AlgoRhythms

Boston Acoustics A70 schematic

9 posts in this topic

Just picked up a decent condition pair of Boston Acoustics A70s for my first restoration project.  I want to develop some chops before tackling something more challenging.

 

Does anyone have a BA A70 crossover schematic?

 

(I had a pair of A40s back in the 1980's and really liked them.  It was the first and only pair of speakers I ever bought without listening to first.  I read the Richard Heyser review in Audio. )

 

Thank you.

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Are you just looking to replace the capacitors?

If so, you could just pull the crossover to verify the capacitor value.  I believe there is just one capacitor in each crossover.

The next question becomes electrolytic vs. film capacitor for the replacements.  Film capacitors are larger, so do not always fit in the existing positions on the crossover.

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Yes, that's exactly what I'll do if I dont fina a schematic.

I most certainly will replace the caps.  I haven't looked inside yet, wanting to see what the paper looks like.  If there are inductor(s) and resistors, I'll replace them as well.

As fare as film vs 'litics..... not sure what way I'm gonna go.

 

Thanks for your reply.

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Looking to know what the value of the inductor is.  I can't tell from seeing it as its covered with hot glue.

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Inductors and resistors generally do not go "bad" like electrolytic caps can over time.

if the intention is a restoration, not sure I would mess with the inductors and resistors, as just the caps would need to be restored (replaced).

 

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16 hours ago, AlgoRhythms said:

Yes, that's exactly what I'll do if I dont fina a schematic.

I most certainly will replace the caps.  I haven't looked inside yet, wanting to see what the paper looks like.  If there are inductor(s) and resistors, I'll replace them as well.

As fare as film vs 'litics..... not sure what way I'm gonna go.

 

Thanks for your reply.

If you're bent on replacing the coils, you'll need to have or find a way to measure what's in there because most coils are not identified. It's most likely an iron or laminate core coil. Those don't go bad over time like lytics do. However, If you want to consider upgrading the coil to a copper foil coil (not sure if this speaker is worth the expense), then It may be worth the effort to determine what the mH and DCR values are of what you have and duplicate them a closely as possible. 

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No, I don't know if i will change anything until i open them up and measure.

I just like having the schematic to look at as its easier to understand than tracing out the circuit from a blob of glue.

I consider these speakers a platform for practicing restoration before attempting an AR or KLH.

 

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I don't think BA's have gotten the attention that AR and Advent has over the years. So, the dearth of xover info. 

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Yeah,  Knowing factory values and layout would be helpful in order to insure that left/right time constants match.

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