500C Earphones setting...can I use without speakers attached?

[sberger]

Is it damaging to my 500C if I use it without a speaker load attached, if I have the speaker selection turned to the Earphones setting? I love the 500C, but I also enjoy a pair of Dynaco MKIII's that I own and when using them I still would like to incorporate the 500C's phono and tuner.

Thanks.

 

[larryderouin]

The 500c, like it's sister 800c and cousin 400, has loading resistors in circuit so you can use the Earphones by themselves without speakers connected. Go ahead and Jam!

 

[sberger]

Thanks Larry! I’ve read conflicting things about this. Last thing that I’d want to do is damage this fine receiver. Appreciate your input.

BTW, do headphones need to be connected for the resistors to kick in or not necessary?

 

[larryderouin]

The load resistors are there whether or not an external load (either speakers or headphones) is presented to the receiver. However I wouldn't advise running it at full steam without a load on.

 

[sberger]

The load resistors are there whether or not an external load (either speakers or headphones) is presented to the receiver. However I wouldn't advise running it at full steam without a load on.

Thanks again.

Are you talking volume wise on the 500C? I'm using a separate preamp so no volume being used with it. Just the phono and tuner, through the preamp.

 

[larryderouin]

I was under assumption you were using the 500c as a normal receiver, but using headphones only.

Howthe #^&$ are you doing that? NOT THRU THE Expander jumpers, I hope. They are at the same place as the Tape REC -REC MON input and output's. Way before the preamp, tone, and volume control. That's not a PRE OUT / MAIN IN. The FISHER's were never designed to have PRE-OUT/ Main in. Using the Expander Jumper as a preamp in can conceivably overload your 500c.

 

[sberger]

Using the tape out. Works fine. I know about the expanders, never would use it.

That said, I'm not particularly happy with the 500C's phono at the moment, so I'm using a stand alone phono. Which means I'll only be using the 500C as a receiver going forward. But just wanted to be make sure that no speakers attached was not going to hurt anything, and I think I got my answer.

 

[larryderouin]

Why not just overhaul the 500c's phono circuit. It's quite simple to do. The PEC's (identified as PC1 and PC2 on the schematic) are very simple to breadboard and replace the originals. Use 1% parts if possible, but no more than 5% parts. I think you'll be surprised at how accurate the phono circuit is on them. Dave did a test of the RIAA circuit in a 400 I believe, (all of FISHER's PHONO RIAA circuits are all basically the same one from the 500 mono all the way thru the early Solid State stuff). and it was surprisingly accurate to the standard. IIRC it was no more than .8db + or -. 30HZ to 20,000Hz.

 

[sberger]

I might. I’ve used and enjoyed the phono’s in several previous Fisher’s that I’ve owned, so I think the sub par performance compared to my stand alone(which btw is a $2000 unit and really good) is tube related. I’m going to roll a bit and see what happens, but it’s not an issue because overall the sound on the 500C is great.

UPDATE: Rolled in a couple of RCA AX7's(not sure if black or grey plates) and the phono magic is back. Probably just a weak tube in there. In any event, all is well the mighty 500C. Still will have to try Dave's updates at some point.