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31st July 2011, 08:32 PM  #11 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

From another forum we have a french guy that also produced 3D
His 3D was more real.
regards, Carlos 
1st August 2011, 12:26 PM  #12 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

Detailing the MKIIIHx
Capacitor substitution and some tips and tricks:
‪Monologue detailing the MKIIIHx power audio amp.‬‏  YouTube regards, Carlos 
1st August 2011, 03:18 PM  #13 
diyAudio Member
Join Date: Nov 2010
Location: Portland, Oregon

numbered schematic & board layout
Greetings,
I put together this numbered schematic and board layout to help myself make a parts list. Note that these have not been carefully scrutinized by either Carlos or Alex. There may be mistakes. The point of posting them is to make it easier for others to put together their parts list. In addition, in the process, people will (hopefully) post my mistakes or make suggestions, so everyone benefits. 
1st August 2011, 03:19 PM  #14 
diyAudio Member
Join Date: Nov 2010
Location: Portland, Oregon

and the board . . .

2nd August 2011, 06:20 AM  #15  
diyAudio Member
Join Date: Feb 2006
Location: Michigan

Comment on use of 3W Resistors
Hello Carlos,
Thanks for getting this builder's thread going. I would just like to comment on your explanation regarding the use of the 3W resistors back on post #7. If you don't mind, I'll try to explain this as simple as possible, so please bear with me. Below is the upper half (positivegoing) output section. Let us do a DC analysis to see what the power is across those 0.47 ohm resistors. The speaker load is RL. A1.jpg To make the explanation simple, let's assume that for all transistors the CollectorEmitter voltage drop (Vce) is 5V when all the transistors are fully saturated (e.g. full output). With a 5V Vce drop on the transistors, we can simplify the circuit. This is an equivalent circuit: A2.jpg Notice that we now have a voltage divider circuit where the speaker load is the lower resistance; and the upper resistance is formed by (5x) 0.47ohm degeneration resistors. Note that five 0.47 ohm resistors in parallel is 0.094 ohms. Therefore, the voltage across the (5x) 0.47 ohms is calculated as: V = (60 V * 0.094 ohms) / (0.094 ohms + RL) First correction: Quote:
Correct answer is worst case condition for those resistors occur when the output load (RL) is shorted to GND. With this condition, those resistors will see the 60V (on this example). However, a shorted power transistor will remove the effect of the CollectorEmitter voltage drop. Now going back to the main topic, regarding the use of 3W resistors: Assuming the speaker load is 2 ohm resistance (we are still in DC analysis). Then the actual voltage and power across all five 0.47 ohm resistors is: V = (60 V * 0.094 ohms)/(0.094 ohms + 2 ohms) = 2.6934 V < Very small, right? However: P(total) = (2.6934 V * 2.6934 V) / 0.094 ohms = 77.175 Watts This total power of 77.175W is spread around 5 resistors. Therefore, each resistor will dissipate about 15.4W. Don't dispair, since this is only the positive half of the signal, the resistors are powered for only 50% of the time. Also, the scenario above occurs only when the amp is clipping. When it clips, chances are (depending on the signal), it only clips for say about 1020% out of the complete period. The scenario above is an extreme case (imagine connecting 2ohm load) so at normal operations (typical home application), those 3W resistor might be fine. However, for professional applications, those 3W resistors will burn at continous high output with critical speaker loads. Also, I noticed that on the schematic, the circuit doesn't have an output protection where the voltage across the 0.47 ohm resistors are monitored. Some designs have this protection where it turns off the output when a certain voltage threshold is present across those resistors. Other things to consider: 1. The above calculations are based off on nominal calculations. It might be wise to factor in the resistor's tolerance rating as well as other parameters (e.g. Vce, supply ripple and actual power supply rating) 2. As explained, the speaker's impedance is really critical on this issue. All speaker impedance rating is somewhat an "average resistance" on the frequencies it was designed for. The actual "resistance" is determined on a particular frequency that is being passed (e.g. some 8ohm speakers will be 4ohm at certain frequencies). 3. The number of output pairs will help in dissipating the power. Therefore, when you plan to reduce the output pairs, you need to increase those resistor's power rating (say from 5 pairs to 2 pairs) to handle difficult loads. Last edited by soltari_knight; 2nd August 2011 at 06:35 AM. 

2nd August 2011, 08:58 AM  #16 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

Thank you soltaire
regards,
Carlos 
2nd August 2011, 09:21 AM  #17 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

Thank you very much dear Byron
Your work will be very helpful for our builders.
I just cannot wait to see these boards....please, charge your camera's batteries to produce pictures for us. regards, Carlos 
16th August 2011, 08:26 PM  #18 
Sin Bin
Join Date: May 2008
Location: Front Row Center

Can MJL1302a/13281a be used in driver stage ..?

16th August 2011, 08:34 PM  #19 
diyAudio Member
Join Date: Jun 2009
Location: Hamburg / Germany

No ... simply because their grid is too large.
Best regards  Rudi_Ratlos 
16th August 2011, 11:01 PM  #20 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

They can work there.... of course dimensions will be wrong
And also you will have lower gain in these power units used in the driver position..they work...but not that good.
I have used in many amplifiers.... i really could not perceive difference in sonics.... maybe for low impedances we gonna need the original transistor gain. You see the current gain is the multiplication of driver and power output gain.... voltage gain there is 1....means no gain as multiplication by 1 does not increase value.... gain of current is the one is very high....output just add current..voltage comes from the Voltage Amplifier Stage (VAS). Imagine that we can have gain 40 in the output power transistor(s) while high current will be crossing these output units...and maybe we gonna have gain 90 to the power transistor while working as driver....multiplication result is 3600.. Now imagine we can have gain 40 in the output power transistor(s) and 200 in the original MJEXXXX driver.... result is 8000..... so...original will help the amplifier to drain much more current from the power supply...and transfer much more current to the speaker...and this means power..... using 8 ohms we will not perceive..but using 2 ohms, for sure you will have losses...got it? regards, Carlos Last edited by destroyer X; 16th August 2011 at 11:08 PM. 
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