Hello,
I'm a beginner and working on a very simple preamp for a mono tape head.
I actually only need one side of the chip to since Im just using a mono head. Is it easy or possible to use the other side of this dual op-amp as an extra gain stage? If so what kind of rules do you generally need to follow?
Thank you!
I'm a beginner and working on a very simple preamp for a mono tape head.
I actually only need one side of the chip to since Im just using a mono head. Is it easy or possible to use the other side of this dual op-amp as an extra gain stage? If so what kind of rules do you generally need to follow?
Thank you!
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Is it easy or possible to use the other side of this dual op-amp as an extra gain stage?
Yes, as long as you use DC blocking capacitors at the inputs and the output.
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Yes, as long as you use DC blocking capacitors at the inputs and the output.
Thanks! Would you be able to guide me a little in the direction to make the second gain stage? Would it involve leaving the first stage as is and then removing the NAB eq from the second stage?
Thanks! Would you be able to guide me a little in the direction to make the second gain stage?
Would it involve leaving the first stage as is and then removing the NAB eq from the second stage?
Yes, the only difference would be the feedback network, which becomes just a resistor
instead of the tape eq. For example, short R1 and C1. Change R6 to 750R, for a flat gain
of x11, or +21dB.
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Yes, the only difference would be the feedback network, which becomes just a resistor
instead of the tape eq. For example, short R1 and C1. Change R6 to 750R, for a flat gain
of x11, or 21dB.
Sweet! So does that mean when looping back in (say from left output to right input on to the second stage) I could also leave out C10 & C8? Or would it be better to leave them in as extra RF blocking?
Sweet! So does that mean when looping back in (say from left output to right input
on to the second stage) I could also leave out C10 & C8?
Right, only one DC blocking capacitor is needed for a connection, not two in series.
The C10 should not be necessary either.
Right, only one DC blocking capacitor is needed for a connection, not two in series.
The C10 should not be necessary either.
Thanks, and is there anything to know about how to avoid or even introduce distortion from this type of setup?
Thanks, and is there anything to know about how to avoid or even introduce
distortion from this type of setup?
Careful construction, with a power supply bypass capacitor, should make it work well.
Clipping caused by too high gain would be the easiest way to add distortion.
Careful construction, with a power supply bypass capacitor, should make it work well.
Clipping caused by too high gain would be the easiest way to add distortion.
So if I added a pot in the feedback network of the second stage and then used a some value of limiting resistor in series with the pot I could obtain distortion correct? I will try it also later
So if I added a pot in the feedback network of the second stage and then used a some value
of limiting resistor in series with the pot I could obtain distortion correct? I will try it also later
Should work.
Should work.
Do you feel like it matters to have the NAB on the first or second stage in terms of noise? Also will changing my VDC from 12v to 9v affect gain or introduce other issues or even bonuses?
On another subject, what would be the proper way to split the output of this preamp so that it went to both a 1/4" out as well as back into a recording tape head? Would that entail just splitting off to a bias resistor (or trimmer) to lower the level back down to acceptable record level or would you need any additional parts to keep the split in signal more protected? (I hope that makes sense)
I know I'll need to attempt a DC bias recording circuit which I have heard is not an easy feat... I'm having a hard time finding examples online somehow, just a ton of AC bias circuits which I can't use for my project.
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Rather than use the max gain you should be looking for actual required gain.
That way you aren't introducing any more distortion than you have to.
Also the bandwidth will probably be better with less gain.
Ok cool, I'll keep that in mind. I'm in need of a good deal more than the circuit gives in its current one stage state. I've also been thinking that having the ability to push things into a bit of saturation/distortion (if I need) in the second stage may be a nice option. Will see if there is "nice" involved in the actual tonalities!
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Do you feel like it matters to have the NAB on the first or second stage in terms of noise?
Also will changing my VDC from 12v to 9v affect gain or introduce other issues or even bonuses?
On another subject, what would be the proper way to split the output of this preamp so that
it went to both a 1/4" out as well as back into a recording tape head?
If the eq is earlier in the circuit, there's more headroom. If the eq is later in the circuit, there's less noise.
Lower supply voltage gives less headroom.
If the eq is in the first stage, you could connect the recording tape head to that output,
instead of going through the second flat stage, if the first stage's gain is enough.
If the eq is earlier in the circuit, there's more headroom. If the eq is later in the circuit, there's less noise.
Lower supply voltage gives less headroom.
Somehow I'm only managing to send the circuit into oscillation in this format. Can you think of anything that I should look at first to avoid this?
Thank you
Somehow I'm only managing to send the circuit into oscillation in this format.
Check that the nfb goes to the inverting input in all stages.
Can you post your schematic?
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Check that the nfb goes to the inverting input in all stages.
Can you post your schematic?
I think I'm am following that but I could be wrong. I have attached my schematic. The unlabeled resistor is a 100k.
I have tried this using 750ohm to ground as you had suggested before for R6 but it has similar style behavior.
Do I need to remove C3 and R5 for this scenario? I'm confused as to how to handle both R5 and R6.
Thank you
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Check that the nfb goes to the inverting input in all stages.
Can you post your schematic?
Ok so I got the feedback to stop, just had something in the wrong place
I'm trying to play with the values of R6 and R5 to raise db without distortion.
I've noticed that it seems like R5 isn't necessary, but is that correct?
You seem to be missing a resistor between pin 6 and pin 7.
The overall gain is set approximately by the ratio of the resistor between pin 6 and 7 and the resistor from pin 7 to ground (via its cap of course). No resistor gives unity gain (and it may not be stable like that).
The overall gain is set approximately by the ratio of the resistor between pin 6 and 7 and the resistor from pin 7 to ground (via its cap of course). No resistor gives unity gain (and it may not be stable like that).
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