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Mini Torii SE Amplifier (Read 36622 times)
Lon
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Re: Mini Torii SE Amplifier
Reply #200 - 04/09/12 at 03:20:17
 
Had a nice ride. We had weeks of rain in March and a few showers early this month, but it's already in the nineties here damnit and I can at least take advantage of the cool evenings for a spin!

Well, I don't really agree that this particular topic is any more full of inconsistencies as any other jazz topic, and I guess you have a right to say "classic bebop means only the bebop that I happen to like" but that seems a little silly! Smiley

Anyway have a nice night. Time to watch Mad Men.
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #201 - 04/10/12 at 00:21:44
 
Raduscha
The thing.....or let me restate this.  ONE of the things about valves is that not alll types or brands of the same tube necessarily sound the same.  Explaining in a nut shell takes the pressure off a bit. Smiley I did not find it to be the least bit fuzzy or vague.  It sort of sounded like a more robust 6F6, which was which I think is what I prefer for headphone listening.  The 6y6 with the 12at7 in front of it was, for some reason, a particulaly nice match with the high impedance Lowthers, and in that sense coupled with the speakers better, with better grip and bite than the 6v6.

We can't speak of any of this in absolute terms, of course, and this tube type preference issue is totally subjective.  My 6y6 in my system might in fact sound fuzzy or totally out of whack to someone else, and that is absolutely fine with me.  It's one of the reasons that it's nice that the Mini Torii was designed to be as flexible as it is.  If someone thought I was nuts about being interested in any of the tubes we have talked about, I would agree that I probably am nuts, but that I know what I like!
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #202 - 04/10/12 at 00:27:11
 
I see:-) I won't go anywhere near the 12at7 right now. I am curious as a cat to try out all of the 6x6 tubes. I understand of course the relativity issues. My speakers are 4ohm I think.
Coffee makes me write short sentences. Maybe I should drink it more often before posting.
you all wish
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Les Lammers
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Re: Mini Torii SE Amplifier
Reply #203 - 04/10/12 at 00:48:37
 
Erik...we are all a bit crazy and I agree 100% on the system dependency and synergy of tubes.

Radushka,

You are too funny! You might find a container of coffee on your doorstep...decaffinated.  ;D

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« Last Edit: 04/10/12 at 00:49:05 by Les Lammers »  
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #204 - 04/10/12 at 01:36:32
 
The sentence I wrote above about the tube I think I like most for headphone listening is ridiculous! LOL

Time for bedtime reading....what else.... Stereophile, Hi-Fi+, it never ends..... Your are right Floridaboy.

Until later, erik
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #205 - 04/10/12 at 01:41:00
 
have a nice sleep all of you while I listen to my favourite band: MT Vcap Auricap Haytron 6v6. They play all kinds of genres, including classic bebop.
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #206 - 04/10/12 at 03:16:02
 
Fireblade,

now that I think of it, I also have strange issues with my 6x4 whistling in my MT. I have a couple of them that I can't use because they whistle loudly. Not through the speakers, just by themselves. I haven't seen anyone report that kind of phenomenon here on the forum. If I am a rare case, perhaps I could measure the resistors running from my 6x4s and compare them against the spec value, if someone knows it. Otherwise I will call Steve. I warn you Smiley
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Fireblade
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Re: Mini Torii SE Amplifier
Reply #207 - 04/10/12 at 13:05:03
 
In spring 2011, Steve decided to replace the 6x4's with EZ81 rectifiers.  I don't know the reasons for this, but it may have to do with that problem.  In any event, I suggest you talk to Steve, and maybe get the list of adjustmentss required to migrate from 6x4's to EZ81's in your amp.  

I would also ask him about the effects of the VCaps in the M-T.  These may pose no problems and maybe they are ruled out due to space constrictions only, but there may be something else.

I would also make sure somehow, the loudness sensitivity issues you are experimenting are a perception and not a real problem.  This is important to rule out 'organic' problems with your gear.

I hope you solve those problems soon.  Good luck!
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« Last Edit: 04/10/12 at 13:06:41 by Fireblade »  

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Rivieraranch
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Re: Mini Torii SE Amplifier
Reply #208 - 04/10/12 at 22:55:19
 
The reason for the switch from EZ90 (6x4) rectifiers to EZ81 (6CA4) was because the 6x4 sounded great, but was the weak link in the amp. My own experience proved this when some, frisky, 6Y6's blew out one of the 6X4 rectifiers
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #209 - 04/10/12 at 23:42:30
 
My experience with valve rectified power supplies is that various rectifiers are intended to be used with specific amounts of maximum capacitance in capacitor input to filter based supplies.  It's less critical when an inductor is used as the input to filter.  In other words, it may not be so much a case of output tube destroying a rectifier as it is the first element in the B+ ripple filter.  From what I remember -- and want to double check this because I have been curious about it -- the rated capacitance for 6X4 cap input to filter design is 10uf.  If an amp with a 6X4 were designed with say 50 or 100uf capacitor right off the rectifier, that can cause a problem.  For example, about 15 years ago I built an amplifier (2a3 single ended) that used a very hoghly regarded Mullard GZ37 rectifier.  That tube is intended for about 4uf in the way of the input to filter capacitor.  However, the design I built used a 10uf capacitor, which is twice the suggested value for the type of filter used.  And we experienced some rectifier failure.

Not saying or implying this is an issue in the MT, but is something I intend to check the next time I open it up.  A schematic sure would be helpful.  I can draw one out long hand by studying the circuit design, but it's just a very time consuming thing to do.  I have schematics for all the amps I have built over the years.  Not this one, though.
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« Last Edit: 04/10/12 at 23:44:03 by erik2a3 »  

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erik2a3
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Re: Mini Torii SE Amplifier
Reply #210 - 04/11/12 at 01:17:38
 
So, if some might be worrying or wondering -- the capacitance rating of the EZ81 for capacitor input to filter design is 50uf.  My MT uses 33uf as the first cap after the rectifier, which is well within tolerance.  The other nice thing about the EZ81 is that it's an indirectly heated rectifier, whereas the 6x4 is directly heated.  Thus, the EZ81 provides a more gradual voltage increase (aka slow turn on) compared to the instant in-rush of solid state diodes and quicker, directly heated valve rectifiers).  If 33uf had always been the value of cap input capacitance, it may over time have eventually taken its toll on the 6X4.  Seems a very prudent thing of Steve and Decware's part to change to the EZ81 -- for a number of reasons, what is mentioned above, perhaps, being possibly associated with it.
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« Last Edit: 04/11/12 at 01:31:54 by erik2a3 »  

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erik2a3
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Re: Mini Torii SE Amplifier
Reply #211 - 04/11/12 at 23:51:56
 
Regarding the choice of coupling capacitor: VCap or any capacitor can be used if the working voltage specifications and values are appropriate for the application.  Mild caution is encouraged in the sense that this is an area that can become an area of too much concern, IMO and at least in my experience.  Lots of builders, and something I've done myself, also experiment with the type of capacitor (as in oil or poly tubular type) used for the aforementioned input to filter capacitor, the first capacitor off the rectifier.  Same goes for the cathode bias resistor bypass capacitor.  

I want to just offer my opinion, which is of course nothing more than an opinion, that what I found so refreshing about this particular amplifier is that the circuit, which in my view is far more critical than the type or brand, rather, of passive parts used, is one that is not dependent on ultra expensive parts to provide, again in my opinion, extremely satisfactory performance.  The most expensive cap in the world is going to do nothing for a compromised design, and in fact might it even worse.  I tend to enjoy experimenting with some of the different tubes that can be used in the MT as a way of finding what works best for us -- and leave the basic circuit as it is.  Certainly one should feel free to do other things if one is so inclined.  If you don't have experience working with high voltage circuits, however, you MUST realize that the shock hazards posed can be extremely serious.  I knew someone once who took this rather lightly and the following week got zapped terribly hard -- by an amplifier that wasn't even plugged in.  The very heavy charge came from power supply reservoir capacitors in an amplifier that did not use a bleeder circuit, as it's called, on the output of the power supply.  I remember how this felt, because the person was me.  Be sure to measure the storage charge with a volt meter before doing ANYTHING.  There are safe ways of releasing these dangerous voltages, which do NOT include simply shorting capacitors to ground. If you're not sure about what you're doing, don't take the chance and get help.  Apologies, but I have to say this.....
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #212 - 04/12/12 at 00:07:59
 
Erik,
every single time I open up the MT I measure compulsively all 8 caps in the power section, although the 6x4 caps hold no current. I always get around 30V each on one side and 20V each on the other side... I discharge them using a led soldered to a 100k resistor to ground. Does that sound acceptable?
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #213 - 04/12/12 at 01:07:50
 
Radu: 20 or 30 volts is much better than 500, and you've got the right idea for bleeding off the storage charge, providing the resistor is a high wattage, power type.
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #214 - 04/12/12 at 01:23:49
 
What's also pretty cool about the Mini Torii is that they achieved such a vanishingly low noise floor with AC on filaments.  It's a very classic way of wiring the amp, and in this case clear proof how good AC heater supplies can sound.
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Fireblade
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Re: Mini Torii SE Amplifier
Reply #215 - 04/12/12 at 02:07:19
 
The way this amp is designed, with such a flexible and robust imbedded tube rolling platform, I believe there's plenty of experimentation potential just by trying out different output, driver and regulator tubes, for anyone to play with, for years.  The possible number of combinations is staggering.

I'm assuming, of course, the amp sounds good enough to satisfy serious audiophile enthusiasts, to the point where the most probable improvement should come from other components in the setup.  Tube rolling would enhance specific character, timbre or tone differences, but always with audiophile SQ results.

Therefore, I would not attempt to change basic design parameters, and would settle instead on a couple chosen tube configuration sets as a reference for my particular system, to be able then to judge everything else.

This is evidently just MHO.  I suppose technically experienced owners may probably disagree, although I think most users will go about it as proposed.  

BTW my M-T order is already on "Parts Pulled"   Hurray!!!   Cheesy

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« Last Edit: 04/12/12 at 02:13:20 by Fireblade »  

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Raduschka
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Re: Mini Torii SE Amplifier
Reply #216 - 04/12/12 at 02:24:11
 
to me the MT is a fantastic little amp which manages to sound incredibly good with not so fancy parts. I of course rolled tubes neurotically until I hit a wall and could not go any further, so... I decided to roll caps Smiley It was a year long transition from no experience at all, where I worshipped the MT as a fetishistic object that I would have to ship to the USA for 200$ a shot in case anything went wrong to now, where I tenderly solder and unsolder parts inside it like a surgeon would operate on a beloved one, or himself. I am slowly becoming one with my MT and feel sad or joyful, just like the sound that comes out of it, depending on what I have just installed, whether it is Mundorf or Vcaps or Khozmo attenuators... I for one found that a change  of cap brought about change impossible to obtain through tube rolling. As always, I make no claim to exhaustive scientific research.
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Fireblade
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Re: Mini Torii SE Amplifier
Reply #217 - 04/12/12 at 02:37:55
 
Point well taken.  I assume this evolution may take place eventually, especially if one does not live in the US (like me).  But in my case, although I'm the analytical type, I'm very clumsy with my hands ... So unless I'm confronted with a real problem and forced to do something about it, I think I would hesitate to even open that chassis.

Good for you!
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #218 - 04/12/12 at 11:30:21
 
Radu:  believe me when I say it's possible to bump into that same wall with capacitor changes (I intentionally refrain from the use of the word 'upgrade' regardless of cost).  What can begin to happen over time with frequent trials and their often attendant errors, is that other parts next to or near those being switched in and out can begin to suffer as well.  Excessive heating from the iron isn't beneficial, and tube socket pins can begin to fatigue and actually even eventually break.  But as I mentioned to you, I completely understand the urge to experiment.  Being very familiar with a specific sound I like to hear feom an amplifier, I found the Mini Torii quite well balanced from top to bottom from the get-go.  Once a deaigner completes am overall circuit design, small subjective changes can be obtained -- seasoning to taste, as it were -- with coupling capacitors, and so forth.  Parts are not at all necessarily chosen because they are the most or least expensive, but because they sound correct without respect to cost.  

So, anyway, just my $.05 worth.  A minor point of interest I do have is concerned with the value of the first capacitor coming off the rectifier.  In the case of the 6X4, 10uf at 450VDC is not so large that it wouldn't fit if it were a poly film capacitor rather than an electrolytic, but again, whether an improvement (vs simply a change) were obtained is certainly not something all would agree upon, and, moreover, adds to the cost of the final product.
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #219 - 04/12/12 at 11:35:34
 
The EZ81 also of course has the added benefit of being a more rubust rectifier in terms of current delivery.  If your amp is using the earlier rectifier, it might just be worth giving that some consideration.  Have a great day, erik
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« Last Edit: 04/12/12 at 11:36:10 by erik2a3 »  

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Raduschka
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Re: Mini Torii SE Amplifier
Reply #220 - 04/12/12 at 12:46:46
 
Yes, there is a point where it must stop, despite the urges. In my case this is the first time I do this, so I have years in front of me hopefully Smiley So far so good, I only swapped a few things.
off to work
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Les Lammers
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Re: Mini Torii SE Amplifier
Reply #221 - 04/12/12 at 13:29:38
 
"I for one found that a change  of cap brought about change impossible to obtain through tube rolling."

Me too. These 'small parts' are like spice and I use them to get the 'sound' I prefer. What works for me may not work for someone
else, your associated gear and room also come into play. The high price parts are not always what will work best in your system. It's all about synergy. However, you can't 'fix' a poorly designed amp
with tube rolling and/or caps and resistors.
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #222 - 04/12/12 at 13:37:59
 
I am finding this out as we speak Smiley
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #223 - 04/12/12 at 14:08:58
 
I have a question, since I do not know much about much:

The volume of the first step on my att is too loud for late-night listening. I have 2 switches available near the inputs on the MT. Can I add two switchable resistors OUTSIDE the signal path, that i can switch on at night and reduce the signal going into the atts and switch back off during the day? If not I guess they can even be IN the signal path, if I can switch them off during the day.
Thank you
ps: and if so what value should they be to achieve useful attenuation?
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #224 - 04/12/12 at 22:06:12
 
does this look right to anyone?  switchable 47k from rca hot to rca ground to achieve 6db attenuation on demand...


47k par raduschkamuschka, sur Flickr
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #225 - 04/13/12 at 02:47:30
 
duh... I figured it out finally. I am afraid there is no way to attenuate the signal without adding an extra resistor in the signal path. Unless I swap some of the resistors in the atts, to make them get silent more abruptly.



mike2 par raduschkamuschka, sur Flickr
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Les Lammers
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Re: Mini Torii SE Amplifier
Reply #226 - 04/13/12 at 10:38:09
 
When did gain become an issue? The AN 2.5 volt DAC? Was it after you went to the OD3 or was it always an issue? There has to be a simple mod to reduce the gain but I am not technical enough to help.
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« Last Edit: 04/13/12 at 13:47:16 by Les Lammers »  
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #227 - 04/13/12 at 11:26:05
 
Do you have the same problem with the analog output from your CDP? IMHO, pehaps an extra series resistor or small voltage divider is not such a crime.  I also know there are people who use a good preamp, passive or active, between a DAC and amplifier -- because it works.  I'm just wondering if going straight from the cd player to the amp would be an improvement.

In any event, best luck working this out -- enjoy listening to some music this weekend, as well.
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Fireblade
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Re: Mini Torii SE Amplifier
Reply #228 - 04/13/12 at 15:37:03
 
Decware's ZStage literature quote:

Just plug the ZSTAGE into the back of your CD player or DAC and you will have the power of an adjustable output level ( from zero to over 5 volts!) which means DYNAMICS are now in your control!  Not to mention the beauty of pure single-ended triodes adding dimensionality to your music that was never there before!

Just my $0.02. It's my next step after break-in.   Wink
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #229 - 04/13/12 at 22:33:34
 
I received instructions on how to lower the output voltage of my dac from Brian of AudioNote, by swapping one resistor and playing with various values. If there is no trade off that I am not aware of right now, this seems to be the most elegant solution.

You bet I will build my own preamp and use my new Khozmo atts in it Smiley
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Re: Mini Torii SE Amplifier
Reply #230 - 04/13/12 at 22:39:01
 
Valuable few cents worth, too.  I think its' a great idea, and of course we must respect Radu's desire to keep things as simple as he wishes them to be.  I remember feeling justas he does.  The inline attenuators I mentioned would help, too.  You out there Radu? Smiley i have those 6dB attenuators if ypu want them.  I think you might meed more than that, but maybe not!  Send your address and I'll mail tomorrow.
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #231 - 04/13/12 at 22:41:37
 
Oh, there you are.  Keep us informed with how this works out. Erik
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #232 - 04/13/12 at 22:43:00
 
i 'm here Erik! That sounds great, you are very kind. Let me try my new idea tonight and if it doesn't work i will try resistor attenuation, especially since now I understood how to wire those resistors. The tech from Partsconnexion, after seeing my drawings said: you are a good artist but you still don't get it.... Smiley

I will solder 2x  2k7 resistors in parallel with the 330R in the dac to lower the resistance to about 290r. Is that electrically correct?
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #233 - 04/13/12 at 22:48:41
 
Fireblade,
changing my DAc's output voltage...isn't it similar to using a preamp to match the gains and get great dynamic performance? Not a rethorical question, but a real one... Anyhow, i am not plugging my CD's dac into my amp again as long as my DIY AudioNote dac is functional!!!!!!!!
Ever!!
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #234 - 04/13/12 at 22:54:09
 

Untitled-1 par raduschkamuschka, sur Flickr
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erik2a3
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Re: Mini Torii SE Amplifier
Reply #235 - 04/14/12 at 00:06:25
 
Raduscha:  remember I said I was an art teacher?  I had thought you could sketch quite well, and with the last drawing above, some very nice use of foreshortening and value.  Your style reminds me a bit of the expressive quality of Van Gogh's achromatic drawings.  Really, I like your work!  Okay, I get it loud and clear that you don't want to go straight from the CDP to the amp.  :)
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Re: Mini Torii SE Amplifier
Reply #236 - 04/14/12 at 00:29:00
 
Zbox really does look pretty good.  I was wondering if it might be based the familiar cathode follower topology, but probably not.  Output impedance is not really low, but not overly high, either -- a bit lower it seems than the audionote.  Nice powder coated finish, too.  I'm glad Fireblade brought this up, because I didn't even think of it!
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Lon
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Re: Mini Torii SE Amplifier
Reply #237 - 04/14/12 at 00:37:00
 
I think you mean ZStage. ZBox won't help, no extra gain.
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Re: Mini Torii SE Amplifier
Reply #238 - 04/14/12 at 00:38:15
 
thanks Erik, I remember you told me that. Thanks
I should post more of my work Smiley
i am on to something here. I added 2k7 on top of 330R and lowered the output voltage (I am told) by some amount. I should measure with the 1khz signal from audioNote and I will. I will try to find a lower value resistor around the house to see what happens if I lower it some more, because as is it is still loud for late at night.
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Raduschka
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Re: Mini Torii SE Amplifier
Reply #239 - 04/14/12 at 01:49:00
 
370 r on top of 330r lowered the output voltage even further. Should be ok for late at night and am in the process of listening for changes in dynamics. I am actually listening to music! Brian ENo and Robert Fripp, Equatorial Stars.
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Lon
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Re: Mini Torii SE Amplifier
Reply #240 - 04/14/12 at 02:12:40
 
What? You call that music? Smiley Just kidding. Glad you're listening to music.
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Re: Mini Torii SE Amplifier
Reply #241 - 04/14/12 at 02:30:11
 
haha,

is that an inexact category again? Smiley
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Re: Mini Torii SE Amplifier
Reply #242 - 04/14/12 at 03:08:18
 
Radu,

Lowering the DAC's output voltage will help you attain a lower volume at that 2nd click, but it does not necessarilly have any effect upon dynamics, IMHO.

The idea behind 'riding the gain' to improve overall dynamics, is to accumulate unreleased gain potential on the input side, so as to be able to release a fraction of it through your amp's volume controls (output side of the equation).  With the ZStage in place, you achieve the desired end volume control, plus the dynamics effect.

It also works the other way around: If the music source is heavy and congested, lean up the input side and increase the conditional volume (end volume is the compounded effect of both input and output controls) on your amp, for a leaner, more transparent sound.  This, also attainable at the desired optimum end volume setting.

One thing is to correct the hyper sensitivity of your amp's volume control (just reducing the DAC's output voltage), another, more synergistic approach, is to achieve the same results but with added, more lively dynamics.

I may be wrong, but this is how I see it.   Great drawings, BTW!
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Re: Mini Torii SE Amplifier
Reply #243 - 04/14/12 at 03:17:32
 
A tube gain stage should be easy to make.... I just need to find a schematic.
But won't it add a layer of circuitry between the source and the amp? A new pair of pots, etc...
I just got a pair of pretty expensive atts!
Won't it blur the details in exchange of better dynamics? I never used a preamp, so please forgive the amateurism.
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Re: Mini Torii SE Amplifier
Reply #244 - 04/14/12 at 03:21:54
 
oh wait, I got it! If I make a tube gain stage I can take out the attenuators from the MT and use it as a power amp? Is that the idea?
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Re: Mini Torii SE Amplifier
Reply #245 - 04/14/12 at 03:42:07
 
Yes to your first question, no to the second.  Indeed, with the ZStage there's another component and a pair of added cables involved, which, from a purist viewpoint, is not ideal.  But in return, you get boosted dynamics.  Decware's components are really transparent, so the ZStage should not pose much in terms of degradation relative to more common preamps.

You already ordered the attenuators and I would suggest (if you want the added benefits of increased dynamics), to replace the current volume pots on the M-T with them.  Then, you can plug in a ZStage (or CSP2+ if you need more inputs) in the signal path between the DAC and the M-T and get the best overall results.  Make sure to use short, good quality IC's.

If you can build your own ZStage-like version, that's even better, except make sure it ends up being really transparent, otherwise you run the risk of adding non-insignificant sonic degradation.

In the end, the attenuators can be useful at pinpointing the exact volume you want (both day and night sessions), and the ZStage will improve upon sound dynamics.  Best of both worlds, on top of already having installed those great VCaps.   Wink







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Re: Mini Torii SE Amplifier
Reply #246 - 04/14/12 at 03:45:18
 
I love your optimism Fireblade! All I need now is a schematic and I could start gathering the parts.
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Re: Mini Torii SE Amplifier
Reply #247 - 04/14/12 at 04:33:28
 
this is the analog output board of my DIY audionote dac (6922 tubes)I rewired the original pcb in point-to-point on a piece of crap-wood from the 1$ store Smiley
If I made the output of this dac variable, would that equate to a zstage? Or rather a zbox, because I couldn't push it higher than its maximum 2.5V. Is it necessary to go up to 5v in order to be able to 'ride the gain' on the MT?

audionote dac2.1 ptp par raduschkamuschka, sur Flickr
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Re: Mini Torii SE Amplifier
Reply #248 - 04/14/12 at 04:35:44
 
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Re: Mini Torii SE Amplifier
Reply #249 - 04/14/12 at 07:24:38
 
I am about to build a zstage, based on the kit4 schematic provided by Steve on the website. i assume this is the same concept as the finished product, minus the frontal switch and the 0c2 rectifier. I ordered parts from partsconnexion and I happen to have a lot of useful parts, including a great transformer that came with the zkit1. I have the auricaps he uses in the zstage, one stereo alps pot lying around, one great 6922, etc. I just do not understand where the solid core copper wire goes from the input rca's. It goes straight to the tube alright, but what does it do there? Shouldn't it rather go to the volume pot ground?
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