Bose 901 Setup - Amp dead, need replacement - recommendation appreciated

[GoldenMaster]

Hi everyone.

I'm really not that big in the HiFi or Audiophile area but I already got a pair of Bose 901 from the 80s and thought it would be a waste throwing them away. 

I know the opinion about these Speakers is divided, I however like them quite a lot. 

Right now my setup is the following (Pictures attached):

2x Bose 901 Series II including (active?) Equalizer,  

Technics SU-V10X Amp
Magnat Quantum 6725A (plugged in via the remote speaker sockets on the Amp)

(and completely irrelevant: The Hitachi PS-38 Turntable)

 

The Equalizer and the Amp are both on 100% "default" settings.

 

So currently the setup still "works" however, the volume shifts without input change, meaning the music gets louder or quieter occasionally without a correlation to other technical systems (TV, iPad, ..) that i was able to observe. 

 

Also sometimes there is a very displeasing high pitched noise that is best noticed when the input is turned off (so no music, just the setup running)

 

I'm a total novice in these topics and English is not my native language so if I explained stuff with the wrong vocabulary please feel free to correct me, knowing the proper terminology helps me search more successfully for solutions on the internet  

 

Due to the problems with the current setup, I was eyeing with replacing the AMP however I do not want to spend more then 700€ on the replacement if possible. 
Now my biggest problem so far was, that I could not find any Amp that would allow input and output as the Technics does to include the Equalizer and I have no idea how else to make sure the signal gets properly adjusted. 

 

Alternatively I am open for suggestions on how to best utilize the Bose 901 Stereo system if the whole system can be purchased with a reasonable price (<1200€) which includes the Sub woofer if possible.

 

Advice on how to properly set up the equalizer and amp to maximize the 901 would also be appreciated. 

 

Thanks for any kind of input in advance

[davide256]

For troubleshooting purposes, have you tested playback without the equalizer in circuit/ use? The symptoms you describe could just as easily

be caused by the equalizer.

[davide256]

I did some looking, seems integrated amplifiers have stopped including tape in/out circuits. The usual place for an equalizer

is inserted between preamp and amplifier. If the integrated amp is bad, you may have to purchase separates .

[GoldenMaster]

For identification purpose I currently have hooked the left speaker on the EQ and the right one is bridged. Still both speakers seem to show the same symptoms. (I initially did it to figure out how the EQ changes the sound but my ear seems to not hear any difference)

 

Currently I have 3 relevant input sources, would that mean I need 3 pre-amps? And whats the price range that should be sufficient? I see they range from 15€ up to multiple hundreds with my quick search. 

And what do you mean with integrated amp? Integrated in the EQ? 

Thank you for sticking with me even though I'm a big novice on these topics

[davide256]

What your current setup does is feed the input source out to the equalizer, which does its job, then passes that altered signal back to the integrated amplifier

so that the volume control can do its job.. All of this is occurring within the pre-amp stage of your integrated amplfier, before the amplifier stage.

This allows you to equalize all inputs the same by sacrificing the tape input/monitor function.

 

A separate preamp and amplifier would allow you to insert the equalizer between the two, different in that you would be equalizing any input used

after volume control was applied. Or an integrated amplifier that had pre out jacks and main( amplifier) in jacks would allow that also. The Bryston

B-60 is an integrated amp example, it has jumpers between the pre out and main in jacks. And I just realized its does have a tape loop function,

perhaps because its relatively unchanged since 2001, so you could use it the same as your current integrated amp.

 

The article below may be helpful

 

https://www.soundandvision.com/content/equalizers-and-tape-monitoring

[GregWormald]

Try another amp and make sure where the problem is.

Capacitors deteriorate over time. As the amp is 1986? vintage it probably needs some servicing—which may be much cheaper than a new amp, and since it already does what you want...

The Bose equaliser could also use a service.

[davide256]

14 hours ago, GregWormald said:

Try another amp and make sure where the problem is.

Capacitors deteriorate over time. As the amp is 1986? vintage it probably needs some servicing—which may be much cheaper than a new amp, and since it already does what you want...

The Bose equaliser could also use a service.

When I checked, the 901 MkII with equalizer was sold in the 70's, so switch and slider electronic solvent  cleaning to clear out ferrites would make sense. Doing the same

to the amplifier might stop the Op's issues, certainly a wise first step.

[GoldenMaster]

6 minutes ago, davide256 said:

14 hours ago, GregWormald said:

Try another amp and make sure where the problem is.

Capacitors deteriorate over time. As the amp is 1986? vintage it probably needs some servicing—which may be much cheaper than a new amp, and since it already does what you want...

The Bose equaliser could also use a service.

When I checked, the 901 MkII with equalizer was sold in the 70's, so switch and slider electronic solvent  cleaning to clear out ferrites would make sense. Doing the same

to the amplifier might stop the Op's issues, certainly a wise first step.

 

Thank you for this tip, also Davide265 thank oyu for linking that post and explaining the terminology, helped a lot

 

Now I just need to get my hands on the proper german name for these kind of cleaning utensil  i will follow this guys guide, is that ok? 

 

Its not the same model, but I hope close enough ?

[davide256]

47 minutes ago, GoldenMaster said:

 

Thank you for this tip, also Davide265 thank oyu for linking that post and explaining the terminology, helped a lot

 

Now I just need to get my hands on the proper german name for these kind of cleaning utensil  i will follow this guys guide, is that ok? 

 

Its not the same model, but I hope close enough ?

Cleaning the front switches and sliders (power disconnected) with the appropriate solvent is ok but

for anything else "under the hood" better to pay a professional who has the the electronics gear to check and locate problems after cleaning.

Something like this + a can of compressed air  to blow out dissolved crap and solution after application should do for switches/sliders

 

https://www.amazon.com/CRC-05103-Electronic-Cleaner-11/dp/B000BXOGNI/ref=sr_1_1?dchild=1&keywords=crc+5103&qid=1590938955&sr=8-1

 

Remember to allow sufficient time after use for the solvent to entirely evaporate.

 

BTB ugly surface dirt doesn't degrade electronics performance but no one likes to work in  a "dirty kitchen". If you have to work under the hood, its just SOP to keep

the dirt from contaminating your materials and any repairs you do. A next step would be to remove and clean board connector plugs... which are likely to be brittle and break on you if you are unfamiliar with them, pull them the wrong way.