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Melquiades Amplifier
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Posted by Romy the Cat on 07-16-2005

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The Super Melquiades Amplifier is essentially the 3 parallel running Melquiades amplifiers optimized for driving my Macondo Acoustic System, with line-level or inner-stage filters. This SET uses a full 6C33C at LF output and ½ of 6C33C for HF and MF channels. The key element – the unique driving stage in the Super Melquiades is identical to the regular Melquiades. Also, the Super Melquiades has an external, explicitly input-choke filtered, hugely overbuilt power supply(s).

The amp was designed/bult with no reservations to price or spent efforts, would it be design, inventory or assembling. The result of that labor of love sounds accordingly with the expectation. This image is just one left channel. The right channel is not done yet and will come to it’s duty sometimes in a couple month.

Rgs,
Romy the caT


Posted by Alex Yakovlev on 07-16-2005

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Romy, how do I get permission to repeat original Melquiades?

Posted by Romy the Cat on 07-16-2005
There is not permission required. You might repeat the original Melquiades if you wish. All that you need is the circuit and ~$1500 per monoblock. Currently I withhold the devaluing the Melquiades schematic as I need to accumulate my own live-supply of "some" critical components, not widely available, that Milq uses. Then I have no problems to offer the amp to public.

The caT

Posted by Alex Yakovlev on 07-16-2005

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Great! Please let me know when you are ready to unveil it. In the meantime, is there something I could start working on? Can you pass me transformer parameters? What about tubes and sockets? Caps?

Thank you.


Posted by Romy the Cat on 07-16-2005

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 Alex Yakovlev wrote:
  Can you pass me transformer parameters? What about tubes and sockets? Caps?
Alex, when the Mild become public then all specification and sources will be reviled. Meanwhile I have no further comments and won’t elaborate regarding replicating the amp.

The Cat

PS: Also, if it possible do not use the forum as a chat room.

Posted by Romy the Cat on 07-17-2005

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It hard at this point to sat anything defiantly about the Super Melquiades sound. Positively to derive the speakers directly from amp with no speaker-level crossover does provide multiple and multiple benefits. So, Even if to subtract all other “differences” then what might be said about the Super Melquiades sound?

It is not far from where it was expected to be with, at this point, 3 clearly identifiable,  “different” moments.

1) The Super Melquiades has bass that way exceeded what was expected in term of its quality and weight. Perhaps this absolutely unheard by me before bass is responsible for the fact that the amp sounds identical at different volume and it does develop full bass even if it plays at insultingly low volume. In fact, I did noted that I tend to listen the Super Melquiades slightly softer then I usually listen my system.

2) The midrange channel is the exact replica of the regular Melquiades but in the midbass region Super Melquiades sounds larger, more fundamental and believe me or not but it subjectively pushes my upperbass horn lower.

3) The HF channel sound very different then Melquiades-Regula. The half of 6C33 do sound different then the whole tube and I still am trying to figure out how can I get the best out of it. The half of 6C33C is not instantaneously gratifying and it requires some thinking to learn and realize what it does….

Rgs,
The Cat


Posted by cv on 07-17-2005

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Romy,
Now you mention the issues here, I am thinking about what the differences in quality might be due to. I notice that you haven't explicitly said which is better, super or regular... so think of this just as brainstorming as to why things are... different.

The single section 6C33 should theoretically be purer sounding than both halves in use.

Now, as regards the small coupling/high pass capacitor, the filter will have a high output impedance at the x/o frequency.

If you are crossing over at 1kHz, then your RC filter will look something like 1.6nF/100k grid resistor(correct me here if I'm way off the mark).

I make that a driving impedance of around 70k into the 6C33 at the x/o frequency.
This is fine relative to the load presented by a 6C33 grid in engineering terms, but as the input capacitance of the 6c33 varies with signal, it may be that the high Zout of the coupling circuit is not dealing with it as well as before, where the Zout was lower.

You might investigate this by trying a 10nF/16k filter but that would start to load down the driver stage.

Anyway, this post was probably very premature, given that you haven't gotten to the bottom of the differences. I merely suggest these points for experimentation should you end up disatisfied with the new treble channels.

cheers
cv

Posted by Romy the Cat on 07-17-2005

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Chris, at this point it is hard to say anything defiantly. Subjectively it sounds like the Super Milq has slightly less HF extension and transient then the regular Milq, although the output transformer of the HF channel of Super Milq runs higher and flatter. From a different prospective the HF channel runs just a half-anode of the 6C33C. I remember that when I experimented with a half of the tube with the regular Milq I had in some way the similar result. Using half of this tube rely nicely removes this tube gilts and schmaltz not I have to lean to do it without loosing some transient bubbleness.

Well, I would not say that Super transient is HF challenged. It rather sound now at HF like any other better amp but it does not has the crassness, sense of instantaneousness and the phenomenal transient that regular Melquiades had. The Super Melquiades at its H sounds very musical and relax but not “revolutionary musical” as the Melquiades-regular did.

I still would like to stay with ½ of 6C33C and in worst care scenario I will put into the Vitavoxes S2 drivers the older aluminum surround diaphragms and they will push out the transient of the transients. Before I move to such a radical solution I think that there is two places in the Super Milq HF channel that have some room for improvement.

The HF channel has 13.5dB voltage devider at input that is made with RN60-55 resistors. They are wonderful resistors and I do love them but there are better. In the regular Milq  there were used S102 in the devider and I defiantly should replace them the RN60s.. Also it will be some resistors cancellation in input stage that would effectively remove one resistor from the signal path. I sincerely feel that it will have a positive effect.

The second thins is even more important. I consulted Dima with it and he explained that in the Super Milq and the regular Milq the between stages capacitors perform very different duties. In the Milq it was juts a coupling cap but in the Super Milq it is a filtering cap. According to him they work very differently and the demands for the cup in the Super Milq is order s of magnitude higher. In the Milq I use a wonderful 2 uF Electrocube 950 (I love this cap) that “sounded” fine. In the HF channel of Super Melquiades I shot to 3.700Hz that requires 410pF cap. None of the known to be good caps have such a small value, and to be over 400V at the same time. So, I put in the game Silver Dipped Mica. I really do not know how it sounds in this application. It is possible that the Mica cap does something with transient. I’m still on the market for a good pF-level coupling cap. Initially I meant to use in there air-caps (like in my phonocorrector) but it looks like it will not work out at 400V. I ordered for a test vacuum capacitors and will have them next week. Will see how then behave. Meanwhile if you have any suggestions for 400-2000pF caps the let me know. Or perhaps with time pass by the Mike will open up… Who knows….

Rgs,
The Cat


Posted by cv on 07-18-2005

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Allo,
Well, the divider may certainly be responsible for some softening of transients - in particualr, what values are you using there?

Also, the received wisdom is that silver micas are created far from equal; no experience with them myself but I believe Thorsten may have something to share in this area.

My concern is not so much the type of cap as to the value; air cap is probably the ultimate type, it should be quite easy to get some that are happy at 400V plus, but I really do wonder if the high output impedance of the 410pF/100k filter you are using is responsible.

So, it will be interesting to see how the vacuum caps compare (though from what I've seen they are probably as big as the amp). In the meantime, may I suggest trying the original big value coupling cap (the Electrocube 950) with a low impedance filter ahead of the amp?  I know this changes everything, but it should provide another interesting point of reference. If your preamp is happy driving it, maybe 4nF/10k or even 10nF/2.5k?

Oh yeah, if you are going to stay at an x/o of 3.7KHz, an aircore transformer becomes even easier...

Cheers
cv

PS Btw, I think I have mentioned this before, but for my planned aircore OPT amp, I will be using a step-down input transformer wound on a tiny toroidal nanocrystalline metglas core. This will

a) provide a 1st order high pass filter (fed via a series resistor to form an LR filter)
b) provide stepdown for gain matching and better drive of the input tube
c) achieve voltage isolation so that the drive can be directly coupled to the output tube (negative supply voltage to the first stage), also battery bias of 1st stage via the secondary

no caps anywhere; the toroid is wound (tediously by hand) with almost a single layer winding: 2/3 of the way round is the primary, secondary 1/3 and it goes all the way up into the MHz.

Result: the only signal path cap is the power supply resevoir to the output valve. input stage needs VR tube regulation - has to be very quiet as the dc coupling/split supply means all psu noise is presented to the opt


Posted by Romy the Cat on 07-18-2005

Chris,

My frustrations with HF of this amp reminds me the Agatha Christie novels….  however, like anything else it has an end, even a temporarily end….
After some experiments and still being dissatisfied with the HF I ended up consulting with Dima.  He spread me a theory according to which the HF was killed by my coupling Silver Mica cap. All my arguments that silver mica work OK he demised claming that it is known how mica works in parallel application but generally people do not use it is serial application. Well, it sounded like a reasonable argument. I personally did not believe him as I firmly stay that sound  (instead of The Sounds) does not come from sonic signatures of the parts but from the global topological implementations. However I decided to try. I placed between the stages my default 2uF Cube 950 (with speaker lever crossover) and it was like return back to home after a long journey. The amp immediately paid back with beautiful and VERY extended HF. In fact they are even more interesting and more extended then with a regular Melquiades!!! Do not forget that now the S2 driver does not see the upperbass’s coil and it makes it sound VERY clean!!! It was exactly one of the main objectives that I visualized for this project.

Now, I still do not know if he Dima was right or wrong about the Mica. It is possible that your proposal of high impedance does play a roll in there as well. Or perhaps Dima was correct and the only cap should be blamed for anything. Dima made me, contrary to my weak protests, to bult my own Cupper Foil with Teflon cap that I most likely will try soon in the HF channel. Perhaps air or vacuum will be next. HOWEVER it still will NOT help in there if the high impedance was the reasons of HF killing.

Frankly speaking I so love the Cube 950 that if I get the correct value I would not even experiment with anything else. The lower value I can get might be 1000pF (.001uf) that would require 40K bias resistors. I do not think I might go so low…

I really begin to hate all of thing! When will that all soldering stopped!!!?

Well, will see.
The caT


Posted by Thorsten on 07-19-2005

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Hi,

 Romy the Cat wrote:
After some experiments and still being dissatisfied with the HF I ended up consulting with Dima.  He spread me a theory according to which the HF was killed by my coupling Silver Mica cap. All my arguments that silver mica work OK he demised claming that it is known how mica works in parallel application but generally people do not use it is serial application.


What you get with Silver/Mica is an extremely transparent capacitor. It is much free'er from electrostatic effects, microphonics etc. than any other type. The dielectric is a notch or two above polypropylene as well.

 Romy the Cat wrote:
Dima made me, contrary to my weak protests, to bult my own Cupper Foil with Teflon cap that I most likely will try soon in the HF channel. Perhaps air or vacuum will be next.


Careful. Copper Foil tends to have sharp edges and teflon flows. In my experience any sensible assembly of PTFE & Copperfoil ameanable to DIY shorts out rather sooner than later.

 Romy the Cat wrote:
I placed between the stages my default 2uF Cube 950 (with speaker lever crossover) and it was like return back to home after a long journey.


It may very well be that to get the sound you require the "sound" of the specific capacitor AND of the speaker level X-Over is needed. In fact, replacing a 1st order speaker level X-Over with a 1st Order line level X-Over does NOT result in the same level & phase AT ALL (because any driver is a reactive load), you need to completely redesign the X-Over frequencies to get the match back.

 Romy the Cat wrote:
Frankly speaking I so love the Cube 950 that if I get the correct value I would not even experiment with anything else. The lower value I can get might be 1000pF (.001uf) that would require 40K bias resistors. I do not think I might go so low…


40K should be no issue. Otherwise, two 1nF Capacitors in series make 500pF.

 Romy the Cat wrote:
I really begin to hate all of thing! When will that all soldering stopped!!!?


Given that nothing is ever perfect and that we seek perfection as well as new experiences, I suspect you will stop soldering either when you give up seeking the new and the perfect or when you are safely six feet under, whichever comes first.

Ciao T

Posted by Paul Scearce on 07-19-2005

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Romy,

There are transmitter air caps available which can handle several killovolts. They aren't cheap, though, and may also be impractical due to their size.

http://www.cardwellcondenser.com/PAGES/jcd.html

Check out the Johnson capacitors, particularly the 153 and 154 series.

I suppose you could try adding an air-cap filter after the Electrocube coupling caps to test out cv's theory that the impedance is just too high to drive the 6C33Cs.

By the way, when you chose the coupling cap and voltage devider value, did you take the input capacitance of the 6C33C into account? They will have something like 75-100pf of input capacitance. This might make a voltage divider of its own with the 410pf coupling cap.

Paul

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Paul,

Thanks for pitching the Johnson capacitors. They do not look “large enough” for me. I used in past the following caps:

http://www.oselectronics.com/ose_p96.htm

They have very good size to value ratio. The ironic part that I just called to the manufacturer and they informed me that their caps are 600V rated. This turn out to be very good news!

Dima, keeps treating me with his worrying that at high voltage the air caps will act as a capacitance microphone and will pick up all acoustic and electromagnetic dirt form air. Perhaps he is correct but I remember how wonderful the air caps were in the corrector…

From a different prospective the result I got from the Cube 950 was so satisfying that it made me very satisfied. So, I ordered a party of Cube 950 1000pF (they turned out to be cheap like dirt) and if a series tandem of them will do OK in this high impedance application then I will try to un-wind some turns from the 950s making them smaller. Also, I can always drop the loading resistor a little… In anyways now I am in good shape, since I learned that the problem was the cap (filter) but not the transformer or any other “bigger” pain.

The problem is that I know that I will always be drooling when I look at the air capacitors… Probably I should burn this amp once in order to get the answers about the air caps. When I designed the chasses I actually made the provision for 2 pair of 1650pF air filters. I have space in there… I have the sealed enclosure for the capacitors… I have the capacitors themselves… I have a life insurance….

I have to do it….

Rgs,
The caT


Posted by Romy the Cat on 07-19-2005

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I did put the coupling air cap into the game. It works fine but I have now some reservations as well. I need to listen it for some time to find out what it going on.



Added in 3 hours:

I gave to the air cap some listening attention and frankly speaking all my enthusiasm very much evaporated. Yes, the air cap provided in SOME WAYS the effect that it did in phonocorrector, in term of clearing up the granularity and grain at HF. The effect is instantaneously notable and very pleasing. However, all together with the air cap the sound become very disgusting.

I kind of hare to convert myself into a Moron who audition different caps and write about it his conclusion, although it looks like I’m turning into this. I king of feel that I am wiling to get very specific Sound of Melquíades’ HF and I know that it is able to give… but there is this cap on my way. Well, at least if I sell this story to myself under this souse then it does not sound too depriving…

Anyhow, returning back to the sound of the air cap. It is, in THIS CASE, very mushy, very echoed, very foggy and with very strange harmonic context. It more sound like a room with heavy clapping echo. Interesting, that it nothing like the air-cap affect that I observed in phonostage when the caps did not care a lot of voltage.

I ma sorry, that my good air-cap hallucination turn out to be a hallucination. Again and again, after trying practically everything in cap world I’m returning to the peaceful and secure world of the Cube 950….

Rgs,
Romy the caT


Posted by cv on 07-20-2005

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Interesting Romy, particularly the "echo" affect and weird overtones with the aircap. I wonder if the thing is picking up resonances and if the impedance issue is responsible for the overtones... signal being modulated by the varying input capacitance of the 6C33. If the latter is true, it shoud all start to sound a bit like bad solid state...

How does the aircap sound compare to the silver mica? If it's an impedance issue, they should probably sound more similiar than different. If it's a mechanical resonance/signal pickup issue, they should sound quite different. I notice the vanes are near some signal wiring - wondering if there picking up the high level OPT primary signal? I guess the 1nF Cube will help solve the puzzle.

let me just point out 2 or 3 things, from an engineering standpoint:
1) If you want to hear what the aircap can really do, the high Zout filter might be buffered by a cathode follower (maybe pentode based), direct coupled to the output stage. This will drive the 6C33 properly but may or may not introduce other sonic issues, depending on implementation etc. Obviously a pain in the cloaca given the amp's built so forget this one for now.

2) In some ways, the best place for the filter is ahead of the amp, so the driver stage will not be trying to reproduce LF - cleaner drive to the output valve. But it may not work with the Melquiades input stage (impedances again). OTOH, you could try the filter ahead of the amp and apply battery bias to the first stage since you have a blocking cap at the input.

3) Don't be afraid to increase the cap value and reduce the resistor at the 6C33 grid. The only issue is that you will start to load down the driver, but if it is happy dealing with it, then the 6C33 can only benefit from the lowerd driving impedance and the smaller grid resistor (the smaller the better from the point of view of keeping the grid locked down).

(3) ain't difficult to try, same with (2) really. Just depends on how happy you are with the small 950 when it arrives...

cheers

Posted by Romy the Cat on 07-20-2005

Chris,

What I most concern is that my pursuing to fix the HF channel I make myself similar to zillion audio Morons who run across Audio like wounded in the ass animals and keep evaluation components, elements, cables, soldering and defectively of the wires. Although I perfectly understand that the validity of this actions but their method I found completely idiotic, furthermore - their objectives almost always condemned to be failed. In dominating majority of cases they do not have methodologically objective evolution methods and practically all of them (including me) get relative and severely conditioned results.

I try never (how about now? :-) to be engaged into voicing of sound by matching parts and even now doing my current crassness I am not happy with what I do. All those endless chasing of the results by selection of parts affects the Sounds but not Sound. Mostly people who play with those foolish games use initially very poor or even horrible, frequency unusable (dispute to be audiophile-approved) components. So, in thier cases the change between the “obvious garbage” and “almost-garbage” produce a “notable result”. I personally use proven, frequency commercial grade, NUTRAL elements that themselves do minimum or nothing to Sound and THEN I try to shape sound by topologic decision instated of the voicing chose. In fact the real valuable Sound does not come from a voicing anyhow and the really serious Topological Sound smashes through anyhow, even through the very crapy “sounding” components.

Well, it wounds like I “use” or I “shape sound”… In realty this exposure of mine to my believes that “I do something” is very temporarily and frankly speaking it started it being instigated by Dima and few other local folks. I hope when I finish the Super Milq project then my amusement with solder will be over and I will return to my quiet lagoon of listening music and beaching/teaching to audio Morons that thier sound sucks…

In the end a few words about the actual subject :-)

There are many different vision what and why going on in there including just an “absurd“ one that the line level filtering is fundamentally faulty because the gain stages do not operate within the full scale of harmonic envelop. I do not know what is going and I feel that the problem with the cap is topological – means the filtering demand to cap is very different then to the compiling cap + high impedance + high voltage. Probably not all caps can handle it. In a couple days I will have my Cube 950 that is my proven default  NUTRAL cap. I should had began with it and do not allow myself to go in o this crassness. I will think about the further reasoning and conclusions after I try the 950 in there.

Rgs,
The Cat


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I hear you... I've never gone for the school of thought that says, let's correct the inadequacies of component/topology A by throwing in some "complementary" inadequacies in B.

Or, as a feline mathematician might put it, if each of the "sounds" is flawed:

Sound =   ( (sounds1 ^ k) + (sounds2 ^ k) + (sounds3 ^ k)...) ^ (1/k)

where k = musical demand coefficient

k = 1 for Patricia Barber Cafe Wotsit
k = 2 for classic multitracked rock
k = 4 for say, Rach 2
k = 8 for Verdi Requiem at full tilt

where the most extreme moron has failed to understand that k is even and is trapped in a circle of listening and tuning to k = 1 music...

???
cheers
cv


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Hellooo

Voicing not BS, but......

Voicing is last thing to do, after system is nearing "perfect"

Which we all know is never gonna happen, sooo....

First fix system, then voice...



cheers Wink

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 slowmotion wrote:
Voicing not BS, but......

I very much disagree. The “voicing”, as far as I see it, demands a very different “mental” discipline. Take an element, or the collection of the elements, that do NOT indicate any expressiveness in their own. Then place them into a topological application and you receive Sound. As the result, the only you specific topology will be fully responsible for the Sound, BUT the actions and efforts of the given components. I can give many examples but for instance the aforementioned Cube 950 has no own expressiveness and completely neutral in all application where I ever used it. As far as I concern if the Cube 950 was used and something does not sound correct then the problems are somewhere else or in the topological application. So, all of it eliminate a huge and very ambiguous variable from the audio frustrations…. Anyhow, whatever I do I try to stay with this approach and it never failed on me. At least I have OK Sound and do not waste myself on selection of “ advertised better” elements or voicing of my audio with the “multiple differences”…

So, voicing is a big totally artificial pile of BS and even the conversations and thinking about voicing is BS.

Rgs,
The caT


Posted by Thorsten on 07-21-2005

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Roman,

Well, what can I say.

Different parts sound different, like it or not.

I agree the topology needs to be "right" first, but once past that you will be surprised just how much difference parts happen to make.

However, cogitating about your current Amp side issue, I think a few other other things need to be taken into account.

Others have commented that the coupling capacitor is rather close in value to the Valves parasitic capacitance. You MUST use a value for your filter probably at least 10 times as high in value to get this problem reduced.

What I'd suggest is as follows:

1) Place a choke/CCS in the driver anode for the driver you use.
2) Use the resistor you normally use as Anode load as gridresistor for the 6S33.
3) Size the coupling cap to match this resistor.

This will result in the same harmonic behaviour in the passband of the driver.

EVEN BETTER would be to limit yourself to ONE driver Valve and to add the relevant highpasses using the above principle (more or less) to keep the amplifiers harmonic profile.

Finally, just a repeat.

If you take a speaker level crossover (first order or not) replacing it with a line level crossover having the same nominal corner frequencies DOES NOT WORK if your goal is to replicate the original filter response.

Drivers are reactive and so are crossovercompinents. Their interactions cannot be replicated in a line-level crossover hence the line level crossover must be tuned completely separatly, from first principles again to give the desired result.

I think you have fallen in the trap of too many variables, different component types, problematic impedance matching AND X-over topology problems. You first need to resolve the topology and impedance matching.

Ciao T

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