Information request for modifying Bose 401s

[SpineyNorman]

Unfortunately, they aren't on the reverse of the terminal block.

 

[Galu]

That's a good view of Bose's wire wrapping technique though!

 

[SpineyNorman]

I guess I am left with having to gently remove the two drivers and the tweeter, remove the poly-fill, and search for the caps that way.

 

[Galu]

Yes, you have no other option.

Are the connections to the woofer terminals wire wrapped?

If so, and you require to disconnect the woofers for ease of access, please note my remarks in post #15.

Oh, and take careful note of which colour of wire goes where!

 

[6thplanet]

 

[Galu]

That's handy!

As I hinted at earlier (post #7), there may be two protection lamps as explained in the centre image.

 

[SpineyNorman]

View attachment 1289422 View attachment 1289423 View attachment 1289424

I have searched for the Bose 401 Service Manual, and have only found the Owner's manual which, for this task, is useless.

 

[SpineyNorman]

Yes, you have no other option.

Are the connections to the woofer terminals wire wrapped?

If so, and you require to disconnect the woofers for ease of access, please note my remarks in post #15.

Oh, and take careful note of which colour of wire goes where!

Yes, I believe the woofer connections are wire-wrapped. I will take your advice from #15 as well as the wire colors and their path! Since I am going this in-depth, would it make sense to replace all of the wire with one of a heavier gauge?

 

[SpineyNorman]

View attachment 1289422 View attachment 1289423 View attachment 1289424

Will you provide the legend for the exploded speaker diagram?

 

[Galu]

legend

The parts you are interested in are clearly labelled, i.e., C1, RT1 and R1.

Where C1 is a capacitor, RT1 is a lamp and R1 is a resistor (but may be a second lamp).

 

[SpineyNorman]

BTW, my 401's are from 1987. I would guess that Bose intends/intended for their speakers to have a long lifespan, so I wish they had included in their design a way to easily access and change the caps which do fail!

 

[Galu]

would it make sense to replace all of the wire with one of a heavier gauge?

Heavier gauge is really only a requirement for a long run of wire such as the cable from amplifier to speakers.

The resistance offered by the short lengths of the current internal wiring is negligible.

Replacing the wiring risks making mistakes, especially if you are a novice.

If you do choose to go ahead, 18 gauge is thick enough for internal wiring.

A heavier gauge can make soldering difficult and its weight may put undue stress on the driver terminals.

 

[Netlist]

BTW, my 401's are from 1987. I would guess that Bose intends/intended for their speakers to have a long lifespan, so I wish they had included in their design a way to easily access and change the caps which do fail!

For a technician, this is a no-brainer, but I understand it's not that straightforward for a DIY-er.
Good luck, I'm sure you'll succeed.

Hugo

 

[GM]

Right, wire sizing is all about voltage drop over distance, so even high power rated speakers need surprisingly small internal wiring with the proverbial lamp cord being way overkill in most speakers, (sub) woofers.

 

[SpineyNorman]

Do you guys have suggestions of places where I can source those caps, resistors and lamps?

 

[SpineyNorman]

For a technician, this is a no-brainer, but I understand it's not that straightforward for a DIY-er.
Good luck, I'm sure you'll succeed.

Hugo

I have re-wired many electrical components and also rebuilt and refurbished vintage radios (hobby only). I build my computers, too, so I have no problem working with electronics. I just like acquiring as much knowledge and tips as possible from those who have more experience than me with particular items!
Thanks!

 

[Cal Weldon]

I find this part of the circuit interesting. If it were removed, I wonder if that might help with the 'dull' sound?
The tweeter might need more protection though?

 

[Galu]

Lamp here (mentions red dot in description): https://www.ebay.com/itm/1337608652...lp:4247815&itmmeta=01HSK6BQZ9TT6V20MMR7V8QY3A

indianajo mentioned Parts Express where you will be able to source any other components.

However, let's wait and see what's actually inside your cabinets!

 

[Galu]

I find this part of the circuit interesting.

Yeah, I was going to ask about that!

What it does do is to furnish a good reason not to replace the existing wiring!

 

[Galu]

I find this part of the circuit interesting.

Could it be there to add inductance in parallel with the tweeter to form a second order HF crossover?