Pjotr said:I beg your pardon Guido?
Making an electronic circuit that behaves like a choke is not that difficult, isn’t it?
Cheers
Feel free to build your own guys. This is DIY.
To be honest I am disapointed by the reactions of some among you.
I launch a new product, share and explain about the background and the way it works, and then acused of robbing people because of the prices of the products.
De beste stuurlui staan aan wal
Guido,
Just a few words. I like your approach and work/research and it confirms some things I have been thinking about. As a result I have been thinking about a somewhat differnet realisation myself and posted here. That has nothing to do with commercial products for sale but is a discussion of the topics.
As you well know I have decided to use your products in my commercial modification packages. When I comment I do not mean to suggest your products are not good, on the contrary, those I have encountered are.
Sayonara
Just a few words. I like your approach and work/research and it confirms some things I have been thinking about. As a result I have been thinking about a somewhat differnet realisation myself and posted here. That has nothing to do with commercial products for sale but is a discussion of the topics.
As you well know I have decided to use your products in my commercial modification packages. When I comment I do not mean to suggest your products are not good, on the contrary, those I have encountered are.
Sayonara
Guido Tent said:
<Off-topic>
Well Guido,
That is not our point, at least not mine. You are answering questions that come up with an undertone that makes it going that way.
Better to be kind and patient and elaborate things to those asking if you want to market something. We don’t blame your product, but may we put up some questions please and have a healthy discussion?
Cheers
Hello Guido, good to see your new product. I'm guessing that the current source has a very high impedance at audio frequencies, and the voltage regulator has some sort of long-time-constant DC servo circuit - which makes the whole thing emulate a low-DCR large-value inductor.
Back when I first built the Amity in 1997, I was appalled just how bad a 3-pin DC regulator sounded on the paired VV32B's. It was nice having less than 10 microvolts of noise appear at the speaker terminals - I've measured noisier preamps - but the sound quality was opaque, closed-in, undynamic, and just plain unlistenable. Switching to AC - a matter of moving a few wires - made all the difference, resulting in a very lively, sparkly sound, completely different. Noise level was OK, about 3mV of 60 and 120 Hz, and no buzz at all.
It wasn't until Christian informed me of the ETF.03 comparison between different types of heating that I considered DC heating at all - it sounds like the current-sourced and paired-choke heaters came out well, which is good news for folks that might want DC - and that could be me as well.
One thought - did you consider paired current sources, so both sides of the filament see a high impedance? Or maybe you already built that and found no difference sonically. Curious what you found ...
Back when I first built the Amity in 1997, I was appalled just how bad a 3-pin DC regulator sounded on the paired VV32B's. It was nice having less than 10 microvolts of noise appear at the speaker terminals - I've measured noisier preamps - but the sound quality was opaque, closed-in, undynamic, and just plain unlistenable. Switching to AC - a matter of moving a few wires - made all the difference, resulting in a very lively, sparkly sound, completely different. Noise level was OK, about 3mV of 60 and 120 Hz, and no buzz at all.
It wasn't until Christian informed me of the ETF.03 comparison between different types of heating that I considered DC heating at all - it sounds like the current-sourced and paired-choke heaters came out well, which is good news for folks that might want DC - and that could be me as well.
One thought - did you consider paired current sources, so both sides of the filament see a high impedance? Or maybe you already built that and found no difference sonically. Curious what you found ...
Pjotr said:
<Off-topic>
Well Guido,
That is not our point, at least not mine. You are answering questions that come up with an undertone that makes it going that way.
Better to be kind and patient and elaborate things to those asking if you want to market something. We don’t blame your product, but may we put up some questions please and have a healthy discussion?
Cheers
Hi Pjotr
If the perception on my reaction is as such, I would like to say that it is not intended. I can be quite short in responding, time is limitted for me.
cheers
Lynn Olson said:
Hi Lynn,
Good to meet you here.
Your guess is right.
I prefer AC voltage over DC, but I do not like intermod increasing by 20dB, due to that AC (for SE that is, I have not measured on PP, but be warned, no hum does NOT mean no intermod)
Yes, ETF03 was fun, not at least because of the heater shootout but we learned a lot
The major advantage of DC heating is that you get rid of the humbucking pot - OUT of the signal.
The main advantage of current heating is that we don not throw away information.
If both sides of the filament see high impedances, how would we arange the cathode to close with the anode current ?
See you in December
cheers
Guido Tent said:
Hmmm, good idea Guido, I knew you were cooking up
some goodies over there but would never have picked
a DHT heater voltage reffed current source, smart thinking!
OK, here's a question, WRT differential audio current generated
in the heater, is it better to reference one end of the heater,
or would a theoretical centre point be better, sort of pseudo
balanced?
Good luck, I'm sure the implemetation is first class.
Terry
Terry Demol said:
Hmmm, good idea Guido, I knew you were cooking up
some goodies over there but would never have picked
a DHT heater voltage reffed current source, smart thinking!
OK, here's a question, WRT differential audio current generated
in the heater, is it better to reference one end of the heater,
or would a theoretical centre point be better, sort of pseudo
balanced?
Good luck, I'm sure the implemetation is first class.
Terry
Hi Terry
Thanks for your kind words
The "where to connect heater to ground question" is a fundamental one.
We couldn't hear major differences between tying either end to ground, in a fixed bias setup.
Any kind of balancing, like done with a humpot, decreases the differential impedance, which we don't want.......
So far I prefer having the + side of the heater to ground, but there still is many ways to experiment
all the best
Hi,
An excellent idea, Guido.
This should be a major help to all those people wondering how to tackle DHT heating properly.
Your solution to the problem is what it should be IMO, congrats.
Curious to see technical suggestions as to why the grounded + side would be prefered.
Even though I heard of people claiming heating IDHT small signal valves with a negative voltage yields a small but audible improvement before, I never found a plausible explanation as to why this would be.
Looking forward to the 2.5 and 10V versions to please the numerous 2A3 fans and 845/211 freaks out there....
Cheers,
An excellent idea, Guido.
This should be a major help to all those people wondering how to tackle DHT heating properly.
Your solution to the problem is what it should be IMO, congrats.
Curious to see technical suggestions as to why the grounded + side would be prefered.
Even though I heard of people claiming heating IDHT small signal valves with a negative voltage yields a small but audible improvement before, I never found a plausible explanation as to why this would be.
Looking forward to the 2.5 and 10V versions to please the numerous 2A3 fans and 845/211 freaks out there....
Cheers,
fdegrove said:Hi,
An excellent idea, Guido.
This should be a major help to all those people wondering how to tackle DHT heating properly.
Your solution to the problem is what it should be IMO, congrats.
Curious to see technical suggestions as to why the grounded + side would be prefered.
Even though I heard of people claiming heating IDHT small signal valves with a negative voltage yields a small but audible improvement before, I never found a plausible explanation as to why this would be.
Looking forward to the 2.5 and 10V versions to please the numerous 2A3 fans and 845/211 freaks out there....
Cheers,
Hello Frank,
Thanks for positive feedback !
On the "where to ground the tube" discusion, may hours will be spend. Anyhow, it is up to the users of what they find sounds best.
Working on the 2.5V version, bit tricky due the low voltages.
The 10V 3.25A version will arive soon !
cheers
Konnichiwa,
I would like an explanation too. I first came across "positive (AC) grounded" in the Verdier and le Maison 300B Amp (the circuit was the basis for my "legacy" Amp). I tried it the other way and positive AC grounded sounded better, DESPITE the voltage reg obviously shortcircuiting any AC developed across the heater....
Sayonara
fdegrove said:
I would like an explanation too. I first came across "positive (AC) grounded" in the Verdier and le Maison 300B Amp (the circuit was the basis for my "legacy" Amp). I tried it the other way and positive AC grounded sounded better, DESPITE the voltage reg obviously shortcircuiting any AC developed across the heater....
Sayonara
Kuei Yang Wang said:
Hi Sayonara,
In the case of DC supply to the heater, the majority of audio-current runs through the side with highest gm, e.g the side when + is tied to ground (or cathode resistor).
With AC on the heater, I never did the experiment as described (AC grounding). Should do it one day though, wonder if it matches with my preference in the DC situation.
The physical current distribution through the tube also depends on the geometry of the filaments. This may also play a role.
I do not have a single answer yet......
regards
I too have been experimenting with filament supply buffering recently. I had found with ac-heating that the type of trafo had a big influence - toroids sounded shrieky and aggressive whereas 1,3A wallknobs sounded muddy and distant. I guessed this was due to poor dielectrics in the trafo, and resolved to build a dc supply with audiofrequency buffering on BOTH filament terminals. The outcome was the most wonderful upgrade I have achieved in five years with 300Bs. Not only that, but all the parts are junk box or radio-rally stock, and best of all, the biggest improvement is worked on the cheapest 300Bs - eg: 1998 vintage Sovteks which you will have put away long ago if you have ac-heating. Gone is the grimy, murky, & noisy sound - now they project into the room with vigour and vivacity.
I briefly considered a complementary current source to isolate both filament terminals, but soon realised a much better circuit with current sinking on the negative, and a gyrator (aka electronic choke) to reject ripple on the positive supply. The schematic tells the tale.
The first (mains) trafo has its output centre tap grounded (300B ground) to eliminate dc and common-mode mains noise. It also serves to keep diode noise and current pulses from feeding back up the mains & into other equipment. Thanks (again) are due to Lynn Olson for voicing this idea.
The second (toroid) trafo is fullwave schottky rectified to minimise the number of clanking diodes compared to a bridge. The target output is 8,7 to 9,5V with 1V of ripple. The high ripple voltage is mandatory to increase the conduction angle and reduce peak current. Ripple is cut to the mV level by the action of the gyrator Q1, T1 and associated passives. The NPN-PNP complementary feedback pair (CFP) works somewhat like a darlington here but with the big difference that when faced with out-of-band signals (limit typically set by C13) the CFP looks like a high (=R3, 1,6K) impedance. So one can try different values for different amplifiers. C13 is also required for CFP stability since there is no output capacitor for the CFP (caps between the filament terminals or to the filament supply return will destroy the performance of this circuit BTW). Be sure you have a scope at hand if you mess with the CFP parts values/types. And for T1 try to get some Zetex FZT1051As from Farnell or Digikey - substitutes will degrade performance if the high Hfe over wide Ic is not available, together with low Cob. For Q1, choose a TO-220 part with Cob < 75pF and Ft > 30MHz. For Q1 and T2, use a 5 degC/W heatsink or better - and mount the sink in free air.
The filament return side is current regulated by T2, T3 and the sense resistor. This simple circuit answers perfectly the requirement for high audiofrequency impedance. Simply select the current sense resistor R4 to give 5,2V across your 300B filaments. 0,5 ohm is a starting value for 1,1A to 1,3A 300Bs, and you then add parallel values to home in. The voltage drops about 5% when warmed up, due to the tempco (-2mV/deg C for Vbe) of T3 - so mount this part in free air.
Do not use LM317 in this position if you want good performance. The dropout and ac impedance are markedly worse, it is noisy, and its thermal cutout preserves a tenpenny chip at the expense of your precious triode.
when set up correctly, there should be about 2V across each power transistor for a 9V supply. Don't let it get below about 1,6V for best ac-performance, and at the other extreme, take care not to use a raw dc supply much above 9V or you will roast the underside of your amp, and probably overstress the transistors. And If you are not comfortable about setting currents in your expensive triodes, or are unfamiliar with stability testing of transistors, or if you cannot confidently calculate and test the thermal design/heatsinking of power transistors, please don't attempt to build this circuit. It will be cheaper in the long run to buy Guido's module and avoid wrecking your DHTs.
I briefly considered a complementary current source to isolate both filament terminals, but soon realised a much better circuit with current sinking on the negative, and a gyrator (aka electronic choke) to reject ripple on the positive supply. The schematic tells the tale.
An externally hosted image should be here but it was not working when we last tested it.
The first (mains) trafo has its output centre tap grounded (300B ground) to eliminate dc and common-mode mains noise. It also serves to keep diode noise and current pulses from feeding back up the mains & into other equipment. Thanks (again) are due to Lynn Olson for voicing this idea.
The second (toroid) trafo is fullwave schottky rectified to minimise the number of clanking diodes compared to a bridge. The target output is 8,7 to 9,5V with 1V of ripple. The high ripple voltage is mandatory to increase the conduction angle and reduce peak current. Ripple is cut to the mV level by the action of the gyrator Q1, T1 and associated passives. The NPN-PNP complementary feedback pair (CFP) works somewhat like a darlington here but with the big difference that when faced with out-of-band signals (limit typically set by C13) the CFP looks like a high (=R3, 1,6K) impedance. So one can try different values for different amplifiers. C13 is also required for CFP stability since there is no output capacitor for the CFP (caps between the filament terminals or to the filament supply return will destroy the performance of this circuit BTW). Be sure you have a scope at hand if you mess with the CFP parts values/types. And for T1 try to get some Zetex FZT1051As from Farnell or Digikey - substitutes will degrade performance if the high Hfe over wide Ic is not available, together with low Cob. For Q1, choose a TO-220 part with Cob < 75pF and Ft > 30MHz. For Q1 and T2, use a 5 degC/W heatsink or better - and mount the sink in free air.
The filament return side is current regulated by T2, T3 and the sense resistor. This simple circuit answers perfectly the requirement for high audiofrequency impedance. Simply select the current sense resistor R4 to give 5,2V across your 300B filaments. 0,5 ohm is a starting value for 1,1A to 1,3A 300Bs, and you then add parallel values to home in. The voltage drops about 5% when warmed up, due to the tempco (-2mV/deg C for Vbe) of T3 - so mount this part in free air.
Do not use LM317 in this position if you want good performance. The dropout and ac impedance are markedly worse, it is noisy, and its thermal cutout preserves a tenpenny chip at the expense of your precious triode.
when set up correctly, there should be about 2V across each power transistor for a 9V supply. Don't let it get below about 1,6V for best ac-performance, and at the other extreme, take care not to use a raw dc supply much above 9V or you will roast the underside of your amp, and probably overstress the transistors. And If you are not comfortable about setting currents in your expensive triodes, or are unfamiliar with stability testing of transistors, or if you cannot confidently calculate and test the thermal design/heatsinking of power transistors, please don't attempt to build this circuit. It will be cheaper in the long run to buy Guido's module and avoid wrecking your DHTs.
Rod Coleman said:
Hi
This is an impressive setup
What is curiious, is that you use current sources, and finally "short" the audio current to ground using a cap
Now very likely the filament supply is less in the signal, that function is taken over by the caps
it shows that traditional regulators are not optimised for this task, and that a decently designed supply meets the requirements way better.
Personally I am in favour of high impedance across the filaments, but as you can see, many ways lead to rome....(they are all long though
I guess balancing the sources is tricky, not ?
Oh, one last word, the Sovtek is not the best sounding tube, to be honest I iuse these for first time testing only......
cheers
Pjotr said:
Only one side of the filament is shorted to ground with a cap. Does not look that curious for a self-biased set up. Apart from the current sink the other side is loaded with resistors, which are relatively high compared to the filament resistance.
Cheers
Hi
Yes. The resistors look like to be the bias resistors. I am not so fond of cathode bias, by the way. I'd rather go for fixed bias and leave the cap out. That is still possible with the proposed filament supply.
cheers
Hi,
Guido,
Regarding the preference (subjective thing, I know) , when the + side of the heater is grounded won't that change the bias with the respective heater voltage amount?
I mean, +5V side grounded means -5V added to negative bias or do I see this the wrong way?
If I am correct that may well account for the audible difference I suppose...
Cheers,
Guido,
Regarding the preference (subjective thing, I know) , when the + side of the heater is grounded won't that change the bias with the respective heater voltage amount?
I mean, +5V side grounded means -5V added to negative bias or do I see this the wrong way?
If I am correct that may well account for the audible difference I suppose...
Cheers,