Pass B1

[TheCoolestOne]

mbhangui, thanks for the update. I will try and replace the transistor if required or swap one from an unused source.

What is your take on the voltage for B1. Can it be reduced to 18v. I read in an earlier posting by Om that a 18-0-18 tarafo would have sufficient to power it up.

Unfortunately my rotel power does not have a volume control so it is a slave to a pre.

 

[mbhangui]

mbhangui, thanks for the update. I will try and replace the transistor if required or swap one from an unused source.

What is your take on the voltage for B1. Can it be reduced to 18v. I read in an earlier posting by Om that a 18-0-18 tarafo would have sufficient to power it up.

Unfortunately my rotel power does not have a volume control so it is a slave to a pre.

removing a component is more tedious. If I am not mistaken, you have kept short legs on the transistors fitted to the source selector kit. Though not a problem if you are careful, but little more heat and you could damage the good transistor. Better replace it with a new one and keep the soldering iron for as short duration as possible when soldering the three legs.

the b1 can be powered by any source of 18-24 v. I am running it at 18v. The preamp typically draws fewer that 0.02 Amps, so current is not much of an issue. If you want a little thump and gain, you could try the SSP kit from Sachin. I have added that in the same cabinet and Bibin has made the appropriate holes for add the SSP in the cabinet. The power supply which you already have also has provision to supply 15-0-15 volts for the SSP. See the picture of my B1 build in my earlier post.

To connect the SSP, remove the volume control connection to B1 and connect it the SSP board. So the volume control will control the the input to the SSP. Short the CW and W points on the B1 (i.e. run pass b1 on full volume) or alternatively connect the SSP output to the 'W' points on the B1 board.

EDIT: You could leave the volume control as it is (i.e. volume control controls B1). Output of the Source selector goes to SSP. Output of SSP goes to the input on B1. Sachin has suggested connecting 1M shunt on the SSP input.
See the post http://www.hifivision.com/diy/21036-pass-b1-128.html

 

[omishra]

1. The source selector board has 7812 regulator. You can also have the voltage as 13v to waste less heat.

2. This could be issue with the transistor. I am also having some issue where 3 leds light up and they become ok after 30 minutes of use.

For 7812 to work, its input must be >14.5V

For 1 st position it might be connection problem. If transistor is bad then relay too won't click. So keep in that position and do power on/off after waiting 15sec of each step. You should hear relay clicking. If not then transistor is faulty or its selector wire is not carrying 12V from selector switch.

Actually you don't need extra wire for LED.

Please see this post. (from http://www.hifivision.com/diy/27797-diy-enclosure-cabinet-poweramp-preamp-43.html)

RCA:


PS:


LED:


Note: Labels (LEDs) on front plate needs to be connected appropriately to the matching labels (RCA) on the back plate. It is in reverse order on the back plate.

Connections are as follows:

LED 1 -> RCA 5
LED 2 -> RCA 4
LED 3 -> RCA 3
LED 4 -> RCA 2
LED 5 -> RCA 1

Also we needed to do following tweaks: (which may help others)
1. The diameter of shaft of volume control is bigger than hole on acrylic front plate of my cabinet. It was filed to make bigger.
2. The length of shaft of selector knob falls short. It is too short to reach the grub screw position which is on front of knob. This is due to wooden face plate thickness. So others using wooden plate please take a note. Plan to do some tweak here.

Hope this helps.

Thanks,
Rohit

http://www.hifivision.com/diy/27797-diy-enclosure-cabinet-poweramp-preamp-43.html#post496458

 

[TheCoolestOne]

For 1 st position it might be connection problem. If transistor is bad then relay too won't click. So keep in that position and do power on/off after waiting 15sec of each step. You should hear relay clicking. If not then transistor is faulty or its selector wire is not carrying 5V from selector switch.

Actually you don't need extra wire for LED.

Please see this post. (from http://www.hifivision.com/diy/27797-diy-enclosure-cabinet-poweramp-preamp-43.html)

Om, we did check for the relay click. That's the first thing Santy checked when the LED didn't switch on. We then cross checked the soldering and finally we checked the connection hooking on a source to the first set of inputs and then to all the others and all the inputs worked flawlessly. That's why we were confused. I personally did not want to remove and solder any component over a LED before I took advice from you and other members who had completed the build.

With reference to the wiring for the LED's we did have a look of Rohit's build but by the time we referred to it we had already soldered all the LED wires on the SS board so we went ahead without making any changes . Your method does look neater but then we didn't want our hard work go to waste so we continued ahead with the build hyeah:

 

[TheCoolestOne]

If you want a little thump and gain, you could try the SSP kit from Sachin. I have added that in the same cabinet and Bibin has made the appropriate holes for add the SSP in the cabinet.

Thanks for the suggestion. I will keep that in mind. I believe that is why many of the FM's in the earlier builds went ahead with a SSP along with the Pass B1. I guess here is where Om 'double decker' B1 also scores above the rest.

Let me enjoy the B1 as it is right now and then start experimenting on it. Let me try the B1 on different setups too. It will help me get a bigger picture. As of now I happy with all other aspects of the B1.

 

[omishra]

By another thought, I hope you verified the LED polarity and connected wires too. Remember longer lead is anode. Or I look into LED and see lead connected to larger surface area is cathode (-ve).

 

[TheCoolestOne]

Om. I had checked that possibility too.

I think I need check the PCB track properly once again as I remember that earlier I had placed the LED on the PCB itself for testing and had then de-soldered to remove it. I do remember checking thoroughly for any breaks in the track before completing the build and Santy too had cross checked before we finished soldering the wires. Will open up and check over the weekend.

 

[Santy]

had changed the regulator IC (thanks to Sachu) but my selector wouldn't work.
When it worked earlier (by shorting pins 1 & 3) the first LED would not glow.
I am thankful to thecoolestone for giving me the spare selector kit. I hope it has all the parts. Going to redo that board when I get time.

 

[Santy]

switch.

Actually you don't need extra wire for LED.

Please see this post. (from http://www.hifivision.com/diy/27797-diy-enclosure-cabinet-poweramp-preamp-43.html)


http://www.hifivision.com/diy/27797-diy-enclosure-cabinet-poweramp-preamp-43.html#post496458

Damn. I didn't think about it.
So why did you give those slots on the board in first place.
BTW now I will try since I am redoing the selector kit

 

[mbhangui]

Damn. I didn't think about it.
So why did you give those slots on the board in first place.
BTW now I will try since I am redoing the selector kit

If you connect it as per the slots on the board, the led light up only when the transistor start conducting. When the transistors start conducting the relay also switches on. If there is any fault with the transistor (i.e if it is conducting without applying any voltage to the base), the led will light up. The other connection which has been done by rohit, the leds will light up only as per the selector position.

I had a problem where 3 of the transistors were conducting (low voltage between collector and emitter) without applying any bias to the base. This I came to know only because I had connected the led to the board slot (but it makes wiring lengthy from the board to the front panel). It would hence be good to connect the leds to the board slot to detect any issue later where a relay gets on without selecting that position. I will draw the circuit diagram by hand and post it here later. The circuit diagram makes it very clear.

 

[magma]

Hi Magma,
they are solid Aluminium knobs made by FM nraghunadh.

Regards,
Sachin

yep i guessed AL
because they are very similar to the ones i had done earlier
in fact i still have some somewhere with some extension rods and spikes

 

[TheCoolestOne]

Damn. I didn't think about it.
So why did you give those slots on the board in first place.
BTW now I will try since I am redoing the selector kit

Santy we did have a look at that but by then we had already soldered the LED wires. In the worst come worse scenario if all else fails I plan to do the same at least for the 1st LED. Without the LED light the B1 looks dead as there is no way of telling whether the unit is off or on :sad:

 

[spirovious]

Santy we did have a look at that but by then we had already soldered the LED wires. In the worst come worse scenario if all else fails I plan to do the same at least for the 1st LED. Without the LED light the B1 looks dead as there is no way of telling whether the unit is off or on :sad:

I connected LED directly to 24V power supply connector with one resistance in series.I am not sure about the value as it was there with my old amp.So LED lights when SSP is turned on.

 

[mbhangui]

Sachin/Om,

I have few doubts regarding SSP and B1. What is the input impedance of the SSP? I have connected 50 K volume pot to the SSP. Will it be better if i connect the pot to the pass b1 instead? If yes, one of the post mentioned connecting 1M resistors as shunts on the ssp input. Why is the shunt required?

 

[omishra]

Sachin/Om,

I have few doubts regarding SSP and B1. What is the input impedance of the SSP? I have connected 50 K volume pot to the SSP. Will it be better if i connect the pot to the pass b1 instead? If yes, one of the post mentioned connecting 1M resistors as shunts on the ssp input. Why is the shunt required?

Input impedance of SSP -

• With volume control is equal to value of volume control.
• Without volume control, its equal to input impedance of your OPAMP. That is somewhere >1MOhm. Here you have to add 1MOhm resistance from W to Gnd because it makes ground reference to OPAMP input. That way settles output offset to minimum, ideally 0. Avoids pop of input on/off. This also makes input impedance 1Mohm.

To get benefit of maximum input impedance you should connect like this -
I/P=>SS=>selected I/P=>SSP(case 2 of above)=>B1 with volume control=>O/P

 

[captrajesh]

To get benefit of maximum input impedance you should connect like this -
I/P=>SS=>selected I/P=>SSP(case 2 of above)=>B1 with volume control=>O/P

What would be the order if the LSA comes into the circuit?

 

[omishra]

Any Volume control could be surrounded by two buffers
Buffer-> Volume control -> Buffer
Buffer could be either SSP or B1.

What would be the order if the LSA comes into the circuit?

If you connect like this -
I/P=>SS=>selected I/P=>SSP(case 2 of above)=>(B1+LSA in place of Vol Ctrl)=>O/P
then it comes as
SSP (input buffer) => LSA (Vol Ctrl) => B1 (output buffer).

Generally all sources are happy to drive impedance of >25K. So we can exclude input buffer and connect like this -

Inputs=>SS => (B1 with Volume Control of 47K) => output.

Still having two buffers is another level of enhancement.

 

[hydrovac]

I was looking around for quite some time trying to find a simple buffer to drive my high gain power amplifier. Too much gain is a curse that afflicts many systems. It's always seemed nuts to me to throw away most of the signal as it comes in then amplify it again, which is what a normal preamp does most of the time.
The B1 starts with the premise that there is enough gain already and that the only tasks of a preamp are switching, impedance matching and attenuation (not amplification), with attention paid to maintaining the musical integrity of the signal (including nuance & timing) that can get lost on the way through.

Ordered the kit from Sachin. Good quality components. PCB is the best I have seen. This is my first put together Pass B1 buffer preamp. Cabinet is an all-metal case with 8mm anodized alloy faceplate(final).

Few pics of the build.

 

[sachu888]

Very neat build,minimum wiring,great work:clapping:

Regards,
Sachin

 

[mbhangui]

Hydovac,

Must commend on a clean, neat build. Admire the pains that you have taken to make a neat build and use high quality components