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Old 10th January 2021, 04:03 PM   #11
cogitech is online now cogitech  Canada
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Originally Posted by calmant View Post
Would it be possible to use an importeed Hammond 1628SEA OPT with a 220V rated power transformer?
Possible? Yes. 100%. The OPTs have nothing to do with what PT you use.

Recommended? No

Why? Because the point of the huge Hammonds is that they do bass really well. However, this tends to compromise their top end performance (they are rolled off significantly compared to smaller OPTs) and their efficiency. Also, they are heavy and expensive.

Since you aren't even going to be using the amp for bass at all, it simply makes no sense whatsoever to buy those OPTs.

But they will "work".

Last edited by cogitech; 10th January 2021 at 04:05 PM.
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Old 10th January 2021, 05:55 PM   #12
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I tend to agree here. I have a pair of 1628SEA's they tend to roll off the treble compared to other OPT's in the same price range.
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Old 10th January 2021, 08:06 PM   #13
calmant is offline calmant  Belgium
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It's still very unclear how this 'Hypex plate fed from the passive crossover' works at all to me.

How can it output any bass if the signal it receives is lacking in that department?

Let's imagine I buy an OPT that has no bass whatsoever.
I hook up my amp to my speakers and start playing music.
How can the Hypex does its job and pumps the bass out, if it's receiving nothing from the amplifier?

I can't wrap my head about how this works. And reading about the Hypex didn't work either.

Georges, you said "The Hypex has DSP capabilities for applying EQ to the bass to fix rolloff in the transformer, but it can't fix saturation induced distortion. In this case a pretty good OPT is needed."

If my OPT is somewhat lacking in the bass department, will the Hypex take over to further amplify the signal?
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Old 11th January 2021, 02:35 AM   #14
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I think I was misunderstanding how those speakers work.

I don't think anyone is recommending buying OPTs which have no bass at all. As you say, the Hypex has to be fed the bass frequencies in order to amplify them (this is the part I didn't quite get before - as I was imagining DSP/crossover before amplification making the Hypex 100% responsible for the bass).

Regardless of that, the point is there are other options that are better than the 1628SEA simply because the 1628SEA has the rolled off top end. A smaller, higher quality OPT will still provide plenty of clean bass frequencies for the Hypex, but will be more efficient and have a better top end. Some options:

Audio transformers • Tube output transformers • Lundahl Transformers

One Electron Transformers

Transcendar Transformers - Single Ended Transformer

Note: Forgive me because this is purely subjective opinion, but for a small room like this at low to medium volume, this speaker choice is puzzling. It makes things far more complicated (and far more powerful) than necessary. A 4-6" full range driver in a mass-loaded transmission line or a horn would surely satisfy.

Last edited by cogitech; 11th January 2021 at 02:37 AM.
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Old 11th January 2021, 02:40 AM   #15
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The Hypex must receive undistorted bass material in order to amplify it and present it to the woofer. An OPT, any opt, even a bad one will not have no bass whatsoever. A bad one, or one that is just too small for the job can do three things with bass, if can reduce its level, distort it, or both. The Hypex has a built in DSP that must be programmed via USB. The DSP is the low pass filter that determines the crossover point between the woofer and the rest of the speaker. It is also an equalizer which can deal with weak bass. It can not fix distorted bass.

The Hypex can be connected two possible ways.

The high level input take the speaker output from the amp, process it, and feed it to the woofer. Undistorted bass must be present in the tube amps output so that it can be used by the Hypex.

The line level input comes from a preamp or other device having a volume control. That feeds the Hypex and the tube amp at the same time. Since this comes from BEFORE the tube amp all frequencies are present regardless of what the tube amp does to the bass. The tube amp feeds only the mid and tweeter, so weak or distorted bass does not matter as long as the mid and high frequencies are clean.

I had a system like this and I used a $29 OPT in the SSE. This setup could be played quite loudly since the subwoofer dealt with all the power hungry bass and the SSE only dealt with the higher frequencies where large expensive OPT's are not needed.

Large amounts of iron and copper are needed to transfer a big enough magnetic field to pass very low frequencies. This large magnetic core tends to restrict high frequencies. That's why that big Hammond has the best bass of any SE transformer I have used, but the highs and the detail is lacking. ALL OPT's must deal with this tradeoff. The fact that you have an active bass amp removes the requirement for all 15 watts being made at 20 Hz.
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Old 11th January 2021, 08:57 AM   #16
calmant is offline calmant  Belgium
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Quote:
Originally Posted by cogitech View Post
I don't think anyone is recommending buying OPTs which have no bass at all. As you say, the Hypex has to be fed the bass frequencies in order to amplify them (this is the part I didn't quite get before - as I was imagining DSP/crossover before amplification making the Hypex 100% responsible for the bass).
The 'transformer with no bass at all' was a thought experiment, just so I could properly understand what the Hypex is actually doing. Now I get it!

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Originally Posted by cogitech View Post
Note: Forgive me because this is purely subjective opinion, but for a small room like this at low to medium volume, this speaker choice is puzzling. It makes things far more complicated (and far more powerful) than necessary. A 4-6" full range driver in a mass-loaded transmission line or a horn would surely satisfy.
Of course, you're not the first one to tell me this. The room I live in now is somewhat temporary. I might move in one or two years to a bigger place. These speakers will always be placed in my living space, which will end up being bigger than the one I live in.

The idea behind choosing these speakers is to get a reference speaker that I won't be upgrading for a very long time. I'm afraid a smaller three-way or two-way will have me regret that I did not go for a bigger option. The possibility to tweak both the bass and the tweeter allows me to tailor them to my room to reduce room-gain for instance. Gravesen uses those in a room that's barely bigger than mine. He advised The-Loudspeaker-III based on my requirements.

Of course it's a big thing, and a bit overkill, but it will do a stellar job even if they end up being played in a room twice as big.

Does that make sense?

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Originally Posted by Tubelab_com View Post
The DSP is the low pass filter that determines the crossover point between the woofer and the rest of the speaker. It is also an equalizer which can deal with weak bass. It can not fix distorted bass.

The Hypex can be connected two possible ways.

The high level input take the speaker output from the amp, process it, and feed it to the woofer. Undistorted bass must be present in the tube amps output so that it can be used by the Hypex.

The line level input comes from a preamp or other device having a volume control. That feeds the Hypex and the tube amp at the same time. Since this comes from BEFORE the tube amp all frequencies are present regardless of what the tube amp does to the bass. The tube amp feeds only the mid and tweeter, so weak or distorted bass does not matter as long as the mid and high frequencies are clean.
I'm still pondering whether it would be a good idea to use a pre-amp as well, as I'm trying to keep the cost to a reasonable 500$-600$.

I'll have to make some calculations, perhaps, the money saved on the OPTs will allow me to build a pre-amp as well.

Otherwise, I'd prefer the amp to handle bass as well.

Quote:
Originally Posted by Tubelab_com View Post
Large amounts of iron and copper are needed to transfer a big enough magnetic field to pass very low frequencies. This large magnetic core tends to restrict high frequencies. That's why that big Hammond has the best bass of any SE transformer I have used, but the highs and the detail is lacking. ALL OPT's must deal with this tradeoff. The fact that you have an active bass amp removes the requirement for all 15 watts being made at 20 Hz.
I understand it now. What I should look for are 15watts OPTs with a very clean high-frequency range and a low-distortion bass. The clean bass signal could then be amplified by the Hypex. Am I correct?
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Old 11th January 2021, 03:34 PM   #17
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Yes. You are correct.
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Old 11th January 2021, 03:47 PM   #18
calmant is offline calmant  Belgium
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Yes. You are correct.
How about the Lundahl LL 1663? I can get two of these for about 300euros.
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Old 11th January 2021, 04:00 PM   #19
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That is an 8W part (when used in single-ended applications) rated at max power @ 30Hz. I personally believe that is easily sufficient, but if you want to stick to the 15W recommendation then you will be spending more to go up to something like the LL2769 8ohm.

High quality, high power, single-ended OPTs are expensive. There's just no way around it.
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Old 11th January 2021, 04:10 PM   #20
calmant is offline calmant  Belgium
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Originally Posted by cogitech View Post
That is an 8W part (when used in single-ended applications) rated at max power @ 30Hz. I personally believe that is easily sufficient, but if you want to stick to the 15W recommendation then you will be spending more to go up to something like the LL2769 8ohm.

High quality, high power, single-ended OPTs are expensive. There's just no way around it.
I see. The LL2769 has a primary impedance of 4.7KΩ. I was only looking at OPTs with a primary impedance of 5KΩ as I read it was important to match that impedance. I read through George's website and couldn't find any indications as to what would happen if it wasn't a perfect match. Would you care to explain?
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