Forums - A dual mono Zen?

astro

Ex Member

A dual mono Zen?
12/09/05 at 13:52:54

Hi all!

I've been fascinated for some time now by the threads in this forum that praise the Zen SE84 (C/CS etc). I wanted to get one for myself but I'm afraid of a bad match as my speakers are JMR Twin and rated 91db, 4ohm with some complex crossover as the mid/bass driver uses two coils.
Also, I do love them and don't have any plan of replacing them.
I need more power and I saw that the Zen can be bridged to produce 5/6 watts as a monobloc.

Now, I'm not an electrician but I just had an idea:
since a Zen can be bridged into mono quite easily, will it be possibe to build (DIY project) a dual-mono Zen?
This is my idea:
In a single enclosure, build two Zens with the following modifications:
1. Instead of 2 OPTs per channel (bridged), install one.
2. Instead of 2 power supply circuits, build just one with a "stronger" power transformer.
3. One pot, one set of input jacks etc.
So you'll have one power transformer with one rectifier, two input tubes (one for each channel), 4 power tubes (two for each channel) and two OPTs (one for each channel) giving you 5-6 wpc.

Again, as I'm not an electrician I don't know if it's possible, but I do have a feeling it is.

What do you think? Is this doable?

Astro

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Eli Duttman Ex Member	Re: A dual mono Zen? Reply #1 - 12/09/05 at 15:52:13 A single O/P trafo/channel changes EVERYTHING. You no longer have a SE amp; you have a PP amp. Building a "beefier" PSU is definitely doable. BTW, 8 WPC is about right for 94 dB. efficient speakers. Your speakers need 16+ WPC.
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Yoda Ex Member	Re: A dual mono Zen? Reply #2 - 12/09/05 at 16:08:44 You may want to look at one of decwares push pull amps like the Taboo or an el34 based amp like the SE34I for those speakers.
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Microbe Man Ex Member	Re: A dual mono Zen? Reply #3 - 12/09/05 at 16:24:45 The SE34-I.2 isn't a good match with 4 ohms so that isn't the best choice. Assuming the Torii is out of your budget, I would try a single Zen and see how it fares. Once you hear the magic you may be inclined to try a more efficient speaker. Take care, Corey
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Mike W

Ex Member

Re: A dual mono Zen?
Reply #4 - 12/09/05 at 17:06:57

[quote author=Microbe Man link=1134139974/0#3 date=1134145485]The SE34-I.2 isn't a good match with 4 ohms so that isn't the best choice.

Assuming the Torii is out of your budget, I would try a single Zen and see how it fares. Once you hear the magic you may be inclined to try a more efficient speaker.

Take care,

Corey [/quote]

I have to agree, I have a set of B&W 803 matrix just sitting there looking nice.....replaced with a single driver BR cab.

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astro

Ex Member

Re: A dual mono Zen?
Reply #5 - 12/09/05 at 18:29:02

OK guys, thanks for your comments.

As I mentioned, I'm not an electrician so I'm just shooting to different directions at the moment.

So if using one OPT per channel turns the amp into PP and I want to keep it SET do I need to have both trafos connected in series? parallel? (for each channel).

Also, what mods do I need to do in the PSU?

The entire idea is to keep the "Zen Magic" as much as possible.

Astro.

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Eli Duttman

Ex Member

Re: A dual mono Zen?
Reply #6 - 12/09/05 at 18:57:45

Astro,

There are additional snags to be concerned about.

Many speakers of recent manufacture have significant dips in their impedance curves. Just because it's NOMINALLY 4 Ohms doesn't mean there are no drops down to 1 Ohm. Such behavior will mate poorly with SE84 style circuitry. Try to obtain the impedance curve for the speakers.

Unfortunately, speaker manufacturers sometimes mislead the public, when they specify the efficiency of 4 Ohm speakers. They give the SPL at a 1 Meter distance for 2.83 V. of drive. 2.83 of drive into 4 Ohms is 2 W., not 1 W. The "true" efficiency of the speakers is 3 dB. less than the published figure. Caveat Emptor!!

"Keep your eyes on the prize." It not tubes or SS that matters. Assembling a SYNERGISTIC combination is what matters. Your JMR Twin speakers may perform best driven by a quality SS power amp. If that's the case, drive the SS power amp with a NICE tubed preamp. You will not get SET magic, but you will get the BEST your speakers are capable of.

I'm VERY dubious about mating your speakers to "flea" power SE tube amplification.

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Microbe Man

Ex Member

Re: A dual mono Zen?
Reply #7 - 12/09/05 at 19:16:30

[quote author=Eli Duttman link=1134139974/0#6 date=1134154665]

Many speakers of recent manufacture have significant dips in their impedance curves. Just because it's NOMINALLY 4 Ohms doesn't mean there are no drops down to 1 Ohm. Such behavior will mate poorly with SE84 style circuitry. Try to obtain the impedance curve for the speakers. [/quote]

Did you mean the SE34 circuitry here? I was under the impression the SE84's liked this and was the only reason these flea powered amps could be used with conventional speakers like these.

Take care,

Corey

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chevelle Ex Member	Re: A dual mono Zen? Reply #8 - 12/09/05 at 19:37:28 The Zen Signatures aren't push pulls.. looking at the prints, the Signature M (non Dual Core Option) is three output tubes parallel wired, and sent to one 3.3K ("blue") o/p trafo. - their is no inverse circuit on it. I cite the following, under the "Circuit" Paragraph: http://www.decware.com/Monoblocks/designnotes.htm
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Eli Duttman

Ex Member

Re: A dual mono Zen?
Reply #9 - 12/09/05 at 19:40:48

Corey,

The SE84 "likes" 2 Ohm loads. Going below 2 Ohms is bad.

The impedance curve for Astro's speakers will tell an important tale. My concern, assuming the dips don't go below 2 Ohms, is the real world power requirement. Is there enough muscle in 2 SV83s? If the sensitivity of the JMR speakers is in fact 88 dB. with 1 W. of I/P power, forget SV83s.

There are 2 open questions at this time. What does the impedance curve look like? What is the speakers' genuine drive requirement?

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« Last Edit: 12/09/05 at 19:41:38 by Eli_Duttman »

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astro

Ex Member

Re: A dual mono Zen?
Reply #10 - 12/10/05 at 11:15:18

Guys, guys please...

My speakers are rated 91db and the impedance curve varies between 3 and 6 ohms.

But forget my speakers for one moment.

I'm asking here if it's doable.
Build two zens in one enclosure but use only one rectifier.
That simple? or not?

After all, you CAN use two monoblocks, can't you?
So I just want to place them in one chassis. But instead of having two power transformers, use one which is bigger.
Seems to me that it's doable, but what trasformer should I use?

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Eli Duttman

Ex Member

Re: A dual mono Zen?
Reply #11 - 12/10/05 at 13:02:49

[quote author=astro link=1134139974/0#10 date=1134213318]Guys, guys please...

My speakers are rated 91db and the impedance curve varies between 3 and 6 ohms.

But forget my speakers for one moment.

I'm asking here if it's doable.
Build two zens in one enclosure but use only one rectifier.
That simple? or not?

After all, you CAN use two monoblocks, can't you?
So I just want to place them in one chassis. But instead of having two power transformers, use one which is bigger.
Seems to me that it's doable, but what trasformer should I use? [/quote]

Astro,

When you bridge, each amp section "sees" only 1/2 of the load. Half of 3 Ohms is 1.5 Ohms. "Vanilla" SE84 circuitry should not be used below 2 Ohms. Toroidal autotransformers that match speakers to amps (impedance wise) are available, but they increase your costs significantly.

IIRC, Mr. Deckert used Hammond 270FX power trafos in quite a few SE84s. The Hammond 270HX has windings with the same voltages as the 270FX at a higher current capability.

Use a 5AR4 as the rectifier. Use 15 muF. as the 1st filter cap. Follow the 1st filter cap. with a pair (1/channel) of 2 H./100 mA. chokes. Follow each of the chokes with a cap./resistor filter network. The arrangement described is known as pseudo dual mono and it makes for GOOD separation between the 2 channels.

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Microbe Man

Ex Member

Re: A dual mono Zen?
Reply #12 - 12/10/05 at 19:36:47

[quote author=Eli Duttman link=1134139974/0#9 date=1134157248]Corey,

The SE84 "likes" 2 Ohm loads. Going below 2 Ohms is bad.

[/quote]

I have heard(well read) Steve say numerous times that the Zen has no problems driving loads done to a near dead short. Going below 2 ohms may introduce a bit less power output but it certainly isn't going to hurt it.

I remember reading at Zenfest when they loaded the Select down with the Crusaders(2 ohms) and the Imperial SO's in parallel and no problems, it loved it.

Take care,

Corey

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StingRay Ex Member	Re: A dual mono Zen? Reply #13 - 12/10/05 at 22:57:07 Quote: I have a set of B&W 803 matrix just sitting there looking nice.....replaced with a single driver BR cab. Mike, You can send those B&W's my way ;D I have a set of 603's, and would be happy to give those babies a happy home.
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Mike W Ex Member	Re: A dual mono Zen? Reply #14 - 12/11/05 at 02:00:00 [quote author=StingRay link=1134139974/0#13 date=1134255427] Mike, You can send those B&W's my way ;D I have a set of 603's, and would be happy to give those babies a happy home. [/quote] I am sure we can work something out
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