foil over the preamp and ground it, it is tolerably quiet. If I take it off, the 60hz hum is extreme-- I would estimate ~60 db.
It might be grounding related. This is my first foray into filament bias.
Regards,
John
Merlin
I dont get to visit this site often hence late reply.
I did ask whether you were taking the o/p for the headphone from the gyrator o/p or the mu follower o/p. I assumed (wrongly?) that you were using Ale,s hybrid mu follower boards.
These have two possible o/ps. One is a gyrator o/p which is high impedance ie the valves Ra. This o/p is too high to drive a headphone direct. It can be used with a step down transformer or a follower. The mu follower o/p has a low impedance, this is what I use. With this o/p the freq response tells me what the o/p impedance is hence my reply.
If you are using just a gyrator then sorry if I misunderstood you.
I dont get to visit this site often hence late reply.
I did ask whether you were taking the o/p for the headphone from the gyrator o/p or the mu follower o/p. I assumed (wrongly?) that you were using Ale,s hybrid mu follower boards.
These have two possible o/ps. One is a gyrator o/p which is high impedance ie the valves Ra. This o/p is too high to drive a headphone direct. It can be used with a step down transformer or a follower. The mu follower o/p has a low impedance, this is what I use. With this o/p the freq response tells me what the o/p impedance is hence my reply.
If you are using just a gyrator then sorry if I misunderstood you.
I am using Rod Coleman's Filament regs.
I have the raw HT and LT power supplies housed together, but in a separate box from the preamplifier--situated about 1 meter away.
The Filament regs are in the preamp box about 22cm from the tubes. I also have the Salas SSHV2 mounted in the preamp box. I am sharing B+ with both channels.
I read a comment on Ale Moglia's site where he briefly mentioned separating the HT and LT raw supplies. Is this necessary for quiet operation?
Thanks again for your input!