Speed Mods

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_DK

_DK

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I was just wondering... Say you have a 1/4" deck with 2 consumer speeds. Let it be A77. How easy or hard is it to modify it to have a third speed of 15 ips? :confused:
Anyone knows? Any websites on that?
 
_DK said:
I was just wondering... Say you have a 1/4" deck with 2 consumer speeds. Let it be A77. How easy or hard is it to modify it to have a third speed of 15 ips? :confused:
Anyone knows? Any websites on that?
Click to expand...

People have done it, but I don't know how. I believe you may have to replace the capstan shaft with a different diameter (which will involve adjusting the pinch roller to compensate).

You might have to swap out the audio cards for 15ips versions. I don't think you can make the A77 into a three-speed unit, though.

This is just for the A77 and B77 - other decks will be very different.
 
I was wondering something similar that might accomplish the same end...

would there be a way to modify a pitch control from +/-30% to +/-100% ?
 
_DK said:
I haven't found any web site that cover that, and what caught my attention is this auction:
He's got the two low speeds in place and he just added that extra one.
Click to expand...
Wow. He must have modified the frequency generator in the capstan driver. I wonder how he sorted out the equalisation, though?
 
jpmorris said:
Wow. He must have modified the frequency generator in the capstan driver. I wonder how he sorted out the equalisation, though?
Click to expand...

Maybe he didn't... I tried emailing him on the subject, but no answer yet.
 
If you were thinking of buying that Ebay A77 I'd be wary. Techs are understandably wary of working on machines that have been modified, especially when there's no documentation of the mods.

The high speed versions had a bigger shaft as already noted. So the only way to get three speeds is to use the big shaft and get more speed irregularities on the slowest speed, or use the smaller shaft and run the motor twice as fast as it was designed to. Neither way is ideal.

These machines also came in super slow versions. 15/16 and 1 7/8. They had a really thin capstan shaft but also a slower revolving DD motor. So the one machine could come with two speeds out of a range of five.


Other Studer Revox models such as the B67 and A700 had the three speeds, using a direct drive capstan motor.

I like the old A77's. Simple and sturdy. My main complaint is the tape path is very hidden. Cleaning heads and guides can be frustrating. The more commercial PR99's had the conventionally raised head block. Much more sensible.

Cheers, Tim
 
I cant be certain but I cannot think of a satisfactory way of getting a A77 to work at
three different speeds.
Apart from actually achieving three speeds mechanicaly there is the problem of setting
bias and equilasation of the frequency response. The equilasation and bias for the 15 ips speed is definately different than the 7.5 ips speed so that takes up one lot of adjustments.

There remains only one set of adjustments left for equilasation and bias and unless the
2 remaining speeds both require identical settings then I cant see how it can be done.
 
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