Hi JPRCO,
Carlos always recommends - as a rule of thumb - to use 5.000µF for each ampere flowing through the output-transistors.
This means, that you should install 20.000µF for the MKII and the SuperCharged version of the DX Blame per rail.
If you install only 10.000µF per rail, you will loose "punch" on the low frequencies, if you play at high volume.
In the DX Blame builder's thread OSTRIPPER recommended a resistor with a value of 220 Ohm on the collector of Q6, the VAS buffer.
NISSMAN inserted a 1K resistor at this position without any effects on the sound, as he said.
AndrewT answered, that 1K is too big.
That is why I recommend you to take a 680 Ohm resistor: half way between 220 Ohm and 1K.
Best regards - Rudi_Ratlos
Carlos always recommends - as a rule of thumb - to use 5.000µF for each ampere flowing through the output-transistors.
This means, that you should install 20.000µF for the MKII and the SuperCharged version of the DX Blame per rail.
If you install only 10.000µF per rail, you will loose "punch" on the low frequencies, if you play at high volume.
In the DX Blame builder's thread OSTRIPPER recommended a resistor with a value of 220 Ohm on the collector of Q6, the VAS buffer.
NISSMAN inserted a 1K resistor at this position without any effects on the sound, as he said.
AndrewT answered, that 1K is too big.
That is why I recommend you to take a 680 Ohm resistor: half way between 220 Ohm and 1K.
Best regards - Rudi_Ratlos
My approach will be to parallel on-board and off-board caps to get to 20000+ uF. It won't be as elegant as an entirely 'on-board' solution, but I don't think it will be too difficult to execute.
Just my opinion.
Ryan
I said 0r0 is too small.
I also disagreed with OST's choice of 220r, again for being too small.
I suggested 1k to 2k, but the higher values would only ever be used to "protect" the transistor when fed from high voltage supply rails. 1k is about right for +-35Vdc, 1k5 is about right for +-50Vdc, 2k0 is about right for +-65Vdc.
Dear DX Blame friends,
since I had some time in the past days, I started with my onw DX Blame MKII.
This is its current status:
I have nearly finished the 1st PCB. I have to wait for 2 capacitors, that I bought from ebay.
I will use an external PSU (with bulb tester), when I power it on for the 1st time.
As you can see, I had troubles fastening the VBE multiplier (BD139) on the heatsink.
I measured a short between the BD139's case and the heatsink and had to replace the metallic screw by a Polyamid one.
Please measure carefully the resistance between any transistors' cases and the heatsink, before you apply power.
Has anybody of you already finished his PCBs?
Best regards - Rudi_Ratlos
since I had some time in the past days, I started with my onw DX Blame MKII.
This is its current status:
An externally hosted image should be here but it was not working when we last tested it.
I have nearly finished the 1st PCB. I have to wait for 2 capacitors, that I bought from ebay.
I will use an external PSU (with bulb tester), when I power it on for the 1st time.
As you can see, I had troubles fastening the VBE multiplier (BD139) on the heatsink.
I measured a short between the BD139's case and the heatsink and had to replace the metallic screw by a Polyamid one.
Please measure carefully the resistance between any transistors' cases and the heatsink, before you apply power.
Has anybody of you already finished his PCBs?
Best regards - Rudi_Ratlos
Last edited:
Hi, Rudi. I've started assembling too but waiting for parts. I see your board is using a trimmer on the BD139 in lieu of the 150ohm in the BOM. With the changes in various fixed resistors on the MKII supercharged, what are the accepted values for quiescent current (60-100ma ?) and DC Offset (3-20mV max ?)? Just wondering if you are planning some "tweaking" with the trimpot. Not many values published for the supercharged version.
Jean
Jean
I believe Rudi have offered you an assembly guide.... anyway, and just in case
*
Click in the England flag, then in Supercharged and finally in assembly guide, scrool to page 2.
In the above site you have an item called assembly guide, please, watch page two and you will have a chart that is very helpfull to assemble, guiding you through the many models from the Dx Blame series of amplifiers, the ES, ST, MKII and MKII Supercharged.
I suppose Rudi board is using the same part numbers, because this is an easier way to do boards respecting some kind of “standard”….. if numbers are the same, the way I believe, then this chart present in page 2 will be helpful even to Rudi boards…if not, then Rudi will, for sure, offer you an assembly guide able to help you during the assembling of his custom board.
I am sure Rudi may be using the same part numbers...so.... the chart will be helpfull:
http://www.youtube.com/watch?v=IEUUYmSoULg
regards,
Carlos
*
Click in the England flag, then in Supercharged and finally in assembly guide, scrool to page 2.
In the above site you have an item called assembly guide, please, watch page two and you will have a chart that is very helpfull to assemble, guiding you through the many models from the Dx Blame series of amplifiers, the ES, ST, MKII and MKII Supercharged.
I suppose Rudi board is using the same part numbers, because this is an easier way to do boards respecting some kind of “standard”….. if numbers are the same, the way I believe, then this chart present in page 2 will be helpful even to Rudi boards…if not, then Rudi will, for sure, offer you an assembly guide able to help you during the assembling of his custom board.
I am sure Rudi may be using the same part numbers...so.... the chart will be helpfull:
http://www.youtube.com/watch?v=IEUUYmSoULg
regards,
Carlos
Last edited:
Jean, the parts' names on my PCB are of course the same ones, that Carlos uses in his schematics.
If you are going to build either the ST- or ES - version of the DX Blame, you should adjust the quiesce current to about 50mA by means of the trim potentiometer.
A friend of mine, who user the SANKEN 2SA1216 / 2SC2922 transistors felt, that the Sound was "better", after he adjusted the quiesce current to approx. 70mA.
Best regards - Rudi Ratlos
If you are going to build either the ST- or ES - version of the DX Blame, you should adjust the quiesce current to about 50mA by means of the trim potentiometer.
A friend of mine, who user the SANKEN 2SA1216 / 2SC2922 transistors felt, that the Sound was "better", after he adjusted the quiesce current to approx. 70mA.
Best regards - Rudi Ratlos
Biasing output
I strongly suggest you you look at the advice for adjusting quiescent levels in the book by Douglas Self (i.e we don't adjust for quiescent current ). This amplifier is a HIJACKED version of his design with trivial modifications.A lot of the advice given here regarding it's operation is just plain incorrect
I strongly suggest you you look at the advice for adjusting quiescent levels in the book by Douglas Self (i.e we don't adjust for quiescent current ). This amplifier is a HIJACKED version of his design with trivial modifications.A lot of the advice given here regarding it's operation is just plain incorrect
Voila!
Rudi, Carlos: Completed 2 boards, MKII Supercharged and as expected, they sound greatttttt. I attach a photo and hope it comes through ok.
A couple of assembly notes:
1- mounted the damping coils underneath just for looks,
2- had some problem like Rudi had with shorting to heat sink but with the MJE's not the BD - poor quality shoulder washer or tightened to much!
3- must remember to mount the board MJE with correct pin allignment- board shows BD139 layout.
4- Opted for a trimpot and the MKII lineup for C19/C20 in the end. Also I might get just away using the 10000uf/63V so far so good. If not I'll add a pair off board.
Great project, now I wonder what design to go with for the other 2 boards.
Thanks again for all your help.
Jean
Rudi, Carlos: Completed 2 boards, MKII Supercharged and as expected, they sound greatttttt. I attach a photo and hope it comes through ok.
A couple of assembly notes:
1- mounted the damping coils underneath just for looks,
2- had some problem like Rudi had with shorting to heat sink but with the MJE's not the BD - poor quality shoulder washer or tightened to much!
3- must remember to mount the board MJE with correct pin allignment- board shows BD139 layout.
4- Opted for a trimpot and the MKII lineup for C19/C20 in the end. Also I might get just away using the 10000uf/63V so far so good. If not I'll add a pair off board.
Great project, now I wonder what design to go with for the other 2 boards.
Thanks again for all your help.
Jean
Attachments
Jean,
I have adjusted the quiescent current, I still have to solder some cables, and then, tomorrow, I will have a big whisky and listen to my DX Blame MKII
(left channel only) for the 1.st time.
Best regards - Rudi_Ratlos
I have adjusted the quiescent current, I still have to solder some cables, and then, tomorrow, I will have a big whisky and listen to my DX Blame MKII
(left channel only) for the 1.st time.
An externally hosted image should be here but it was not working when we last tested it.
URL]
Best regards - Rudi_Ratlos
Strange things happening
Dear DX Blame friends,
after adjustment of the quiescent current (to about 50mA) and measurement of the DC voltage on the speaker's output (between 3 and 6 mV),
I powered up the 1st channel of my DX Blame MKII:
and - Aaarrrgh: Smoke coming from the PCB.
I forgot to unsolder the 100 Ohm resistor, that I used during the adjustment procedure, and this resistor melted away
.
The fuse, that I inserted into the fuse-holder after my adjustments have been completed, is 2A. I measured it; it is o.k.
This should have never happened, because the current is flowing through the fuse now!
I am using 15.000µF power caps, and the power to the PCB is currently delimited to <60 Watts by means of my light bulk tester.
These things are very strange.
Has anybody an explanation for what is happening?
Best regards - Rudi_Ratlos
Dear DX Blame friends,
after adjustment of the quiescent current (to about 50mA) and measurement of the DC voltage on the speaker's output (between 3 and 6 mV),
I powered up the 1st channel of my DX Blame MKII:
and - Aaarrrgh: Smoke coming from the PCB.
I forgot to unsolder the 100 Ohm resistor, that I used during the adjustment procedure, and this resistor melted away
.The fuse, that I inserted into the fuse-holder after my adjustments have been completed, is 2A. I measured it; it is o.k.
This should have never happened, because the current is flowing through the fuse now!
I am using 15.000µF power caps, and the power to the PCB is currently delimited to <60 Watts by means of my light bulk tester.
These things are very strange.
Has anybody an explanation for what is happening?
Best regards - Rudi_Ratlos
Patrick,
I have been able to adjust the quiescent current according to Carlos recommendation, I measured very little (2-7mV) DC on the output, ...,
the AMP worked as designed during the adjustment phase.
When I connected a source and a speaker to it, something happened.
Moreover: I am currently no more able to adjust the quiescent current to "low values" (about 50mA).
The minimal quiescent current, that I can achieve when I turn the BIAS trim poti to its maximal value (500 Ohm), is about 80mA.
This is strange as well.
I did a mistake somewhere. But currently I have no idea, where.
Best regards - Rudi_Ratlos
I have been able to adjust the quiescent current according to Carlos recommendation, I measured very little (2-7mV) DC on the output, ...,
the AMP worked as designed during the adjustment phase.
When I connected a source and a speaker to it, something happened.
Moreover: I am currently no more able to adjust the quiescent current to "low values" (about 50mA).
The minimal quiescent current, that I can achieve when I turn the BIAS trim poti to its maximal value (500 Ohm), is about 80mA.
This is strange as well.
I did a mistake somewhere. But currently I have no idea, where.
Best regards - Rudi_Ratlos
DIY picture of the month ...
... or re-definition of Ohm's Law.
The rail-current is not flowing through the fuse (which is intact) - that would be too easy -, but through the 100 Ohm resistor,
that I used during the setup procedure, and melts the resistor.
I measured the fuse afterwards: it is o.k.
http://www.abload.de/img/fusexey2.jpg
Best regards - Rudi_Ratlos
... or re-definition of Ohm's Law.
The rail-current is not flowing through the fuse (which is intact) - that would be too easy -, but through the 100 Ohm resistor,
that I used during the setup procedure, and melts the resistor.
I measured the fuse afterwards: it is o.k.
http://www.abload.de/img/fusexey2.jpg
Best regards - Rudi_Ratlos
Soon you will find the bug...check AC voltage in the output terminals
Maybe you gonna need more compensation because of different transistors and different board.... if you obtain AC in the output, without signal entering, then increase the Miller capacitor till this stops.
Good luck.
regards,
Carlos
Maybe you gonna need more compensation because of different transistors and different board.... if you obtain AC in the output, without signal entering, then increase the Miller capacitor till this stops.
Good luck.
regards,
Carlos
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