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quick tape out wiring question

jpk

pfm Member
I am still working on my preamp project (based on the Starfish, see here) and want to add a tape out / pre out in order to be able to connect my headphone amp to it. Looking at the early Naim preamps there are just 680 Ohm resistors to the tape out: would that be fine, and if yes should I take them from the output of the source selector or from the input of the volume pot? In other words: I am not sure if the tape out should be taken before or after the 729 circuit...
 
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Tape out and pre out are different things... Tape out comes from before the volume control, hence a recording you are making stays at the same level no matter what you do with the vol control.
For tape out take it from the output of the source selector.
A nice extra is to use a buffer between source selector and tape out. This isolates the two so if whatever is connected to tape out presents a highly non linear load when its switched off then this can't affect the main signal path.
 
Many thanks! So a dedicated buffer would be the best solution: I draw a diagram, see below, the version with the extra tape buffer is marked with "C":
9AOdB9K.jpg

If not using an extra tape buffer, would it be OK to take the tape out through a 680R, and if yes, as in "A" or in "B"...?
 
if your headphone amp has any kind of buffer then just take an output straight from the input selector switch, no resistor or 324 circuit required I used to have the same for my tape machine out for recording, I never liked the tape out on old amps it just seemed to muddy the sound ?
For headphone out I now use a Salas DCG3 Pre amp which includes a headphone out
Alan
 
C would ensure that no item of equipment which is plugged into tape out can "drag down" the rest of the pre amp. The problem usually happens when the item plugged into tape out is switched off. Many things are harmless in this regard but quite a few are not.... I designed and built a passive with active tape out buffers for a customer whose AV gear plugged into tape out was causing bad distortion to his usual pre amp when the AV receiver was switched off....

IF you can be completely certain that whatever you are driving from tape out is harmless and has a high input impedance even when switched off then "A" is the purest signal path to tape out.

The 680R resistors are no doubt to help give a little isolation but are not really adequate.
 
Just an FYI:
A is how the 42/62/92 did it, albeit with a 324 buffer
B is how the NAIT1 and 2 did it, but without any buffer
C is how the 32/72/52/82 does it.
 
Yep. With some logic/switch wiring to prevent the tape output feeding into its inputs.
 


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