Bose 601 Series III Poor Sound

[batusenn]

Hello i have a pair of bose 601 series iii speakers they sound really good with my pioneer vsx-808 even at high volumes but when i connect them to my sony ta-n55 power and ta-e77es pre amp after quarter volume they start to make different sounds and volume is decreasing by itself. But i have 5 more pairs of speakers when i connect them to my sony amps i dont have any problems with sound and volume. I also connected speakers as mono but problem is still same. I think the problematic part is bose speakers. Can you please give me any idea ? Firstly im thinking of changing capacitors of bose but i cant find any schematic what kind of capacitors i should use ?

 

[eiraved]

Welcome to AK!!
Are you sure you had no loose strands on your speaker wires when connecting to the Sony? Were you using only the pair of Bose or were you using 4 speakers when this issue occurred? What music source(s) were you using when the issue occurred (tape, CD, LP, etc...)?

 

[Stuart Pedaso]

601 III has a built in protection circuit that lowers volume output when excessive power input could otherwise damage the tweeters. The circuit consists of a lamp connected in parallel with a thermal resistor (RT-1 & K-1) seen in the schematic below.


If you have the equipment, the circuit can be tested for correct function according to the service manual procedure:

As to crossover capacitors, there is only C1 as shown in the schematic above. If it's a film capacitor then it's unlikely to have degraded over time. If it's a non-polar electrolytic you might consider replacing it with either a fresh electrolytic or a film cap. The capacitance value of the cap could be one of three possible, as it has varied over production life of 601 III:


Replace with whatever value is found installed in your speakers. Though a failing capacitor probably wouldn't cause the symptoms you're experiencing.

 

[batusenn]

Thank you so much sir @Stuart Pedaso

 

[batusenn]

@eiraved i was listening to cd on technics sl-ps900, after that problem happened i connected my computer with aux, then i used other inputs on my pre amp but nothing changed. Also i tried 2 outputs of my cd player fixed and variable. After this problem when i connected other speakers no problem with cd player, aux and other inputs. I also would like to add my power amp never turns on protection mode.

 

[eiraved]

@Stuart Pedaso is on to something and hopefully following up on it takes care of your issue.

 

[batusenn]

@eiraved thank you so much too sir

 

[Ziinda]

I have to add that I have found more likely to have large ceramic resistors run out of spec than any other component in crossovers. Most people won't even check them and just replace the caps. The failed resistors I've found were reading in the "k" ohms while rated to be 1 to 8 ohms. That value could change once they warm up too.