| Bas Horneman |
Hallo Guido,
Is this the DHT supply that Triode Dick was raving about? (But could not yet reveal?
Could you explain in layman's terms what is new about this idea?
Regards,
Bas |
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| Sch3mat1c |
And why would you give someone else your money for something that you can make out of LM317s?
I mean, spending money makes things sounds good, but that's beside the point.
Tim |
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| Frank Berry |
| ... and no short circuit protection? |
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| Pjotr |
Don’t get it either. As far as I understand Guido’s page it is a voltage limited current source. Probably it will be baked when short circuited?
;) |
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| ultranalog |
A current source fed back from a voltage reference...
is a voltage source. |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by ultranalog
A current source fed back from a voltage reference...
is a voltage source. |
Hmmm. I have no idea what Guido's circuit looks like, but I have been thinking about stuff like this myself. It is quite trivial to design an "electronic filter choke" which can (as a side-effect) operate as voltage regulator, but which has an impedance rising at a rate of 20db/decade (impedance multiplies by a factor 10 for each decade in frequency), whihc could have very significant levels of Impedance even at 100/120Hz.
This would certainly combine the behaviour of a CCS and a CVS with a certain transtition region at very low frequencies.
Sayonara |
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| ultranalog |
That is exactly the point that has been mystified in this story.
A first order is easily achieved with an L200. Myself, I'd go for a 1 Hz, 4th order turnover or something alike. |
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| Pjotr |
Quite right KYW,
IMHO it is more effective to keep mains and rectifier related noise away from the DH cathode by proper LC filtering. A simple LM317 or LM338 will do then as a voltage regulator and electronic low frequency filter.
Just my 2 cents ;) |
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| Guido Tent |
| quote: | Originally posted by Bas Horneman
Hallo Guido,
Is this the DHT supply that Triode Dick was raving about? (But could not yet reveal?
Could you explain in layman's terms what is new about this idea?
Regards,
Bas |
Yes, it is what excited Triode Dick...............
read the site, I put a lot of background info there !
cheers |
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| Guido Tent |
| quote: | Originally posted by Pjotr
Quite right KYW,
IMHO it is more effective to keep mains and rectifier related noise away from the DH cathode by proper LC filtering. A simple LM317 or LM338 will do then as a voltage regulator and electronic low frequency filter.
Just my 2 cents ;) |
Hi
It is not only about filtering, it is about exposing the filaments to an external impedance.
Read the presentation for background info
regards |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by ultranalog
That is exactly the point that has been mystified in this story.
A first order is easily achieved with an L200. Myself, I'd go for a 1 Hz, 4th order turnover or something alike. |
Well, lets look a simple theoretical circuit. We take an LM317 for simplicity, 390R/1K2 voltage set resistors for 5V and a 1,000uF coupling capacitor for the AC and a 1R sense resistor. We get a turnover of 0.5Hz and thus at 50Hz 100 times the sense resistor as Impedance (100R) and at 100Hz 200 times.
If we increase the Capacitor (and sense resistor) we can achieve quit high levels of impedance. Using standard values for a 300B Heater supply without wasting too much power we may with to use 4,700uF/16V as coupling capacitor and 2R2 as sense resistor and 1k/2k7 "set" resistors for the LM317 we get over 4KOhm impedance at 100Hz (theoretically at least) and around 4.75V DC, just ideal for a 300B.
In this design we are loosing around 3.3V in the 2R2 Resistor, which suggests a supply with a minimum of 10V prior to the whole shebang. Using a pair of 16V 4,700uF Capacitors with a little LC common mode filter (at least 2A rating) and a 9V winding plus schottky bridge we should have a nicely working supply, very low noise, high AC impedance and a 7.5 second timeconstant, giving a nicely slow start.
The resistor could be replaced with a choke, making the slope 2dn order, but it needs a pretty beefy choke, 4.7mH/2A might be usefull there as it will reduce the required voltage level and will increase a little in 100Hz impedance on the Resistor.
Anyway, some thought experiements on "electronic chokes", which would make a nice DHT supply using inexpensive off-shelf parts.
Sayonara |
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| Bas Horneman |
| quote: | | read the site, I put a lot of background info there ! |
I did Guido!
But I simply don't know/understand how your design differs from a simple voltage reg followed by a current reg?
I am not an EE. And I think that most of your potential clients for that board will fall into that category.
Telling these kind of people to read the datasheet won't help you endear your product to them. At least I don't think so.
It's the same for your oscillators. I don't want know necessarily why they are better...but I understand that 3 ps is better than 200 ps.
But I can't understand why your filament reg is better than the vr/cr type circuit. Because I don't even know the specs of a typical LM317 vr/cr....such as I plan on building for a friend/customer (Cleo V with Doede's VR/CR. )
Regards,
Bas |
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| ultranalog |
| quote: | It is not only about filtering, it is about exposing the filaments to an external impedance.
|
Please, elaborate on the difference between a filter and a (frequency-dependent) impedance. |
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| Guido Tent |
| quote: | Originally posted by Bas Horneman
I did Guido!
But I simply don't know/understand how your design differs from a simple voltage reg followed by a current reg?
Bas |
Hi Bas,
A voltage source has a low impedance, compare with car battery, it maintains the output voltage, "regardless" of the load
A current source has a high output impedance, it maintains the output current, regardsless of the load.
My design has a high output impedance, hence does not short the differential audio current generated in the DHT
This to me is the main reason why it sounds better
And it does sound better, to many ears already
cheers |
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| Guido Tent |
| quote: | Originally posted by ultranalog
Please, elaborate on the difference between a filter and a (frequency-dependent) impedance. |
Remco,
My design filters as well, as does the traditional voltage regulator.
In addition, my design has a high output impedance, this contrary to a traditional voltage reg.
regards |
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| ultranalog |
| quote: |
A current source has a high output impedance, it maintains the output current, regardsless of the load.
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| quote: |
Output current: automatically adapts to required level to reach voltage specified above
|
This doesn't compute. |
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| Guido Tent |
| quote: | Originally posted by ultranalog
This doesn't compute. |
If you look at the data at my site you will understand it computes
It maintains stable voltage for DC, and high output impedance for audio frequencies |
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| ultranalog |
The power is delivered by a voltage source. In other words, this circuit behaves like a choke.
And it's priced likewise... |
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| Guido Tent |
| quote: | Originally posted by ultranalog
The power is delivered by a voltage source. In other words, this circuit behaves like a choke.
And it's priced likewise... |
You're free to put a choke in your designs. It is actually where I started.
It''ll be chunky, as it needs to show quite some impedance quite early in the frequency domain, and it would be fine if it is 0 ohm DC, say thick wire and loads of iron, to achieve Henries and amps, otherwise you keep adjusting the whole thing during use and the voltage source in front needs to be stable and low drop due to heat requirements.
Yes, when you've done that, you're about there. Recalculate system solution price, dealermargins included, and put it in contrast with size, weight, performance and 5 years of warrantee.
cheers |
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| Pjotr |
I beg your pardon Guido?
Making an electronic circuit that behaves like a choke is not that difficult, isn’t it?
Cheers ;) |
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| Guido Tent |
| quote: | Originally posted by Pjotr
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 |
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| Kuei Yang Wang |
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 |
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| Pjotr |
| quote: | Originally posted by Guido Tent
Feel free to build your own guys. This is DIY.
To be honest I am disapointed by the reactions of some among you. |
<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 ;) |
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| Lynn Olson |
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 ... |
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| Guido Tent |
| quote: | Originally posted by Kuei Yang Wang
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 |
Hi Sayonara
I haven't had bad feelings with your reaction, actually your the one who needed the least information before understanding the principle and turning it around into some DIY version.
best regards |
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| Guido Tent |
| quote: | Originally posted by Pjotr
<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 |
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| Guido Tent |
| quote: | Originally posted by Lynn Olson
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 ... |
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 |
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| Terry Demol |
| quote: | Originally posted by Guido Tent
Hi Bas,
A voltage source has a low impedance, compare with car battery, it maintains the output voltage, "regardless" of the load
A current source has a high output impedance, it maintains the output current, regardsless of the load.
My design has a high output impedance, hence does not short the differential audio current generated in the DHT
cheers |
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 |
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| Guido Tent |
| quote: | Originally posted by Terry Demol
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 |
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| fdegrove |
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.
| quote: | | So far I prefer having the + side of the heater to ground, but there still is many ways to experiment |
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,;) |
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| Guido Tent |
| quote: | Originally posted by fdegrove
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 |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by fdegrove
Curious to see technical suggestions as to why the grounded + side would be prefered. |
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 |
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| Guido Tent |
| quote: | Originally posted by Kuei Yang Wang
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 |
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 |
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| Rod Coleman |
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. |
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| Ciscokid |
Hi Guido Tent,
Very nice board! Look forward to giving a pair a try later this year.
Regards,
Danny |
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| Guido Tent |
| quote: | Originally posted by Rod Coleman
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. |
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 |
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| Pjotr |
| quote: | Originally posted by Guido Tent
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 |
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 ;) |
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| Guido Tent |
| quote: | Originally posted by Pjotr
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 |
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| fdegrove |
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, ;) |
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| Guido Tent |
| quote: | Originally posted by fdegrove
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, ;) |
Hi Frank
Yes, the bias changes when reversing polarity. In the listening tests we corrected for this change. After all, the effective (negative) grid voltage had to be changed, which may change the ease of drive. I assume this effect is of minor importanve though.
I still think it is in the current distribution of the tubes, which is never symmetrical.
best regards |
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| fdegrove |
Hi,
Guido,
| quote: | | In the listening tests we corrected for this change |
Ah...I wasn't sure you had compensated for that.
| quote: | | I still think it is in the current distribution of the tubes, which is never symmetrical. |
Exactly.
Current distribution may well vary from tube to tube though as I can't imagine a factory worker being able to tell the direction .
So some experimenting may be called for before deciding how hooking it up, I suppose.
Thanx.
Cheers,;) |
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| Pjotr |
| quote: | Originally posted by Guido Tent
Yes, the bias changes when reversing polarity. In the listening tests we corrected for this change. After all, the effective (negative) grid voltage had to be changed, which may change the ease of drive. I assume this effect is of minor importanve though.
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But the anode-cathode voltage also changes by 5V given a constant B+. This will change the load line. Did you compensate for that too?
Anyway the AC audio current has to flow through the DC gradient across the filament when the filament is only grounded at one side. But it is still AC. Whether you ground the + or – side of the filament, that gradient stays the same.
It is known that with lo mu tubes (with wide grid spacing) magnetic fields influences also electron flow...? In this case the magnetic field generated by the filament current?
Up till now, just some observations but no explanation. Think it will be hard to find some explanation, although it stays intriguing
Cheers ;) |
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| Rod Coleman |
hi Guido
| quote: | Originally posted by Guido Tent
Hi
This is an impressive setup
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Thanks!
| quote: |
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 :-)
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I agree! The resistors on the cathode are the self-bias resistors, using different values according to Thorsten advice to balance the currents flowing from either end of the filament -
http://db.audioasylum.com/cgi/m.mpl...=31256&session=
The 100uF Cerafine is the cathode bypass capacitor.
| quote: |
I guess balancing the sources is tricky, not ?
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No need to balance the +/-.
On the positive side (T1 - Q1) Is only a ripple smoother - it drops about 2V or so and rejects noise. It's more like a voltage source (at dc) than a current source.
On the negative side T2 - T3 is the current source which is adjusted to make the right voltage appear across the filament.
| quote: |
Oh, one last word, the Sovtek is not the best sounding tube, to be honest I iuse these for first time testing only......
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The interesting thing about the Sovtek is the big difference between ac and current source heating. It's so noisy and bad sounding on ac - but sounds wonderful using the circuit in post #35.
The construction of the old Sovtek 300B uses a very thin filament, which at least partly accounts for the bad sound and microphony
If you're using Sovtek or another cheap DHT with ac heating, you owe it to yourself to try current-driven heat! Get Guido's heater supply, or, if you're transistor-competent, build your own design! It's much cheaper than upgrading to fancy 300Bs and probably just as good. |
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| Guido Tent |
| quote: | Originally posted by Rod Coleman
I agree! The resistors on the cathode are the self-bias resistors, using different values according to Thorsten advice to balance the currents flowing from either end of the filament -
http://db.audioasylum.com/cgi/m.mpl...=31256&session=
The 100uF Cerafine is the cathode bypass capacitor.
No need to balance the +/-.
On the positive side (T1 - Q1) Is only a ripple smoother - it drops about 2V or so and rejects noise. It's more like a voltage source (at dc) than a current source.
On the negative side T2 - T3 is the current source which is adjusted to make the right voltage appear across the filament.
The interesting thing about the Sovtek is the big difference between ac and current source heating. It's so noisy and bad sounding on ac - but sounds wonderful using the circuit in post #35.
The construction of the old Sovtek 300B uses a very thin filament, which at least partly accounts for the bad sound and microphony
If you're using Sovtek or another cheap DHT with ac heating, you owe it to yourself to try current-driven heat! Get Guido's heater supply, or, if you're transistor-competent, build your own design! It's much cheaper than upgrading to fancy 300Bs and probably just as good. |
Hello Rod,
Yes, the balancing of DC current distribution (density) due to different values in the cathode is a nice one.
Still, the AC distribution can be defined by adding external cap(s) to ground.
On the current source: One follows the other, correct ?
I'll pay more attention to the Sovteks - thanks !
best regards
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Guido |
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| Rod Coleman |
How about another circuit idea for Push-Pull DHT amps like the Lynn Olson AMITY etc. (Idea ONLY so far - I don't have an AMITY yet, sadly):
Most of the circuit shown in post #35 of this thread can be kept as-is, but with the two push pull valves each having their own return circuit (current sink). That way the two valves can have different voltages (to cover production tolerances):
2 x 2A filaments, like the KR300BXLS can be accommodated easily with this circuit. If the transistors are MJL1302A (PNP) and MJL3281 (NPN) - AND mounted on heatsinks of 2~4 deg C/W you can even have shorted filament protection! What's more you can have one filament shorted and the other will carry on working normally, avoiding the risk of cathode stripping in the good valve. Just be aware this means ONLY that the filament is shorted; I don't mean you can short the positive side to the raw supply return. Bypassing the current sink part of the circuit will vanish the safety feature. But if you properly insulate the return node you should be protected against all reasonably likely faults.
Be sure you can cope with the stability test and thermal ratings design/test as noted in post #35 if you attempt to build this circuit; you could burn up your DHTs if you don't check & burn in thoroughly. |
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| Kuei Yang Wang |
Konnichiwa,
This one has been among the dead for a while, time to voodoo it back among the living.
Over the recent times I have been thinking to and fro how one might achieve similar effects to Guido's circuit, preferably short circuit protected, simple and with as few parts and 3-legged fuses as possible. The following Circuit is what I came up with, it SHOULD work (P-Spice says it does) but I have not specifically build it (yet), so beware....
The idea is to make a Circuit that is a high impedance at AC. We already know the "simple" LM1085 Curret Source seems to work fine sonically, but when supplying normal DHT's you need to re-adjust it as valves age and when you change Valves, far from ideal.
In my circuit the 1mH Choke (around 0.5R DCR) together with the 1,000uF Capacitor in effect establishes an AC Current Source where the transconductance of the 3-Pin Regulator in effect amplifies the impedance of the 1mH Choke. The 1,000uF Capacitor together with the 1K resistor between adj and out froms a highpass at 0.16Hz so at DC the whole thing will slowly turn bacvk to a low DCR resistance source.
In order to set the Output voltage accuratly a LM/TL431 is used, here the output voltage would be 5V. In order to stop the LM431 from "regulating away" our nice high output impedance the lower part of the voltage divider which stes the output voltage is bypassed (1st Order LPF at 0.03Hz), thus making sure that audio frequencies the impedance remains high. In the audio range the impedance is limited by the 10K unbypassed resistor in the voltage sensecircuit.
Added to this is a simple common mode filter and Schottky Rectifier Bridge, basically "best practice" for DHT Heater DC Supplies, lest you like to use Thyratron or high current mercury vapour rectifiers like this dude here:
300B SE Amp with 101D Driver, 300B Rectifier and 314A rectified heater supplies....
As usual comments etc welcome.
Sayonara |
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| Rod Coleman |
Wang san, sumimasen!
Sure its worth raising this one again, its a dinner-money upgrade with far more impact than a mortgage-busting pile of boutique glassware, dielectricware or even old fashioned ironware!
I accept that you're going to have some adjusting to do when you only have a current loop controlling heater power. I did think about adding a voltage loop - with multiple-pole cutoff <1Hz - but decided I don't need it. The heater voltage with the gyrator/transistor current source shown above is plenty stable enough (over the few hundred hours I've run it), and can easily be made adjustable with a low power 20 ohm fixed in series with a 100 ohm/10T trimmer (all across the sense resistor).
I found it worthwhile to spend time finetuning the circuits in both heater terminals - I would certainly recommend testing your circuit with an effective ac break between the rectifier -ve and -F. In that position I like a PNP darlington gyrator formed with FZT1151A (Zetex, superbeta) and a PNP power transistor (smallest you can get which satisfies your safety margin). The specified Cob of the PNPs is what counts (35pF = good; >130pF = bad). The reason for the obsession is (as you know) the -ve current pulses that form the rectifier noise - with plenty of energy >100MHz.
General observation: With 3-terminal regs the multiple internal circuit paths from IN (& ADJ) to OUT risk degrading the insertion loss as frequency gets really high. So, in your circuit, watch out for the ac path from +F through the 1000uF into ADJ!
clic the pic - Easy to build circuit on plain copperclad board (hacksawed pattern) with SMD parts - (2512 cathode resistors, FZT1051A/2SD2061 gyrator, FZT1051A/2SC5511 current source with R47 R56 shunted sense resistors, SANYO 560/10 SVP (20mOhm ESR) caps.....
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by Rod Coleman
Sure its worth raising this one again, its a dinner-money upgrade with far more impact than a mortgage-busting pile of boutique glassware, dielectricware or even old fashioned ironware! |
Absolutely.
| quote: | Originally posted by Rod Coleman
I accept that you're going to have some adjusting to do when you only have a current loop controlling heater power. |
Yes, I had exactly that issue with my simple LM1085 CCS, which I had enhanced with the addition of a little choke (a few mH, small size) and a common mode choke.
In fact, this very simple supply:
Schottky Bridge
10,000uF
2.2mH/2A
LM1085 CCS
CMC Filter
actually sounded as good as ANY other heater supply I have been using so far, including serious choke filtered stuff, but it was too hasslesome when conducting for example comparison tests with 6 or 7 different 300B's.....
I have noticed your circuits previously (nice work actually), but they have no protection against overload. As I tend tend to tinker a lot I consider such mandatory. Any circuit that cannot survive the slip of a screwdriver or a 'scope probe is not to my liking.... I get to angry with myself if I have to swap out all the blown threelegged fuses each time....
| quote: | Originally posted by Rod Coleman
General observation: With 3-terminal regs the multiple internal circuit paths from IN (& ADJ) to OUT risk degrading the insertion loss as frequency gets really high. So, in your circuit, watch out for the ac path from +F through the 1000uF into ADJ! |
Thanks, good one. I did wonder what it was (I showed up in the P-Spice simualtion) but I figured it would still "do". The solution is of course simple, add another resistor (1K) between the adj pin and the junction where the 1,000uF Cap, LM431 cathode and 1K resistor join.
My main idea was at any extend to come up with something that offered reasonable performance and mainly "aparent" simplicity (eg. simplicity in implementation, all the complexity is hidden inside the LM1085 & LM431).
I could have used a discrete pass transistor instead of the LM1085, but the 1085 makes a nice enough pass transistor with build in SOAR protection....
I might consider adding a second "electronic choke" in the negative Line as well, may be worth it....
| quote: | Originally posted by Rod Coleman
clic the pic - Easy to build circuit on plain copperclad board (hacksawed pattern) with SMD parts - (2512 cathode resistors, FZT1051A/2SD2061 gyrator, FZT1051A/2SC5511 current source with R47 R56 shunted sense resistors, SANYO 560/10 SVP (20mOhm ESR) caps..... |
One might also build a more or less functional equivalent using LM1085's as current sinks and as Filters, with short circuit and overheat protection.... Performance at HF would be worse of course, all a matter of design goals, still, very nice job on this.
Ciao T |
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| Rod Coleman |
Konban-wa Wang san
| quote: | | but they have no protection against overload. As I tend tend to tinker a lot I consider such mandatory. Any circuit that cannot survive the slip of a screwdriver or a 'scope probe is not to my liking.... I get to angry with myself if I have to swap out all the blown threelegged fuses each time.... |
Don't let shortcircuit worries hold you back, if you're considering a discrete heater circuit. Provided the sense resistor is protected (use two series parts so the end-to-end gap exceeds a "pliers-span") you are OK. If you short across F+/F- the current stays at 1,3A - so the currentsource transistor's dissipation rises to ~10W (for ~9V raw input) - fine for TO220 types mounted on <10 deg. C/W. In the gyrator side nothing happens!
If that's still not tough enough, you could try some Raychem Polyswitches next time you're at Rapid - e.g. type RGE300
http://www.rapidelectronics.co.uk/r...31870&XPAGENO=1
As for whether the gyrator contributes greatly to the improved sound, I suspect that varies with the leakage capacitance (through the filament transformer) back to the "B-" terminal of the rig in question. Big leakage = current path for diode recovery pulses.
Thanks for your kind words on my heater posts; they boost my enthusiasm for "converting" some of the ac-heated DHT designs out there. It's the only change I can remember getting unreserved plaudits from my "expert witness" listener - sings in the wonderful Armonico Consort http://www.armonico.org.uk/
Especially for those that have the lower cost/quality DHTs, if you're on ac-heat now, find out what you're missing! |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by Rod Coleman
If you short across F+/F- the current stays at 1,3A - so the currentsource transistor's dissipation rises to ~10W (for ~9V raw input) - fine for TO220 types mounted on <10 deg. C/W. In the gyrator side nothing happens! |
Shortcircuit +F to the negative rail will do nicely.
BTW, improvement to your gyrator....
Add a resistor of 0R47 in series with the emitter, connect a 1K resistor in series bith the base of the small signal transistor, return a 47uF or so capacitor from +F to the base....
| quote: | Originally posted by Rod Coleman
As for whether the gyrator contributes greatly to the improved sound, I suspect that varies with the leakage capacitance (through the filament transformer) back to the "B-" terminal of the rig in question. Big leakage = current path for diode recovery pulses. |
Of course, with good layout and schottky diodes, plus CMC filtering this is mostly taken care of anyway....
I am thinking again, sadly immediatly sending complexity through the roof again.... Use an improved gyrator (the one with the added rc noted above) and make one in each line (one PNP Darlington and NPN Darlington. Set the voltage between the base's via a Phototransistor or the like, use a CC in series with a LED and a TL431 as sense element to get the voltage right....
I thinlk I'll stick with LM1085....
Sayonara |
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| Rod Coleman |
| quote: | Originally posted by Kuei Yang Wang
BTW, improvement to your gyrator....
Add a resistor of 0R47 in series with the emitter, connect a 1K resistor in series bith the base of the small signal transistor, return a 47uF or so capacitor from +F to the base....
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A bootstrapped second-order gyrator! Ideal if you run out of schottkys...
| quote: | Originally posted by Kuei Yang Wang
I am thinking again, sadly immediatly sending complexity through the roof again.... Use an improved gyrator (the one with the added rc noted above) and make one in each line (one PNP Darlington and NPN Darlington. Set the voltage between the base's via a Phototransistor or the like, use a CC in series with a LED and a TL431 as sense element to get the voltage right....
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you're on to something there. If we shift it to a Kirchoff-architectured circuit, some of the simplicity comes back. We could increase the current source to the maximum expected 300B, eg 1,5A and bleed off a variable amount until 5V appears across the filament. How about -
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For the current sources, choose discretes or regulators according to taste.
A circuit that 'flows' like that lays out nicely on 'hacksaw-matrix' copper with hardly any spaghetti wiring.
The great benefit is that voltage control is achieved without any compromise to the high dynamic impedance (looking back into the power supply) from either filament terminal.
For those that like twinkling LEDs, we could put one in series with the base - LED lights only after the filament has warmed up! Actually, the LED would also help align the bleed to zero when 5V is achieved... getting around the 2V saturation of a 431. |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by Rod Coleman
A bootstrapped second-order gyrator! Ideal if you run out of schottkys... |
Yup. You can also use it with a nice FET (I use 2SK2610) as small, cheap and lightweight replacement for HT Chokes.... Another trick for that one is to actually tap off the lowered and filtered DC reference from the rail of an earlier stage in the Amp which gets an RC Filtered supply directly from the first reservoir capacitor leaving minimal componentry for the bootstrapping...
| quote: | Originally posted by Rod Coleman
you're on to something there. If we shift it to a Kirchoff-architectured circuit, some of the simplicity comes back. We could increase the current source to the maximum expected 300B, eg 1,5A and bleed off a variable amount until 5V appears across the filament. How about -
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Yes, I thought about that too, the shunt across the heater may be an issue up to a point, plus we reject a lot of extra heat...
| quote: | Originally posted by Rod Coleman
For those that like twinkling LEDs, we could put one in series with the base - LED lights only after the filament has warmed up! Actually, the LED would also help align the bleed to zero when 5V is achieved... getting around the 2V saturation of a 431. |
I would probably use some kind of optocoupler and use the LM431 with the LED in the Cathode line and a J-Fet CCS from ahead of the positive gyrator. I'll draw out what I have in mind when I get the time....
Sayonara |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by Kuei Yang Wang
I would probably use some kind of optocoupler and use the LM431 with the LED in the Cathode line and a J-Fet CCS from ahead of the positive gyrator. I'll draw out what I have in mind when I get the time.... |
I forgot, I recently had to put P-Spice on my work PC, so here a quick drawn out IDEA. A real circuit would add short circuit portection, the darlington transistors obviously could be replaced by LT1085/1033 for NPN/PNP respectively for people like me who like "bullet proof" stuff....
Sayonara |
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| Rod Coleman |
| quote: | Originally posted by Kuei Yang Wang
Konnichiwa,
I forgot, I recently had to put P-Spice on my work PC, so here a quick drawn out IDEA. A real circuit would add short circuit portection, the darlington transistors obviously could be replaced by LT1085/1033 for NPN/PNP respectively for people like me who like "bullet proof" stuff....
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One difference between our two circuits (& one would probably need to build to know if it was important) has to do with the dynamic impedance across the filament as frequency increases beyond the control loop's bandwidth.
On one hand, the current source (ie collector facing the filament) goes high-Z as the loop loses control; for the gyrator/voltage source, or a regulator IC in any configuration, (ie.: emitter facing the filament) a low impedance is presented.
It begs the question whether any (low level) shunting of AF or noise HF across the filament affects DHT performance.
Fun to build & find out, I expect! |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by Rod Coleman
One difference between our two circuits (& one would probably need to build to know if it was important) has to do with the dynamic impedance across the filament as frequency increases beyond the control loop's bandwidth. |
Hmm. The loops turnover in both cases will be pretty low, in my case there is a 2nd pole, so it would a 2nd order rather than 1st order handover to the bootstrapped gyrator (which in effect behaves much like a choke). The final limit actually will be in either case the 10K resistor which remains across the filament from the 431 Voltage sensor.
| quote: | Originally posted by Rod Coleman
On one hand, the current source (ie collector facing the filament) goes high-Z as the loop loses control; for the gyrator/voltage source, or a regulator IC in any configuration, (ie.: emitter facing the filament) a low impedance is presented.
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It is my understanding from discussions with GR and others that if the cathode delivers different current levels (due to signal) it will cool/heat up more which will shift emission, thus we want low impedance at very low frequencies (say below 0.5Hz) but high impedance in band for the audio signal.
| quote: | Originally posted by Rod Coleman
Fun to build & find out, I expect! |
I do to.
But guess what, my next 300B Amp gets a simple Schottky, Cap, Resistor Cap and Common Mode Choke supply, no fancy schmancy 'tronics....
But the one AFTER THAT will get electronic chokes in the +B Supply and the heaters.... ;-)
Sayonara |
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| Rod Coleman |
| quote: | Originally posted by Kuei Yang Wang
Konnichiwa,
It is my understanding from discussions with GR and others that if the cathode delivers different current levels (due to signal) it will cool/heat up more which will shift emission, thus we want low impedance at very low frequencies (say below 0.5Hz) but high impedance in band for the audio signal.
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Makes sense and aligns with Guido's words at the start of the thread. There seems to be a performance gain with current driven heating (high signal impedance drive) that is lost with (low Z) voltage drive (reduced further by the regs output cap).
| quote: |
Hmm. The loops turnover in both cases will be pretty low, in my case there is a 2nd pole, so it would a 2nd order rather than 1st order handover to the bootstrapped gyrator (which in effect behaves much like a choke). The final limit actually will be in either case the 10K resistor which remains across the filament from the 431 Voltage sensor.
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Looking from the viewpoint of audio signals across the filament (looking backwards if you like), they will pass current from emitters to collectors much easier (Z = 1/gm) than Collector to emitter (Z = Megohms). The low impedance loop is closed through the power supply caps. So I reckon we need to see a collector (or drain) facing one side the filament if we are to expect a high impedance.
| quote: |
But guess what, my next 300B Amp gets a simple Schottky, Cap, Resistor Cap and Common Mode Choke supply, no fancy schmancy 'tronics....
But the one AFTER THAT will get electronic chokes in the +B Supply and the heaters.... ;-)
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I have to admit to getting poor results with B+ gyrators so far.. but I need to get some decent HV capacitors stocked up to do it right - What do you recommend? Are those LCR audio grade types worth trying? |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by Rod Coleman
Looking from the viewpoint of audio signals across the filament (looking backwards if you like), they will pass current from emitters to collectors much easier (Z = 1/gm) than Collector to emitter (Z = Megohms). The low impedance loop is closed through the power supply caps. So I reckon we need to see a collector (or drain) facing one side the filament if we are to expect a high impedance. |
The question is "how high an impedance"?
A bootstrapped gyrator with a darlington transistor amplifies the 0.5R emitter resistance by it's transconductance (which is huge) up to quite high frequencies. Together with a few smallish value L's that should kill any issues.
But I'll have a think how we can have two collectors facing the Filament.
| quote: | Originally posted by Rod Coleman
I have to admit to getting poor results with B+ gyrators so far.. |
Hmmm, never had any problems, I use them quite often, both bootstrapped type and normal (Capacitor Follower) type.
| quote: | Originally posted by Rod Coleman
but I need to get some decent HV capacitors stocked up to do it right - What do you recommend? Are those LCR audio grade types worth trying? |
No idea. I use high quality MKP's and that's that.
Sayonara |
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| Rod Coleman |
| quote: | Originally posted by Kuei Yang Wang
BTW, improvement to your gyrator....
Add a resistor of 0R47 in series with the emitter, connect a 1K resistor in series bith the base of the small signal transistor, return a 47uF or so capacitor from +F to the base....
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The bootstrapped gyrator looks, on reflection, too good to miss. So I added it to my amp last night (on one side) and played a few LPs through it.
No great surprise to report a positive feeling about the result: a general sense of added freshness is as near as I get get to describing it. But OS-CONs are involved, and mindful of the counsel enshrined in SANYO OS-CON Technical Manual 5.2 (1997) one must "age the tone quality of OS-CONs" specifically "it is recommended to wait at least ten hours before evaluating and analysing the OS-CON's tone quality"
It will be a few days before I can get the professional ears round again, but by then the organic caps will be deeply composted :Pumpkin: and I'll be able to give a considered report.
I'll need the second opinion (first opinion in weight) to counter my autosuggestibility where design changes aimed at reducing filament noise are concerned. Previous gyrator tweaking (transistor types, Szlikai vs Darlington) was well worth the effort and I'm expectant of every degree of noise reduction to be perceptible... maybe it's time to ransack my book of UHF chip filters, or look at RF power transistors..
Meanwhile, Wang-san, I tip my hat in your direction for a top circuit.
IMPLEMENTATION
9,2V supply, second order gyrator, Darlington of FZT1051A(Zetex) + 2SD2061(ROHM).
First stage 1K (ROHM 1206 chip) 560uF/10V SANYO SVP.
Bootstrap stage: 1K (C film) 47uF/16V OS-CON (Nippon Chemicon 16FF47M) 0,47 Ohm nonmagnetic wirewound (a bit of L in this helps rather than hinders, I suspect). |
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