Hi guys, I want to step up the output from my cassette deck into my Korg DSD recorder and would like your advice about using the Lundahl LL1545a to do the job. I am competent at soldering and can follow a diagram but clueless about impedance transfer. The cassette deck has 2.2kohm output impedance - unbalanced RCA - and the Korg has 50kohm input impedance unbalanced. The LL1545a can be used 1:2 to double the voltage - 500mv to 1V in this case. Any comments would be useful thanks.
> used 1:2 to double the voltage - 500mv to 1V in this case.
Cassette (any analog) playback level can be ALL over the place. If it actually says "500mV", it is surely +/-5dB from there depending on tape and recording choices.
And the Korg DSD recorder's nominal input IS -6dBV which is a half-Volt. I'm sure the level control can trim to the actual level off your tapes. This isn't microphone-level work, and not KORG's first rodeo.
RCA
Connector : RCA (Unbalanced)
Input impedance : 50kΩ
Nominal level ( – 12 dBFS / – 12 dB-SACD)
: – 6 dBV (REC LEVEL = 0 dB)
Maximum level : + 10 dBV
Cassette (any analog) playback level can be ALL over the place. If it actually says "500mV", it is surely +/-5dB from there depending on tape and recording choices.
And the Korg DSD recorder's nominal input IS -6dBV which is a half-Volt. I'm sure the level control can trim to the actual level off your tapes. This isn't microphone-level work, and not KORG's first rodeo.
RCA
Connector : RCA (Unbalanced)
Input impedance : 50kΩ
Nominal level ( – 12 dBFS / – 12 dB-SACD)
: – 6 dBV (REC LEVEL = 0 dB)
Maximum level : + 10 dBV
Thanks for your reply PRR. When making recordings from the cassette deck - Nakamichi CD1 - I don't get enough level about -20db - and so am not making the most of the 'bits' available to me. That is with the output of the cassette deck set on maximum and with a TDK SA tape. I have tried increasing the gain by using the mic inputs of a Profire 610 audio interface. This works and I can now record up to -4db. This sounds better than the straight connection. I would like to get the best quality from the tapes that's possible hence the possible use of transformers here.
A somewhat modern mobile recorder should have something around 100 dB of dynamic range. (BTW, which one is it, Korg seems to have made at least 3 different models?) If you're peaking at -20 dBFS that still leaves 80 dB... more than enough for cassette tape I would have thought. You can boost levels digitally in the audio editor and Bob's your uncle, assuming you're recording in ordinary 24-bit PCM like any sane human being would.
A 1:2 transformer would also quadruple the already high 2.2k source impedance (and present the tape deck with 1/4 the recorder's input impedance). Overall, way more trouble than it's worth. This one calls for an actual line-level amplifier if you can't scrounge together enough input dynamic range as-is. It may be easier to find a higher-performance recording device / soundcard / audio interface if need be, a little over 100 dB of dynamic range really is not outlandish performance these days. The cost of two of these Lundahls would buy you something pretty nice.
A 1:2 transformer would also quadruple the already high 2.2k source impedance (and present the tape deck with 1/4 the recorder's input impedance). Overall, way more trouble than it's worth. This one calls for an actual line-level amplifier if you can't scrounge together enough input dynamic range as-is. It may be easier to find a higher-performance recording device / soundcard / audio interface if need be, a little over 100 dB of dynamic range really is not outlandish performance these days. The cost of two of these Lundahls would buy you something pretty nice.
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If you're 20dB down, a transformer will not help. Even the best transformers will have issues with that much gain - like all amplifying devices transformers have a fixed GBW so the bandwidth drops with increasing gain. At line level you should not target more than 6dB using a transformer, and even that is pushing it.
Your best bet is using active circuitry to increase gain, like you're finding out. One way to combine both technologies is to use balanced drive on a 1:4 (6dB) step up transformer, so you'll get 12dB voltage gain (6dB from the balanced drive). This allows you to have no gain from the amplifying stage but still achieve 12dB total gain.
Your best bet is using active circuitry to increase gain, like you're finding out. One way to combine both technologies is to use balanced drive on a 1:4 (6dB) step up transformer, so you'll get 12dB voltage gain (6dB from the balanced drive). This allows you to have no gain from the amplifying stage but still achieve 12dB total gain.
So would this work - Sangram - if the transformer had unbalanced inputs and balanced outputs and then go into the balanced inputs of my Korg MR2000S DSD recorder which has 22k input impedance and has the ability via its controls to increase/decrease the gain?