DC-Coupled B1 Buffer Build

wushuliu · « **on:** 22 Aug 2010, 02:15 am »

The DC Coupled B1 Buffer (DCB1) is a DIY project designed by Salas and others on the diyaudio.com forum. It based on the popular B1 Buffer Preamp by Nelson Pass, also from the diyaudio.com forum. There are several threads on both projects with hundreds and hundreds of pages, so I decided to do tutorials on both for those who would just like to roll up their sleeves and build.

The DCB1 takes caps out of the signal path and uses a shunt regulated power supply; the goal being greater transparency and improved sound quality. There are many testimonials to the success of this design and personally I have found it to be a worthwhile upgrade to the original B1. Plus all the pretty lights from the LEDs.

The emphasis of this thread is on building the DCB1. If you have technical questions regarding the design itself, I'd recommend posting on one of the main diyaudio.com threads as they are very responsive and far more knowledgeable than I. I'm just a solder slinger with an itchy finger. Many thanks to Salas, Tea-Bag, and others.

Main Threads:

http://www.diyaudio.com/forums/pass-labs/145201-building-symmetrical-psu-b1-buffer.html

http://www.diyaudio.com/forums/group-buys/147075-gb-dc-coupled-b1-buffer-shunt-psus.html (Group Buy)

Boards

The boards are only available from the Group Buy (GB) thread listed above. There have been several versions released already and the latest GB has passed, but you can always ask if anyone has spares and/or petition/sign up for another GB. This is very fluid, so it's just best to keep an eye on that thread.

8/22/10 - There are only about a dozen boards left. If you're going to get em, get em now!!!
Contact Tea-Bag at diyaudio.com. Links below.

BOM

The Latest BOM is Blue Edition v1.0.4. You can source almost all parts from Mouser, Digikey, and Newark/Farnell. The newest board has also been designed to accommodate a greater variety of 'boutique' components.

http://www.diyaudio.com/forums/blogs/tea-bag/attachments/191d1279907485-salas-dcb1-blue-edition-blue-dcb1-v1.0.4.pdf

This link is from Tea-Bag's blog:
http://www.diyaudio.com/forums/blogs/tea-bag/296-salas-dcb1-blue-edition.html

MATCHED/UNMATCHED FETS

You will need 4x matched 2SK170BLs per the BOM. The easiest way to get these would be to contact 'Blues' or 'Spencer' at diyaudio, who sells them. Spencer is probably the better option as you can also get the unmatched SK170BLs from him as well.

Or you can order bulk from someplace like Ampslab and use the DMM measurement setup
to match Idss. You will want 6mA or higher. This will be explained later. If you're eyes are glazing over, then contact Spencer.

http://www.diyaudio.com/forums/swap-meet/131284-toshiba-2sk170bl-sales-49.html

Additional Equipment

DMM (Digital Multimeter) - This is a must for this build. Avoid the urge to cheap out.
As someone had mentioned in another thread, it's not just useful for audio projects, but
for testing AC/DC in any number of situations including home wiring, auto, etc. And look at her with a straight face when you say that and you should be okay. Safety first, right honey!

Solder - I prefer low temp, eutectic solder. Kester is the standard, but hard to find in
smaller quantities. Cardas Quad, however, is available on ebay in 10, 20, and 50ft. spools for dirt cheap. Melts like butter at low temp.

Iron - If you're still new to soldering and have a wonky Rat Shack soldering iron or a single-tip Weller , then an inexpensive upgrade would be this set from Part Express:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=374-100

http://www.parts-express.com/pe/showdetl.cfm?&DID=7&Partnumber=374-102

Best of all, it comes with 4 or 5 different tips (sold separately). I've found the medium sized chisel-tip
to be a godsend for quick and easy soldering. But it's just great to have a size for almost
any situation. And the adjustable temp doesn't hurt either.

10ohm Resistor - for measuring SK170BL fets
1k Resistor - for measuring LEDs

wushuliu · « **Reply #1 on:** 22 Aug 2010, 02:15 am »

So you've got a whole lotta weird looking stuff in a box from Mouser, Digikey, Partsconnexion, etc. and this Baby Blue Board. So we'll just go one component type at a time, one packet a time, and put this thing together.

With the exception of the 4 matched jfets and matching LEDs, the build is straightforward. Values and part names are indicated on the board. However, as some of the components look alike (BC550s, 60s, 517, etc), double check before you solder. What I do is only open one component packet a time, add part to the board, then toss or put away the bag/packet.

I like to start with the lowest height components first. Last thing you want to do is start with the capacitors and then find they're blocking/hampering your access to resistors and LEDs, etc.

Resistors

The BOM linked above provides parts #s and tips for resistors. The new board is designed to accept larger sizes so you have a lot of flexibility.

Note the 470 ohm is vertically placed.

These 4 are critical for audio performance. If you're gonna splurge/upgrade, start here. The BOM
indicates which parts are more critical to sound quality, which is nice.

The values used here will be dependent on just how far you want to push your DCB1 aka HOT-ROD . To be discussed later...

Schottky

Since we're in the area, put in the IN4001 Schottky.
Note the white stripe one side.

Be sure that the orientation of the IN4001 matches the stripe on the board.

MUR120

Note the white line diving the MUR120s. This indicates a jumper is needed. Use some wire or a lead off a component.

12VDC Relay

Plop the Relay in. Then take your iron with a little solder on the tip and solder one of the legs, while your other hand keeps it in place. This will keep it more or less in place and free up both hands agsin. Now properly solder another leg, then another. Be sure to push the Relay in occasionally as you do this until it is seated flush/properly. Repeat until done.

wushuliu · « **Reply #2 on:** 22 Aug 2010, 02:15 am »

TRANSISTORS

There are a number of them used in this design, so once again, deal with one packet/value at a time.

BC560

Note the board shows you how to orient the fets. So be sure the flat of the back and rounded
front are facing the right way.

BC517

BC550

UNMATCHED 2SK170BLs

wushuliu · « **Reply #3 on:** 22 Aug 2010, 02:15 am »

L7812

.1UF Bypass

100UF Caps

Make sure the polarity is correct. Striped side of a cap = Negative (-).

Film or Electrolytic for these.

Power Supply Caps

The new board can accommodate larger sizes and values.

wushuliu · « **Reply #4 on:** 22 Aug 2010, 02:15 am »

MATCHING LEDS

A number of LEDs are used in this design. The goal is to have the voltage from one side of the LED banks match the voltage on the other. Salas recommends using 1.8v LEDs, but you'll notice that the Mouser LEDs in the BOM are a bit higher - around 1.95v. This is acceptable. The main thing is that the total voltage from the LED strings are matched on either side of the board.

The Mouser LEDs are recommended because they are very closely matched, so no need to go order and sift through a 100 LEDs to match the voltages.

However, it's still a good idea to at least test some of the LEDs from Mouser just to be sure the specs are still tightly matched. So here's an easy way to do that.

This is also useful if you have some on hand or would rather run to Radio Shack or another vendor.

You'll need your DMM, 1k ohm resistor and a 9v or 12v battery. I happen to have a AA 12v battery holder, so I used that.

Although not necessary, something to hold the LEDs while checking is useful - in this case I used a cheap dip socket from Radio Shack.

LED

Long Lead = Anode (+). Short Lead/Flat Back = Cathode (-)

Connect one side of the 1kohm Resistor to the Battery (+), the other to the LED (+)
Connect the Battery (-) to the LED (-)

Place your DMM (+) on the (+) resistor and the DMM (-) on LED (-), and record the voltage (DC)

As I said, the Mouser LEDs have been closely matched. To be thorough you should order a few extra and test them all, just in case.

Now start plopping them in. The board has an LED symbol with a flat back/cathode to indicate which direction you're LEDs should be facing.

wushuliu · « **Reply #5 on:** 22 Aug 2010, 02:15 am »

JUMPERS

Several areas on the board are marked for jumpers - just a piece of wire or whatever you have handy.

This one is to be used if you bought a 12v relay.

J2

J3

MATCHED SK170BLS

Next up, the 4 BLs w/ matching Idss. Again, note the orientation as provided by the board

IRFP240

Be sure to not mix up the IRFP240 and IRFP9240s, since they looks so similar.
Vertical/horizontal placement is up to you depending on if you intend to use heatsinks, sink to the chassis, etc.

IRFP9240

INPUT/OUTPUT MOLEX

wushuliu · « **Reply #6 on:** 22 Aug 2010, 02:16 am »

OK, the board's all populated now you need to fire her up!

TRANSFORMER

Here is a cheap 25vct Radio Shack transformer. I have used 2 of them and they work great, no problems but some have reported buzzing issues in the past.

Note the center tap (CT) goes to the middle. If you have a transformer with secondaries, please refer to the manufacturer instructions for wiring the CT.

Since everyone's wiring needs/preferences are different I won't go into the AC/Fuse/RCA/Potentiometer stuff. You're on your own there.

CHECKING THE VOLTAGE

Once you have your transformer and AC all set up, turn on the board. ALL LEDS SHOULD LIGHT UP!
Now, grab your Digital multimeter and check the +/- Voltage. Set your DMM to DC Volts. Place one probe to V+, the other to G. Note the voltage. Should be over 10v. Now check (V-) and G. Should be similar amount. Doesn't have to be exact. If there is a gross difference, you'll need to trouble shoot.

wushuliu · « **Reply #7 on:** 22 Aug 2010, 02:16 am »

Volume Pots

Just a heads up. Unlike the regular B1, there is no on-board input for volume pots. You will want to wire the dcb1 inputs from whatever pot you're using.

Also, for anyone who could use multiple inputs you can check with Tea-Bag at Diyaudio.com for the Mezmerize boards. These are earlier generation boards that allow up to 6 inputs and can connect directly to a selector switch. They also have on-board volume pot wiring.

HOT ROD

Hot Rodding a DCB1 increases the current going to the board. The stock current is around 60mA(?) w/ 34ohms (those parallel 68Rs on each side). But the more current you feed the mosfets, the better the sound quality as a general rule. Salas indicates this occurs in tiers, ~200mA being the next tier, 600mA after that, and then around 2A(!). But there's a catch: Heat. The more current, the hotter those mosfets get. Stock values you can forego heatsinks, but beyond that you'll need them. I'm pushing 600mA on my DCB1, using the entire 12x12 enclosure of my integrated amp as a heatsink with the mosfets bolted to the chassis AND a fan installed.

Is it worth increasing the current. Yes. Definitely the 200mA tier at least. Soundstage, three-dimensionality increases.

How do you increase the current? Resistors. The resistors by the PS caps. The BOM lists parallel 68R (=34ohms) as basic value (though the board shows 47R, which is fine as well), and 10ohm 5W for hot-rodding. You do not use 2 10R per side, just 1. This a guideline, you can increase or decrease values as you deem fit.

If you do Hot-rod, it is recommended to get a slightly larger transformer, preferably a 15v w/ 50-100VA. Also the BOM lists the MUR820 diodes instead of the 120s for hot-rodding. Note their placement by the PS in the pics above.

toxteth ogrady · « **Reply #8 on:** 22 Aug 2010, 07:48 pm »

Nice work, W. I should have my boards by the end of next week.

Sincere thanks for your efforts on this thread and the others you contributed to.

poseidonsvoice · « **Reply #9 on:** 23 Aug 2010, 03:35 am »

Good on you wushuliu!

This is what the Lab forum is all about...

Anand.

GBB · « **Reply #10 on:** 23 Aug 2010, 03:50 am »

It's easier to insert the parts in the board if you bend the leads to exactly the right length. A tool like this turns out to be extremely useful:

You can buy this at various places on the web. Mouser carries a couple of these - part number 5166-801 is for 1/4 watt and 1/2 watt resistors while part number 5166-901 is for 1/2 watt and 1 watt parts. I find that the smaller one is fine for most of my work.

Here are a few other sources:
http://www.productiondevices.com/Speedy%20Bend.htm
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=106884
http://evilmadscience.com/partsmenu/68-bender

---Gary

wushuliu · « **Reply #11 on:** 23 Aug 2010, 09:22 pm »

Quote from: GBB on 23 Aug 2010, 03:50 am

It's easier to insert the parts in the board if you bend the leads to exactly the right length. A tool like this turns out to be extremely useful:

You can buy this at various places on the web. Mouser carries a couple of these - part number 5166-801 is for 1/4 watt and 1/2 watt resistors while part number 5166-901 is for 1/2 watt and 1 watt parts. I find that the smaller one is fine for most of my work.

Here are a few other sources:
http://www.productiondevices.com/Speedy%20Bend.htm
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=106884
http://evilmadscience.com/partsmenu/68-bender

---Gary

That would have been pretty handy alright. Thanks Gary. There really is something for everything.

mjosef · « **Reply #12 on:** 24 Aug 2010, 05:06 am »

Great DIY thread Wu...as I was perusing the pixies, I had a similar thought as GBB...then I saw his post. Never saw that neat tool he mentioned, but you can accomplish the same results using a needle nose pliers...the tapering ends allow for differing lead bend length, simply measure the component against the space on the board, use the pliers to grip where you want to bend and you are done...takes more time than the tool shown, but just about everyone has a needle nose pliers in their toolbox.
Nice job Wushu...

poseidonsvoice · « **Reply #13 on:** 26 Aug 2010, 01:59 pm »

Quote from: mjosef on 24 Aug 2010, 05:06 am

Great DIY thread Wu...as I was perusing the pixies, I had a similar thought as GBB...then I saw his post. Never saw that neat tool he mentioned, but you can accomplish the same results using a needle nose pliers...the tapering ends allow for differing lead bend length, simply measure the component against the space on the board, use the pliers to grip where you want to bend and you are done...takes more time than the tool shown, but just about everyone has a needle nose pliers in their toolbox.
Nice job Wushu...

This is exactly what I do. I seem to have an 'eye' for how much I should bend so it falls in perfectly flat & flush with the board. Just remember that in areas of higher current where the resistor dissipation is more than say 1 watt, you should have the the resistor standing a little bit for better heat dissipation. Probably not really an issue with this build, and more with tube amp builds, etc...

Quote from: wushuliu on 22 Aug 2010, 02:15 am

MATCHING LEDS

A number of LEDs are used in this design. The goal is to have the voltage from one side of the LED banks match the voltage on the other. Salas recommends using 1.8v LEDs, but you'll notice that the Mouser LEDs in the BOM are a bit higher - around 1.95v. This is acceptable. The main thing is that the total voltage from the LED strings are matched on either side of the board.

The Mouser LEDs are recommended because they are very closely matched, so no need to go order and sift through a 100 LEDs to match the voltages.

For the LED's the voltages should match on both sides of the bank, not necessarily be 5.4V DC (for 3 LED's each being 1.8V) or 9V DC (for 5 LED's). Got it, thanks.

Anand.

wushuliu · « **Reply #14 on:** 13 Sep 2010, 05:16 am »

OK, this is about done. I'll add a little info about checking DC Offset. I won't go into wiring specifics since everyone's needs are different and there are plenty of resources for that info.

poseidonsvoice · « **Reply #15 on:** 13 Sep 2010, 01:53 pm »

Quote from: poseidonsvoice on 26 Aug 2010, 01:59 pm

This is exactly what I do. I seem to have an 'eye' for how much I should bend so it falls in perfectly flat & flush with the board. Just remember that in areas of higher current where the resistor dissipation is more than say 1 watt, you should have the the resistor standing a little bit for better heat dissipation. Probably not really an issue with this build, and more with tube amp builds, etc...

For the LED's the voltages should match on both sides of the bank, not necessarily be 5.4V DC (for 3 LED's each being 1.8V) or 9V DC (for 5 LED's). Got it, thanks.

Anand.

I'll second the mouser recommendation for LED's. All the ones I have measured thus far (34 of them!) have been very close to 1.936V or thereabouts. Some are 1.934V but most are within 1.934V to 1.937V, which is super tight matching!

Anand.

toxteth ogrady · « **Reply #16 on:** 13 Sep 2010, 11:17 pm »

I've started to populate my board with the resistors I have on hand. A couple questions...

What is the Hot Rod version you referred to earlier in the thread? I suspect the answer to this question may shed some light on why I have two 47R resistors when it appears the board requires four.

Also, as stated in the BOM I ordered four 68R resistors but I can't find a home for them on the board.

wushuliu · « **Reply #17 on:** 13 Sep 2010, 11:56 pm »

Quote from: toxteth ogrady on 13 Sep 2010, 11:17 pm

I've started to populate my board with the resistors I have on hand. A couple questions...

What is the Hot Rod version you referred to earlier in the thread? I suspect the answer to this question may shed some light on why I have two 47R resistors when it appears the board requires four.

Also, as stated in the BOM I ordered four 68R resistors but I can't find a home for them on the board.

Not sure why there is a discrepancy b/w the BOM and the board w/ these values. But neither value are considered considered hot-rod. Use the 68R resistors.

toxteth ogrady · « **Reply #18 on:** 14 Sep 2010, 12:36 am »

Wushuliu,
Just so it's clear as to which resistors I'm referring to, see the last photo of your 4th reply in this thread; It's the four brown resistors located next to the 4700uf caps. The board is marked 47R x 2 but you're suggesting to use the 68R in their place? Thanks.

wushuliu · « **Reply #19 on:** 14 Sep 2010, 12:45 am »

Quote from: toxteth ogrady on 14 Sep 2010, 12:36 am

Wushuliu,
Just so it's clear as to which resistors I'm referring to, see the last photo of your 4th reply in this thread; It's the four brown resistors located next to the 4700uf caps. The board is marked 47R x 2 but you're suggesting to use the 68R in their place? Thanks.

Yes