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SSE with Zu Omens

kaos2088

Member
2012-08-24 10:40 pm
I'm interested in building a Tubelab SSE to power my Zu Omens. Bought them with the goal of building a tube amp for it and I keep hearing great things about the SSE.

I really want to gear the amp to the Omens and about the only decisions I've made thus far is that I need to include a choke and auxiliary cap and am planning on running in triode mode. I am still unsure what I should use for tubes. I was just going to hunt around on eBay for something that looked interesting.

As I start to put together a parts list my first question is if the Omen's 12Ω impedance is going to cause any issues. I had been looking at the Transcendar TT-312-OT OPT, but it is meant for an 8Ω impedance. Should I be looking specifically for a 12Ω OPT?

This is will be my first build so any suggestions for parts/ways to gear the SSE to my Omens would be appreciated.
 

cotdt

Member
2005-10-30 12:57 am
Why not the TSE? It's only slightly more expensive, and you can use tubes like 45 or 300B.

12 ohm impedance is the perfect load for most tube amps. Most 8 ohm speakers are actually 5-6 ohms and sounds better on the 4 ohm transformer tap. 12 ohm should be awesome on the 8 ohm tap.
 
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kaos2088

Member
2012-08-24 10:40 pm
Really only went with SSE cause it was a simpler design and easier to build. As I research this more, those don't seem like good reasons, the TSE doesn't seem too much harder to build. The Omens are 97dB so they should be able to handle those tubes fine.... Thinking I should build the TSE now..
 
I'm interested in building a Tubelab SSE to power my Zu Omens. Bought them with the goal of building a tube amp for it and I keep hearing great things about the SSE.


As I start to put together a parts list my first question is if the Omen's 12Ω impedance is going to cause any issues. I had been looking at the Transcendar TT-312-OT OPT, but it is meant for an 8Ω impedance. Should I be looking specifically for a 12Ω OPT?

This is will be my first build so any suggestions for parts/ways to gear the SSE to my Omens would be appreciated.

It depends on how efficient your Zu Omens are and how loud you like to
listen to music, also room size will be a factor.
If the Omens efficiency is over 92db you'll be okay especially in ultra
linear mode with KT88 tubes.
If the efficiency is in the upper eighties (88-90 db) you'll still be okay
in a small to midsize room when using KT88 in ultra linear mode.

Below 88db efficiency the rule of diminishing returns kicks in especially
when using the amp in triode mode.
 
Really only went with SSE cause it was a simpler design and easier to build. As I research this more, those don't seem like good reasons, the TSE doesn't seem too much harder to build. The Omens are 97dB so they should be able to handle those tubes fine.... Thinking I should build the TSE now..

Well, with your speakers rated at 97db you will have no problems at all
regardless of which amp you choose.
 
The SSE is more flexible, as it uses "standard" tubes that are still in production. The TSE is a superior design, but is more complex and uses more expensive and hard-to-find NOS tubes. It also puts out less power than an SSE potentially can, especially if you go with 45s.

I'd use an 8 ohm secondary with those speakers, though you can expect less power from the amplifier with that load unless you compensate with the primary.
 
Kaos2088: The output transformer reflects the speaker load back to the output tubes.

For example, with a 5K/8 ohm transformer with 8 ohm speakers the tubes see 5Kohm impedance. If you connect a 4 ohm speaker to these 8 ohm taps, the tubes will see 2.5Kohm load with this 5Kohm primary. So if you connected 16 ohm speakers to these taps the tubes would see 10K load and so on.

In your case, depending on what tubes you want to run, you can select an appropriate output transformer primary impedance to be happy with a 12 ohm load, like 2.5K-3.5K/8R or so depending on what output tubes you want to use. Some output transformers have multiple primary taps for added flexibility like the James 6123 for example.

Look at the "Tubes and transformers" page on the Tubelab website for either amp to get an idea of power out, distortion, etc for different tubes, primary impedances and B+ voltages.

As Russ K already mentioned, a higher impedance load in general has the effect of reducing output power and distortion slightly. And a lower impedance load will provide more power out and more distortion. This is shown in Tubelab's tables.

If your speakers are 97db sensitivity then you need a mouse-fart worth of power, and a Tubelab SE with 45's would probably rock the house, or any Tubelab SSE config.
 
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kaos2088

Member
2012-08-24 10:40 pm
Thanks for the info everyone. I went ahead and ordered a TSE board and am going to go with the 300B design. I've been debating between the 45 and 300B, but in the end I want to be certain I will have enough power... even if I'm not using such an efficient speaker.

For the OPT, I am now looking at the Electra Print "Albert Pagan" design as recommended in the Tubes and Transformers page. I sent an email to electra print to get the specs and price as I really don't know anything about it at the moment.

For the power transformer, I'm not finding many recommendations except for the Hammond 272JX. This seems to be below the recommended 640~650V, but according to what I'm reading, it will work. Is there another power transformer I should consider for the project?

The other part that is confusing me at the moment is the High Voltage Mosfet Toshiba 2SK3563. Its out of stock and I found this statement "The 2SK2700 mosfet has gone extinct due to ROHS laws. Toshiba decided to discontinue the part rather than make an unleaded version. I have found two suitable substitutes, the Fairchild FQP1N50 and the Supertex DN2540N5." Just want to confirm that the 2SK3563 is the same thing as the 2SK2700 and can be substituted by the Sopertex as that is the only one I can find.
 
Apparently, he has forgotten what the "Albert Pagan" design is. Hopefully he knows the Tubelab SE well enough by know to be able to make what you want. If not you'll need to feed him the exact specs that you need. I think TM3KB is a generic design of his that you can use.

For the power transformer, you can consider the XPWR131 which was designed for use with the TSE:

edcor-xpwr131.jpg


There are several threads on here about the FETs for the TSE. I'm not up to speed on this, as it is a constantly-moving target. I would search this forum for recommendations. For example:

http://www.diyaudio.com/forums/tubelab/181369-mosfets-tubelab-se.html
 
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Thanks for the info everyone. I went ahead and ordered a TSE board and am going to go with the 300B design. I've been debating between the 45 and 300B, but in the end I want to be certain I will have enough power... even if I'm not using such an efficient speaker.

For the OPT, I am now looking at the Electra Print "Albert Pagan" design as recommended in the Tubes and Transformers page. I sent an email to electra print to get the specs and price as I really don't know anything about it at the moment.

For the power transformer, I'm not finding many recommendations except for the Hammond 272JX. This seems to be below the recommended 640~650V, but according to what I'm reading, it will work. Is there another power transformer I should consider for the project?

I* use Angela Instruments Power trafo in my 300B TSE. I know of two other people who built their TSE with the exact power transformer.

http://angela.com/angelauniversalpowertransformer.aspx

With one 5V of the taps not being employed([email protected] 1.5A), it barely get warm to the touch even after hours of being use in my amp.

*Not affiliated to the vendor whatsoever!


Abe
 
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Really only went with SSE cause it was a simpler design and easier to build. As I research this more, those don't seem like good reasons, the TSE doesn't seem too much harder to build. The Omens are 97dB so they should be able to handle those tubes fine.... Thinking I should build the TSE now..

Hello
I run one of my speakers (Fostex 167E in MLTL crossover less @ 94dB) with my SSE using El34. No problem and still a lot of power to spare(room is 22 feet by 24 feet by 12 feet).

abe
 

kaos2088

Member
2012-08-24 10:40 pm
Alrighty, gotten a lot of new information and need help understanding. So I had a convo with ZU and they told me that while the speakers are rated at 12 ohms, they actually act more like 16 ohm speakers. Additionally the speakers don't need a lot of electrical feedback so I should aim for a damping factor of 2 or 3.

I took this information to Jack over at EP and got a quote of $200 each for 5K to 16ohm OPTS. Little more than I was hoping for but I'm sure they would sound amazing.

I see two options right now:
1) the EPs
2) James JS-6123HS EBAY


I had hoped I could use these: 5K or 3.5K into 8 ohm transcendars EBAY

But given this new information I don't think they will work very well with my speakers. The 3.5K would actually look like 7K.

Now as for the damping factor, are there any modifications that I should make to the circuit to take this into consideration? Don't see too much info about this in the forum.
 

imnewbie

Member
2010-06-02 2:46 am
I'm using Omen speakers with SSE and my other SE amps. My Transcendar OPT is 5K primary and 1st thing I noticed with the omen's is that the volume needs to be turned higher, compared to my 8 Ohm Usher speakers. Decision to go with 3.5k primary is good idea. The SSE and all my other SE amps have to be cranked at max with omen's. While it plays just as loud with the Usher's at much lower volume. Although I must say If you go with 5K OPT(and making the primary look like 7K), the sound will be much much cleaner v/s 3.5K(making around 5.5K). And because of Omen's higher sensitivity, the lower Watts per channel does not really matter. I can still play my SE amps at ear splitting levels on the Omen's.

Regardless, you are in for quite a surprise when you pair up your Omen's with a DHT SE amp like the TSE.
 
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I see two options right now:
1) the EPs
2) James JS-6123HS EBAY

FWIW, I'm running the James 6123's in my 300B TSE and it's presently my favorite amp. I'm using Tang Band W8-1772's in Half Chang Enclosures (95db). The James is nice because it offers several impedance taps.......and is potted and comes in black or champagne :p I'm using the 5K taps at 360V and 60ma IIRC.

I also have a 45 version of the TSE running Electraprint 5K transformers.

I had a pair of trancendars but sold them before I built anything with them but they are well regarded for a mid-priced transformer. Gery at Transcendar builds them with and without UL taps; for a TSE build there is no need for UL taps.

As far as damping factor goes, it works like this:

Damping factor is the relationship between the amp output impedance and the speaker impedance. Amps with low output impedance are said to have a high damping factor since the low output impedance driving a high speaker impedance allows the amp to have great control over woofer cone movement, since the amp's low output impedance allows the amp to provide the current when the speaker calls for it.

The addition of feedback in an amp does several things, it increases bandwidth, reduces gain, and reduces output impedance. So amps with lots of feedback (think SS amps) have a high damping factor due to their low (sub 1 ohm) output impedance. The damping factor is simply the ratio of the speaker impedance divided by the amp's output impedance. Some high feedback SS amps have DF numbers in the 100's into typical 8 ohm speakers.

A SET tube amp without feedback (like the TSE) will have an output impedance of a couple of ohms, so you will end up with a low DF, say around 4 or so, maybe around 6-8 with your speakers (these are guesses on my part-Tubelab George probably has a more quantitative number). This means that the (relatively) high output impedance of the amp has less control over the woofer cone, resulting in more perceived bass. Sometimes, very low DF ends up with "loose" or "wooly" bass depending on the amp/speaker combo. Conversely, driving some speakers (typically full range speakers) with a high DF SS amp results in very thin, tight/weak bass. I definitely notice this with my 1772's if I drive them with a high powered SS amp.

I wouldn't think that you would need any circuit mods to the TSE to drive your speakers except for picking the correct transformer primary impedance to match well with your speakers impedance.
 
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imnewbie

Member
2010-06-02 2:46 am
I thought Zu Omens were meant to be efficient? Because those Ushers are extremely inefficient, and they are louder than the Zu's?

It has nothing to do with efficiency. It's just that 5K/8 ohm OPT used with 12 Ohm speaker makes the primary look like 7K, which lowers the WPC. However, using 8 ohm speaker with same 8 ohm tap OPT will keep the primary at 5K. This has already been discussed here in earlier posts of this thread.

Another thing is, it's common misconception that inefficient speakers suck with SE amps. IF the 86-89db speaker have flat frequency response then it can too pair nicely with an SE amp in a small or medium sized rooms. BUT still I use the Omen speakers for my SE amps because the sound is much cleaner because of higher load resistance. My Millett Jonokuchi amp sounds cleaner than any other SE amp I have, since the 7K load probably looks like 9K to 13EM7 tubes.
 
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kaos2088

Member
2012-08-24 10:40 pm
Regardless, you are in for quite a surprise when you pair up your Omen's with a DHT SE amp like the TSE.

I hope you mean I'm in for a good surprise. Only heard excellent things so can't wait until I can try them out.

Got my board in the mail, which was the only thing holding me back from ordering everything else.

Hadn't looked at the UBT-2 , but thats definitely another option. Slightly less expensive than the other two, so thats always a plus.