Salas hotrodded blue DCB1 build

where are the LEDs on your LED volume control Oliver ? :confused: well i've started building up mine, in the new place now and its about 6-7m to the monitors so thought id try them out. I too have ordered some mills, great resistors, love them and they have that really cool looking hand made chic look too. i'm going to see about getting some from isabellahnute (sp?) for this position also. the boards are going together nicely and quickly, well specced project guys. using TO220 zero recover diodes for the rectifiers at the moment, but considering cutting the trace and using a discrete rectifier stage with a couple of big *** rifa supply caps and suplying DC to the buffers. output resistors are just 1/2W PRP for now
 
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I look forward to hearing your findings Oliver.
I altered the resistor on mine to 5ohms but went back to the 10R; the sound seemed to take on an edge; became very hifi so your opinions will be very interesting.

Yes dvb-projekt,

Your input on the 600mA current setting is much appreciated. I want to really know if going from 200mA (10 ohm) to 600mA (3.3 ohm) is worth it sonically, or if we are already pretty far ahead already.

Best,
Anand.
 
decided to get some 7.5R mills as well as the 10R to just try a bit more current (~266ma) first up and I will parallel another pair for 3.75 to find subjective improvements. what size caps for bypassing the LED refs are people using? is 0.22 a median number have people found improvement by going up to 1uf or higher films here?
 
I finally completed installing all the components in the regulator section, and fired it up. All the LED's lit up. Output voltage measured at +10.58/-10.56. Waited a few minutes...... then I notice a bit of smoke rising!

I shut it down immediately and tried to spot which component was smoking, but no visible evidence. I also noticed that the heatsinks on the postive rail MOSFETS were substantially warmer than those on the negative rail.

I then proceeded to power it back up for a few seconds at a time, and take some quick voltage measurements. What I found was that the total voltage across the three current setting LEDs on the positive rail was 7.6v, and should be slightly under 6v. This would explain why the MOSFETS are running hotter, probably closer to 400ma than 200ma (using 10R current setting resistor).

So it appears that the current being drawn from these LEDs is much too high. Could it be that I have a bad JFET between the LEDS and the 100R resistor that is causing the extra current draw?

The regulator section of my build is now working after replacing all of the components in the current source section of the positive rail. I'm not sure which component was the culprit, but apparently the bad component caused others to fail as well.

It has become apparent to me that managing the heat from the MOSFETs is important considering their proximity to the Vref LED string. At 10R, using Aavid "Big Chief" heatsinks, my build is running a tad hotter than I'd like. Using the 5 second touch test, I can go 5 seconds but not much more. What's more concerning however, is that the Vout drops 2-3 tenths after having run for ~ 5 minutes. I suspect that the heat coming from the "Big Chiefs" is effecting the Vref LED string.

AAVID THERMALLOY|ML524-30-B|HEAT SINK BIG CHIEF TO247/218 | Farnell United Kingdom

At this point I just want to get this project done, so I think I'm going to go with a 15R Iref resistor rather than change heatsinks. However, you guys who used the massive blocks facing away from the Vref LEDs did the smart thing. Live and learn.
 
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The regulator section of my build is now working after replacing all of the components in the current source section of the positive rail. I'm not sure which component was the culprit, but apparently the bad component caused others to fail as well.

It has become apparent to me that managing the heat from the MOSFETs is important considering their proximity to the Vref LED string. At 10R, using Aavid "Big Chief" heatsinks, my build is running a tad hotter than I'd like. Using the 5 second touch test, I can go 5 seconds but not much more. What's more concerning however, is that the Vout drops 2-3 tenths after having run for ~ 5 minutes. I suspect that the heat coming from the "Big Chiefs" is effecting the Vref LED string.

AAVID THERMALLOY|ML524-30-B|HEAT SINK BIG CHIEF TO247/218 | Farnell United Kingdom

At this point I just want to get this project done, so I think I'm going to go with a 15R Iref resistor rather than change heatsinks. However, you guys who used the massive blocks facing away from the Vref LEDs did the smart thing. Live and learn.

I did as Salas suggested and fastened mine to the chassis floor; keeps the heat away from everything.
 
Finally got this thing built now. It's taken longer than I thought what with work and waiting for Texas resistors.

The only real deviation from normal is that I will be using a separate power supply. BC components 3300uF caps in CLCRC. I just happened to have these spare and wanted to use them rather than buying new ones. Transformer will be 50VA R-core 15-0-15V.

Hopefully get it up and running this week. I am slightly concerned with Terry's reports of excessive heat with the Big Chief heatsinks as I will also be using 10R Caddock MP930 resistors. we will see what happens. I have these in the basket just in case:

AAVID THERMALLOY|OS512-100-B|HEAT SINK MAX CLIP - STANDARD | Farnell United Kingdom


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Hi, I just fired up my DCB1 for the first time, and so far it's looking good. I haven't listened to it yet since I haven't put together a dedicated PSU (fuse, switch, xformer...), it's now being powered from my benchtop PSU.

I built the 10R version for now, maybe I'll up the current later. The power resistors I used are non-inductive planar 10R 5w thick film resistors (BI Technologies BPC5100J). The noise figures are comparable with metal film it seems. I just thought I'd give these a try, and since I'm using many fancy flavoured parts (at least for my taste) it fits the bill. I had to remove the original legs, which were some clamp-on soldered types, and fit them with bent copper leads since the original spacing was too small for the board.

The MOSFETs are IRFP140N/9140N. The 5-LED chain is matched to 9.30V/9.29V (values measured in circuit), using 12VDC and 1k in series with it. The 3-LED chain was matched to 5.59V/5.58V (measured in circuit). The 5-LED chains are fed by 2SK170 that I once measured to have an I_dss of 9.42mA/9.54mA. The 3-LED chain is fed by 9.29mA/9.36mA JFETs. The other two JFETs in the shunt section measured 8.49mA/8.39mA.
For the BC550/560 I used ON semi parts since they have the smallest noise figure according to their datasheet.

The resistors at the IRFPs' gates are 470R 5% 0.5W Allen Bradley carbon comp resistors. All other non-audio resistors are MRS25 1% 50ppm 0.6W metal film resistors, except for the 1R resistors which are MF50 1R 1% 50ppm 0.5W metal film.

In the buffer itself I used the following parts: The 2SK170 pairs are matched to 8.02mA/8.00mA (upper/lower) and 7.97mA/7.95mA. The 221R resistors are Vishay-Dale CMF55D and the 1M/221k resistors are Vishay-Dale RN55D.
The relay is a Nais TQ2-5V.

The PSU caps are Nichicon FW 4700uF/35V types, the other electrolytic caps are Nichicon Muse 100uF/50V.
The bypass caps for the 5-LED chain are NCC (Nippon Chemi-Con) FNX-HS 0.47uF/100V film and foil polypropylene. I am using them as the input coupling caps in my headphone amp and I believe they sound right. I left the leads long so they can be easily changed, should I once fell the urge to see if a different cap in this place makes an audible difference.

Now for some numbers I pulled from the circuit (remember, they're fed from a benchtop DC PSU; numbers in brackets are other channel/polarity; voltages in reference to ground unless otherwise noted):

V_input = 19.85V(-19.93V) before rectifier
V_before10R = 19.18V(-19.26V)
V_after10R = 17.85V(-17.67V)

Therefore V_drop10R = 1.33V(1.59V)
and assuming the resistors are R=10Ohm we have a current of
I_through10R = 133mA(159mA)

The first IRFP140 measures -13.66V/-9.95V/-17.67 (pin 1/2/3 G/D/S) and the second one -5.96V/GND/-9.95V

The other polarity's first IRFP9140N measures 13.61V/9.94V/17.58V and the second one 6.02V/GND/9.94V (again pin 1/2/3 G/D/S)

The supply voltage for the buffer is 9.94V(-9.95V) accordingly.

Over the LED chains (not to ground, mind you) I measured 9.30V(9.29V) and 5.59V(5.58V).

After 20 minutes the output offset measures -1mV(-2mV) and seems to stay there; the inputs were not grounded taking this measurement. The heatsinks, salvaged from a SMPS, get warm (maybe 40°C/104°F) but not hot.


One problem I might have to solve is that I didn't have a BC517 on hands and used a BC547 instead. It seems that the relay briefly oscillates before it latches. Not good.
 

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I am going to try a hotrod version also, using another box for the transformer, so my problem is the way to transfer power, AC or DC?

Using DC
transformer >>> rectifiers >>> a big cap of 22000uf (I have alot of them...cheap rubicon)>>> cable 1m >>> one 4700uf (or another one 22000uf?)>>> DCB1
Is this a good configuration?
thanks