Help connecting a sub to a Fisher 500b amp

What would be the best way to connect a sub-woofer to the Fisher 500B integrated amp?

I'm using bookshelf speakers with this amp and would like to add deeper bass to the sound. I have a Martin Logan Dynamo 500 sub.

Not having much experience with vintage amps and subs, I'd appreciate help in what should be a fairly easy set-up.

Cheers.

 

Center channel out of fisher to line level inputs?

 

So, the Center Chanel Output of the Fisher 500B acts like a multi-channel system and it would be connected to the LFE input of the Martin Logan sub (bypass mode)?

 

I also have a Martin Logan Dynamo 500 sub. The only inputs on it are line level inputs. I also happen to have a Fisher 500C.



This is going to be a little bit tricky. But is can be done, here's how...



The best, easiest, most direct way. You see the little RCA connectors on the left? The one's with the little "U" pins going out of one and in to another.

Let me explain what you are looking at first.

You fisher has two main parts the preamp stage, which includes the phono inputs, and the AM/FM radio and other line level inputs. The job of the preamp stage is to provide the primarly low level amplification.

That amplified signal exits the preamp through a pair of RCA connectors, one for the left channel and one for the right channel.

The second stage on your Fisher is a power amp stage. It is where the final amplification takes place that drives your speakers.

On older amplifier's they had external RCA connectors for the output of the preamp stage and the input of the power amp stage.

Those little "U"'s are what connects these two stages together, pull these pins out, the two stages no longer talk to each other and no sound comes out.

Don't do that (yet).

When you raise and lower the volume of the 500B, it raises and lowers the voltage of the line output of the preamp stage.

This controls the volume of the power amp stage.

In order for you to connect they Dynamo 500, you will need to run an RCA cable pair (left and right channels) from the preamp's RCA output connectors to the input line RCA connector's on the Dynamo.

You can do this by pulling out these little "U" shaped pieces of steel and getting them out of the way, then you can plug in a pair of RCA cables to the preamp output RCA's and run the cable to the input RCA's on the rear of the sub.

There is only one small problem with doing this and that is, when you pull out these pins, to plug in the RCA cable to go to the sub, you no longer have a connection from the preamp section of the 500B to the power amp section of the 500B.

Meaning, that you will have sound coming from your sub (as you turn up the volume) but you will no longer have sound from your 500B coming out of your speakers.

The good new is, that your sub will now be connected and working!

Remember, you did ask how you could hook up your sub.

Well, while that is all well and great, I'm sure that you would like to have sound coming out of your sub and out of you speakers, yes?

OK, here is how you do it.

You are going to purchase two "Y" connectors from Amazon. that look like this. They are available on Amazon prime for 9.99/each.

Mediabridge ULTRA Series RCA Y-Adapter (12 Inches) - 1-Female to 2-Male for Digital Audio or Subwoofer - (Part# CYA-2M1F-P )



Remove the first "U" pin. Then connect both male ends into the two female RCA connectors where the pin was.

Do the same for the second "U" pin.

Make sure that you had the radio or some music playing before you pulled the pins and make sure that that music is still continuing to play after you have replaced the "U" pins with the two male RCA connectors.

What you have done is to replace the "U" pins with a RCA splitter cable, times two.

Now, all you need to do is to buy one RCA Male to Male extension cable (which is a standard system interconnect cable) to go from the famale ends of the "Y" adaptor to the left and right female inputs on your Dynamo 500.

This Mediabridge is a sturdy well shielded cable. I use them myself.

Here are three different lengths, make sure you get a length long enough to run the cable fro your receiver to your sub. make sure that is is long enough but it is best that you don't use a cable that is longer than you really need it to be. That will cut down on any interference.

KabelDirekt RCA Stereo Cable/Cord (10 ft/feet short, Dual 2 x RCA Male to 2 x RCA Male Audio Cable, Digital & Analogue, Double-Shielded, PRO Series) supports (Amplifiers, AV Receivers, Hi-Fi)



KabelDirekt RCA Stereo Cable/Cord (15 ft/feet long, Dual 2 x RCA Male to 2 x RCA Male Audio Cable, Digital & Analogue, Double-Shielded, PRO Series) supports (Amplifiers, AV Receivers, Hi-Fi)

or

KabelDirekt RCA Subwoofer Cable / Cord (20 ft / feet long, 1 RCA Male to 1 RCA Male Audio/Video Cable, Digital & Analogue, Double Shielded, PRO Series) supports (Subwoofers, AV Receivers, Hi-Fi)

That's all there is to it!

S&G

 

I did this with a REL sub and blew it up. There is power coming out of that center channel.

 

I've used the center channel out to a sub with two different Fishers, and X-100 and a 400, and the results were fine.

 

What were the subs? We’re they powerd? I got and immediate “pop” and my REL has been dead ever since?

 

It was a powered RBH sub, nothing fancy.

Bummer about your REL!

 

I’m hoping it was just a fuse but trying to open it up to find one became very complicated, a bit like opening up an iPhone.

The lesson learned is that there is power coming out of the center channel output in those Fishers.

 

I used the center channel out on my Fisher 400 to run a sub and it worked well.

 

What was the sub? I was using your 400 and blew up a REL.

 

Thanks - very much appreciated. I will order those cables and give it a try.

 

OK, everybody is missing the point here.

First it is OK to use the mono center channel "speaker" output to run a sub. But ONLY if that sub accepts speaker level inputs.

Which the OP's sub definitely DOES NOT!

The OP should never do this or he will blow out the LINE LEVEL inputs on his Dynamo 500 (pictured).

The OP can only use line level inputs from any preamp section to power this sub.

To the OP, some subs allow you to connect you speaker wires directly to speaker connectors on the sub, where the sub is specifically designed to take a very tiny amount of electricity from the signal that goes to the speakers to get the speaker level inputs to power the sub. The speaker wires then go in to the speaker.

The wires could go to the speaker and then from the speaker to the sub, it doesn't matter.

But, the sub has to be designed this way, which your Dynamo 500 is NOT.

Here is the back "plate amp" off of a Polk Audio sub.



If you look at the bottom you will see two pair of speaker connectors, one pair going in from the amp to the sub and one pair going out from the sub and continuing on the the speakers. Note: the speakers won't even know that the sub is there.

F.Y.I., Alternately, you could use speaker outputs from a mono center channel to either speaker input on the sub, the sub does not care, you don't have to have a stereo signal going in to it. The sub only take the signal from the left and the right channels and combines those channels into a mono input.

You will note, that directly above the speaker in/out spring connectors are a pair of red and white RCA connectors which are marked "Line In". These are the same type of connectors that you have on your Dynamo 500.

Suggest you try my way, as it will not harm your receiver, nor will it harm your sub.

S&G

 

I believe there are a few 500b owners in the forum, so this is a great resource for anyone wanting to hook up a sub. Thanks again

 

This forum is FULL of vintage pre 1967 Fisher receiver's! You can thank SH for that!

A bunch of us also late 50' and early 60's tube integrated amplifier's, which are excellent sounding also. So of us feel, even more so than the more powerful Fisher receivers. I have a couple of Scott integrated's from this period.

I don't generally use the 500C, because it has something like nineteen tubes in it. I prefer something more simple for everyday use. But I do really like it.

Just following up, did you get the cables that you ordered and were you successful in setting up your ML sub?

 

Cool receiver! Have the tubes "spoken" to you yet?
Do what @SandAndGlass said, BUT additionally I would add one of these
Line Level Crossovers
crude but effective ways of cutting the low bass load out of your amp and main speakers, thereby increasing the dynamic range. Otherwise your sub will add low bass, but your bookshelf speakers will still be straining to put out those same low notes which is silly. There are some more expensive active crossovers as well. If you need help selecting reply/PM me, glad to help.

 

I just ordered the Y adapters (I have a 2 year old - so my stereo hobby sometimes gets setbacked lol) - but I will update this thread when I get it set up.

 

Love the Fisher amp. It sounds fantastic - best $500 CDN I've spent.

 

S&G
I finally connected my sub via your instructions. Easy to set up and sounds very nice. Thanks so much.
Ed (SHF ID = canonlon)

 

I'm glad that everything worked out for you!

 

I want to revive this thread as I have a 50’s Sherwood s5000ii that I want beefier bass on. CH3/mono out to (powered sub?)