Hello everyone,
I am on the process of swapping the OPTs of a push pull EL34 amplifier with higher quality (and hopefully better sounding) OPTs.
With the occasion, I was thinking about moving the OPTs outside the amplifier chassis, in separate enclosures, and wire them with a connectorized cable.
In that way it'd become very easy to swap the transformers for an A/B comparison, and also it would reduce the weight of the amplifier, which is not an irrelevant advantage considering that I suffer of back pain and that the new OPTs weigh 10 kg each.
Any thoughts?
I am on the process of swapping the OPTs of a push pull EL34 amplifier with higher quality (and hopefully better sounding) OPTs.
With the occasion, I was thinking about moving the OPTs outside the amplifier chassis, in separate enclosures, and wire them with a connectorized cable.
In that way it'd become very easy to swap the transformers for an A/B comparison, and also it would reduce the weight of the amplifier, which is not an irrelevant advantage considering that I suffer of back pain and that the new OPTs weigh 10 kg each.
Any thoughts?
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Each monoblock has a push-pull of 8x EL34 the output stage, so it needs big irons to sing.
I have seen an amplifier with 'external OPTs' a few years ago at an audio show. I don't remember about being particularly positively or negatively impressed by them.
My main concerns with ther external OPTs would be:
1) Longer wires terminated on a high impedance load could be more susceptible to inductive noise. Although it is also true that the inductively coupled noise would most likely still be very small compared to the signal swing on the primary of the OPT. And also the magnetic field outside the chassis is most likely much smaller than inside of it, consid that most of the magnetic noise comes from the AC filaments.
2) Cable stray capacitance might form a LPF with the transformer resistance, although I think that the cable stray capacitance would still be negligible compared to the transformer's winding capacitance.
3) It's a high voltage connection coming out of the chassis so it can be somehow dangerous, although the danger can be minimized by using proper construction.
I have seen an amplifier with 'external OPTs' a few years ago at an audio show. I don't remember about being particularly positively or negatively impressed by them.
My main concerns with ther external OPTs would be:
1) Longer wires terminated on a high impedance load could be more susceptible to inductive noise. Although it is also true that the inductively coupled noise would most likely still be very small compared to the signal swing on the primary of the OPT. And also the magnetic field outside the chassis is most likely much smaller than inside of it, consid that most of the magnetic noise comes from the AC filaments.
2) Cable stray capacitance might form a LPF with the transformer resistance, although I think that the cable stray capacitance would still be negligible compared to the transformer's winding capacitance.
3) It's a high voltage connection coming out of the chassis so it can be somehow dangerous, although the danger can be minimized by using proper construction.
Post #3 contained the main points. There are no real advantages to that approach.
But there are significant disadvantages.
If you want to compare OTs, make up two stereo chassis, and transfer the pcbs between them.
Or just build two complete stereo amps.
Mono blocks, on the other hand, are just the opposite.
They have many real advantages, and no disadvantages (other than cost and size).
But there are significant disadvantages.
If you want to compare OTs, make up two stereo chassis, and transfer the pcbs between them.
Or just build two complete stereo amps.
Mono blocks, on the other hand, are just the opposite.
They have many real advantages, and no disadvantages (other than cost and size).
I have an old pair of Audio Note transformers each weighing 10kg and that is about the limit of what I can carry because of health problems. I will soon use them in another amp with a layout similar to this.
This was just a test version. In my next version, I will enclose each in its own upside-down wooden box and lay them on another larger box containing the rest of the amplifier. Hopefully, the wood varieties will be the same.
A bamboo box from Kmart.
Connections will be via these Y2M-3TK connectors.
The square connector half will be attached to the top plate of the large box with two short wires going to the HV power supply and the tube plate. The two HV wires going to the transformer will attach to the other half of the connector. The connector has a locking mechanism and will be hidden by the top box. The speaker connections will be attached to the small box.
Testing is a problem since I can't turn the assembled amplifier upside down. This can be solved by an extra pair of the same model of connectors linked by two appropriate-length temporary wires.
My biggest problem will be finding appropriate size boxes made of a similar wood to the top of the amplifier.
ray
This was just a test version. In my next version, I will enclose each in its own upside-down wooden box and lay them on another larger box containing the rest of the amplifier. Hopefully, the wood varieties will be the same.
A bamboo box from Kmart.
Connections will be via these Y2M-3TK connectors.
The square connector half will be attached to the top plate of the large box with two short wires going to the HV power supply and the tube plate. The two HV wires going to the transformer will attach to the other half of the connector. The connector has a locking mechanism and will be hidden by the top box. The speaker connections will be attached to the small box.
Testing is a problem since I can't turn the assembled amplifier upside down. This can be solved by an extra pair of the same model of connectors linked by two appropriate-length temporary wires.
My biggest problem will be finding appropriate size boxes made of a similar wood to the top of the amplifier.
ray
There is a line of commercial power amps in Europe with separate output transformers.
They do it for about 30 years as far as I remember :
https://www.malvalve.de/Power_Amplifiers-E.htm
In the main page description you read "external power transformer", but it is a typing
error.
The amps are of "parallel push-pull design" (more or less the same as "circlotron"), not
directly comparable to standard tube output stage wiring, the typical load impedance is
only a quarter.
They do it for about 30 years as far as I remember :
https://www.malvalve.de/Power_Amplifiers-E.htm
In the main page description you read "external power transformer", but it is a typing
error.
The amps are of "parallel push-pull design" (more or less the same as "circlotron"), not
directly comparable to standard tube output stage wiring, the typical load impedance is
only a quarter.
Longer wires is never a good thing because of the factors you listed. More of everything you don’t want es if it is an ultimate fidelity amp. If you want to compare them do only one side and compare it to the other. If it’s better finish the job. If not, you only have half as much work to put the old one back!
I have thought about doing the same, i.e. putting the OT external to the output tube chassis. What I plan to do is purpose build the two boxes (one box for the tube chassis; the other box for the OTs) and have a locking mechanism to keep them connected when in use. The connecting wires are short jumpers from screw terminal to screw terminal and covered by a screwed-in protective plate of polycarbonate or such.
Maybe use a sub chassis for the opts. Then you still have a single chassis with the ease of just swapping in a different sub chassis with different set of opts. If you standardized the sub chassis to hold your largest opts then you make three or four identical sub chassis but each with a different set of opts. Use gold banana plugs and thumbscrews to make the swap out easier with no need for tools to do it. Computer chassis are modular like this you can swap power supplies, disk arrays, etc because the sub chassis drop into standard spaces.
In particular danger of death... I don't call that "somehow", you have to use rated connectors and cables and get the connector gender right so the lethal voltages cannot be touched. High voltage DC can be more dangerous than AC too.
The risk can be avoided by not moving the OT outside the original enclosure.
If I wanted to transfer my PT and OPT to another chassis, that's what I would do.
Female Amphenol chassis connectors on the PT and OPT side, male chassis connectors on the PCB side, all internally, without connecting cables.
I mention the Amphenol brand because I worked with them in another life and it is really very good quality and all the characteristics are provided.
Like 38999-Style series .
Try to build a base , metal, with the holes of old trafo ( and spacer, 20mm, p.e.) , then on it mount the new one iron
It is simply way
Of course you need a proper connector but the lenght is short