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Bose 901 series 1 EQ question

viennadad

viennadad

Active Member
Good afternoon!
Been awhile since I posted here but I have been enjoying my setup.
But, the bug bit a few weeks ago when I saw a pair of 901's at an auction house. Won them, but no EQ
came with them.
Took a couple of weeks but I found an EQ and it came today.
I cleaned it up a bit and went to connect it, but before I did I hooked up the speakers to get a reference sound. They didn't sound bad using the tone controls on the receiver. But when I connected them according to the manual, I got no sound when I activated the tape monitor. The manual says if that happens it is not connected correctly. So instead of muttering " I know what I'm doing, been hooking stuff up for 50 years", I rechecked the connections. All is proper.
The only indication I have is the power button on the EQ lit up.
Where do I start trying to diagnose the issue?
 
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Aside from making sure it's hooked up correctly, the tape switch is notorious for getting dirty - might be worth a round of deoxit before you proceed.
 
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Connections are right and Tape monitor switch on receiver functions. It's a Carver MXR-130. Both tape monitor selections work for other inputs. I gave the EQ a good shot of DeOxit yesterday.
 

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I would try it on tape 1. I have a reciever that will not do a feed through on monitor 2. I am using it with an eq and I have to have the eq on tape 1.
 
If your receiver has preamp out/power amp in jacks,, that would be a more straightforward place to install it and you can eliminate any issues with the tape monitor circuits in the receiver and/or equalizer.

The switches and the rear jacks on the equalizer are notorious for getting oxidized and causing problems so you might want to hit it up with some DeoxIt D7.
 
Don Lubin said:
If your receiver has preamp out/power amp in jacks,, that would be a more straightforward place to install it
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For diagnostics I would try that but the use of the eq is recommended to be in a tape loop if possible. Lower noise

You can test a tape loop by using a RCA cable and go out to in and then switch the cable (tape loop) into the circuit to see that it is a working tape loop.
 
Blue Shadow said:
For diagnostics I would try that but the use of the eq is recommended to be in a tape loop if possible. Lower noise

You can test a tape loop by using a RCA cable and go out to in and then switch the cable (tape loop) into the circuit to see that it is a working tape loop.
Click to expand...

Since it should be a linear system, I'm not sure you will gain anything on noise. As the preamp output levels can often run higher than at the tape monitor circuit, depending on volume, you could see some improvement in equalizer noise contribution since the signal to noise ratio could be higher. I never found it to be an issue either way.
 
Don Lubin said:
As the preamp output levels can often run higher than at the tape monitor circuit,
Click to expand...
this is very rarely true. Using the tape outputs is a fixed signal nice and high well above noise. The preamp output, depending on the amplifier input sensitivity can be very low. I have amps that need only 0.5V for full volume, they could easily be driven to full output by a high output cartridge into the preamp using the tape outputs since the nominal tape output is in the range of 150-250mV for the lowest input level for the different sources.
 
I used the pre out and main in jacks on a Pioneer SX-939 and then a Yamaha AX-630 to hook the equalizer for my 901's and had no problem.
 
Blue Shadow said:
this is very rarely true. Using the tape outputs is a fixed signal nice and high well above noise. The preamp output, depending on the amplifier input sensitivity can be very low. I have amps that need only 0.5V for full volume, they could easily be driven to full output by a high output cartridge into the preamp using the tape outputs since the nominal tape output is in the range of 150-250mV for the lowest input level for the different sources.
Click to expand...
I bought my 901s new shortly after they came out. Back then, most demo rooms drove the 901s with a power amp as even the highest power receivers available were usually not more than 50 - 60 wpc. Typical setups would use things like a Marantz 250, Crown DC300, or a Phase Linear 700. All the setups I remember used the equalizer to drive the power amp. As the 901s began to become popular, Bose actually went to specifying how the demos were to be installed. This included using Bose supplied "walls" behind the 901s, and later when they began manufacturing electronics, their power amps. None of the demo rooms I spent time in used the tape monitor loop for the equalizer. I think the inclusion of the tape monitor loop was purely for people not using separate preamps and power amps as receivers with preamp out/power amp in jacks were extremely rare back then.
 
Had a few pair, almost always with an amp and preamp since that is my main rig. Always used the tape monitor for better sound. Sold gear back in the day and understand the need to put the eq external as it was unknown which preamp or possibly big receiver would need to be hooked up to make the 901s correct for that presentation. The guy buying the KR-9600 wanted to hear the 901s with that receiver.

EchoWars explains it. I'm in agreement with that. You can enjoy your hook up your way.

https://audiokarma.org/forums/index.php?threads/equalizer-connection-question.191925/#post-2231125

Just checked the Series III OM and it recommends the tape loop for ease of use with other than 901 speakers or headphones and mentions the lower noise floor using this method.

In the directions for the pre-power connection they recommend lowering the volume control on the power amp if possible because that will mean the preamp output will be at a higher level and not get lost in the noise floor of the eq on its way to the power amp.

This lower noise floor us more for lower level listening so if you don't listen below 85 dB or so it will make less difference which way you hook up the eq.
 
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I sold a pair of 901 Vs to a friend and talked to him about installing them in his 'dog house' a 30x40 out building, half loft, car lift. He hung them. He followed my recommendation to put reflective material behind the speakers.

Chris Front.jpg

Chris Reflection Wallboard.jpg

He also followed Bose info to tilt the speakers UP to get the rear reflection to come down. There is an amazing sweet spot between the speakers about 15-18 feet back from them. About where the front corner of a car pulled in to be lifted would be.

I don't think his gear is 'dedicated' so I don't know if he is using the tape loop or the pre-power connection. He has a choice of preamps and is using a Crown PSA-2 power amp and has a second set of 901 Vs to hook up when the party is happening. That system rocks for a party rig.
 
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@viennadad have you gotten this to work, yet?

If you don't get eq with it positioned between the pre out and main in, your EQ might be sick and needing some work. If it does work there, then the tape monitor should work, too.
 
HB3 said:
You can get a replacement equalizer at deercreekaudio.com if you want to go in that direction.
Click to expand...

There have been sporatic reports that Bose may still service/support originals too, through repair or exchange program. But, I've not personally looked into that. Maybe I'll give them a call for curiosity sake, since I have a pair of Series II and a pair of Series VI (both eqs working, albeit after I repaired the Series II eq).
 
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Several years ago I had my Series II eq repaired by Bose...I had lost one channel, and it was not the tape monitor switch. Had choice of exchange or repair, I took repair. It was serviced in one of the Carolina's and did not take long. I should say I am an original owner of the set since 1974...
 
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