I have some times thought that it would be better to have the OPT near the crossover a little depending on what you think about cables, may be GNFB could be delicate.
Has any of you actually tried it?
Søren
Has any of you actually tried it?
Søren
Having an OPT near the speeks was done all the time with PA systems. It isn't done otherwise since the audio cable would also be carrying the HV for the finals, and you'd have a safety issue there. It also isn't convenient for production amps where you never know what speeks the end user is likely to connect.
Until now the answer is no, so far we have not heard from people who have tried it.
I find that having HV DC in the cables makes things easier as you can have long cables without loss, I guess that the some times heated discussion about cables could disappear.
Safety should of course be taken care of but I do not find it more difficult than all the other HV cables in the house, it is mostly a question about choosing a reasonable plug standard.
I thought that in Europe the normal standard for PA was 600ohm symmetric.
My point is that if you are a DIY'er then you should take all the advantages of it and not try to make products which already exist on the commercial market.
I have some Tamura OPT's laying around and find that they are too good not to be used so I am thinking of some bizarre circuits in the 1-2 watt range which I have not seen before.
Søren
I find that having HV DC in the cables makes things easier as you can have long cables without loss, I guess that the some times heated discussion about cables could disappear.
Safety should of course be taken care of but I do not find it more difficult than all the other HV cables in the house, it is mostly a question about choosing a reasonable plug standard.
I thought that in Europe the normal standard for PA was 600ohm symmetric.
My point is that if you are a DIY'er then you should take all the advantages of it and not try to make products which already exist on the commercial market.
I have some Tamura OPT's laying around and find that they are too good not to be used so I am thinking of some bizarre circuits in the 1-2 watt range which I have not seen before.
Søren
A slightly different variant that does get mentioned sometimes (Tubecad) is to keep the OT at the amplifier, and run the global feedback back from the speaker terminals, instead of from the OT secondary terminals. That will lower the damping factor right at the speaker, and put less (effective) capacitance into the feedback with a low Zo signal.
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Yes, this is called remote sensing, and should include BOTH conductors of the speaker wire. It'a a type of Kelvin connection.
Hello Søren
Back in the old days this was quiet normal. As an example please have a look at an radio from Telefunken, build in 1931.
Katzenkopf T 340 T340W RENS1204 Radio Telefunken Deutschland
You see, there is no speaker and no output-transformer.
One of the speakers for this radio is the Telefunken Arcodyn 505 with a field coil speaker and a build-in output transformer.
Arcodyn 505WT Speaker-P Telefunken Deutschland TFK, Gesellsc
The output transformer has taps for different tubes, from the tiny RE134, over RES164, RE304 up to the RE604, the predecessor of the AD1.
Best regards
Michael
I have always found two magnetic fields close to each other interfere with each other.
In the past I have had mains transformers close to valves and output transformers and picked up a lot of hum.
I would have thought the speaker voice coil will radiate and be picked up in the output transformer and then into the feedback loop ?
In the past I have had mains transformers close to valves and output transformers and picked up a lot of hum.
I would have thought the speaker voice coil will radiate and be picked up in the output transformer and then into the feedback loop ?
Magnetic fields in air do not "interfere" with each other, as air is a linear magnetic medium. Nearby magnetic items can couple together, which is why some 1950s radios start humming before the valves have warmed up. This, though, is not "radiation" but simple local induction.
Søren,
Perhaps then a reason for not having tried it. In a sense, as in re-inventing the wheel. What advantage would one expect?
Perhaps I should first ask what length of cable you are looking at. One can use a fair length of not over-expensive loudspeaker cable before audible disadvantage would set in. Losses can be calculated; I see no disadvantage in lengths of loudspeaker cable applicable to domestic audio. (Not to open a can of worms, but the 'loss of damping factor' effect is overrated and mostly erroneously applied.)
On the other hand, yes, instability could set in with long feeds of anode circuit cable, apart from the dangers already mentioned. So in my view no advantage, but some disadvantages in using long anode coupling cables.
Johan,
as you may be remember, I was asking if some one had tried it, I did not ask for advices of which I got plenty, but nothing new to me.
Looking in another thread I found this:
"Second round started with the VV52. We focused on F-7003 and F-5002 only. The result still the same but the owner of F-7003 said "I feel the detail of F-7003 was hidden somewhere"
So, we moved both OPT to the Spk terminal to use #35 SWG 20cm long of Spk cable and used 5 meter for HV cable from VV52 to OPT. Believe it or not, both OPT gained in detail and F-5002 showed more volume and clearer bass than the F-7003, even better than F-2007, I think. I thought this contradicted the idea that F-5002 has weak bass."
I found it in this thread:
http://www.diyaudio.com/forums/tubes-valves/109987-best-se-output-transformer-300b-shootout.html
It is from 2007.
So I still think I will try it although not in the very near future do to other projects.
Søren
as you may be remember, I was asking if some one had tried it, I did not ask for advices of which I got plenty, but nothing new to me.
Looking in another thread I found this:
"Second round started with the VV52. We focused on F-7003 and F-5002 only. The result still the same but the owner of F-7003 said "I feel the detail of F-7003 was hidden somewhere"
So, we moved both OPT to the Spk terminal to use #35 SWG 20cm long of Spk cable and used 5 meter for HV cable from VV52 to OPT. Believe it or not, both OPT gained in detail and F-5002 showed more volume and clearer bass than the F-7003, even better than F-2007, I think. I thought this contradicted the idea that F-5002 has weak bass."
I found it in this thread:
http://www.diyaudio.com/forums/tubes-valves/109987-best-se-output-transformer-300b-shootout.html
It is from 2007.
So I still think I will try it although not in the very near future do to other projects.
Søren
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