Dx Blame MKIII-Hx - Builder's thread

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Hi All

Now that the latest group buy is in full swing, it would be good to have an accurate schematic that incorporates all the useful improvements discussed in the last 200 pages in this thread.

radioFlash, I've compared your schematic with the original from destroyer X on the first page. I've marked your changes in RED.

Is everyone happy with these changes?
Are there any other improvements that should be made?
 

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Gentlemen!..... this is so dangerous.... so nearby the oscilation threshold

that you should think twice before to install 56pf.

Yes, i did it at my home.... and resulted fine with my transistors, my sample, my units..... and they can be different than yours in gain, also in capacitance.

A so small value can trigger oscilations...you should test monitoring your amplifier with a scope.... install a speaker or a dummy load with a capacitor in parallel (2uf) and using your generator make a sweep of frequency from 10 to 50 kilohertz.... fast increase and decrease and observe the waveform (square) searching for oscilations.... superimposed or ringing.

Dangerous stuff...that can provide you some increase in treble brightness..... may help a little to identify an instrument, in special metals.... timbre...but the cost may be too much high.

I did it to find the minimum possible value that can keep my unit, my amplifier, that sample at my home, that can be different than yours..... stable.... in the threshold.... with 47pf was already oscilating.

Usually, the practice says that you find the value that triggers oscilation and increase two steps.... this means the minimum of 68pf (from 47pf the next value is 52pf and the next is 68pf..then you have 82pf and 100pf).... so.... 68pg should be reasonable and 82pf means you gonna work at the safe side.

This can have effect in high frequencies.... and above your audibility limit... this can change the timbre a little, very hard to perceive because is due to harmonics...so....the danger may be bigger than the advantage you may have while listening....for sure at instruments this may change a lot...but you are not an instrument...you are human!

I do think you should not do it...better to install 82pf and stay in the safe side.

This amplifier is already very good...much better than average amplifiers you find in our forum and in the professional market...even high end ones....you do not need to extract the last drop of juice of this fruit...it has already a lot of excelent juice.

- "Because you can do this does not mean you should do"

by Bridges


regards,

Carlos
 

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All them are fine.... analogic electronics are not that precise

I hope you are not an obsessive mind..because this will never match with analogic audio, that is very unprecise by nature... components are so alike stones.... each one of them have their own characteristic that has identification only inside its own group or production batch.

Relax.... all schematics tested, all them works fine..this one is my prefered one...last upgrade is the removal of the capacitor... i found it not that good...amplifier is more stable without it, even considering the gain reduction that is also a good idea.... 390 ohms in the gain network is dangerous..820, 680 and 560 are much better options...too much gain is not a good idea...all this unstabilizes.

Our audio world is a non perfect world.... speakers are a hell bad stuff...stupid air pumps, very noisy, very ancient ridiculous machines...they distort as a hell, are not fast enougth...you send order for them to go backwards and inertia pushes it to go on forward..... home acoustics is a problem...you are inside a wooden case (in USA), plenty of wall noises and resonances..... here, down in South America, we use stupid tiles..this reflect audio of high frequency..... our ears goes bad after 22 years old..... we loose high frequency sensitivity (almost deaf) at 40 years old.... after 50 you cannot listen above 14 kilohertz.... above 60 you need a real strong high frequency tone to be heard..sometimes not even possible to listen to it.

All has tollerances of 10 percent.... frequencies together beat one with the other generating harmonics not present in the original sound...so..the search of perfection, in my personnal point of view is non sense...better to search for something that sounds good to human ears...that are also not perfect.

Your ears adjust...reason why everybody love everything after a few seconds...we put bass where there's no bass, we filter also....are you listening the bass beat in your cell phone small speaker?.... there's no bass there!...this is your brain/mind creation...your musical experience providing the filling of tone gaps.

Well...my amplifiers are not perfect...anything perfect in this non perfect world....thanks god is this way...or would be very boring if different than that.

I cannot show you the scope waveform...my amplifier was dismounted..i have removed some parts i had the need to other projects.

All these models, or schematics, or ideas, or updates, or ugrades, changes a little bit what is already very good, or even excellent....this changes this way...from a rate of 9.965 to a rate of 9.972 and to a rate of 9.988...... well.. all them above 9 in this example...almost 10.... why to bother with 0.010...when you are unable to listen these differences...only test instruments will show you something different..... and the speaker will reduce the rate to 4.... and the home acoustics may reduce to 3...and your ears to 2....why to bother about it?

regards,

Carlos
 

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Post1761
the redraw is excellent.
Note the difference between Signal Ground and Power Ground.
All the changed resistor values are good if you need a high gain amplifier. Due to the higher gain there is less feedback. That would explain the reduced value of the compensation capacitor.

But the ratio of C03:C06 has not been maintained when R09 was changed. Either C03 must be made smaller, or C06 must be made bigger, or a combination of both. This should be determined by the required input filter the user needs for his bass preference and then the NFB cap adjusted to a significantly WIDER passband than the input filter.

I like the splitting of the rail diodes with the 100nF (never tried this, but looks worth experimenting with). I like the decoupling on both sides of the supply rail fuses.
The RGND resistor (10r between signal ground and power ground) should have a pair of inverse parallel diodes connected across to limit the fault voltage that can be applied here.

Note: the 50mA of output bias current gives 23.5mVdc across the output emitter resistors. Match these resistors before building. The change to 5mA in post1764 cannot be correct !
 
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Gentleman .... a comunication from the Corporation

We have a very constant, free of charge activity , of a freelance consultant activity performed and conducted by competent master AndrewT.

I would like to put to you, that the views of that gentleman, not always match and not always respect the same ideals and philosopy that moves the creator / adapter / designer / tester of this circuit presented in this thread... the so called Dx Corporation, a fancy name result an association of passions of some assemblers and myself not always agree with our principles, methods and techniques applied as result of 5 decades of research done, based on many years of practical experience and not just referenced by the theory and standard rules and practices .. our amplifiers contains techniques that are resultant from the practice of everyday life building, testing and making experimentations.

Post and put that way, I would like to remind you that the said expert AndrewT is not representative of my person and the Union of audiophiles, I proudly and worthily represent, and that, therefore, the suggestions placed by him has not always my consent and agreement, and which you should check, asking the topic or heading directly to my private email address where you will be received with the respect and attention you deserve

Sadly, we do not share, Mr. AndrewT and myself, a harmonious relationship, which makes me less interested to read his comments.

carlos.eugenio1951@yahoo.com

regards,

Carlos
 
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Stopper Resistors

If you are building the MK III and do not have access to a scope I strongly recommend that you change the driver base stopper resistors to 56 ohms. Several builders have experienced the oscillation that radioFlash reported. Without a scope you will never know if it's there. The resistor increase has worked in every case.
 
Bonfis.... you message is for Ranchu or for uncle charlie?

I have a scope...maybe Ranchu does not have.

I have tried there (when creating the amplifier), 100 ohms, 82 ohms, 68 ohms, 56 ohms, 47 ohms, 39 ohms, 33 ohms, 27 ohms, 22 ohms, 15 ohms, 10 ohms and 4.7 ohms.... and i have watched the scope screen while tweaking generator up and own the frequency...inspected burst, sinusoidal, triangular and square wave..output with load, resistor + capacitor and a real speaker was connected too.

regards,

Carlos
 
I have a scope...maybe Ranchu does not have.

I have tried there (when creating the amplifier), 100 ohms, 82 ohms, 68 ohms, 56 ohms, 47 ohms, 39 ohms, 33 ohms, 27 ohms, 22 ohms, 15 ohms, 10 ohms and 4.7 ohms.... and i have watched the scope screen while tweaking generator up and own the frequency...inspected burst, sinusoidal, triangular and square wave..output with load, resistor + capacitor and a real speaker was connected too.

regards,

Carlos

Hi Carlos
My post is for the information of new builders. Those who do not have scopes might encounter this problem as did several earlier builders. It seems wise to guard against it if a builder, unlike yourself, does not have the equipment to detect it. Obviously it does not appear in everyones MK III.
 
I really do not know dear Meanman

I have studied that in 1970.... then i have applied this when i have designed a whole television Studio (3 Million dollares studio) in 1980... i cannot even remember what is ballanced and unballanced.

Really....i do suspect it is not that important...because if was that important, all audio equipments would come with this feature...and i know Behringer, Crown and some few others.

regards,

Carlos
 
I see...i was at google and wikipedia made me remind the stuff

Really?..... want to know what a think about it?.... bull sheet! (paper sheet:D)

But if you really want..then develop the ballanced input and call it Meaman ballance system and put it to work together our amplifier.

I am not interested on that...to talk true to my old friend...from the Bull i like the "Filet Mignon"... and not other parts.

the stuff is alike a question hundreds (brazilians) use to make to me:

- Why not switching mode power supply?

I use to say that i could answer many things..but the most important thing is that people is not using..and people is not idiot...if it is good..then people would be using....say...all factories running to use it instead of 2 or 3 or 10 in thousands.

Here is google:

http://en.wikipedia.org/wiki/Balanced_audio

Heheheheheheh!:)

Carlos
 
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Hi all...

What capacitors (or "condensers" as Carlos calls them) would you suggest. I am thinking:
- Polypropylene caps for all small values (e.g. 100pf, 220pf, 0.1uf, the highest voltage ones with 5mm lead spacing that will physically fit.
- The 220nf R25 bypass cap, I was thinking a plain ceramic would be adequate?
- Electrolytics: Panasonic FC or FM. I'll be running 70V rails and figure 80V would be inadequate, 100V would be ideal. Are there any locations where low voltage electros will suffice?
- Not sure about the compensation cap. Should I use Polypropylene, Silver Mica or something else altogether?


1% metal film 0.25W resistors in all locations, except:
- 5% wire wound 1W 2R2 base stoppers on the output devices
- 5% wire wound 5W 0R47 emitter resistors on outputs
 
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