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Mini Torii SE Amplifier (Read 24304 times)
erik2a3
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Re: Mini Torii SE Amplifier
Reply #250 - 04/14/12 at 12:22:43
 
Lon: I surely mean ZBox for the very reason that is simply an interstage impedance buffer.  Gain is the last thing that is needed in this case.  However, the input  voltage to it can be attenuated, which is precisely why it is particularly well suited here.  The output impededence spec. satisfactory, but not really low, which wouls be better, and have the additional capability of being able to drive the increased capacitance associates with longer ICs.
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #251 - 04/14/12 at 12:25:51
 
So, your about to build a preamp!  ;) do enjoy the process!
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Lon
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Re: Mini Torii SE Amplifier
Reply #252 - 04/14/12 at 13:33:27
 
Okay, sorry.
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Fireblade
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Re: Mini Torii SE Amplifier
Reply #253 - 04/14/12 at 14:02:30
 
I guess theZBox will work too, absolutely: †The source is 2.5 V and the amp may go full power at 2 Volts or less, depending on the driver tube (1 Volt with the 12aT7). †In any case, there's a positive output voltage differential between the ZBox and amp, enough to boost dynamics riding the gain through the ZBox output control. †

In this case, the volume settings between the two components would be adjusted so that there's a positive voltage (gain) differential between the ZBox output and the amp's output.  In the case of a 12aT7 driver, this difference is a little less than 1.5 V and significantly less with the 12aU7 driver, although probably still enough.

Same principle, only in this case the extra gain of the ZStage (up to 5 Volts) is not required due to the excessive source output voltage and the amp's highish gain. †A simple passive preamp would work the same way, as would an output-controlled DAC.

Those brand new attenuators will play a role in better dialing-in (fine-tune) that volume level on the amp to precisely allow listenable volumes and at the same time improving the dynamics through the ZBox output control. †
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« Last Edit: 04/14/12 at 14:11:22 by Fireblade »  

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Raduschka
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Re: Mini Torii SE Amplifier
Reply #254 - 04/14/12 at 14:08:38
 
good morning Sirs,

Brian of AudioNote casually wrote that the output of my DAC is rated at 2V. The specs say 2.5V. Right now I have lowered that considerably by lowering the value of some resistors on the digital board. Don't ask me which.
I just woke up, but soon I am going to measure the output voltage of that thing with a 1khz signal.
I am a little confused now, isn't a passive preamp just a set of good quality volume pots btw the dac and the MT?
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Fireblade
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Re: Mini Torii SE Amplifier
Reply #255 - 04/14/12 at 14:18:32
 
If the original source is high voltage, a passive preamp will allow this source voltage to be reduced to a point where the differential with the amp (still positive) is optimal for riding the gain dynamics at the chosen (in this case lowish) volume levels you're interested in.

You have already solved (theoretically) the excessive loudness sensitivity of your amp. †We're suggesting the improved dynamics boost by either a ZStage, ZBox or simple passive preamp. †The advantage of the ZStage is for lower output sources you may have in the future or if you would move to that famous designer's home with plenty of listening room †;)
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« Last Edit: 04/14/12 at 14:20:06 by Fireblade »  

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Raduschka
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Re: Mini Torii SE Amplifier
Reply #256 - 04/14/12 at 14:25:38
 
I have to design and build it first Smiley
So it may be overkill for my high output DAC right now, but I can get the DAC's output back to 2.5V and LOWER that using the zstage. The Zstage seems more future-proof then than the Zbox. Plus I have a lot of its ingredients, so it would cost me around 60$ to build one, starting Tuesday (I am within overnight delivery timezone from PartsConnexion).
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #257 - 04/14/12 at 14:44:27
 
...indeed, with the lowered output V on the DAC, my atts get wonderfully louder over 24 of the 48 steps!!!!! Thank you all for helping me fix this, it was teamwork.
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #258 - 04/14/12 at 14:59:52
 
Lon :  absolutely no apology needed!  I just wanted to clarify thatmgain is not what is needed, IMHO.  He already has excessive gain.  I suggested a preamp, too, thinking Radu might already have one, as a way to attenuate the output of the DAC.  His DAC already has enough voltage to drive the amp into clipping.  Thus, less voltage is needed not more.  Passive in-line attenuators add far less to the signal chain than would an active linestage.  This situation is exactly what they are designed for.  But each to his or her own Cheesy
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #259 - 04/14/12 at 15:04:07
 
alright, alright! Smiley

if I install volume pots on the incoming signal, should I be experiencing that 'riding of the gain'?

I have room in the back of the MT, and even holes, to possibly install the vol pots I took out. You suggested this at a certain satge, Erik.
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« Last Edit: 04/14/12 at 15:05:19 by Raduschka »  

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Raduschka
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Re: Mini Torii SE Amplifier
Reply #260 - 04/14/12 at 15:06:36
 
forgive me for foruming you into the ground, but it turns out I don't know how to measure output voltage on my dac and I can't find it on google. I do have a 1khz signal though on cd.
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Lon
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Re: Mini Torii SE Amplifier
Reply #261 - 04/14/12 at 15:12:36
 
Sure I can see how that should work. I will say however. . . in my experience I've never quite experienced an increase in dynamics with a ZBox (I sometimes think I've experienced a slight diminishing of dynamics) and ZBoxes can introduce or reveal hum issues.
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #262 - 04/14/12 at 15:27:03
 
I get 0.1 V out of my Cd player and 0.9V out of my dac now.
Perhaps I do not need a zstage then, I am not overly attached to any particular construction, not even to the purist approach. I f I install pots on the incoming wires and find they sound great, so be it. I have too much detail right now anyway. I can mail you some Erik, if you send me your address Smiley
By the way I would love to try your inline attenuators if you are willing to go through the trouble of mailing them to me.
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #263 - 04/14/12 at 19:30:35
 
I thought I would give back some of what I took, especially to Erik Smiley But I hope you can all recognize yourselves in there...


forum par raduschkamuschka, sur Flickr
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Lon
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Re: Mini Torii SE Amplifier
Reply #264 - 04/14/12 at 19:59:46
 
Awesome Rad!
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #265 - 04/14/12 at 20:51:58
 
That does NOT remind of Van Gogh, but too funny!  Hey, am I right in understanding that your DAC once had output level controls?  Not too much trouble at all to send those attenuators, but I don't think 6dB will be enough...
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #266 - 04/14/12 at 20:55:55
 
It never had output controls Erik. Right now it puts out 0.9 volt and I am tempted to think it always put out 2V, not 2.5V RMS as mentioned in the specs. Somehow I don't think that with 0.9V it will be useful to install the volume pots on the signal. Ig I go back to 2V perhaps? Do you think that would allow me to experience and understand the 'riding the gain' thing?
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Les Lammers
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Re: Mini Torii SE Amplifier
Reply #267 - 04/14/12 at 23:06:34
 

The drawing is too cool!

I hope your gain issue is under control now. I may ask Steve if there is a way to lower the gain a bit when my amp is being built.



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Raduschka
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Re: Mini Torii SE Amplifier
Reply #268 - 04/14/12 at 23:46:30
 
I am waiting for Rivieraranch to notice the reference Smiley
Total bliss at the moment. I reinstalled the source selector switch and wired it as in the image. One position takes the 2.1Volts of the dac directly to the attenuator, the other one goes through the stock volume pots which are now sitting at the back of the MT and allow me total control of the input gain!
Late night audition, here I come!


vol  pot par raduschkamuschka, sur Flickr
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #269 - 04/14/12 at 23:57:23
 
Florida Boy,
while everything else remained the same, I now have 48 step 100K shunt attenuators in the MT and all trace of a gain problem has disappeared (except that late night 1st step volume, which I solved as explained above and which will not be an issue for anyone less paranoid than me). So I suppose it was the volume pots?


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Les Lammers
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Re: Mini Torii SE Amplifier
Reply #270 - 04/15/12 at 00:17:12
 
Radushka,

Have you had the gain issue from the time you first received the amp?
Or did it start when you got the AN DAC? I don't inderstand how attenuators could have caused it.
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #271 - 04/15/12 at 00:51:33
 
I had it from the start. I suppose it got worse when I got the dac, but not by a large measure. No wonder, my cd has a tube output stage an is rated at 2V. The dac is arted at 2.5V, but I measure 2.1V. SO btw 2V and 2.1V there sin't a world of difference.

I suppose that even with the atts the volume rises too quickly, but it isn't an issue for me anymore, because I have plenty of useful steps. I would love to know how one can lower the gain of the MT, it must be very easy. I am just curious.

Remember my biggest issue was with how little room I had on those pots and how they wouldn't stay put. Just to remind you, out of 9 steps I could use the first 2, maximum 3. 3 was very loud for an appartment, 2 was acceptable, 1 was my regular listening level. Which is quite low, since I like my music at low volume and the MT delivered detail and clarity at ..step one. It is hard for me to tell if you would have the same issue with it.
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Fireblade
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Re: Mini Torii SE Amplifier
Reply #272 - 04/15/12 at 13:54:41
 
I have the same concern.  I assume you have 12aU7 drivers and even though your DAC's maximum output voltage may be somewhat higher than the 2.1 V you have measured (as it may have peaks depending on the source signal), it probably is still well under the 2.5 V.  For example, my DAC is rated at a 'maximum' of 2.25 V output.

My speakers are also 94 dB (@ 4 Ohms), which means we will share basically the same configuration and probably the same loudness sensitivity issues.  Other than not having so much volume restrictions in my listening room, I'm probably headed for the same problem ...

What puzzles me, is I have not heard other owners complain about the issue.  I remember Rivieraranch stating he did not feel his volume adjustment being over-sensitive, although he could not pass the middle mark on the dial before clipping set up (I hope I'm remembering this right).  Half-dial leeway is not that bad.

Or it could well be your, maybe, extreme low-volume listening style?  Again, I would like to know if the issue is relative or absolute (loudness vs perception of loudness).

Also, there may be some less 'beamy' 6_6 family beam tetrodes to try at the output stage?  I find myself with more questions and doubts now that when this thread started  :o
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #273 - 04/15/12 at 14:17:43
 
doubts and fears are not that bad, sometimes it's a sign of advancing, which means resolution might be underway Smiley
I have the 12au7 indeed. I DO have a low-volume listening style. I wish I could somehow objectively translate the volume behaviour to you, but I am afraid I can't.
My listening room is about 4x8metres, or perhaps 5x10.
I can show you over Skype, but now I have attenuators instead of the old pots. I am now going to my parents' place, it is Easter time in Eastern Europe and surroundings.
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #274 - 04/15/12 at 14:20:56
 
I think Erik has 6y6 in his right now, but coupled with 12at7, which seem to have higher gain?? I tried the 6l6 variety and found it very fuzzy and unfocused, basically nothing to do with the 6v6 in my experience.
I have all gas voltage regulator types and I always end up liking the 0d3 better for punchiness and tightness in the bass. Dynamics seem more lifelike with that one.
skype pseudo is :  raduschkamuschka
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Les Lammers
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Re: Mini Torii SE Amplifier
Reply #275 - 04/15/12 at 14:22:43
 
FB and Radushka,

I agree that there must be an easy way to reduce the gain. I ordered my amp with a stereo pot because I did not want dual volume controls.

Radushka,

Did you order your amp with the dual stepped attenuators?
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #276 - 04/15/12 at 14:26:37
 
I had ordered my MT with the stock volume pots (they are called stepped volume controls) and they are not stepped attenuators. They are now in the back of my MT controlling input signal on one of the two switch positions (the other being direct through).
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #277 - 04/15/12 at 14:28:26
 
my AudioNirvana speakers are fullrange and I just read that they are at least 95db inside cabinets. So who knows, mine could be 98db as far as we know.
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #278 - 04/15/12 at 15:54:07
 
I can't think of any other way to say this, because there in fact IS not just a simple way, but an add-them-to-your-system-with-your-eyes-closed-simple way of curing the problem.  You are doing less "harm" to the precious signal thatnyou would with an impedance buffer like the zbox (of which there are many kinds) or active linestage.

Please see here: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=266-244

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Fireblade
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Re: Mini Torii SE Amplifier
Reply #279 - 04/15/12 at 16:05:38
 
I think it may be a combination of room dimensions, apartment status, loudness preferences and hyper-sensitive speakers. †Besides, the Mini Torii is supposed to be a 'beamer amp' relative to, say, a SET, with more punch to it.

Ruling out defective volume pots (as you are using them normally again), hopefully that's the case, and the rest of us mortals won't necessarily share the same issues. † Smiley
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« Last Edit: 04/15/12 at 16:07:17 by Fireblade »  

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Fireblade
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Re: Mini Torii SE Amplifier
Reply #280 - 04/15/12 at 16:13:09
 
Good idea, Erik. †Now, what's the correspondence between volts and dBs in this case? †Let's say I want to reduce my DAC outpout signal as it goes to the amp, by 1 Volt. †How many Dbs of attenuation is that?

The only minor problem I see with this idea is the additional pair of cables required.
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« Last Edit: 04/15/12 at 16:13:44 by Fireblade »  

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Les Lammers
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Re: Mini Torii SE Amplifier
Reply #281 - 04/15/12 at 19:05:15
 
FB,

The attenuators appear to connect to the IC's so you won't be adding a set of cables...just 'extending' them. Looks good to me.
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #282 - 04/15/12 at 19:24:30
 
Fireblade - i know, it always seems there's a compromise some place, doesn't it? As Florida Boy mentioned, there is not (necessarily) a need for another pair of IC.  I've used these several times over the years, and my dad is not using the 12dB attenuatora I sent him to use with a Dynaco ST70 amp I rebuilt and gave him.  His speakers are also very efficient, probably in the range of Raduscha's.  He had hair trigger volume pots, too, and these attenuators solved the issue, leaving the controls still just a bit sensitive but much less so.  What is good is that, at least to me, did nothing in terms of degradation of HF response or anything else.  They just knocked the level down.  I used them straight into the back of my amps, but the Mini Torii's inputs are of course on the top.  This might be a visual or aesthetic concern that Raduscha won't want.  The attenuators aren't that long though.  There is a more high end company that also sells these, but I can't recall their name off hand.  Regarding the math of this: Iused to have it on the tip of my tongue when I was using them before, but I just can't remember.  What's just easier is to just get a a couple of values and try them.  On the IC, thing, though, if one were to build a buffer or line stage for this, another pair of ICs would be mandatory, not to mention the extra circuitry, power supply (hum can be a problem with high efficiency, crossoverless drivers), another power cord, etc.  these attenuatorsmare the first thing I mentioned.  They actually really work quite well, at least in my experience, and like you guys I'm picky about this sort of stuff too.
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Les Lammers
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Re: Mini Torii SE Amplifier
Reply #283 - 04/15/12 at 19:31:43
 
Erik, thanks for the link.

FB,

The reviews said they did not degrade the sound and they are a lot less $$$ than a buffer etc. I am done with the gain obssession/anxiety. Grin
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« Last Edit: 04/15/12 at 19:32:09 by Les Lammers »  
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #284 - 04/15/12 at 20:13:01
 
Sure!
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #285 - 04/15/12 at 21:22:12
 
even though I am at my parents< place for easter, i gotta say this:
I lowered the output voltage of my dac from 2.1-2.5 to 0.9 and that lowered the volume (db) only marginally. Very marginally, it did not even solve my late night volume issue!!!!

Since i am not shy with a soldering iron I would think that soldering  2 resistors per channel inside the amp would be a better solution than the rca attenuators because one would bypass one extra connection point, that is the metal casing of the external atts. I tend to think more and more that I would not notice any degradation, now that I have more experience with what does and what does not degrade sound. Low output from the dac plus thin silver wire plus my atts resulted in distorted music at low levels.
The old pots seem to be ok, yes. i have to turn them down 3 steps from maximum to achieve useful attenuation on that 1st step of mine.
I am now thinking I will install the pots so that they affect the first step of the atts only! For that i will have to open them up.

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Raduschka
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Re: Mini Torii SE Amplifier
Reply #286 - 04/15/12 at 21:27:25
 
Erik, maybe FB (although FB could mean both Florida Boy and Fireblade Smiley) is in bigger need of those attenuators than me at the moment. I would think 6db is not enough though.
The technician from ...i can<t remember...Partsconnexion I think, said 2 47k resistors connected at the rca input in a way i can easily draw for you, would lower the volume by more or less 6db. let me know if you need the schematic.
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Les Lammers
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Re: Mini Torii SE Amplifier
Reply #287 - 04/15/12 at 21:32:39
 
I won't have the amp for 3 months so.... Wink
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Re: Mini Torii SE Amplifier
Reply #288 - 04/15/12 at 22:15:07
 
Florida Boy & Erik,

You're absolutely right. †For a moment I thought of it as an adapter between cables. †I just did not see those attenuators could simply plug to the amp directly duhhh!!!

Excellent solution, then, and a relief in case I may feel the need to tame that gain.  For the time being though, I'm inclined to assume Radushka's case is somewhat special, and not necessarily typical.  Even with my higher max DAC output voltage (2.25), I still think my 94 dB speakers and a less restrictive loudness condition should keep things manageable.

In two more days the theoretical 12 weeks are over, so we'll soon learn whether I'm right or not.
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« Last Edit: 04/15/12 at 22:29:38 by Fireblade »  

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erik2a3
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Re: Mini Torii SE Amplifier
Reply #289 - 04/16/12 at 11:40:58
 
I have no issue whatsoever with the Mini Torii and excessive gain.  It also worked very well with the volume controls turned up about 3/4 and a preamp in front of it.
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Re: Mini Torii SE Amplifier
Reply #290 - 04/16/12 at 15:41:51
 
Great, Erik! †That seems to be the general case. †Do you know your DAC's or CDP's ouput voltage? †Since mine is slightly higher than normal (1/8th higher, no big deal), I would like to rule out that maybe yours is under average and that may explain you're able to even use the 12aT7 (higher-gain) drivers without gain issues.

If your DAC (or CDP) output voltage is within the 1.8-2.0 V range, this would be even more reassuring, although I don't foresee problems with gain in my case as it is.

Happy listening (...and tweaking †;) †)
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« Last Edit: 04/16/12 at 19:07:04 by Fireblade »  

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Re: Mini Torii SE Amplifier
Reply #291 - 04/16/12 at 18:43:33
 
I have a pair of ez81 and adapters to use them directly in place of the 6x4. I have 10 pairs og 6x4, out of which I can only use 2 pairs because of whistling issues.

The cap that goes to ground from the 6x4 is 47uf, apparently high for 6x4 and kind of ok for ez81.
Indeed, the ez81 take a while before they power up compared to the 6x4.

If I switch to 10uf I wonít be able to use the ez81, right?

I canít make a decision on my own, unfortunately, because I donít know much about this issue.

Please help!
ps: solid core silver input wire inside the MT to replace the original MOGAMI, brings substantial detail and life back into the music this morning.
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Re: Mini Torii SE Amplifier
Reply #292 - 04/16/12 at 19:16:05
 
Radu,

I don't have an answer for your question, sorry (Erik or Kevin will, I'm sure), but I was surprised by your P.D. message: 'solid core silver input wire inside the MT to replace the original MOGAMI, brings substantial detail and life back into the music'

What is that, an internal wiring for the inputs built by Mogami? †I know they build quality wires but was not aware Decware used them internally. †Moreover, they are supposed to be the best, how come a silver core wire improved over them? †Is this silver core wire insulated like the Mogami? †Did you check for interferences or noises getting through?

Man, this is getting more interesting by the minute ...  Happy Easter, BTW.
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« Last Edit: 04/16/12 at 19:17:09 by Fireblade »  

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Re: Mini Torii SE Amplifier
Reply #293 - 04/16/12 at 19:57:44
 
I am talking about the wire going from the rca to the atts and then from there to the 2k7 resistor and the input tubes. I cannot tell you why I think it is mogami, I must have read it while they were out 'cause I can't see it in the pics I took.
I replaced both back and forth with 28awg pure silver in cotton from VHaudio (also found in my interconnects, w. eichmann bullets). WHile I initially thought they were a tad bright, once I switched back to the original Mogami Low noise wire used by Steve I wasn't able to listen to the MT anymore, all detail was gone.
I will find a way to shield them at a certain point, right now I couldn't be happier. Am even considering putting an end to the modification spree.... We'll see how THAT goes.

wire par raduschkamuschka, sur Flickr
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Re: Mini Torii SE Amplifier
Reply #294 - 04/16/12 at 20:49:05
 
Amazing!  Seems like that Mini Torii of yours spends more time with an open hood than a hot rod!

Could you estimate for us the level of subjective improvement in sound stemming from the combination of VCaps and now this wiring swap?  Assume the original M-T configuration equals to 100%, what % over that do you think it has improved through these two changes?

Thanks!
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Re: Mini Torii SE Amplifier
Reply #295 - 04/16/12 at 21:14:01
 
I like that question! I had a whole class on psychometry this semester Smiley
I spent 500$ on these modifications and 2000$ on a new diy DAC. The new DAC made a huge difference of course...
The Vcaps brought a big improvement in detail and timbre, which became fully evident only when I replaced the 0.1 caps with mundorf's supreme. The 2k7 from shinko revealed some more.
Attenuators made everything more coherent. Same with bypassing the source selector. SIlver input wire 'takes away a veil' compared to the original wire.
Of course everything is not just more detailed now but also much more enjoyable, although it was pretty enjoyable to start with. I particularly salute the tightening and detailing of the bass, which seemed a little unassuming and bloated in the beginning. I also salute the timbre which is to die for now. And also the detail, which makes the music come through, and alive.
The layering is far more diverse and identifiable. Soundstage depth hasn't budged an inch though...
Also, after the Vcaps I noticed surprising dynamic changes in places I know by heart. A tom tom strike in one channel, a guitar note, they come right out at you in the foreground. There was none of that before.
Dynamics, but also detail, seem to be crucial to enjoyment.
All in all I feel I own a little gem.
Subjective improvement, as far as I am concerned: from 100% to  150-180%. I don't know what more I could want, but I also don't know what is out here.
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Re: Mini Torii SE Amplifier
Reply #296 - 04/16/12 at 21:39:41
 
Thanks for sharing this, Radushka.  That is a whole lot of improvement, to say the least!  

How much of this improvement is due to the new DAC, do you think?  The reason I ask, is to differentiate or assess improvement potential from the Mini Torii itself.  A better DAC is an investment proposition.  I'm more interested in validating the tweaks to the existing M-T design.

I know this is not easy to quantify, so please just give it your best shot.  After all, you've been there since the beginning.    ;)
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Re: Mini Torii SE Amplifier
Reply #297 - 04/16/12 at 21:49:52
 
all I said above took place (or was perceived) well after I diy-ed the dac. It is all indeed very hard to assess and extremely subjective. Someone else might feel that the Vcaps are way too expensive for the change they brought about, or not like the change. I was hesitant in the beginning.
I noticed a marked worsening of the soundstage when I replaced the 47k and 240K resistors with tantalum 2watt AN and Kiwame 2watt respectively, so I went back to the original 240k and to AN 1/2 watt 47k. One of the original 47k was defective.
I tried 400V 0.1uf auricaps and did not like their metallic sound. My girlfriend said they sounded metallic too.
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Re: Mini Torii SE Amplifier
Reply #298 - 04/16/12 at 21:53:03
 
Mogami are the best? They do say so on their website:-)
My father was smoking 'the best' cigarettes yesterday, I forgot what they were... Check out VHaudio, there is a diy receipe for IC that are better than the best apparently. I made them myself and they do sound great. They are called flavour ......4 or 3, I can't recall.
All the best!
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Re: Mini Torii SE Amplifier
Reply #299 - 04/16/12 at 21:56:39
 
A lot of hard work trial-and-error.  I guess you've had much fun going through it too.  Take good care of that little gem. Congrats!
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