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PostPosted: Tue Aug 30, 2016 2:54 pm 
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Lavantha wrote:
I thought it was always a French company started by two brothers near Marseilles. It was my understanding they opened a facility in Quebec where only a few models like the Arpege were made.....

Appears I've learnt something today....


No...I have learnt something today!!!

You are correct...it was a French company that then opened up a facility in Quebec.

Thanks for the clarification.

http://www.6moons.com/audioreviews/audiomat/opera.html

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PostPosted: Tue Aug 30, 2016 2:56 pm 
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Lavantha, did you send your amp to Montreal for that?


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PostPosted: Tue Aug 30, 2016 3:28 pm 
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I thought I would add the quotes from the threads I found where a couple different guys share their tube rolling experience. these two threads are what prompted me to get the Sylvanias, i did get the 1959 version that is supposedly the best.

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Over the past months I've patiently done some tube rolling in the preamp section of my Audiomat Prelude Reference integrated, to see what might replace the trio of factory-installed Sylvania 12AX7 in there (early 60s, green label, Sylvania JHS 12AX7). The modest group of tubes I tried were Mullard (Great Britain); Mullard (Australia); Heerlen Amperex; RCA Clear Top, GE TMBP 5751, Sylvania TMGP 5751; and for fun a NOS trio of Sylvania green label JHS12AX7 with the exact same date codes as those that came with the amp. I lived with each group for at least several listening sessions with a variety of music.

Cutting to the chase, the only group that was able to match the tone, rhythmic drive, musical flow, treble and bass extension, presence, and musical nuance of the modest factory tubes, was the (once common-as-water) duplicate NOS Sylvania. The preamp section of this integrated is supposedly passive, using the 12AX7 only as drivers, and I was expecting minor and modest differences. Au contraire!

In comparison I thought that in my Audiomat and with my Reynaud speakers the Aussie Mullard 12AX7 tubes had plenty of drive along with nice bass and beautiful midrange tone...but rolled off in the highs. The Amperex sounded awful in the Audiomat for me--via a relatively thudie bass and shouty midrange. The Great Britain Mullards were comparatively muddy and nearly put me to sleep. The RCAs were veiled. The 5751 tubes seemed thin/not full.

So I guess the French designers of this piece might have known what they were doing with those Sylvania tubes ;)

Similar experiences, comments?

Jim



Quote:
Hi Stuart,
I will also recommend you to stay with stock or MUTINE provided 12ax7 replacement tubes, and only when needed.

If my memory is correct, all my Audiomat amps ship with NOS
Sylvania 12ax7 and a Radio Tech 12au7's in the Solfege Unit.

I was able to tube roll with 1950's Mullards, 1960 Tele's, and even tried NOS Mullard Miltary Issue tubes, they will change the tone of the sound but I always went back with the tubes that shipped with the unit, it just always had the best balance sound with the stock tubes.

If your unit was purchased second hand, you may have to verify if your 12ax7's are stock or replacements.

Many folks describe these small tubes as "Preamp Tubes", my dealer explained to me these small tubes are for the amplifier section, one (1) tube is a phase inverter and the other two (2) are drivers. The Volume control is a primary passive design.

It is also my understanding these drivers/phase inverter tubes should lasts many+many years with trouble free use.

If all your tubes are stock and in great shape, I would spend any extra dollars at other parts of your system they may need upgrades and get back to just listening to music, you can spend big dollars on tubes and also many hours of your time with tube rolling in these Audiomat Amps, then find yourself right back where you started.

Again, Nick Gowen at True Sound would be the person to ask about how these amps operate, if you have the correct tubes, and any possible suggestions how to improve the performance of your system with the Arpege inserted. Nick will provide facts about these units.

Best of luck and enjoy your unit,
Steve


-- 30 Aug 2016 23:30 --

Quote:
Hummm, to make it shortly my friend you just bought a FIAT ...

''fix it all the time''. :wink:


lol...don't think so, these amps appear to be very reliable, they do need proper configuration...something many audiophile shy away from, gives them gas.

-- 30 Aug 2016 23:35 --

Here is the low-down on the green label Sylvanias....913 date code

Quote:
Often found relabelled as Baldwin tubes, these Sylvania manufactured green labelled 12AX7 tubes are all very good sounding but some are definitely better sounding than others. In 1959, some really strange things occurred at the Sylvania factory with producing 12AX7 tubes. A 17-mm long grey anode plate version with copper grid posts and a 90-degree O-shaped ring getter first appeared in the 13th week of 1959. In the 39th week and 52nd week of the same year, similar long plate and copper grid post 12AX7 tubes were produced; however, the 90-degree O-shaped ring getter was replaced with a strong pronounced 90-degree square-shaped getter. This is most unexpected, as the early 1950's square-shaped getter had been phased out and was practically non-existent during this time period. In the very early part of 1960, production returned back to using the 90-degree O-shaped ring getter, which continued on throughout the early to mid 1960's. I have compared most of these Sylvania 12AX7 tubes side by side. The 913 date coded variety sounds simply stunning when compared to the 1960's Sylvania variety. To my ears, no other manufactured 12AX7 tube competes to the 913 Sylvania variety. I have rolled far too many 12AX7/ECC83/E83CC/5751 NOS/UOS tubes to list here and I have settled on this particular 12AX7 tube to be the "best" sounding to my ears.


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PostPosted: Tue Aug 30, 2016 6:48 pm 
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Just a clarification a few things.
Quote:
1. Preamp is passive, the three tubes in the amp are drivers and a phase splitter.
2. Power tubes have a fixed bias, which means that tubes must be selected to perform in a specific range of operation that will require closer matching of power tubes.
3. I remember reading somewhere that this amp has no global negative feedback…this will become important later.
4. Prelude Amp was originally voiced and came stock with 1960’s Sylvania 12ax7’s and Winged C Svetlana EL34.


#1 is correct. First thing in the signal chain is the volume control. Nothing out of the ordinary here. Hundreds of manufacturers do it this way.
#2 is basically correct. Your terminology is wrong. The amps use cathode bias which is a fixed resistance on the cathode. What happens is if your tubes are in the high range of current draw, they can run too hot, and have a short life. If they are on the low end then they may have higher distortion due to being under biased. These also need to be at least a matched set per channel. Audiomat likes to supply the tubes in a known specified range to give a good balance between lifespan and sound quality. It's as much marketing as anything else, because you could have your new tubes matched to your old ones without spending huge money buying them from Audiomat.

FYI - Fixed bias is when you have a fixed negative voltage on the tube to bias it. The interesting thing is that the "fixed" voltage may be adjustable. It's fixed because you can fix the current from any tube to a fixed draw. Whereas cathode bias is tube dependent and will vary depending on tubes used.

#3 is not necessarily correct. The last two Audiomat amps I saw had a place to solder in a feedback resistor. One amp did not have the resistor, the other had a resistor and capacitor in place and did have feedback. Both were the same model - Opera. I have also seen this in the Solfege as well IIRC.

The last thing is the AC bias. To set this you need an oscilloscope and signal generator at the very least. A distortion meter is better.
FYI the difference is negligible.

There are no mysterious secrets here. It's just a way to ensure your amp stays as manufactured (to be optimistic) or a marketing scam to get you to buy tubes and service from them (to be pessimistic)

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PostPosted: Wed Aug 31, 2016 6:22 am 
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Hi kukakunga

I didn't have to ship the amp. I contacted Joe at Acoustique about tube type, cost and availability as well as I needed a few of the chassis machine screws which were close to being stripped. I was very happy with the service and guidance I was provided.

I had read about having units recapped but Joe didn't believe it was an issue due to the age of the amp. It was going to be cost prohibitive if shipping of amp was needed plus I didn't believe having the unit bounce around in parcel delivery would do it any good. If shipping was going to be required I had been seriously considering the True Sound in California which appeared to have positive feedback on-line. The Mutine gear looks and feels like it is built for a lifetime and so far, fingers crossed, my unit has been without problems.


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PostPosted: Wed Aug 31, 2016 6:33 am 
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I was hoping you would drop in on this one Dan! Thanks!

The clarifications you provided are much appreciated, my assumptions were cobbled together with bits and pieces from forums etc. My goal here is to allow myself and others to maintain these amps and source tubes for them without being held hostage.

A couple of questions arise from your answers....

#2 You mention that you could use the old tubes to spec for the new ones. Is that a reliable method given the tubes may have drifted over time etc? What measurement under what circumstances would one be able to take to determine what the "known specified range" of the amp is? Assuming I have that info then I should be able to provide that to my tube seller to supply the corresponding tubes?

Concerning AC balance....Is there any reason that AC balance is more critical in these amps, or is it an adjustment that gets overlooked in most amps that have it? I've seen suggestions for other amps to just adjust the pots to the middle and be happy. Also, if a guy like me buys a scope, it shouldn't be rocket science to adjust the AC balance right? I've seen a couple of methods, one guy suggests putting the probe at the cathode resistor while another says the measurement is better at the plate....what's your take. Is there an easy spot on top of the board to tap into either? Aside from that it appears pretty straight forward going for a null with a dummy load, 1kHz tone with the scope set to split 180 degrees. I can probably find a local tech and ride along so I could do it next time around....or just have at it!

I really appreciate the clarity you are providing, so far scouring the net I've found only suggestions to send it to Mutine, I like to know why and understand better the beast I'm dealing with so thanks again for your input!


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PostPosted: Wed Aug 31, 2016 11:18 am 
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Quote:
Hi kukakunga

I didn't have to ship the amp. I contacted Joe at Acoustique about tube type, cost and availability as well as I needed a few of the chassis machine screws which were close to being stripped. I was very happy with the service and guidance I was provided.

I had read about having units recapped but Joe didn't believe it was an issue due to the age of the amp. It was going to be cost prohibitive if shipping of amp was needed plus I didn't believe having the unit bounce around in parcel delivery would do it any good. If shipping was going to be required I had been seriously considering the True Sound in California which appeared to have positive feedback on-line. The Mutine gear looks and feels like it is built for a lifetime and so far, fingers crossed, my unit has been without problems.



That's interesting! Personally, I will find a local tech to do whatever configuration is necessary, like Dan said....there really is no mystery. I'm curious about the simple tube swap, did Joe ever mention the AC balance adjustment? This should be done after an output tube change for optimal performance, however there may not be noticeable signs, especially if things are close enough. I haven't done anything after swapping 12ax7's last night and the thing still sounds fantastic. If you have the opportunity to get some of those Sylvanias, do it! Seriously, my mind was blown last night, the sound with them in it now is so damn good I'm just dumbfounded.....listening last night with shivers down the spin. I'm very happy that the guy who did suggest these tubes in a thread was right! Those tubes will eat any Electroharmonix or JJ's and spit them out! Lol...they are that good man.


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PostPosted: Wed Aug 31, 2016 1:28 pm 
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Quote:
#2 You mention that you could use the old tubes to spec for the new ones. Is that a reliable method given the tubes may have drifted over time etc? What measurement under what circumstances would one be able to take to determine what the "known specified range" of the amp is? Assuming I have that info then I should be able to provide that to my tube seller to supply the corresponding tubes?

It will get you pretty close to where you need to be. Quite frankly the range is pretty broad, you just need to stay away from really hot tubes, or really cold tubes. The biggest issue is everybody measures and specs their tubes differently so you generally get stuck with one tube supplier.
You are measuring cathode current for a given plate voltage. Again it's as much marketing and the want of the sales as anything else. But you do want to keep the amp in spec.
Quote:
Concerning AC balance....Is there any reason that AC balance is more critical in these amps, or is it an adjustment that gets overlooked in most amps that have it?

With an amp that has no negative feedback it is more critical than with feedback. The FB tends to balance things. However, while it is measurable, in a properly designed amp it probably isn't audible to have good AC balance. It will show up most near the clipping point of the amp as you will have unequal drive to the output tubes.
Most amp manufactures don't bother with this any more, but it was quite common in older amps. It depends on the design where you take the measurement from and to some degree your test gear. There may be a bypass cap on the cathodes which will give no result, so the plate is usually the safest bet.

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PostPosted: Thu Sep 01, 2016 7:49 am 
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Thanks Dan, much appreciated!


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PostPosted: Thu Sep 01, 2016 10:54 am 
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I have a brand new set of tubes coming from Mutine...hopefully in the next couple of weeks.

Would that be the ideal time to have them tested so I know in future what values I should be looking for?

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PostPosted: Thu Sep 01, 2016 11:31 am 
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Quote:
Would that be the ideal time to have them tested so I know in future what values I should be looking for?

Absolutely. Just be aware that the test for current varies from tester to tester, and from supplier to supplier. So a good number from Tube Depot, might not be the same as from the Tubestore. You more or less lock in to one supplier.
As I said previously, it is a pretty broad range that will work fine in these amps.

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PostPosted: Thu Sep 01, 2016 4:04 pm 
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the non adjustable fixed bias is the reason this brand was dropped from my list of want to try tube amps.

understand its personal but not knowing where the tubes are at electrically, not having the ability to optimize after tube age drift or even the personal preference to easily run hotter or colder bothers me. I'm curious about the sonic signature of a fixed bias amp but regarding audiomat why the lack of an adjustable fixed bias is beyond me.


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PostPosted: Thu Sep 01, 2016 4:26 pm 
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Hate to be a naysayer but I foresee a valiant effort followed by a sale ... hope I'm wrong. :(


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PostPosted: Thu Sep 01, 2016 4:33 pm 
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BinkyTheCat wrote:
the non adjustable fixed bias is the reason this brand was dropped from my list of want to try tube amps.

understand its personal but not knowing where the tubes are at electrically, not having the ability to optimize after tube age drift or even the personal preference to easily run hotter or colder bothers me. I'm curious about the sonic signature of a fixed bias amp but regarding audiomat why the lack of an adjustable fixed bias is beyond me.


Well...I suppose if 'musicality' is not at the top of your reasons to purchase an integrated amplifier then I can well understand where you are coming from...it's fun to be able to tinker around and play 'pseudo engineer'...lol

...however...as a friend of mine who owns one writes:

"...that Opera is one hell of an amp...the signature of the sound is similar to my Arpege Reference but only much more emotional...you are really connected to the music that most other amps fail....they call it ZEN...same as the Decware amps that I have."

http://www.6moons.com/audioreviews/audiomat2/1.html

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Last edited by Voodoo Funk on Thu Sep 01, 2016 4:49 pm, edited 1 time in total.

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PostPosted: Thu Sep 01, 2016 4:45 pm 
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Hate to be a naysayer but I foresee a valiant effort followed by a sale ... hope I'm wrong. :(


Valiant effort at what? The thing sounds terrific! Getting matched power tubes and possibly getting AC balance adjusted in the future doesn't scare me one bit. I'm pretty sure the outputs in mine are stock, if they are then to me it's pretty good testament to the amp's stability and reliability. It's bizarre how some of you guys seem to have top secret information you are hiding from the rest of us..lol....sheesh, demystify man!

This amp lets the music happen, you need a snappy snare right there...whap! There ya go, need a huge volley of complex bass notes....doodoo voodoo, done! It really does just stand up to whatever comes down the pipe, never sounds like it's struggling in any range and just lets the music flow in the most dynamic way I've seen in any gear I've owned, I'm a fanboy now. :oops: haha


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