Fisher 400 high level inputs

[ggn71]

Hello all,
I've been listening to my 400 with no problem at all since rebuild for almost 2 years now. Now that I want to use my iPhone as a secondary music source, I find that my wonderfull receiver lacks high level inputs.
I have a Thorens TD145 connected to the "phono low" input, and a modified Marantz CD65Mk2 to the "aux/tape" input.
I tried the iPhone on every available inputs, jut to hear what I could get out of the receiver:
Phono high: I have sound, no bad at all... But definitely not as good as on the "aux/tape" input.
Tape head: very distorted, not usable at all
Rcdr out: cuts out everything, no sound at all
Tape mon: I have sound with the "tape monitor" switch ON, good sound but at a considerably lower level than on the "aux/tape" input.
I plan to use the "tape mon" input for my iPhone, and my question is:
I would like to know why I have lower level on this input, and eventually how to mod the receiver in order to correct this.
Many thanks to all!

 

[rwj0j0]

So... tape head has too much gain - right?
maybe just padding tape head will work.

 

[amphead4]

Tape head also provides some eq that a straight input like aux/tape would not have. I have a similar issue with a TA-600 and was hoping to use the tape head input jacks but mod the circuit to bypass the tape head eq. I took a look at the input selector switch and decided the project required brainpower so I put it on hold.

 

[Dadbar]

Why don't you move the Marantz to the tape monitor input and use the aux for your iphone?

 

[JonL]

You could use an outboard selector box for your high-level sources. There are lots of them out there, including some cheapies from Radio Shack.

 

[kpaxfaq]

You could use an outboard selector box for your high-level sources. There are lots of them out there, including some cheapies from Radio Shack.

That's a good idea. The single AUX input on Fisher receivers has always annoyed me.

Kory

 

[ggn71]

Tape head also provides some eq that a straight input like aux/tape would not have. I have a similar issue with a TA-600 and was hoping to use the tape head input jacks but mod the circuit to bypass the tape head eq. I took a look at the input selector switch and decided the project required brainpower so I put it on hold.

:tresbon:, that is exactly what I was thinking this afternoon in front of the input selector switch. That's why I was wondering if someone ever worked for the community and modded one of the inputs to behave like the "aux/tape" input.
As some of you advised me, I can buy an external selector box but don't you think it will degrade the signal quality?
And I would like to understand why the "tape mon" input gives lower level than the "aux/tape" input as they are electrically connected and seem to share the same path except for the "tape monitor" switch on the faceplate.

Edit: I found this from Audiodon: "tape mon only uses one tone amp tube, so the absolute phase will be reversed and the gain won't be quite as high"
I guess I have my answer, even if this statement applies to a 800b it is certainly very similar in the 400.

 

[JonL]

:tresbon:, that is exactly what I was thinking this afternoon in front of the input selector switch. That's why I was wondering if someone ever worked for the community and modded one of the inputs to behave like the "aux/tape" input.
As some of you advised me, I can buy an external selector box but don't you think it will degrade the signal quality?

I guess the "purest" solution would be to convert any unused positions on the internal selector switch to become additional high-level positions. Then you've only got one set of contacts in the signal path. Using an outboard selector does add an additional set of contacts, but with a decent selector switch the effect on high level signals shouldn't be too worrisome.

 

[bhamham]

I use an RCA jack splitter on my AUX input to run my CD player and a squeezebox - I think it'd be similar to an I-phone.

 

[maransansui]

how is it that i'm able to get a sound through 'tape-mon' connection when my selector's at 'aux-tape'? and why does that config have much volume than when my interconnects are simply at 'aux-tape'? also, when i bring up the volume to about equal levels, the sound through 'tape-mon' connection seem rolled off yet smoother and aux-tape bright in comparison, which i'd like to blame on the bunk amperex tubes up in the chain from the dac. what's going on here? and what should i be using?

 

[empirelvr]

how is it that i'm able to get a sound through 'tape-mon' connection when my selector's at 'aux-tape'? and why does that config have much volume than when my interconnects are simply at 'aux-tape'? also, when i bring up the volume to about equal levels, the sound through 'tape-mon' connection seem rolled off yet smoother and aux-tape bright in comparison, which i'd like to blame on the bunk amperex tubes up in the chain from the dac. what's going on here? and what should i be using?

That's because the "Aux/Tape" and "Tape Mon" jacks are electrically connected together via a resistor for each jack.

I can't say why, but it appears that the Fisher engineers designed it so you can only have one high level source connected to the unit. They also put the tape monitor switch *after* the first gain stage before the tone control stage. That's why the sound is lower in output when you listen through that switch.

I think they thought of the Tape Monitor switch as only a confidence switch to check material being recorded for those using a three head deck to the unit. In normal use you were supposed to use the "Aux-Tape" switch on the rotary source selector to listen to tape playback.

Happily though, if you're good with a soldering iron, both "problems" are easily solved. On my 400 receiver I disconnected the resistors joining the "Aux-tape" and "Tape In" jacks thereby making them two totally separate and distinct inputs, as well as wiring the tape monitor switch to hit the first gain stage to bring the levels up to the rest of the sources.

Maybe my modification would not please Fisher purists, but it gave me a CD input and the ability to use the tape monitor switch as we would on a modern unit. It's also 100% reversible, so it can be made "stock" if it's ever needed.

 

[audiodon]

I like empirelvr's solution.

You've got to remember though that this is a receiver. They thought they had it all back in '63 or so because the phono and FM and tape mon were built into it.

It really was a long time ago.

 

[empirelvr]

I like empirelvr's solution.

You've got to remember though that this is a receiver. They thought they had it all back in '63 or so because the phono and FM and tape mon were built into it.

It really was a long time ago.

Yep, at that time what other source would you want to plug into it? Maybe TV sound, but TV's with an audio out were rare if available at all. And forget AM radio...the reason you had a receiver like the Fisher was to get away from "low fidelity" sources like AM. (Not my own opinions...I know AM can sound very fine indeed. This is just my impression of the thinking back then.)

 

[kpaxfaq]

Yep, at that time what other source would you want to plug into it? Maybe TV sound, but TV's with an audio out were rare if available at all. And forget AM radio...the reason you had a receiver like the Fisher was to get away from "low fidelity" sources like AM. (Not my own opinions...I know AM can sound very fine indeed. This is just my impression of the thinking back then.)

Exactly...FM radio was HUGE in this time period. I can imagine it was like when broadband internet became mainstream for me. It was the same old internet but much much better! I remember begging my parents to get rid of dial up being the young geek I was at the time. I was that first kid in school who knew what napster was and had a 2x cd-burner. It was the same FM radio but way better!

Just think of all the hits of the time, and the high quality fidelity of the broadcasts at that time...It was the primary source of music for most people. Must of been something to spin the dial and hear the new beatles, stones, or hendrix cut. Did I mention how much I loathe my generation...

Kory

 

[chadbang]

That's because the "Aux/Tape" and "Tape Mon" jacks are electrically connected together via a resistor for each jack.

I can't say why, but it appears that the Fisher engineers designed it so you can only have one high level source connected to the unit. They also put the tape monitor switch *after* the first gain stage before the tone control stage. That's why the sound is lower in output when you listen through that switch.

I think they thought of the Tape Monitor switch as only a confidence switch to check material being recorded for those using a three head deck to the unit. In normal use you were supposed to use the "Aux-Tape" switch on the rotary source selector to listen to tape playback.

Happily though, if you're good with a soldering iron, both "problems" are easily solved. On my 400 receiver I disconnected the resistors joining the "Aux-tape" and "Tape In" jacks thereby making them two totally separate and distinct inputs, as well as wiring the tape monitor switch to hit the first gain stage to bring the levels up to the rest of the sources.

Maybe my modification would not please Fisher purists, but it gave me a CD input and the ability to use the tape monitor switch as we would on a modern unit. It's also 100% reversible, so it can be made "stock" if it's ever needed.

I'm interested in doing this mod. I am missing have two high level inputs with equal output levels. Would just removing the resistor between the Aux-tape and tape in jacks do this? Or do I also have to wire the tape monitor switch. It is also this procedure which I could use some more instruction accomplishing (a visual would be nice!)

 

[notdigital]

I'm interested in doing this mod. I am missing have two high level inputs with equal output levels. Would just removing the resistor between the Aux-tape and tape in jacks do this? Or do I also have to wire the tape monitor switch. It is also this procedure which I could use some more instruction accomplishing (a visual would be nice!)

And I'll be looking over your shoulder

I'm currently using an external switcher after experimenting with splitters a la Bruce's suggestion above. With my Audio Engine wireless dacs, it just didn't work :thumbsdn: This workaround would be ideal :yes:

 

[notdigital]

I have a 500-c opened up on my bench as we speak. If it'll help, I could put up some pics of the switch and the jacks. Sometime tomorrow if there's enough interest.

 

[beatcomber]

Exactly...FM radio was HUGE in this time period. I can imagine it was like when broadband internet became mainstream for me. It was the same old internet but much much better! I remember begging my parents to get rid of dial up being the young geek I was at the time. I was that first kid in school who knew what napster was and had a 2x cd-burner. It was the same FM radio but way better!

Just think of all the hits of the time, and the high quality fidelity of the broadcasts at that time...It was the primary source of music for most people. Must of been something to spin the dial and hear the new beatles, stones, or hendrix cut. Did I mention how much I loathe my generation...

Kory

Rock'n'roll was pretty much confined to AM until late 1967 or so. Rock programming on FM pretty much started with KMPX-FM in San Francisco, but they weren't playing Top 40 hits.

Before '67, FM was exclusively mood music, jazz and classical.

 

[larryderouin]

Guys. Go to Dave Gillespies 400 rebuild thread (the one that had like 6-8 revisions to the schematic done by eduarsan). In it he details how to remove the bleeder circuit from the Aux/Tape circuit to separate the AUX and TAPE Monitor. Plus some other stuff that will make the 400 scream like a 41 Willy's gasser.

 

[dcgillespie]

Chad -- If you simply remove the components between the Tape Monitor input jacks and the Aux/Tape jacks, that will allow you to then have two completely separate inputs without any bleed over between them. However, the two inputs will still have distinctly different sensitivity levels, with the Tape Monitor input requiring a higher volume setting to achieve the same sound level from an otherwise equal input signal level presented to both inputs.

In my thread where I modified the 400, I addressed this problem as part of a whole suite of areas I addressed in this receiver, electrically moving the switch in the circuit so that the Tape Monitor input now has the same sensitivity level as the Aux input does. Of course, the bleed over components were removed as well.

You could easily remove the bleed components, and also electrically reconfigure the Tape Monitor switch as I did in that thread. The underside of the 400 can look daunting to those tackling such issues for the first time, but in this case, its mainly just a rewiring exercise, requiring no new components to be installed.

Dave