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Søren

Separating the OPT from the amplifier

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I have often thought that there would be advantages in having the OPT near the loudspeaker and the rest of the amp near the preamp. Have any of you tried it ?

 

Some people try to tell me that it is a bad idea, but when I ask if they have tried it, the answer is no. So what do you think ?

 

Søren

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Imagine the length of the OPT primary wire, and B+ (or wires for a PP amp) going from the tube plate and or plates to the location of a speaker.

A push-pull output transformer may or may not have feedback from a secondary tap to the cathode of the driver tube.

So one would have to run a longer wire for feedback from the OPT secondary from the location of the speaker, back to the amp.

 

Quite a few OPTs have a chassis ground. There's another wire to run from the OPT back to the amplifier.

Doesn't seem practical in the least IMO, and I have no idea what advantages there would be from using high voltage primary wires as glorified speaker leads.

 

I have never tried it however.

 

What advantages do you think of having the OPT near a loudspeaker?

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This was commonly done in console radios using field coil speakers.  I agree with Mike that long runs of wire carrying B+ are inadvisable. If you have mono amps, you could try placing them very close to the speakers.  But you would need very well shielded cables to connect the preamp or source to the amps.

 

 

Maynard

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You also see it on the antique guitar amplifiers inside the case. Never heard of doing so with a home system. It could be dangerous on a number of levels without having any consequential advantage.  

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I disagree with you that long runs of B+ are a problem, here in the house there are many meters of 230VAC carrying wires around. Of course you should take care of plug standards so you do not mix them up, but you have to be careful in all cases if you are playing with tubes.

 

The idea behind could be that it is the best to keep the relatively long distances at a high voltage and high impedance and then first at last transform it to the low consumer impedance. By the way, that is what the power plants do.

 

Long time ago I saw on the net that a person had modified/repaired an amplifier on the working bench and for some reason was unable to test it as it was in parts. So he placed the OPT near the speaker for other reasons and was surprised that it sounded better than normally.

 

My main surprise here is that nobody seems to be curious to try it, everybody says that it is a bad idea, but not why (except the B+). A possible explanation if it is better could be that the loudspeaker cable such to say disappears.

 

Søren

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The PWK Klipsch Main Amplifier discovered in the museum basement did this. A little different instead of outputs at the speaker he split it into HF and LF outputs since in 1946 quality outputs were rare. This is currently being built but safely with everything in one chassis. I personally don't wan't b+ from the plates flying across my room. YMMV...

 

 

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Even with properly rated wire insulation I would not be comfortable having an exposed run carrying 400 volts.  You can certainly try it and let us know your conclusion.  But I don’t see why doing that would offer any sonic advantage.

 

Maynard

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In the last 20 years I have separated the first part of the PSU from the preamplifier which makes it easier to avoid hum and noise. The voltage is about 315V with only a few mA B+ 

and there are (small) fuses but it covers also the filaments. It works very well.

 

Here in Burgundy and in Greenland where I spent 50 years the main voltage is 230V which gives a peak voltage of +-325V. So that is what you are dealing with using everyday household applicants, lamps and so on. If you are behaving reasonably it is not a problem. Again there will be fuses and a certain (unofficial) plug standard.

 

I have a number of Tamura PP OPTs and I think they are too good not to be used. The amp which I have in mind should work at a B+ at about 215V.

 

There is a little disclamer which is that in the best case it will take most of a year before I can realize it because all my audio equipment is in eastern Greenland so I have to wait for the ice to melt so much that a cargo ship can sail; the idea of sending khorns and OPTs as airmail is probably not so realistic...

 

Søren

Edited by Søren
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Separating a p/s from a preamp or amp is different from separating an OPT from the amp chassis.  Will you be running a feedback loop from the secondary to the driver?  Even if you are not it is usually a good idea to ground the secondary in case there is ever a primary to secondary short (unlikely but possible).  Can you post the schematic of the amp?

 

Maynard

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On 11/29/2020 at 4:19 AM, Søren said:

I have often thought that there would be advantages in having the OPT near the loudspeaker and the rest of the amp near the preamp. Have any of you tried it ?

 

Some people try to tell me that it is a bad idea, but when I ask if they have tried it, the answer is no. So what do you think ?

 

Søren

 

Is this Jeffery?

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Is this Jeffery?

No, quite the opposite; it is Søren and I do not think that Jeffery has spent 50 years in Greenland, I would have heard about it. But your post was very subtle.

Søren

 

 

 

 

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On 11/29/2020 at 7:19 AM, Søren said:

I have often thought that there would be advantages in having the OPT near the loudspeaker and the rest of the amp near the preamp. 

 

What are the advantages?

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Just some more audio rubbish talk. Electrical engineers might be able to measure the difference but hardly any significance in real world either negative or an advantage. In other words 99% will never hear a difference. The other 1% hear a lot of things. But if one wants to go ahead and tell us about it. This is not to say that the original poster did not ask a good question.   😁

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21 hours ago, Søren said:

It will probably be something like this:

 

http://diyaudioprojects.com/Tubes/Junk-Box-Audio-Amp/

 

but in a little more simple version. It started as a simple project but became more complex as modifications arrived. To start I will make it triode connected, no NFB and also a few other things. ECC82 and EL84. 

 

Søren


Inverterless (or self inverting) push pull amps were quite the rage back in the day.  In fact, a guy has been after me to resurrect a low budget version of my “Little Pee-Pee” SIPP (my wife named it and I have never had the nerve to ask about the source of her inspiration...).  I am vacillating but may consider it next build season.

 

Maynard

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