Choke input less stressed filament transformer -via rectifier-, so smaller power (smaller current) is enough, or filament transformer's overheating is decreasing.
The behaviour of rectifier diodes also differs, so less "SS rectifier noise" generating.
The "necessity" of filtration or regulation depends on the design of system.
For example the cathode (auto) biased (R or D string // C) design is less effective to ALL filament supply quality, the filament biased is affective.
If the design is sensible even few ten uV disturbance in filament, more filtration (both static -LC, CL, CR chains- AND active regulator) needed.
If not, omissions are possible.
No general solution.
The behaviour of rectifier diodes also differs, so less "SS rectifier noise" generating.
The "necessity" of filtration or regulation depends on the design of system.
For example the cathode (auto) biased (R or D string // C) design is less effective to ALL filament supply quality, the filament biased is affective.
If the design is sensible even few ten uV disturbance in filament, more filtration (both static -LC, CL, CR chains- AND active regulator) needed.
If not, omissions are possible.
No general solution.
If you are using Rod Coleman's regs then his new V9 design is better/quieter than the previous ones (V4-V8). With the older regs I found a choke input supply did make a small audible difference, but for the 6C4C and 10Y in filament bias (current 1 amp plus) the chokes required were large and generated quite a field around them which was a design problem. I'd put my money on Rod's V9 regs for a start. Add a LC supply if you can manage the fields around the chokes, but I'm not so sure you'd hear a big difference.
Yes - you can put the filament supply in a separate enclosure. I did that several times. I had some very big chokes and it was still a challenge to get the supply hum free.
just saw this thread, i have been build all dht both a1/a2 amps for a while. Here is 211 driving 211 via a source follower. All monolith parts nano crystalline., and now i am using all elrogs Molybedum 211s
last one 211 driving 845, and I am currently working on 801A driving 300B via interstage, will post that once its done
For the 801A -- IT -- 300B monoblocks, I am planning to use the Intact Audio LC Filter https://intactaudio.com/fil.html feeding to V9 of Coleman Reg. The power transformer is an Antek Torroid that will feed both the tubes per monoblock. I will need a dropping resistor to bring down the voltage for 300B filament, and slagle's module has a slot for a dropping resistor.
I have all the parts, waiting for remodel of our house to complete, so I can start the work 🙂
I have all the parts, waiting for remodel of our house to complete, so I can start the work 🙂
IT loaded 801a VAS stage, even with 1:4 SUT, unable to drive 300B up to A1 limit - 2V RMS input -.
If I am not wrong, I have calculated one needs from 3.5 to 4 V RMS at the input of the 1:4 transformer (well, for a -75-80v bias and some headroom)
Last edited:
I use an Rme adc/dac that puts out 6.9Vrms that feeds to a PAL Icon4 passive linestage that uses Slagles Autoformers. Given this is for my office setup, I felt could get away without additional gain. Let me know if I am thinking about the gain structure correctly
From lessons learnt over the years, I am trying to keep the gain structure just right, and do away with active preamps as i have high output dacs. Also, I converted all my vinyl to 24/96 digital using the RME ADC, and in my old age with hearing aids, I can;t make out the difference, so the source is only RME 🙂.
thx
- 300B biased at -70, and 801A is biased at -22V
- Gain of 801A is 8, so I would need 9V in or close to 18Vpp to drive 300B to full power
- 6.9Vrms from RME translates to 2√2∗6.9=2.828∗6.9 = 19.51Vpp, so just about there to drive to full power
From lessons learnt over the years, I am trying to keep the gain structure just right, and do away with active preamps as i have high output dacs. Also, I converted all my vinyl to 24/96 digital using the RME ADC, and in my old age with hearing aids, I can;t make out the difference, so the source is only RME 🙂.
thx
Curious, given the gain calculations I put out, why do you think I need 1:2 if I am not blasting it to full power? Any my calculations wrong?
thx
thx
Euro21 will certainly be able to give you an authoritative answer, but I think you would have almost no headroom. If not using full power maybe, but how much is not blasting it to full power?
Nothing wrong with a bit of additional headroom, especially if you listen to types of music / recordings that are not as compressed as others . . . . but I really don't understand the obsession with getting full power.
If an amp is putting out 50% of full power then going from there to full power is a 100% increase. That will give you an extra 3db which is the equivalent of moving 1m / 39" closer to your speakers.
If an amp is putting out 75% of full power then going from there to full power is a 33% increase. That will only give you an extra 1db and that's if you are actually listening to the amp turned up all the way.
If an amp is putting out 85% of full power then going from there to full power is a 17.6% increase. That's probably the equivalent of leaning forward in your chair slightly so that you're maybe 6" closer to the speakers.
Unless you listen to music very loud you're probably listening at 1 or 2 watts, even less than 1 watt, if you have very efficient speakers. Presumably listening levels in an office environment are considerably lower than in a home environment.
If an amp is putting out 50% of full power then going from there to full power is a 100% increase. That will give you an extra 3db which is the equivalent of moving 1m / 39" closer to your speakers.
If an amp is putting out 75% of full power then going from there to full power is a 33% increase. That will only give you an extra 1db and that's if you are actually listening to the amp turned up all the way.
If an amp is putting out 85% of full power then going from there to full power is a 17.6% increase. That's probably the equivalent of leaning forward in your chair slightly so that you're maybe 6" closer to the speakers.
Unless you listen to music very loud you're probably listening at 1 or 2 watts, even less than 1 watt, if you have very efficient speakers. Presumably listening levels in an office environment are considerably lower than in a home environment.
The 300B bias depends of anode current and anode-cathode voltage.
The most of OPTs datasheet recommend 80mA.
If you want to use power tube about 400V (or a little more), the bias (depends of tube manufacturer) rather -80V than -70V.
So the required grid swing (to A1) is 160Vpp.
The 801a theoretical gain is 8 (if you load it with infinity impedance), but de facto IT loaded VAS stage gain is well below 7 (most of 1:1 interstage must be loaded with few ten kOhm on secondary, terminates the bump at few ten kHz), sometime nearer six than seven.
Practically this VAS stage input need more than 9V RMS to achieve on 300B grid 160Vpp swing.... and it's without any headroom.
The most of OPTs datasheet recommend 80mA.
If you want to use power tube about 400V (or a little more), the bias (depends of tube manufacturer) rather -80V than -70V.
So the required grid swing (to A1) is 160Vpp.
The 801a theoretical gain is 8 (if you load it with infinity impedance), but de facto IT loaded VAS stage gain is well below 7 (most of 1:1 interstage must be loaded with few ten kOhm on secondary, terminates the bump at few ten kHz), sometime nearer six than seven.
Practically this VAS stage input need more than 9V RMS to achieve on 300B grid 160Vpp swing.... and it's without any headroom.
I have Zu audio Omen's which are 100dB, given my office needs I felt the gain structure is more than enough with Zu Audio speakers.
300B operating points I am shooting for are: Vp = 375V, B+ = 385V, Ip = 80mA, Vg = -75V. The fixed bias supply is from rod coleman. These are just paper operating points, the actual ones should be close to it once I built it out.
Once I build it out, if I need additional gain, was planning to add the 1:2 stepup
cheers, and appreciate all the input
btw here is picture of 100th amp, really cool looking tube
300B operating points I am shooting for are: Vp = 375V, B+ = 385V, Ip = 80mA, Vg = -75V. The fixed bias supply is from rod coleman. These are just paper operating points, the actual ones should be close to it once I built it out.
Once I build it out, if I need additional gain, was planning to add the 1:2 stepup
cheers, and appreciate all the input
btw here is picture of 100th amp, really cool looking tube
If you have efficient speakers, 100dB @ 1watt-1meter, but normally listen at 85dB…what wattage are you using and what is the headroom?
The point I was trying to make is that squeezing the maximum power output from a particular tube doesn't offer much in terms of practical listening benefits. It might be satisfying from a technical design standpoint but in terms of increased volume and headroom the difference between 85% and 100%, for example, is minimal and in many cases imperceptible.
It takes 10x the wattage to make something sound "twice as loud" subjectively. So if your amp is running at 85% (just a random example) and you need more volume / headroom you'd get better results by using an amp / tube that provides significantly more power than by trying to squeeze all the power you can from your existing amp. Or by using more efficient speakers.
As for your question, I'm not real good with math but I'll take a shot at it. I'm sure others can provide the exact formula.
Every time you double the power (x2, a 100% increase) you get an extra 3db when measured at 1m. So, conversely, every time you cut the power in half (x0.5, a 50% decrease) you get a 3db decrease when measured at 1m.
So if 1w produces 100db then .5w will produce 97db . . . and .25w will produce 94db . . . and .125w will produce 91db . . . so 0.0625w will produce 88db . . . then 0.03125w will produce 85db.
So, if you listen at a distance of 1m from your 100db speaker it looks like you'd be using just over 0.03w to produce 85db. If you sit further away from your speaker it would require more power to produce the same 85db.
Other factors also come into play such as room acoustics and the fact that most people are listening to a pair of speakers unless you run a mono system. Seating position, whether on axis or off axis, would be another. So I'm sure this is an oversimplification.
I suppose the amount of headroom would depend on how much power your amp has. A 2w amp will have less headroom than a 30w amp if both are used under the same conditions.
But the importance of headroom varies significantly depending on the recording.
Some types of music tend to be recorded with significantly more dynamic range than others. More of a difference between the quietest and the loudest portions of the recording. Classical music recordings tend to be considerably more dynamic than more popular types.
Some genres tend to be recorded with a significant amount of compression in an effort to make the recording sound louder. The average volume level can be increased because the dynamic range has been reduced during the recording and mastering process.
Also, tube amps tend to clip "softer / more gracefully" than SS so in the event that you run out of headroom it might not be as noticeable or bothersome.
Last edited: