Axess Electronics BS2 buffer/splitter

drmathprog · Post by **drmathprog** » 24 Jan 2008, 13:16

I'm not so interested in the splitter, but does anyone have any information on the design of the BS2 buffer? I've been assuming it was an elaborate circuit of some sort rather than a simple buffer stage, but after seeing how simple some of the boutique OD/distortion circuits are, perhaps I'm wrong.

soulsonic · Post by **soulsonic** » 24 Jan 2008, 17:56

Judging from the description, there doesn't appear to be anything fancy happening in there. Most likely, just a standard textbook opamp buffer circuit. Since it recommends against using a switcher supply due to reports of some of them damaging the unit - that tells me that it also likely uses a MAX1044 to run the opamp on a bipolar supply, since those voltage converters seem to be prone to damage from funny voltages (though they could easily protect it, if they'd take the time to do so).

Oh, and this:

The BS2 Guitar Audio Buffer/Splitter prevents the loss of: (1) signal level (2) high end frequency response (3) low end punch that is caused by cable capacitance and poorly designed input stage/circuitry of some effect pedals.

These performance characteristics are typical of nearly all opamp buffers.
I like that the BS2 comes with a transfomer isolated out; that's a nice feature to have. If they have a nice transformer in there, then the price is probably pretty reasonable too since transformers can be expensive. Though, if you weren't interested in the transformer, you could probably roll your own for less than $20.

seniorLoco · Post by **seniorLoco** » 25 Jan 2008, 01:01

I have seen the guts and it's opamp indeed

sorry no pics tho ...

drmathprog · Post by **drmathprog** » 25 Jan 2008, 01:19

Sorry for the newby question; I don't understand the significance of the transformer; why is that good?

seniorLoco · Post by **seniorLoco** » 25 Jan 2008, 02:37

transformer to eliminate troublesome ground loops inducing buzz, hum, noise ...

Lovepedal Detective · Post by **Lovepedal Detective** » 25 Jan 2008, 16:46

I don't believe there is a MAXX chip in there. I used to have one, and don't remember seeing a voltage doubling circuit. It was awhile ago though.

LPD

soulsonic · Post by **soulsonic** » 25 Jan 2008, 19:18

Lovepedal Detective wrote:I don't believe there is a MAXX chip in there. I used to have one, and don't remember seeing a voltage doubling circuit. It was awhile ago though.

LPD

Okay, it may not have one... I'm just guessing here. Though that does make me wonder even more why they'd have a prejudice against switching supplies. It's so easy to add some simple cheap regulation that would not only remove the noise, but also protect the circuit from any power irregularities. They're missing an important piece of the design puzzle if a certain style of power supply causes them to fail frequently.

Maxwell · Post by **Maxwell** » 25 Apr 2009, 23:19

I'm interested in this buffer circuit as well. I can post an a schematic I've traced so far...but I'm sure it has mistakes. If others will help iron them out, maybe we can come up with a decent clone circuit. The two IC chips have the names removed, so the main thing confusing me is trying to understand what their pin configuration is (single dual etc). Plus the board is really small and multi-layered. Is it possible to deduce the pinouts by looking at the circuit?

The reason I'm interested in this particular buffer circuit is that it sounds good for 9VDC, and I want to use it in a custom amp switcher project I'm working on.

Maxwell · Post by **Maxwell** » 26 Apr 2009, 18:44

soulsonic wrote:Judging from the description, there doesn't appear to be anything fancy happening in there. Most likely, just a standard textbook opamp buffer circuit. Since it recommends against using a switcher supply due to reports of some of them damaging the unit - that tells me that it also likely uses a MAX1044 to run the opamp on a bipolar supply, since those voltage converters seem to be prone to damage from funny voltages (though they could easily protect it, if they'd take the time to do so).

I believe you are indeed correct. Analyzing the circuit, I see there is an IC chip in there (name removed) that converts the + 9V DC input to (approx) +/- 9VDC in order to power the op amp buffer.

jimosity · Post by **jimosity** » 06 May 2009, 13:36

I've got gut shots if anybody can help me figure out what the IC chips are; there are two of them.

Here's pics.

Bernardduur · Post by **Bernardduur** » 06 May 2009, 14:22

What did they use to sand off those IC's? They look really 'well' sanded off

RnFR · Post by **RnFR** » 06 May 2009, 14:24

wow they did quite a job on those IC's. i've never seen anyone ever sand off that much material before.

jimosity · Post by **jimosity** » 06 May 2009, 14:36

My GRX4 is the same way...I'm hoping I can figure out what those are as well.

JimiB · Post by **JimiB** » 06 May 2009, 20:11

holy crap looks like they took a belt sander to em!

soulsonic · Post by **soulsonic** » 07 May 2009, 06:44

Here is a traced schematic provided anonymously by a forum member. He's verified it on breadboard and says it works and sounds exactly like his original.

: Axess BS2

Maxwell · Post by **Maxwell** » 11 May 2009, 15:56

Cool Thanks! Now I can correct some of the mistakes in my own trace... One thing I'm not sure about is C7 - I have mine connected to a different ground plane but that could be wrong.

I take it that although it certainly is a dual op amp, the 5532 is not verified? If it was I'd be curious about the designer's choice use of using 1/2 of the 5532 dual op amp when a 5534 with a compensation cap could work instead...but then I suppose using a comp. cap would be giving out a clue to the chip's identity.

Krinkle · Post by **Krinkle** » 11 May 2009, 17:02

From what I read in the data sheets, 5534 is not recommended for unity gain due to possible instability, which is how this circuit is operated.

soulsonic · Post by **soulsonic** » 12 May 2009, 06:59

Honestly, you could probably build this with nearly any chip and get pretty much the same sound.

Krinkle · Post by **Krinkle** » 12 May 2009, 14:34

soulsonic wrote:Honestly, you could probably build this with nearly any chip and get pretty much the same sound.

+1

Maxwell · Post by **Maxwell** » 16 May 2009, 03:00

Yeah I know, though adding a 22pF capacitor between pins 5 and 8 you can use the 5534 at unity.

Krinkle wrote:From what I read in the data sheets, 5534 is not recommended for unity gain due to possible instability, which is how this circuit is operated.