Revox B 36 tape recorder banana plug output

[MOF]

I'm posting on the forums all day and I never have problems with missing posts... but what can sometimes happen is that someone else posts while you're typing and then when you hit the Submit button the forum software automatically holds your post in limbo and presents a warning page about the other post... This is intended to allow you to change your post before submitting, in response to the new one.

I also once used an iPhone emoji instead of the SOS supplied ones and that didn’t work.

[timoc]

I was going to say that the 'protection' for the valve output stage seems to be that the 4mm plug is only pushed in part way and thus the internal speaker still works. Not a very satisfactory arrangement to my mind and one that could lead to damage? Personally I would not want to risk the OP traff in that venerable old Revox.

A 6r8 'Allyclad' resistor costs about 3 quid at CPC and and a metal box about a fiver. Add input and output jacks, a small amount of sweat and you have a load box for under a tenner?

Or, get a tech to fit a pre VC line feed.

Dave.

Thanks, I may have to do the latter, given I don't know how to make a load box.

I think the manual states that if you've pushed the banana plug all the way in and still hear the original speaker, you can push a second plug into the left adjacent socket halfway to kill the speaker sound:



What could go wrong with the method described by others of plugin in a banana - rca cable and turning up the volume slowly?

[James Perrett]

Thanks, I may have to do the latter, given I don't know how to make a load box.

I think we've worked out that you don't need a load box with this particular design of output. Just do what you originally intended and use a couple of banana plugs - they're easily available from most component suppliers or on Ebay.

[Hugh Robjohns]

Thanks, I may have to do the latter, given I don't know how to make a load box.

It really doesn't need a 'load box'. The manual is quite explicit: the external speaker output doubles as a fully compatible unbalanced line-level output which can be connected to high-impedance line input and it will serve as a 'high fidelity' connection!

Think of it as a powerful mono headphone socket!

I think the manual states that if you've pushed the banana plug all the way in and still hear the original speaker, you can push a second plug into the left adjacent socket halfway to kill the speaker sound

Not quite. You need to (fully) insert both banana plugs to access the unbalanced output to feed an external speaker or line input. The right-hand socket is the ground reference (black plug in your converter lead) and the left-hand socket (red plug) carries the (hot) signal voltage.

Normally you would push both plugs all the way in, in which case a break contact on the left (hot) socket will disconnect and mute the internal speaker. However, if you want the internal speaker to continue working you can achieve that by pushing the left plug in only half way, since that will still pick up the signal but not activate the break contact.

What could go wrong with the method described by others of plugin in a banana - rca cable and turning up the volume slowly?

Assuming the machine appears to work normally on its own, I dont think anything can go wrong with deriving a line output in the manner described.

[ef37a]

That is one weird output stage

Dave, I agree, I wondered what is going on here! But my valve knowledge is mainly RF with a bit of 'light' audio at the end point!

I am sure the likes of Revox knew what they were at but to me, putting 3 RCL coupled stages in an NFB loop then inviting the connection of an unknown cable capacitance is asking for trouble!

The series NFB will push the output impedance sky high so I guess that is how it becomes 'safe'? That will however cause HF loss in the external cable AFAIK.

It all seems very complicated when a simple load resistor could serve the same purpose?

Where is Merlin Blencowe when you need him?

Dave.

[timoc]

Assuming the machine appears to work normally on its own, I dont think anything can go wrong with deriving a line output in the manner described.

Thanks, Hugh, that's extremely useful information! I appreciate you and everyone taking the time to help me out with this.

No one is selling a banana - rca cable, so I've ordered some banana plugs (black and red) and will try to do that myself. Shouldn't be too hard, I hope.

Cheers!
Timo