Tone Audio reviewed, and loved, the SE84C+ with Zu Essence (97db, 12 ohm).  Nice point of reference!!

https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1273174068

You can select output transformers from the shopping cart when you price a SuperZen.

a) for speakers between 2 and 6 ohms
b) for speakers between 6 and 16 ohms.

It does not change the price.

While it's true running an 8 or 12 ohm speaker with option a) will put less power to the speakers, that is in fact what I sent Tone Audio.   The reason the comments were still positive is because the speakers were efficient enough that the reduced power was insignificant.

Obviously SOME speakers are going to fall in the middle and work with either a) or b).  That is because a speakers impedance is really a varying load across it's frequency response.  

Here is a typical 8 ohm speaker's impedance plot:



You can see around 50 Hz and between 100 & 500Hz the speaker is actually closer to 4 ohms.  

Option a) would put out more power as the impedance drops, meaning a nice solid hitting bass and mid bass.  

Option b) would put out less power as the impedance drops, making for a leaner sounding bass and mid bass.  Low bass below 40 Hz would be slightly improved if the speaker has any real output there.


Of course every loudspeaker's impedance plot is different.  And it's only important to know what it is if you plan to run 6 ~ 8 ohm speakers as they fall in the zone where either transformer might sound best.

As a general observation I can tell you that if you have high efficiency single driver speakers that are rated at 8 ohms, option b) is almost always the best, giving the speaker more weight and midrange tone.  

Here is a plot of a popular 8 inch fostex driver to support this statement.



-Steve

Very helpful post, Steve.  Could you tell us the optimum impedance for best power transfer for each case, i.e. for the Super Zen, standard output tranny, in stereo, x ohms(?); bridged Super Zen, standard output tranny, x ohms (?); etc. That would be good info to include on the "which amp to choose" page.

Busterfree, do you happen to have an impedance graph for your speakers?  If you do, you can use that info, combined what Steve posted, to determine the best match for you.  A bridged zen will see half the impedance across the board but the shape of the curve doesn't change.  For example, take the first impedance graph that Steve posted of a typical 8 ohm speaker and halve the y-axis impedance scale; now the low areas at 50 hz and from 100-500 hz (the frequencies demanding the bulk of the power) are more like 2 ohms, thus would probably be an excellent pairing with bridged zens.  That would provide very good power transfer throughout the primary power band, and give a nice, warm, full presentation.  Or so one would reasonably guess, looking just at these few specifics.  

Along with Busterfree, I too am still curious as to how bridging affects output impedance.  The fact that I distinctly prefer a single zen with my own big box, "8 ohm nominal" impedance, high sensitivity speakers tells me that in spite of the reasoned approach to impedance matching and power delivery, that something else is going on.  Specifically, if the output impedance jumps as a result of bridging (not sure if this is the case or not, please correct me), it would be even more reactive into a speaker load.  Those of us using big box, three way, high sensitivity speakers (those not specifically designed to be an easy, flat-ish impedance load for SET amps) may be looking this speaker/amp matching issue right in the face.

My main speakers are Tekton 8.1en's which are based on the Fostex 206en rated 96dB 1m/1w @ 8ohms. I'm thinking of ordering the SE84CKC which needs a pre-set impedance decision. According to Steve, selection "b" would be the one.

What happens if you run speakers rated at 4 ohms?  I currently use the Tektons with my DIYSE84 with plenty of volume with the pot set  ~40%. I don't have any speakers rate at 4 ohms, but any speakers available at Decware seem to be around 4 ohms.
Regards,
Hank

Buster, I once had the Forte I's with a Select....nice!!  I only wish I still had the select when I upgraded the Forte's with Bob Crites' crossovers and diaphragms.   If you're keeping your Forte, I'll bet mucho money that the Crites upgrades and the CKC will be the business!!   Fresh Sonicaps capacitors go a long way in discharging the signal quicker (less absorption of the signal).  Doesn't change the impedance because all values of the caps, resistors, and transformer are the same...just better quality and fresher (not 35 plus years old)

I have ordered the SuperZen and based on what has already been discussed have selected speaker option B, since the speakers I currently have are nominally rated at 8 Ohms.

For me right now speaker matching and impedance ratings is an unlearned science.  So if I were thinking for some time in the future investing in DM945's or MG944's what would be the consequences of the option B?

Regards,
Hank

Rivieraranch,

What's the transformer sound difference you heard with your Zen? I have the new Super Zen and just spoke with Steve about sending mine back for the B because I'm getting distortion at the 1 o'clock volume position, yet the volume is barely reaching my "normal" moderate listening level.  This is with Tekton Lore 98db/8ohm speakers.

I don't know know if this will help you, but I am powering my Zu Superfly's with a Torii that I ordered with 8 and 16 ohm taps. Sounds great with both, but I like the litte extra weight the 16 ohm taps gives. I have the volume maxed and use the volume control on my Dac (2 volt) signal. I never adjust the volume more then half way, unless I am listening to high quality high rez files. Then I go a bit higher due to the transparency and smoothness of the higher rez files.

SuperZen is on the way! should have it on Monday.It will be hooked up to my idecco (dac only) & Squeezebox touch to my Zu Superflys with a Rel T3 sub. What do u guys think if I used the idecco as a pre amp so I could use the remote control? Pretty sure it would degrade the sound, but was just thinking I would give it a try. Anyway I'm thrilled to finally have a Decware amp! thanks Bob     

Thanks Lon, I"ll try that

Wow this is great news! Thought it might suck, now i can't wait to try it. I"ll try it both ways and compare. Good to know i don't have to get another pre amp right away, not that i could right now. Thanks OC

No, i haven't pulled the trigger on those yet. Mine sound so good i don't know if i need too, but i did talk to Gerrit at zu for a minute and he said its a big improvement so im sure i'll get that bug soon. I noticed you have a squeezebox touch, nice looking system by the way,have you tried listening to MOG yet? Its very high quality! If you have a ipad you can listen to almost any artist with the touch of ur fingertips. I pay 4.99 a month and its well worth it. The app i use is squeezepad, very cool.

I have so much music, just have not got around to checking out subscription services. Usually most limit to 320 bit rate. I am very sensitive to lossy formats and even 320 I find irritating after awhile. Maybe it's all in my imagination.

I put my order in for the nanotech drivers. Zu is back ordered like Decware, so mid to end January I should receive them. I am a bit nervous as I love what I am hearing now, but then again no one I have talked to would go back. Just might mean some more tube rolling. I really can't imagine a more revealing driver, but they say it is.

I love the Anedio. I tried many other dacs but the Anedio is just so honest and revealing with sweet, smooth highs. Like a vast clear blue sunny sky. Any other Dac I tried felt like it was a bottle neck for the Torii. It's also nice having a remote control to control the volume of the Torii.

I'm getting quite a buzzing noise from the speakers now that was not there when i was using just my idecco. I've done the normal unplug this and that and its definitely coming from the idecco when i power it up. Im using it as a pre and dac. There plugged into a ps audio duet. Any suggestions?

It is, i had the volume on the Zen all the way open, so i backed it off a bit and turned the volume on the dac up a bit. Buzzing is gone. Thought i read somewhere in the post you could have it wide open but whatever. Thanks Lon

Back to page one (1)....I am not worried about my Zu Unions with my 2 - 6 ohm SuperZen CKC or SE84CS:

99dB SPL @ 1W/1m
8 ohm, nominal full bandwidth (5.5 ohm minimum at 300 Hz)

http://www.zuaudio.com/docs/Union-1A_Specs.pdf
Impedance Plots

....also as Steve stated in his first post on page 1, the Essence at 12 ohm was still efficient enough that it did not matter (the 2-6 ohm he sent the Reviewer was fine). I also like being able to swap back in my current 6 to 8 ohm Speakers. No worries....     .  -Stone

....what I should do is......send my SE84CS in for the Hazen Grid Mod (CCE) and the Jupiter Caps (CKC) and have option b) 6 - 16 ohm put in. I'll have my CKC to listen to while it is gone and then have both impedance Trannies when it returns.....with full upgrades on both....now I'm thinkin'.

The ZEN is designed around the standard transformer. Steve said that there is a slight sonic compromise with using the EX transformer for the higher impedance speakers.

I frankly have no interest in a ZEN with other than the standard transformer. I use mine with good 4 ohm impedance speakers and it performs as a champ.

So is anyone hearing what im hearing from this superzen . I hope so because its a killer. I have this amp since novenber 2nd , with single drivers that are very effiecent , theres  probably very few amps that are better,and I'll bet the other ones are made in Peoria . Just have to get the money to update the rest of my zens.

Yes the superzen does play louder ,or is it more dynamic . which ever it is its terrific. Are you using the 274 with it, found one (valve art) that does'nt flash at turn on .

I think you're right; the Super Zen definitely has a more dynamic sound. whatever it is, it's great. So, you're utilizing the 274 with it? I came across one (the valve art) that doesn't light up when turned on.