SE, SSE or SPP?

[calmant]

Dear all,

I'm trying to get a clear answer regarding which tube amp I should start building. I emailed Georges, but perhaps my question is too much of a bore to be answered (he must be tired of these).

I planned on building the SE-II to power a set of speakers I’m in the process of building, Troels Gravesen’s The-Loudspeaker-III (The-Loudspeaker-III). They’re somewhat efficient (92db), and require 15W per channel. They have an active subwoofer powered by an Hypex plate-amp (FA251).

But after readings so many forum posts debating which of your designs fit what kind of system, I’m now completely lost.

The room my speakers will be installed in is fairly small (I attached a plan, the red rectangles are the speakers), and I’m not looking to listen to music at deafening levels. Actually, my speakers will play at low to medium volume most of the time.
My priorities are details, dynamic range and bass capabilities (fairly standard priorities I guess). I have a budget of about 500-600$ to get a basic amp, which I could upgrade later on. (500-600$ does not include the cost of enclosure, as I’ll be making a wooden case in my workshop).

So, SE, SSE or SPP?
I have trouble understanding the watt per channel output of each amps topologies, and I can't for the life of me seem to be able to find an answer.

Room plan

 

[overtheairbroadcast]

Tough call and I will say, a bit unfair of a call to make.

I have built the Simple SE and ran it through Cornwalls (which are 100 dB efficient?) and it will shake the windows, BUT the speakers are exceptionally efficient. You could run a DHT amp that is flea powered through those speakers and it will fill a room. I never tried the SSE with other speakers because my friend bought it, but for the time I had it, I liked it for jazz, pushing the tuner though it, and instrumental music -- it was so easy to listen to and not fatiguing. It may not do as well as a PP would for fast and heavier music like full orchestra or hard American rock and roll, so maybe the SPP would work better for that.

So look at your music profile, figure your speakers into the equation and how the frequencies will roll off at the high and low ends, and go from there.

If you want to be sure, then build both. I kid you not -- I have another "experimental" SE amp (not George's design) where certain components are swapped in and out and it has it's use -- jazz and blues like Stevie Ray Vaughn just sounds so much better. Then I have a messy Pass Aleph J and that has it's job (mostly in the winter) and it is amazing and exacting. I have a EL84 Baby Huey PP and that sounds different and is great for some rock music. Actually, all of my amps are messy because of the same problem I am having as you -- I am deciding which one do I build as the ONE amp I am going to keep (getting older has done that to me)? One of these topologies will be rebuilt with really good parts, good chassis, and then left alone... I know the next SE will be of George's SSE as I have a spare set of boards, so his is still in the running and the current SE will be parted out for that build. But damn they all sound so good.

 

[calmant]

Thanks for your answer. I see your point. I guess I will at some point end up building more of these beauties, as I start switching transformers, etc.

What I'm most concerned about is watt per channel. As Gravelsen says 'as low as 15watt', I wonder what it means. Would there be any benefits at running the speakers with a 50watt per channel setup?

Also, are any of the tubelab design capable of outputing 15-20W/channel? On the SSE page, I only see the SSE going just below 10W with KT88s. I feel like there's something I'm not understanding here.

 

[colnago55]

I have built all three of George's amps and they all sound great and have enough power to drive my Monitor Audio speakers (89db). I would start with the SSE as it has the best build documentation and the simplest design. It has plenty of power. My front end is a CD player and a Sonos.

Enjoy.

 

[w5jag]

I think I would rely more on what the speaker manufacturer states is needed to drive them, and rely less on the sensitivity claim. An SSE with KT88 or 6550 tubes, running in ultra linear, should do 12 - 13 watts output with sufficient drive. That should be close enough to your speaker manufacturers requirement.

An SPP would make as much or more power, and could be smaller and lighter, because it is push pull. Push pull amplifiers also have significantly less distortion than single ended amplifiers.

 

[Tubelab_com]

Dear all,

I'm trying to get a clear answer regarding which tube amp I should start building. I emailed Georges, but perhaps my question is too much of a bore to be answered (he must be tired of these).

I got your emails, and read through your other thread last night asking these same questions, and came to the initial conclusion that all three of my boards should work in your room. For 10 years I ran 88 dB Yamaha NS-10M Studio monitors in a room a bit smaller than yours (10 sq meters). I also used a single active sub, but it was fed from the line stage in front of the tube amp. All three of my amps worked fine in my room, but the TSE with 45 tubes (2 WPC) was obviously not super loud. The 300B version was plenty loud, but a 300B TSE with good OPT's might be beyond your budget. Both the SSE with KT88's and the SPP with EL84's were "turn it down" kind of loud, and handled Pink Floyd, Nervo, Depeche Mode, Tangerine Dream and similar. The Yamaha's have zero response below 70 Hz so the sub handled everything below 100 Hz.

Then I did some quick checking to see what transformers are available in Europe that will fit within your budget. As stated Toroidy has OPT's that will work in all three amps. I got a set of their SE OPT's about a year ago, and they do sound far better than I expected for the price. Their power ratings are highly optimistic if you expect them to deliver full power in the bass region. Toroidy also has some power transformers that may work in Tubelab amps, but I have not actually tried them. The transformer MUST be rated to work with your line (mains) voltage. You can use a 240 volt transformer on 220 volts, and the output voltages will be about 10% less. Attempting to use a 120 volt US spec power transformer on 220 volts will make smoke.

When I saw sunshine this morning for the first time this year, I dropped everything and went outside to work despite the 3 degrees C temperature. After that I have sufficiently thawed out, I thought about it.

I had to look up your speakers because I am not familiar with them. I don't have the time to dig through all of the documentation for those speakers, but its apparent that there is a large plate amp built in to power the 15 inch bass drivers. The external amp only powers the midrange and tweeter. The link for the plate amp / DSP brings me to a page discussing several different plate amps, each with different possible methods of connecting everything up. How things are connected up does make a difference in this case.

You stated in the other thread that the tube amp will be fed from the crossover in the speakers. From my quick skimming of the Hypex link it appears that their amps can be fed directly from the speaker outputs of the power amp, which would be the tube amp in this case. Their amps have a line level input, which means that the Hypex could be fed directly from a preamp or line stage that has a volume control.

If the tube amp is feeding everything, then the OPT in the tube amp must be capable of passing the bass frequencies through to the entire speaker system so that they get fed to the Hypex. 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 a preamp is feeding the line level inputs of the Hypex, and the Tube amp input is connected to the pass through on the Hypex, then a budget OPT can be used on the tube amp since the tube amp is only feeding the midrange and tweeter. This is how my system was set up.

What is not known is the characteristics of the crossover inside the speaker system, especially its impedance in the bass region. If it is a relatively high impedance then the OPT for the tube amp can be chosen only for the mid and high frequencies.

I realize that this does not tell you exactly which amp to choose. I can state that I had several versions of each of my amps and I switched them out often. At one time I had several amps and speaker wired up with a switchbox. The low powered TSE with 45 tubes would be my favorite overall, but it was used mostly in the evenings when the volume was kept low. 2 WPC may not work with your speakers in a larger room.

The best overall amp, and the one that got by far the most use was the SSE. It had mode switches so that I could pop in some KT88's in UL mode for 15 watts, turn on the cathode feedback for some big bass to handle DSOTM at full crank, or pop in some EL34's in triode mode for the mellow stuff with near 300B sound quality.

I also have a TSE with 300B's in it for about 10 WPC. It did have a better sound quality for simpler music, it also used some OPT's that cost over $200 each today.

I had a SPP with EL84's built "by the book" it made about 18 WPC. I liked it for cranking vintage rock as loud as it would go without distorting. I also made a hot-rodded version that got almost 30 WPC. It got louder when I cranked up some 70's and 80's rock, but that seemed to be the only time I used it.

Again, these are MY preferences. I can not possibly predict what you will like with different speakers in a different room with different music.

I have since moved to a large house with a 1800 sq foot basement. The 2 WPC amp is nearly useless here even with the same speakers placed about the same distance from me. The SSE with KT88's does good, and is my current daily driver, but I am working on a new SE amp with about 30 WPC, and building a vacuum tube kilowatt amp, just because I can and already have all the parts.

To chose one, as my only amp, it would be the SSE with the best OPT's that your budget could handle, some KT88 tubes, and get a set of EL34's later.

 

[kstolleis]

I agree with Colnago - starting I would do an SSE but I have to say that I have a TSEII now in a small room (10x12) with Klipsch bookshelves (92db/wt) and a subwoofer and with 300Bs it sounds amazing! Like George I mostly listen to rock so that is just my preference but the vocals are something I have never heard before...

If you have a sub then the SSE with the smaller, cheaper OPTs will sound great. The larger ones only seem to matter at the lower freqs.

 

[calmant]

To chose one, as my only amp, it would be the SSE with the best OPT's that your budget could handle, some KT88 tubes, and get a set of EL34's later.

Georges, first of all let me say how grateful I am for your answer. It clarified a lot, even beyond what I had initially asked about.

When I saw sunshine this morning for the first time this year, I dropped everything and went outside to work despite the 3 degrees C temperature. After that I have sufficiently thawed out, I thought about it.

Really enjoyed that detail. Funny, here in Brussels, Belgium, we're also having a wonderful sunny "froid sec" as we say in french (dry and cold weather). It's the first of the year and we probably won't see another one in a while!

I'm going to go for an SSE build, and slowly source out each part as I go along.

I contacted Troels Gravesen, the speaker's designer. He said that as long as the amplifier is capable of outputing a solid 15WPC, I won't need anything else, or won't need to use a pre-amp with a line input.

Correct me if i'm wrong but, if I invest in a very good set of OPTs with KTT88s, that should do the trick? (OPTs capability equates output quantity? )

EDIT: I've found the answer by looking at your website properly, my bad.

I'll look into options for the OPTs. I'm sure I'll find something in the ballpark of a Hammond 1628SEA. That's what I would've gotten if I had been living in the states.

 

[calmant]

Would it be possible to use an importeed Hammond 1628SEA OPT with a 220V rated power transformer?

 

[cbueche]

Calmant, you should consider Toroidy or if you want EI-form check Ogonowski.eu - profesjonalne transformatry do wzmacniaczy lampowych. Great service and good products. I'm not affiliated with either of them. Leszek made me custom-version of the PSU tranny for the SSE.

 

[cogitech]

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".

 

[Tubelab_com]

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.

 

[calmant]

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?

 

[cogitech]

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.

 

[Tubelab_com]

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.

 

[calmant]

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!

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?

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.

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?

 

[cogitech]

Yes. You are correct.

 

[calmant]

Yes. You are correct.

How about the Lundahl LL 1663? I can get two of these for about 300euros.

 

[cogitech]

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.

 

[calmant]

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?