After reading that there was another version of the BA735 with both analog and digital inputs, I looked at the pc board in the speaker and realized the board of the digital-only version has component locations for analog as well. Whether it's worth your time to modify is up to you - I did because I like the speaker system and enjoy the challenge. You will need to add 5 components - 2 surface- mount resistors, 2 surface-mount caps, and a right-angle stereo 3.5mm jack. You may also need to scrape away some of the potting goop they used to secure the jack assembly. I used 33k ohm for R10 and R16. The existing feedback resistors are 75k, so this gives the amp stage a gain of a little more than two - this seemed to produce good results - use smaller values for R10 and R16 if you want more gain. I used 4.7uF non-polarized capacitors for C25 and C38 (Boston probably used electrolytics here). The more challenging work involves the audio input jack. All 3.5mm types I found with this pin placement had the normally-closed and signal-in pins reversed from what this board wants. As such, I had to bend the inner pins outward to reach the holes intended for the outer pins. I also bent to outer pins to the side and soldered small leads from them to the extra holes inboard from the inner pins. Sounds confusing, but if you look at the jack data sheet and the board traces, it makes sense. I used a CUI SJ1-3555 jack (Digi-Key CP-3555NG). Perhaps you can find another jack that has the pins reversed and would make the modification easier. I did not add C20 to the board...looks like there are already a couple 470uF caps in parallel with C20 as it is. That's it - the circuit is smart enough to detect an analog audio in signal and pipes that to the amplifier. I could find no schematic diagram for this product, so I need to guess at the component values. Someone that has an actual dual input (analog and digital) version may want to open it up and see what component values Boston really used here, but this seems to work fine.
Thread Recap (last 10 posts from newest to oldest)
Apr 03, 13 at 3:03pm
Hello ! to All
Thanks to all for the valuable information for modifying the BA735 Speakers.
These Digital Speakers were found in the trash and retrieved by a friend of mine.
I hooked them up with a Digital Audio Coax Cable to my computer and worked fine!
So I attempted to modify them with the information found in this forum.
I used 2 4.7 uF caps and 2 33K ohm, 1/2 watt resistors.
Instead of mounting a jack to the board I soldered a 3/c cable to the pads.
They are working and sounding great with the analog input from my Ipod Video.
I meant to take pictures of the finished modification, but I was anxious to see if they would work properly, which of course they did!
I may still open it back up and take pictures if any one is interested.
REYESFA or MAD MAXX or anyone who has a copy. Thank god for this. It is awesome.
SO happy to not be alone in my endeavors!!!!!!!!!!!!!!!!! Picked up two sets the same day out yard saling and both have this awfull hum. The c59 caps were called out on another forum as being the culprit but replacing them only cut the hum in half.... but that is another story. Of these two there are one dual input and one digital so I am in the middle of the mod. My intent is to use this attached to my phone and computer, two different input amplitudes though so the phone is queiter than the computer. Does anyone suppose that the smt resistor could be replaced with a stereo pot to allow for input gain adjustments????? And does anyone have the ability to share the schematic??? Any input would be appreciated. email@example.com
Thanks to everyone, including the digikey P/N's
Dec 01, 12 at 5:30pm
Got the schematic from José. Thanks so much. Greatly appreciated.
Dec 01, 12 at 4:23pm
I'm new to this thread but want to mod my BA735s as well. I wonder if reyesfa or Madd Maxx could send me the schematic as well. I'd be very greatful. Thanks.
Oct 28, 12 at 12:58pm
Yes, Madd Maxx, Could you please try sending it to me in case Jose's email still won't come through for some reason. Thank you both very much for trying to get it to me. firstname.lastname@example.org
Oct 25, 12 at 6:37pm
You're welcome Max,
Maybe you can try to send it to BDPowers?
thanks for your help, José
Oct 25, 12 at 6:14pm
I got the schematic. Thanks so much Jose.
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