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Author Topic: Technics RS1500 head rewiring  (Read 28682 times)

Offline xcortes

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Technics RS1500 head rewiring
« on: January 19, 2007, 12:09:40 PM »
I've been studying Charles King's and Doc's various posts regarding the rewiring of the RS1500. While I appreciate the beauty of Charles methods of directing the wire to the back I'd like to do this as simple as possible thus I'll take the wire out from the front.

I have one question: when attaching new cables directly to the heads, do the heads retain the old connections? If so, can I assume that you could use the deck either from the new outputs to a head preamp or using the deck's electronics? This would be very cool.

Thanks

Xavier Cortes
Xavier Cortes

Offline ironbut

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Re: Technics RS1500 head rewiring
« Reply #1 on: January 20, 2007, 03:59:43 AM »
I think that you'd have to add some sort of switch since the stock playback electronics on the rs1500 are on when the machine is powered up. I have my seduction connected to the taps on the 1/2>1/4 track switch and out the front as illustrated in the original rs1500 pics on the Bottlehead seduction web site. So it is no longer connected to the stock playback electronics.
steve koto
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Offline stellavox

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Re: Technics RS1500 head rewiring
« Reply #2 on: January 20, 2007, 07:48:19 AM »
Xavier,

I'd suggest wiring the cables from the outboard tape preamp to the center contacts on the headblock switch.  This retains the ability to select either 2 track or 4 track playback head - so you can play both tape types if you have them.  As I mentioned in my mod post - the switch is of very good quality, with gold wiping surfaces.  I do suggest taking it apart carefully and cleaning / lubricating, it as the few I worked on were pretty dirty.

A word of caution - don't lay the machine down on its face without some way to prop it up slightly or you risk breaking the switch lever on the headblock, along with the possibility of bending the reel table posts.

I used the Cardas cable which Doc likes - its available from Welborne Labs.  It has two center conductors so I suppose you could get by with only one cable - but run the risk of crosstalk - anyone tried this?

Another 1500 series "foible" I stumbled across was a noticeable reduction in tape tension when the machine was on its back versus standing upright.  Anyone else noticed this? Solution?

Charles

Offline docb

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Re: Technics RS1500 head rewiring
« Reply #3 on: January 21, 2007, 05:24:05 PM »
OK folks,
I just rewired one of my machines and photographed the process. Scroll down the page about halfway, to
Photos of the easiest way
http://www.bottlehead.com/et/adobespc/Seduction/bottleheadtapeheadpreamp.htm
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline xcortes

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Cool!
« Reply #4 on: January 21, 2007, 08:33:44 PM »
Thank you all!

Doc: Did you know that uploading those pictures just raised the price of the RS1500 market! Glad I purchased mine before.

Xavier Cortes
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Offline docb

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Re: Technics RS1500 head rewiring
« Reply #5 on: January 21, 2007, 09:52:52 PM »
Hah! Don't get me started! I think we raised the price of RS1500s and every other tape machine when we started demoing with tape a few years ago. Just recently someone tried to sell me a "studio ready" RS1500 for $800, and someone else was asking $3600 for a Stellavox. I could buy a decent ATR 100 for $3600! What the heck does "studio ready" mean? The heads on 6 out of 8 RS1500s we've acquired in the past couple of years have been totally shot, yet they were sold as "in great shape". Every RS1500 we've acquired has a nightmarish shriek from the tape counter idler wheel that appears in FF or REW, never mentioned by the seller. There are essentially no rosewood veneered end panels that aren't "only slightly dinged" or much worse. And though the fronts are usually great looking from a distance, none are "mint", they all have teeny edge scratch here, a little scuff on the headblock there.

An RS1500 that has been gone through is a fabulous machine. But honestly, for what you will have to pay to get them in top shape, most used RS1500s are worth somewhere around $150 to $400. The only situation where I am willing to value them higher is in a trade.

One cannot evaluate the condition of a tape machine visually. I would suggest that anyone who is considering a machine ask the seller if it runs without wow or flutter, if they have tested the record capability, if it rewinds and fast forwards properly and if you can see a picture of the heads. If the seller is reticent about sharing the info, lowball your offer.
« Last Edit: January 22, 2007, 09:58:41 AM by docb »
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline ironbut

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Re: Technics RS1500 head rewiring
« Reply #6 on: January 21, 2007, 10:36:02 PM »
I was super lucky with the one I got. I was pretty sure of that but your post confirms it. Even the side panels are in great shape. I do have a scratch on the headblock and on one knob but it works perfectly. Thanks for the pic's on the head rewiring but,.. that's way too easy for me! I'm probably going for some fancy smancy cables. I was wondering what kind of wiring you use in the repo amp. I think it's best to use "like" wiring as far as is reasonable especially with very low signal levels.
BTW I noticed from the CES pic's that you were using what looks like Revox hubs with the flanges. Did you have to alter them at all to fit over the pins on the Technics. I have a pair of the stock black plastic ones that I saved for some crazy reason from an A77 that I sold in 1982! The cut-out for the tabs are too small to fit over the pins on my 1500 so I thought that the aluminum ones wouldn't either. I'd like to get some ( they look soooo cool!) if they fit.
steve koto
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Offline docb

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Re: Technics RS1500 head rewiring
« Reply #7 on: January 22, 2007, 12:22:21 AM »
The ones we used seem to be original Revox hub adapters. It looks from what we can see that the aluminum ones are just the stock plastic Revox ones with spun alu trim rings mounted over them for extra bling, so that they look like a real solid alu Studer hub adapter. There are also repro ones out there now, even on ebay. Don't know what to say about the ones from your A77 not fitting your RS1500. The ones we used at CES happened to be found on an old Sony tape machine, they were branded Revox, and they fit the RS 1500s just fine. They look really hip. They are not really as rugged as real studio type NAB adapters. They are certainly better than the stupid Technics ones that have to mount on the reel before you can mount the reel on the turntable.
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline Mikey

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That sure is a lot easier!
« Reply #8 on: January 23, 2007, 12:19:44 PM »
OK folks,
I just rewired one of my machines and photographed the process. Scroll down the page about halfway, to
Photos of the easiest way
http://www.bottlehead.com/et/adobespc/Seduction/bottleheadtapeheadpreamp.htm


Hi Doc!

Nice writeup.
You're right, this method of bypassing the internal preamp is much easier that the way I've done it.
No need to remove the drive motor, the internal shielding, etc......very slick!


Mike

Offline AZ_Gary

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Re: Technics RS1500 head rewiring
« Reply #9 on: January 23, 2007, 12:31:20 PM »
If you wanted to have the ability to switch between the internal preamps and the external, could you just add RCAs for the external preamp and a switch to select? If you did this would you introduce unwanted noise, etc? What if the switch were mounted on top or other place more accessible from the front where the deck is in a cabinet or entertainment center, would the additional run add undesirables? Doc's "easiest" solution is beautiful, just wondering about an enhancement.

Thanks,
Gary

Gary Marklund
Sun City, AZ - USA

Offline PJ

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Re: Technics RS1500 head rewiring
« Reply #10 on: January 24, 2007, 12:19:48 AM »
>> If you wanted to have the ability to switch between the internal preamps and the external, could you just add RCAs for the external preamp and a switch to select?

Of course.

>> If you did this would you introduce unwanted noise, etc?

Of course. The question is, whether it would be enough to notice? Only one way to tell!  :^) If you do, please post results!

>> What if the switch were mounted on top or other place more accessible from the front where the deck is in a cabinet or entertainment center, would the additional run add undesirables?

See above...  :^)
Paul Joppa
Bottlehead R&D

Offline ketchup

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Re: Technics RS1500 head rewiring
« Reply #11 on: February 05, 2007, 07:17:26 PM »
I have a 1506 and am trying to figure out what pins are what on the 1/4 track and 1/2 track playback heads.  My goal is to wire them directly to a Seduction.

Can someone with experience tell me what is R, L, and ground on these heads?

I would really appreciate it.  Thanks.

Offline docb

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Re: Technics RS1500 head rewiring
« Reply #12 on: February 05, 2007, 08:37:19 PM »
Try doing the way I suggest, through the head selector switch and stock cabling, first. The switch is a good quality one and you will retain the ability to play both 1/4 track and 1/2 track tapes.

I don't know which channel is which right and left wise, but on the 1/2 track head one channel is brown + yellow -, the other channel is blue + black -. For the quarter track head one channel is white + yellow -, the other channel is red + black -.

Coming off the output of the switch orange corresponds to red + 1/2track/blue + 1/4 track and violet corresponds to brown + 1/2 track/white + 1/4 track.
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline ketchup

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Re: Technics RS1500 head rewiring
« Reply #13 on: February 05, 2007, 09:47:10 PM »
Thanks, Doc! 

Much appreciated.

You said:
1/2 track:
one channel is brown + yellow -
the other channel is blue + black -

1/4 track:
one channel is white + yellow -
the other channel is red + black -

OK.  Two heads on my deck have those color wires going to them.   The head with the brown, yellow, blue, and black wires appears to have two THIN bands on the heads surface which are not centered on the head.  I would *think* that this is what the 1/4 track head should look like.

The other head, with the white, yellow, red, and black wires has two THICK bands that are centered on the head's surface.  I would *think* that this is what a 1/2 track head would look like.

Am I confused as to what the 1/2 and 1/4 track heads should look like, or is my deck wired differently?

I'm not sure if this would help or not, but the head with the brown, yellow, blue, and black wires is the last head that the tape touches before the take up reel, and the head with the white, yellow, red, and black wires is the first head that the tape touches after it comes off the source reel.

Thanks again!

Offline docb

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Re: Technics RS1500 head rewiring
« Reply #14 on: February 06, 2007, 12:22:36 AM »
Your description of the bands on the heads sounds accurate. The way the wiring is shown in the RS1520 service manual is what I described. So it sounds like yours heads are wired to the opposite sets of wires from what the manual shows. This is certainly possible. I would suggest some experimentation with a prerecorded quarter track tape if you are still uncertain. You would hear both sides of the tape with the half track head and only one side with the quarter track head - assuming the heads are in pretty good alignment.
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project