Dx Blame MKIII - Builder's thread

destroyer x

Compulsive builder
Here you can post your images...from your amplifier, your parts bought and selected by you, pictures of your amplfier... from youself...family and whatever you want and need to post.

Also this gonna be used to instruct people about adjustments.... tips and tricks, upgrades,updates, modifications and so on.

Group buy for this amplifier is in it's last days, so, i have opened this thread in order to post some final instructions, updated schematic, adjustments and some tips and tricks.

First of all, the schematic:

It has lifted ground (low noise ground) in the input..that 10 ohms resistance (1 watt or more) lifts the input ground.

I have removed that...but Alex though i have missed and he has installed in his layout... in the reality it was not missed...i have decided to avoid the lifted ground because this demands special connectors to the input jack, insulated connectors not to short the chassis ground with the lifted ground.... because this deactivates the low noise ground producing a bypass in that input lifting ground resistor.

Also if you use a metalic potentiometer into your input, and also a metalic knob, then you will produce noises (from mains captured by your body) when touched...this demands you ground the potentiometer...and you cannot use the ground comes from the shielded cables because they are lifted ground and will make electrical contact (continuity) with the chassis.... and our chassis is grounded..the secondary center tap goes attached to ground... so.... once again you deactivate.....because of that i have removed..and Alex mm installed....well...this is not bad...can be this way too... it is all right.

But that resistance was not in the schematic.....now it is in the schematic.

regards,

Carlos
 

Attachments

  • Dx Blame MKIII-Hx updated July, 28th - 2011.pdf
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destroyer x

Compulsive builder
I will show you the previous schematic ground

and the new ground scheme that matches the layout made by Alex mm.

regards,

Carlos
 

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destroyer x

Compulsive builder
How to monitor your amplifier current...the stand by current

My suggestion is to adjust your trimpot (preset is 500 ohms...or midway) in order to measure 1 milivolt above the power transistor's emitter resistor.

But for protection, as you can have mistakes in your board (errors and mistakes while building) install 100 ohms resistance - 5 watts, in series with your rail voltages..one resistance to each rail..so, they interrupt the connection and forces supply current to cross them...when supply current crosses develops a voltage drop over these resistances...and this can be measured in volts DC....you should read 4.4 volts... and this is 44 miliamperes to the positive rail...if you have different readings, then adjust your trimpot in order to obtain this voltage.

In the image you see a voltimeter and an amperometer together this resistance...you will use only a DC voltimeter...avoid amperometer.

Current is the voltage divided by the resistance...so....4.4 volts divided by 100 (100ohms) is 0.044 and this is 0.044A or 44 miliamperes.

Why we do this?

If you have mistakes in your board..or if your trimpot is misadjusted (the preset for first moment of power on is 500 ohms), then you may have huge current (max. 350 miliamperes with your trimpot in maximum resistance that is 1K).or much more if you have mistakes..current can be 10 amperes or more if you have shorts in your board caused by bad soldering method... solder balls shorting....melted solder connecting leads and so on....this will overheat and may burn your protective resistance......and it is better this resistor to be burned then you face board damaged with traces melted and board carbonized....the resistance goes first..as 10A represents 1000 watts and we will not install a 1000 watts resistance there because of that.

With normal current of 44 miliamps, then your resistor will be dissipating 3 watts...so...your resistor will be hot..more than warm...but if something goes wrong, the voltage will be higher and this resistor will smoke.

Check off set...it must be small... 1 to 25 milivolts will be fine.

Both.... the offset and the bias trimpot adjusting...operating..shows your amplifier is fine.... if offset is strange (high) and trimpot does not adjust properly, then check your construction because you made mistakes (this happens... a lot....humans does that)

regards,

Carlos
 

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destroyer x

Compulsive builder
Byron made the kindness to produce parts list

I have checked but i use to make mistakes (eyes not that good anymore)... help me to check this.

I have removed supplier name, but you may have this making contact with Byron if you want....i want correct parts, not matter what the supplier is.[video=youtube;Og-HtewlxkE]http://www.youtube.com/watch?v=Og-HtewlxkE[/video]

regards,

Carlos
 

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destroyer x

Compulsive builder
Do we really need 5 watt resistor to each power transistor? say, the emitter resistor

This is another fashion thing that is used since the dawn of the electronic civilization and no one discusses....and everybody think it must be 5 watts.

In normal operation you will never have high watt dissipation there...... the only condition you may have high wattage there is if your power transistor blow out and produces a short from colector to emitter...then you will have 64 volts from the supply crossing it...136A or something alike that will flow...and now you will have the need of a 870 watts resistor..... 5 watts resistor will smoke anyway...so.... the use of 1 watt will smoke under this conditions... 2 watts will smoke also, and 3 watts will go on flames...... 5 watts will be destroyed..... and so on.... only a 870 watts resistor will survive, but will overheat and will burn your pcboard anyway.

What is the normal?....it is the worst case scenario when someone uses 8 ohms crazy speakers that may have 4 ohms in some frequency of the audio spectrum... and will be operating full undistorted power that will be reached from time to time...this is 400 watt average... this is normal high power for this amplifier...the way people may use to have clean sound...playing standard music (not PA use or continuous tone amplification)

So, if someone wants to have this resistor surviving after a long therm short in some power output transistor...and when the supply can feed 136 amperes (no supply can do that..even the mains cannot do that) while keeping 64 volts over this resistor... and this does not happens in real world, but if the one decides to calculate this way...then must install a 870 watt resistor to each power transistor..imagine the size of this thing?

You see, 1 ampere will cross these resistances while your amplifier will be producing 1 Kilowatt of sound (10 percent distortion)..... well....first i doubt you will have a supply that can do this job, secondly you will not tollerate the sound at this level of distortion continuously...will transform your ears in a garbage can and you will not tolerate unless you have it as a peak, as a transient of sound...short therm distorted peak during high level dinamic transient..... under this condition, 10 amperes will be shared by 10 output transistors in each rail...each one of them will manage 1 ampere... and this will be 0.47 watt dissipation in that resistor (power is current multiplied by voltage..... and voltage is 0.47V.... current is one ampere)... and this is not a realistic way to use it.

I do believe you understood... the ones does not understand use 5 watts...i do think some designers use this value because they have never think about the stuff.... this is automatic alike a rule:

- "Power emitter resistors are 5 watts units"...and then everybody goes doing this way...and they feel angry when someone has the arrogance to use a different value....ahahahaha!

regards,

Carlos
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destroyer x

Compulsive builder
Be aware that high power amplifiers are not that easy to build

Not only because supply voltage is high (64 volts X 2) but also because you have a lot of current available to start some fire.

When we have huge amount of energy available in an audio amplifier .... energy from the power supply, if we make a mistake creating an unbalanced circuit, then we will have all this power available to be redirected to the junctions of semiconductors ... and this will burn them .... it is basically what differentiates one high-power unit from a low power unit .... The fact that we have available energy from the power source will be the determining factor that will trigger the destruction of several components.

regards,

Carlos[video=youtube;sh9muZEFIGo]http://www.youtube.com/watch?v=sh9muZEFIGo[/video]
 

destroyer x

Compulsive builder
Fixed a mistake...updated schematic

attached.

regards,

Carlos
 

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  • Dx Blame MKIII-Hx published.pdf
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Canonnica

New member
A tight fit it's gonna be...

I did a paper model of a MKIII-Hx based on a Hifi2000 Pesante Dissipante, 3U high, 360mmx400mm cabinet.

It's a dual mono with two 500VA transfos. Two LS-prot mounted on the back panel. The soft-start has its own 12v transfo.

Your thoughts?
Martin.
 

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destroyer x

Compulsive builder
Detailing the MKIII-Hx

Capacitor substitution and some tips and tricks

regards,

Carlos[video=youtube;cpTqgu8kfhk]http://www.youtube.com/watch?v=cpTqgu8kfhk[/video]
 

Canonnica

New member
Would it be a good idea

Because filtering caps are located on the amp board (probably half of total filtering capacity, for each rail), would it be a good idea to move the R5+L1 and R6+L2 to the exit of PSU card? This would create an exact half and half split reservoir for each rails.

Please see the attached images.
Martin.
 

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destroyer x

Compulsive builder
About power... transformer specifications, heatsink dimensions and so on

The big heatsinks i am suggesting is to face heavy duty work ... and i have suggest people to use 7 heatsinks, each one of them this size shown in the bellow 3D attached image... 15 by 30 centimeters heatsinks...one at left side, other at right side, other in the bottom panel (back panel) and other in the front panel and more three attached in the top cover...also a full aluminium case...this is to face continuous distorted 2 kilowatt operation at 2 ohms loads...so... i have published this text somewhere and now i am explaining how you will manage to select parts, heatsinks and transformers, to your own customized use..and suggesting your the most reasonable way to use (saving money, protecting speakers and having highest quality audio reproduction)

--------------------------------------------------------------------------------

Full power, distorted power of 10 percent.... continuous distorted power...playing already distorted masters, modern electronic music or Heavy metal distorted music.... two channels driven and using two huge transformers of 2 kilowatts each one of them....so.... the available power, when distorting, will be huge, will go to 1 kilowatt each channel.

And believe me or not, there are guys that does not perceive that as bad sound...they understand that sittuation as "loud sound"...some guys feels distortions as "crisp" sound because introduces harmonics and sound starts to have more "body".... seems more solid...i do think it is awfull, but i see that many guys does not mind... the ones loves distorted, already clipped guitar tones (already present in the audio source recording) do not mind...for them this is much more an effect than a defect.

For "normal", standard use... to average listeners.... the ones does not accept distortion, these 15 by 30 centimeters heatsinks (2 pieces of 15 by 15 attached together in the picture), to one channel, will be good enougth to operate at 8 ohms with continuous undistorted tones (250 watts RMS) and will be good also for musical 500 watts... seems the average is 250 watts and you have peaks that will reach 500 watts or more.... listening normal music, not modern electronic music.... a jazz music, a classical music for instance.

My suggestion to use 7 times this heatsink shown is to heavy duty.... two channels as i said...pumping horrible continuous distorted sound at 10 percent THD levels...two channels playing.... so... power transistor will survive to such kind of torture.

You do not need to do this way if your transformer is smaller....your power to each channel will be, let's say limited, by 50 percent (aprox.) of your transformer power....so, if you select two 600 to 700 watts transformers, then your avaiable power may be around 350 - 450 watts RMS to each channel and this heatsinks shown in the 3D picture will be good for 8 and for 4 ohms...and i do think this is the most rational use.... instead to push the unit to produce 2 kilowatts in stereo with 10 percent distortion (chip amplifiers uses 10 percent specification because people really goes to this level... average people... no audiophile people...less demanding people)

Please, watch the power specifications to 8 ohms and 4 ohms.... this gonna be the most used condition i suppose... watch the demand of transformer power, the continuous power and distortion levels.... your transformer power will be what will decide the power you will be able to put out from your amplifier...so.... take care about this decision and select heatsinks, rectifiers, electrolitic condenser bank.... all this in order to face your custom use...not to waste money buying giant transformers that will never be needed to your particular application.

So, select your power transformer in order to match your power needs...if you need 150 undistorted watts to each channel, if you do not tollerate distortion, then you will be running at this maximum power level...maybe to match your expensive speaker power ration, then select two 300 watts transformers or a single 600 watts transformer.... this will limit your power if you do not increase further entering distortion.... will protect and match your speaker and will save your money in heatsinks, rectifiers, electrolitic condensers, size of your case and transformer...will avoid to waste money and will save your speaker coil to be melted by a crazy kilowatt. sustained power.

Observe that your selection will save money a lot.... to 200 watts you will need 10 thousand plus 10 thousand microfarads to each channel.... two 5A bridge rectifiers will be good...heatsinks will not be that huge...transformer will not be that big too.

Do not use "L" shape adaptors...install your transistors directly into your main heatsinks in order to obtain full heat transference.

Adjust your power amplifier iddle current in order to read 1 milivolt Dc developed across your power emitter resistors, the ones are installed at the power transistor emitters, you have one resistor in each emitter, they may read not that different voltage if they are matched...this will guarantee cool operation.

regards,

Carlos
 

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destroyer x

Compulsive builder
Something about input ground lifted by a resistor...the low noise input ground

regards,

Carlos[video=youtube;QwyN-LlmTgs]http://www.youtube.com/watch?v=QwyN-LlmTgs[/video]
 

destroyer x

Compulsive builder
About input ground... a movie showing the connector

also image attached.

regards,

Carlos[video=youtube;xuqAk5EI9oc]http://www.youtube.com/watch?v=xuqAk5EI9oc[/video]
 

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destroyer x

Compulsive builder
About potentiometer noise pickup and star ground

regards,


Carlos[video=youtube;mMF_2z3yw8Y]http://www.youtube.com/watch?v=mMF_2z3yw8Y[/video]
 

destroyer x

Compulsive builder
Here you see the most used way to make star ground...

This is very good too.... using a more centralized spot to solder the star ground...you see the transformer center tap is the thick white line indicated by a horizontal red line.

Both ways works great!

regards,

Carlos
 

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destroyer x

Compulsive builder
How to install a volume control into the Dx amplifier

Here you have a video explaining.

regards,

Carlos[video=youtube;6Wthen4iGAU]http://www.youtube.com/watch?v=6Wthen4iGAU[/video]
 

destroyer x

Compulsive builder
How to prepare a hom made supply for your MKIII-Hx

Here you have instructions.

regards,

Carlos[video=youtube;rlsIjiWh760]http://www.youtube.com/watch?v=rlsIjiWh760[/video]
 

destroyer x

Compulsive builder
Transistors suggested to be used together Dx amplifiers...in special units that uses

higher voltage supplies alike the MKIII Hx model.


This was posted in many places, also video was made suggesting I know that in our board layout we have other transistors suggested…but the ones I do point as “tested units” are the ones you see in the attached picture.

The problem is that i have not these more modern models in my simulator, reason why the schematic produced by the simulator are showing different transistors compared to the ones i suggest..the ones i have used to test my amplifiers, the ones i trust the most, because stronger than others.

These power transistors are alike cousin, they belong to a family... their characteristics and specifications are not all that different...they compete offering almost the same performance.....but these ones are one of the best, top performers, to this case style..... for a while, because soon will be beat too.

The suggested transistors, are the ones accept to work with a little bit more current with our voltage supply of 63 volts, they are good for amplifiers from 50 to 70 volts as they deliver high current under this voltage....more than several others... reason why they where selected in order for you to overdrive your amplifier while using 2 ohms loads.... as you will distort, will reach 1 kilowatt or more of power without destroy the output transistors....this is good...this is reliable...even if someone decide to push the amplifier hard..even if speaker coil starts to short nearby windings and reduce the impedance...even this way the amplifier may survive... reliability was the intention when i have selected these transistors....but of course, other models may fit too.

These ones you bought are good too...but not that good to face 2 ohms... i do think they will work with 4 ohms in a very comfortable way...so.... these transistors pointed are not wrong...they are just less powerful.

If you will not push your amplifier hard..if your speakers are not that powerful..if you do not like distorted music, if your application is hobby, home music...then these transistors pointed in the schematic will be good.

But if you will distort, push the amplifier hard, if you will install series and parallel connections of multiple speakers, PA applications, parties, clubs, meetings, big halls needing powerfull sound, cinema, outdoor uses, heavy duty applications, rock bands, theater and so on..then it is better to use the heavy duty transistors, giant heatsinks, fan blowers and boards with speaker protection too.

regards,

Carlos
 

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  • Suggested power transistors to Dx amplifiers.jpg
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destroyer x

Compulsive builder
Heatsink dimensions, how to figure out their capabilities

Here you have it.

regards,

Carlos[video=youtube;prbALja3Zf4]http://www.youtube.com/watch?v=prbALja3Zf4[/video]
 
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