Neoseeker.com Forum Thread: modify BA735 for analog input - page 1

reprinted from http://www.neoseeker.com/forums/
original thread: http://www.neoseeker.com/forums/153/t846623-modify-ba735-for-analog-input/


Author:   hitest
Date:   Mar 01, 07 at 5:31pm (PST)
Subject:   modify BA735 for analog input
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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.



Author:   Jatt
Date:   Mar 03, 07 at 4:36am (PST)
Subject:   re: modify BA735 for analog input
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Ya i have the Dual version with 1 Analog and 1 Digital input.



Author:   Ruinous
Date:   Mar 29, 07 at 2:34am (PST)
Subject:   re: modify BA735 for analog input
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I have the BA735 with dual inputs and one with digital only. I was wondering what information to look for in the dual input pair to add analog-in to the other digital pair.



Author:   hitest
Date:   Apr 26, 07 at 11:01pm (PST)
Subject:   re: modify BA735 for analog input
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You should look at R10, R16, C25, and C38 to see what values were originally used. Also, look if C20 is installed on the dual units and if so, what value.



Author:   bobdylan17
Date:   Jun 04, 07 at 4:06am (PST)
Subject:   re: modify BA735 for analog input
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Any chance you could supply some pictures to help me with this modification?



Author:   bobdylan17
Date:   Jun 11, 07 at 3:45am (PST)
Subject:   re: modify BA735 for analog input
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Well, I got them working after a round of very carefull soldering. The hardest part was not loosing the resistors as they are so tiny. Thanks for the tip. Now I can continue to enjoy these speakers with my analog sound card.



Author:   bigbill53
Date:   Jun 30, 07 at 11:37pm (PST)
Subject:   re: modify BA735 for analog input
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thank You hitest I went to radio shack picked up some parts close to your recommended values and now my speakers work. i used 30k 1/2 watt and .47uf caps they were a little large but they fit.



Author:   jeff price
Date:   Oct 01, 08 at 9:40pm (PST)
Subject:   re: modify BA735 for analog input
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does anybody have the ba735 analog that they could pull apart and tell us the actuall parts used.



Author:   drussell
Date:   Oct 02, 08 at 5:17am (PST)
Subject:   re: modify BA735 for analog input
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if you use the caps and resistors listed above it will not ge loud@ all... I just did mine last night... e very careful when soldering



Author:   dulobast25
Date:   Oct 02, 08 at 5:20am (PST)
Subject:   re: modify BA735 for analog input
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select diff resistor like hitest stated above to adjust gain. This system puts out like 4 watts per channel and like under 8 watts to the sub..you will need all the power you can get. Make sure if you get a jack steer clear of the SJ1-3555NG



Author:   dulobast25
Date:   Oct 02, 08 at 5:22am (PST)
Subject:   re: modify BA735 for analog input
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c20 is missing on both the dual board and the digital only board. Hitest, did you drill out the subwoofer case to access the jack? I never install the "c20" cap.



Author:   hitest
Date:   Oct 02, 08 at 3:34pm (PST)
Subject:   re: modify BA735 for analog input
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It's been quite awhile since I did this modification, but I seem to recall that the rear case needed to be drilled out to access the jack.
I'm pleased to see that several folks have modified their speakers...mine are still working great after 1 1/2 years.




Author:   drussell
Date:   Oct 03, 08 at 5:21am (PST)
Subject:   re: modify BA735 for analog input
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HITEST, why do't you visit here more often? we have questions for you? For instance, i use thos resistor values and my system works, but the volume has to be all the way up for decent sound



Author:   jeff price
Date:   Oct 04, 08 at 12:45am (PST)
Subject:   re: modify BA735 for analog input
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to dulobast: you said that c20 was not on the digital board or the dual board. If you have the dual board can you tell me the exact parts(the numbers printed on the componants and can you tell me if the capicators are polarized.



Author:   hitest
Date:   Oct 06, 08 at 5:13pm (PST)
Subject:   re: modify BA735 for analog input
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As for checking this site, I have only visited when Neoseeker sent an email saying someone has replied to this post. For whatever reason, there haven't been any of these emails for many months until last week.
Addressing the gain question, if we have installed the same resistor values, the gain of the amp should be identical. The first place I would check would be your audio board setup to see if there is a volume adjustment in software that might make a difference. Have you tried connecting a different pair of speakers to see if the audio board is putting out enough signal? Otherwise go ahead and change the resistor values to increase the gain. Since you already have surface-mount resistors installed it is often easier to add a resistor in parallel by just soldering another one on top of the existing resistor, that way there is less risk of damaging the solder pad on the board by repeated removal and resoldering of parts. If you have more 33k resistors, try soldering another one on top of each resistor - that would increase the gain by 2. Or try 10k - 20k for even more gain.
It would still be interesting to hear from anyone with the dual version as to the original values of these parts.



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