Forums - Low Power and distortion from a Taboo mk2

EasyRider

Verified Member

Posts: 3

Low Power and distortion from a Taboo mk2
06/23/25 at 07:35:17

Dear Sirs,
i'm a proud owner of a Decware Zen SE84CS, Zen SE84ZS, and i recently acquired a Taboo speaker amp, willing for more power.
The serial is 066 and it has the V-cap mod together with the Hazen Grid one.

The issue i get is that the amp is producing hearable distortion on both channels way before the low powered ZEN i have, it's playing music feeded by an RME ADI-2 DAC straight to the amp and driving Tannoy SRM 15X.
If i play music to very low level, distortion goes away. Seems like a power issue.

Impedance of speakers is always 8ohm and with a few peaks to 18ohm.

Even with the ZENs, that has 1/3 the power and engineered for lower impedances i get a great sound from this speakers at the listening levels i'm used to and way above.

So i can't Explain why the taboo seems not able to drive them.

OFC i swapped all the tubes, with different types, and checked the voltages coming from the DAC, to avoid saturation and so on.

I live in europe, so the first thing that came to my mind: sending it back to Steve for a check, might be very costly.
Any suggestions of what i can try to find the problem? i'm quite sure something is not working as intended. Embarrassed

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Crazy Bill the Eel Killer

Seasoned Member

Tubes Rule !!

Posts: 250

Re: Low Power and distortion from a Taboo mk2
Reply #1 - 06/23/25 at 13:13:58

Hello Easyrider,
You sure about the Hazen Grid mod ?
The Taboo is a single ended PENTODE amplifier, meaning the Hazen grid cap should not be in there. The grid should be fed by a separate feed from the B+ supply. If someone actually did the mod on a Taboo, it would mess up the B+ feeding the suppressor grid. Take a look.
Now, I'm no whizbang at this stuff, so I may be off base here. But the Hazen grid mod on a pentode amp raises a red flag to me.

Cheers and good luck, Crazy Bill

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CAJames

Seasoned Member

"I've run every
red light on memory
lane."

Posts: 2573

Re: Low Power and distortion from a Taboo mk2
Reply #2 - 06/23/25 at 15:11:19

Quote:

Posted by: Crazy Bill the Eel Killer Posted on: Today at 05:13:58

Hello Easyrider,

You sure about the Hazen Grid mod ?

The Taboo is a single ended PENTODE amplifier, meaning the Hazen grid cap should not be in there...

Yes, I agree there should be no Hazen grid mod in a Taboo, unless someone rewired it (badly) for triode. Also, are you sure that it has a power transformer compatible with European voltage?

One other thought, I believe early models of the Taboo used a ECC83/12AX7 input tube instead of the ECC88/6DJ8 type tube the current models use. I don't know which the MK2 uses, but if it you are using an ECC88 and it should be an ECC83 that would explain the lack of gain.

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Lon

Seasoned Member

"Love without
guts is
worthless!"
Philip K. Dick

Posts: 26086

Re: Low Power and distortion from a Taboo mk2
Reply #3 - 06/23/25 at 15:41:14

You may well be onto the solution James. I haven't been able to find what input tube the Mk II used, the Mk III used a 6922. . . . Hmmm.

I finally found the manual for the Mk II and here is the input tube info--seems perhaps the 12AX7 may be the best choice if the amp is used without a preamp:

INPUT TUBE INFORMATION
The SE84TS is designed to use your choice of
three different input (or signal) tubes.
12AX7 - Most Gain
12AT7 - Medium Gain
12AU7 - Low Gain
Each of these tubes will lend a different signature to the overall sound of the amplifier. If
you are using a standard 2 volt source like a CD
player with NO preamp, you will probably find
the 12AU7 to have not enough gain. With a
preamp, it could become your favorite tube.

https://www.decware.com/newsite/SE84TSowners%20manual.pdf

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CAJames Seasoned Member "I've run every red light on memory lane." Posts: 2573	Re: Low Power and distortion from a Taboo mk2 Reply #4 - 06/23/25 at 16:39:48 Thanks Lon. I couldn’t find a manual but looking in the old Taboo forum it seems like the MK3 is where it changed from 12A_7 tubes to the current 6922/6DJ8/6N1P types.
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Donnie Seasoned Member Why does it hurt when I pee? Posts: 2354	Re: Low Power and distortion from a Taboo mk2 Reply #5 - 06/23/25 at 16:54:02 I looked up the RME DAC and see that it puts out 4 volts. Could that have something to do with the distortion?
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Lon Seasoned Member "Love without guts is worthless!" Philip K. Dick Posts: 26086	Re: Low Power and distortion from a Taboo mk2 Reply #6 - 06/23/25 at 16:55:36 Hmm. . . I don't think that would necessarily cause distortion without giving full volume. . .
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EasyRider

Verified Member

Posts: 3

Re: Low Power and distortion from a Taboo mk2
Reply #7 - 06/24/25 at 08:37:52

Thank you all guys for the valuable help here!
let me clarify some points:

-yes, it was shipped from Steve with 240v wired power supply
-i thought Hazen grid mod can be beneficial if using SV83, i didn't realized it was only for triode operation. but i will de-solder one leg of the cap today and see what happens.
- i need to understand if someone rewired it at one point for triode operations, but I'm not that good to understand it by myself, but very glad if posting some pics someone can understand it.
- yes, it was supposed to use 12ax7,au7 or at7 depending on the gain needed. EL84 as power tubes and 5u4g as rectifier.
-RME can put out voltage from 0 to 9.9v but i'm paying attention to not overload Decware input stage.

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EasyRider

Verified Member

Posts: 3

Re: Low Power and distortion from a Taboo mk2
Reply #8 - 06/24/25 at 08:57:35

Looking in the details of the Hazen grid papers, Steve wrote this:

"The next test was to see what happened on our pentode wired EL34 push pull amp called The TORII MK II, and again the same results were observed. The final test was to do our original Zen Triode amp with the Russian 6P15P-EV tubes, and again, simply amazing. In every case an increase in performance was seen and dynamics improved with head shaking improvements in clarity and imaging."

So I expect the mod is effective and beneficial also on pentode wired amplifiers, like my taboo.

From the internal pics i can't recognize any visible alteration, but i have no original to compare and also don't have the schema.
If i can see the original schema, surely troubleshooting will be easier.

For sure I'm excluding transformer, tubes, voltage input issues.

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