I would like to make a simple OTL.
Does not need to have lots of watt, something up to 5 watts is enough.
I would put small fullrange drivers in series like 12 drivers with six ohms, 72 ohms alltogether. If it helps impedance matching. Maybe 15 ohm drivers if I can get some.
High output impedance of an OTL amp would make it automatically work as a current driven amp?
I would like some Smps as power supply if possible.
Would an electrolytic in the output help to protect the loudspeakers?
I just do not like copper graves like big transformers. And good ones are expensive.
Does not need to have lots of watt, something up to 5 watts is enough.
I would put small fullrange drivers in series like 12 drivers with six ohms, 72 ohms alltogether. If it helps impedance matching. Maybe 15 ohm drivers if I can get some.
High output impedance of an OTL amp would make it automatically work as a current driven amp?
I would like some Smps as power supply if possible.
Would an electrolytic in the output help to protect the loudspeakers?
I just do not like copper graves like big transformers. And good ones are expensive.
Futterman/inverted Futterman with Triode connected horizonatal sweep tubes would be my idea- 6JN6, 6AV5GA, 6DQ6, etc. You'll want quite a bit of negative feedback to bring the output impedance down to acceptable levels, and the swing of the driver stage needs to be fairly high to drive it all.
Generalizations:
A typical OTL has output tubes in series.
Cathode follower on top, Plate output on the bottom.
For more power, there are 2 or more parallel tube cathode followers, and 2 or more parallel tube plate outputs.
The plate(s) of the bottom tube(s) are connected to the cathode(s) of the top tube(s).
Before you apply global negative feedback to an OTL circuit:
An output tube cathode impedance is 1/Gm (The impedance is Resistive, it is not a Voltage source, it is not a Current source).
A Triode output tube (example, a 6AS7) plate impedance is rp (u/Gm).
That plate impedance is Resistive, it is not a Voltage source, it is not a Current source.
The cathode(s) resistive impedance(s) are in parallel with the plate(s) resistive impedance.
Then when you apply traditional global negative feedback, the output impedance is reduced (guess what, it is still Resistive impedance).
If you do not like big output transformers, then build push pull amplifiers, do not build single ended amplifiers.
If you do not like Big Power Transformers, then build either single ended amplifiers that have output transformers, or build push pull amplifiers that have output transformers.
A typical OTL Power Transformer has more weight . . .
Versus the Total Weight of: power transformer plus the output transformer of a single ended amplifier; or the total weight of the power transformer plus output transformer of a push pull amplifier.
Just my understanding, and just my opinions.
A typical OTL has output tubes in series.
Cathode follower on top, Plate output on the bottom.
For more power, there are 2 or more parallel tube cathode followers, and 2 or more parallel tube plate outputs.
The plate(s) of the bottom tube(s) are connected to the cathode(s) of the top tube(s).
Before you apply global negative feedback to an OTL circuit:
An output tube cathode impedance is 1/Gm (The impedance is Resistive, it is not a Voltage source, it is not a Current source).
A Triode output tube (example, a 6AS7) plate impedance is rp (u/Gm).
That plate impedance is Resistive, it is not a Voltage source, it is not a Current source.
The cathode(s) resistive impedance(s) are in parallel with the plate(s) resistive impedance.
Then when you apply traditional global negative feedback, the output impedance is reduced (guess what, it is still Resistive impedance).
If you do not like big output transformers, then build push pull amplifiers, do not build single ended amplifiers.
If you do not like Big Power Transformers, then build either single ended amplifiers that have output transformers, or build push pull amplifiers that have output transformers.
A typical OTL Power Transformer has more weight . . .
Versus the Total Weight of: power transformer plus the output transformer of a single ended amplifier; or the total weight of the power transformer plus output transformer of a push pull amplifier.
Just my understanding, and just my opinions.
Just came to mind the Arg 6C33 OTL from Eng.Eugenny Kreminsky RIP, from Lviv,UK, it used one 6H6n + one 6C33 to glorious 5W output, but more with a pre-amp, it was intended to drive hi impedance FR drivers, no Xovers.
https://www.gstube.com/catalog/?key=6h6p&submit=Find
https://www.gstube.com/catalog/?key=6h6p&submit=Find
Attachments
From the speakers side 12 50ohm K50FL speakers from Visaton as a line array would do. Would be 600ohms or 16 of them giving 800 ohms like Phillips AD3800 fullrange driver
https://www.visaton.de/de/produkte/chassis/kleinlautsprecher/k-50-fl-50-ohm
El86 otl Design is here to be found
https://www.jogis-roehrenbude.de/Leserbriefe/Siemens-EL86/EL86.htm
16 drivers with 80db efficiency would give
Drivers. Efficiency
1. 80
2. 83
4. 86
8. 89
16. 92
Or take one driver like Fane Sovereign 15-300tc and let it be rewired to 800ohms. There are services which can do that. For the purpose the cone travel can be reduced to +- 1mm giving more efficiency.
https://www.visaton.de/de/produkte/chassis/kleinlautsprecher/k-50-fl-50-ohm
El86 otl Design is here to be found
https://www.jogis-roehrenbude.de/Leserbriefe/Siemens-EL86/EL86.htm
16 drivers with 80db efficiency would give
Drivers. Efficiency
1. 80
2. 83
4. 86
8. 89
16. 92
Or take one driver like Fane Sovereign 15-300tc and let it be rewired to 800ohms. There are services which can do that. For the purpose the cone travel can be reduced to +- 1mm giving more efficiency.
I made an OTL that delivers about 10W into 72R. Quite a simple circuit with off the shelve power Transformers. If you have any question please ask.
https://www.diyaudio.com/community/threads/beam-power-pentode-otl.391888/
https://www.diyaudio.com/community/threads/beam-power-pentode-otl.391888/
16 drivers with 80db efficiency would give
Drivers. Efficiency
1. 80
2. 83
4. 86
8. 89
16. 92
This increase in efficiency are only in parallel connection, in series connection the drivers SPL are always the same, in this case always 80dB.
@FullRangeMan
Isn't it that in series you need less voltage to drive the loudspeakers?
However here it is used for impedance matching to the amp what is important
Isn't it that in series you need less voltage to drive the loudspeakers?
However here it is used for impedance matching to the amp what is important
If you have an 8 ohm speaker, and you want it to play 1W, you must put 2.83V across it (2.83V^2/8R=1W). Put two in series and you need 2x2.83V so each can still have 1W. So in series you need more voltage, but the same current. That is the advantage for OTLs: these are generally current limited, but have enough voltage swing. More information here.
https://www.tubecad.com/2010/12/blog0195.htm
The amplifier I posted has a low output impedance, so voltage source. Still, when you use a lot of speakers in series, each speaker sees the series connected RDC of all the other speakers, so in fact one has a very low damping factor on each speaker, which makes them current driven.
https://www.tubecad.com/2010/12/blog0195.htm
The amplifier I posted has a low output impedance, so voltage source. Still, when you use a lot of speakers in series, each speaker sees the series connected RDC of all the other speakers, so in fact one has a very low damping factor on each speaker, which makes them current driven.
The RDC of a single driver is only one of the factors that determines the driver damping.
For two drivers in series, RDC continues to be one of the factors that determines the driver damping; for two drivers you have 2 x RDC, but you also have 2 x driver Z.
The impedance of each driver is now an Additional factor that contributes to the damping of the series drivers.
OTL or not:
Design an OTL amplifier, and then design a loudspeaker to work with it.
Or,
Design an amplifier that works with a very large number of loudspeakers (commercial loudspeakers, kit loudspeakers, diy loudspeakers).
Just my Opinions.
For two drivers in series, RDC continues to be one of the factors that determines the driver damping; for two drivers you have 2 x RDC, but you also have 2 x driver Z.
The impedance of each driver is now an Additional factor that contributes to the damping of the series drivers.
OTL or not:
Design an OTL amplifier, and then design a loudspeaker to work with it.
Or,
Design an amplifier that works with a very large number of loudspeakers (commercial loudspeakers, kit loudspeakers, diy loudspeakers).
Just my Opinions.
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IMO yes, because there is no increase of 3dB in SPL, which requires more power from the amp mainly in the bass, in my practical experience DHT is also lower in series. Iam more confident using a serial connection than a parallel one.
To say it in other words. If you have 10 drivers with 8R each connected in series, you have a load of 80R. This requires 28.3V so each driver plays 1W.
If you look at a random speaker, it will see the signal from the amplifier coming through the added RDCs of the 9 other speakers, so 72R source resistance playing the 8R of given speaker, so damping factor is very low.
Do you agree?
If the efficiency of one driver is 90dB, 2 will play 93dB, 4 = 96dB, 8 = 99dB and 10 drivers will be about 100dB? I
If you look at a random speaker, it will see the signal from the amplifier coming through the added RDCs of the 9 other speakers, so 72R source resistance playing the 8R of given speaker, so damping factor is very low.
Do you agree?
If the efficiency of one driver is 90dB, 2 will play 93dB, 4 = 96dB, 8 = 99dB and 10 drivers will be about 100dB? I
Fredom666,
I think you may, or may not, use vacuum tubes. But for some of the readers on this thread . . .
You said:
"However here it is used for impedance matching to the amp what is important"
Welcome to the lowly, unimportant, bad, expensive, heavy, large, reasonable efficiency, and widely disliked impedance matching device:
The Output Transformer!
For those who want to move away from using an output transformer, I suggest a move to the Solid State Threads of diyAudio.
You can get non-feedback Emitter followers to have output impedance of approximately 26 / Emitter current in mA.
26 mA current = 1 Ohm output impedance, not a bad starting place.
A PNP emitter and NPN emitter output totem pole with 26mA quiescent current has about 1/2 Ohm output impedance with both devices on (Class A), and 1/2 Ohm output impedance with one device on (56mA) and the other device off (Class AB).
Just my opinions and experience.
I think you may, or may not, use vacuum tubes. But for some of the readers on this thread . . .
You said:
"However here it is used for impedance matching to the amp what is important"
Welcome to the lowly, unimportant, bad, expensive, heavy, large, reasonable efficiency, and widely disliked impedance matching device:
The Output Transformer!
For those who want to move away from using an output transformer, I suggest a move to the Solid State Threads of diyAudio.
You can get non-feedback Emitter followers to have output impedance of approximately 26 / Emitter current in mA.
26 mA current = 1 Ohm output impedance, not a bad starting place.
A PNP emitter and NPN emitter output totem pole with 26mA quiescent current has about 1/2 Ohm output impedance with both devices on (Class A), and 1/2 Ohm output impedance with one device on (56mA) and the other device off (Class AB).
Just my opinions and experience.
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It has always been my opinion that OTL is really only of benefit for subwoofer applications at which point it must be either a really heroic amplifier or a very sensitive subwoofer (e.g. horn). A good OPT can handle most instruments (down to 32Hz) pretty well and I personally would be fine with sand for the last octave (16Hz-32Hz).
One could do a wide band OTL just for giggles but I think the advantages may well be over blown. I do have a couple of salvaged 8" FR drivers that measure DCR of about 40 ohms IIRC which could work on OTL. Headphones might also be a good application as long as you made sure B+ could never end up on the output.
One could do a wide band OTL just for giggles but I think the advantages may well be over blown. I do have a couple of salvaged 8" FR drivers that measure DCR of about 40 ohms IIRC which could work on OTL. Headphones might also be a good application as long as you made sure B+ could never end up on the output.
https://www.diyaudio.com/community/threads/what-tubes-for-a-otl-tube-amp.161112/
I built mono blocks based on the atmasphere M60 that Ralph so graciously shared. This was a few
years ago. They've been rock solid ever since. No they don't eat tubes and they are the best sounding amps that I've personally heard. Spending time to get the power supplies right pays off.
YMMV
I built mono blocks based on the atmasphere M60 that Ralph so graciously shared. This was a few
years ago. They've been rock solid ever since. No they don't eat tubes and they are the best sounding amps that I've personally heard. Spending time to get the power supplies right pays off.
YMMV
I was in denial about this for a very long time. It’s incredibly hard to achieve very low output impedance with tubes.
These days I tell myself “I’ll add solid state diamond buffer as an output stage and I’ll crack that nut.” But, I must not believe myself because I am yet to put that thought in action.
Personally, unless I had a line array like this I don't think I would want to go through the fuss of putting together an OTL. 25 drivers in series still only comes to 200 ohms- but it will be so sensitive as a compound driver array that it wont take much swing at all to get good results.
I would, however, want to do something really interesting- like horizontal sweep tubes as the outputs, with floating screen supplies. Wrap some feedback around the whole thing, get a decent driver to swing the needed voltage.
I would, however, want to do something really interesting- like horizontal sweep tubes as the outputs, with floating screen supplies. Wrap some feedback around the whole thing, get a decent driver to swing the needed voltage.