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Author Topic: input impedance 47k or 100k?  (Read 4190 times)

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Offline xcortes

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input impedance 47k or 100k?
« on: November 29, 2010, 04:56:37 PM »
my kit manual, schematic and parts include 47k for input resistors. shouldn't these be 100k for the tape version?

thanks
Xavier Cortes

Offline Paul Joppa

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Re: input impedance 47k or 100k?
« Reply #1 on: November 29, 2010, 05:24:06 PM »
We have used 100K in the Repro, because that has worked well with the extended response tape head from Flux Magnetics. However, unlike phono preamps, there is no real standard for tape heads. The circuit will work fine with any value below 500K, so you can substitute whatever works best with your tape machine. In the early days, we used 250K or even 500K adjustable trimmers, but a single resistor is going to be more reliable and quieter.

I do show 47K in the schematics for all Eros variants. But I've always expected that builders would substitute if they wanted a different value, or a better quality resistor.
Paul Joppa

Offline xcortes

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Re: input impedance 47k or 100k?
« Reply #2 on: November 29, 2010, 05:26:31 PM »
i have 100k in my seduction and i'm pretty sure my repro is 100k so i guess i'll use that. my tape machines are a technics with an extended response head and an atr 102.

thanks
Xavier Cortes

Offline Doc B.

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Re: input impedance 47k or 100k?
« Reply #3 on: November 29, 2010, 05:29:13 PM »
I doesn't make a huge difference, but if you really want to get super tweaky the best bet might be to put in a 249K trimmer and find the sweet spot for the particular playback head you are using by running a tone tape and looking at the 1K, 10K and 15K tones. Adjust the trimmer for the flattest top end response. Old high inductance heads like early Ampex might like a bit higher load. Newer medium inductance heads are probably happy with 47K to 100K without showing much change in top end response, and some low inductance heads might like 47K (or maybe even  a bit lower?) best.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline xcortes

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Re: input impedance 47k or 100k?
« Reply #4 on: November 29, 2010, 05:33:47 PM »
since i already installed a 47 k i guess i will try that. thanks
Xavier Cortes