How to do head to Eros wiring (partly in reply to an old question by Video FX)

[PS2500]

As VideoFX's question is already old (10 months ago), it was recommended that I start a new thread, so here goes. It may help, if not to VFX, then someone else in the same situation, though the good info is from the people who know what they're talking about - they've replied to a few other comments on this subject, including one from me.

The original thread is here

http://bottlehead.com/smf/index.php?topic=7322.0

And the question was, how should you do the wiring if you want to go direct from playback head to RCA output to Eros?


As a non-techie, I'm open to correction on anything I say below.

To do the wiring, you're probably going to need a service manual for your deck (Hi-Fi Engine for that, you'll have to register to download, but downloads are free), unless you're already very familiar with the internals.

Based heavily on Doc B's reply to me a while back, which you can find somewhere in this section of the forum, after you take the head cover off, observe the wires attached to the playback heads and follow them back into the deck all the way to where they are connected at their other end to the deck electronics. You have to disconnect them (I'm assuming by desoldering) and rewire them to the RCA output (actually I am a little unclear on this part - they either go to the existing RCA outs on the deck, or - some comments seem to indicate this -to RCA outs that you add yourself). Luckily, you won't need to disconnect those wires where they are attached to the playback heads - I had originally assumed you had to do completely new wiring, and for some reason, the penny didn't drop even for some time after Doc. B's reply to me (definitely my fault not his).

That's the basic description; ease of access for the ends of those wires that you have to disconnect is going to vary somewhat depending on the deck model you're working with. I think you're likely to have to unscrew boards to get to them properly, it looks that way on my deck.

If you do no more than that disconnection/reconnection procedure, you will lose playback metering (record metering will be unaffected). If you wish to keep it, you'll have to rig a Y-cable arrangement. That's a little beyond my current experience with wiring, most of which came from putting together a Crack amp, though if I can do it, I will, just to keep the playback metering. I assume if you can do the other steps of the procedure, this extra step is not much more trouble.

Ideally, I want to make a modification that allows switching to and from the deck's own electronics as desired, even if that can only be achieved by taking off the enclosure and flicking a switch (added by me) inside.

If anyone knows how that can be achieved, I'd really like to hear it. I have a sort of picture in my layman's mind of some kind of switcher attached to the playback cables between the head and the decks electronics which can divert the signal down an alternative wire to the RCA output and from there to the Eros. And when it's switched back to the deck electronics,  you can plug the deck to a regular integrated amp.

Achievable? Nonsense? Difficult?

[Doc B.]

You could put a switch in to switch between the internal playback electronics and external. However if you throw that switch while the electronics are active it is very possible that you will magnetize the playback head. You must stay aware of this or risk hosing up a tape from a head that needs to be demagnetized.

The short answer is why install a switch you will only use once? The Eros will sound much better than the stock electronics.

[PS2500]

Sure I see your point, that may well be the better way to go about it. It simplifies the issue too, and I'm all for that!

Bear in mind most of us don't hear any specific BH product until we've built the kit and switched it on. I have a Crack amplifier. Other than that, I've never seen or heard any Bottlehead gear and I'm not within 1000 miles of a listening venue. There _is_ a leap of faith involved, hence the hesitancy, though from what I've heard with the Crack, I expect only musical goodness.

For the Eros, we don't just build the kit, but modify other hardware to drive it. I've only just in the last few months spent enough time in the back of a tape deck to feel I have enough confidence to make a wiring mod in there.

[Doc B.]

Instead of a switch you could cut the internal cables. Run the part of the cables left connected to the internal preamp to a second pair of RCA jacks, as well as running the end left connected to the playback head to a pair of RCA jacks. Then you can use an interconnect to connect the head either to an outboard playback preamp or loop it back into the internal preamp. That's basically how I use my Nagra T, with different connectors.

In many decks the head cables actually terminate with some form of plastic header pin type connector. If yours is like that you could scrounge up a suitable mate to that connector and make a pin header-to-RCA cables adapter. That way you could return the deck to stock.

[PS2500]

You're right, I've had a look in the service manual, and those cables are terminated with headers. That's going to simplify matters vastly I think.

Thanks for the heads-up.