Means precisely nothing to anyone here, which was why ARC marked them this way. They are selected from an inventory of types that only they know. You are not going to improve the performance by swapping them for something else without having ANY idea what the important parameters are and indeed anything about these Fets.
What you propose is really unlikely to result in any audible improvement, and you may end up with a broken pre-amplifier, if you don't break it it is just as likely that the proposed changes will substantially degrade its performance.
Some presumably competent engineer at ARC designed this unit and selected components specifically to work in it under a wide variety of conditions including production tolerances of other components, aging, temperature, etc. It's OK not to like the end result of that process, but I doubt you will have much success second guessing him without a whole lot more information.
It might make sense to sell this unit and buy or build something you like better, at least consider it.
What you propose is really unlikely to result in any audible improvement, and you may end up with a broken pre-amplifier, if you don't break it it is just as likely that the proposed changes will substantially degrade its performance.
Some presumably competent engineer at ARC designed this unit and selected components specifically to work in it under a wide variety of conditions including production tolerances of other components, aging, temperature, etc. It's OK not to like the end result of that process, but I doubt you will have much success second guessing him without a whole lot more information.
It might make sense to sell this unit and buy or build something you like better, at least consider it.
This means that there is feedback between the tape deck's input and output.
This is typically caused by not having a "tape monitor" switch.
Disconnect the playback cables from your recorder and it will stop
if this is the problem.
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From the schematic, this unit does lack a tape monitor switch, so never select tape playback when recording.
The preamp does not have any special provision for tape playback, it's just an "AUX" input wired like the other line inputs.
The tape out is also always enabled.
I'm sure there was one sentence about it, buried near the back of the manual.
Instead, they could have used the relay control circuit to enable tape out only
if tape playback is not selected. Very simple, just one extra relay for the tape out.
Wire the coil in parallel with the tape in coil, but normally on, instead of normally off
like all the other relays.
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Make sure to never select tape playback when recording. That will prevent the feedback.
Based on the schematic it appears you have to select phono in order to record as record out is after the selector relays. I also just noticed this phono stage is a mix of passive and active EQ and there is EQ on the output.
I think the answer here is that an external buffer is required between the recorder and SP16 record out.. I would use something like the OPA2134 as a unity gain buffer with an input impedance of up to 1M ohm..
I think the answer here is that an external buffer is required between the recorder and SP16 record out.. I would use something like the OPA2134 as a unity gain buffer with an input impedance of up to 1M ohm..
I suspect he was trying to record without selecting phono, and leaving the selected input as tape.
Then he'd have feedback, and not notice that he couldn't record.
If that were the case the reported results would make a lot of sense.
Given the design of the phono stage it still needs to be isolated from the relatively low input impedance of the recorder which is 47K which will affect the accuracy of RIAA equalization badly.
I have no idea what they were thinking when they designed this thing.
Given the design of the phono stage it still needs to be isolated from the relatively low input impedance of the recorder which is 47K which will affect the accuracy of RIAA equalization badly.
I have no idea what they were thinking when they designed this thing.
Yes, I did that in some of the tube preamps that I built for those with tape decks.
Otherwise, the RIAA stage is messed up by the tape machine loading and cable.
The alternative is to enable the tape out jacks only when recording. I did that as standard build,
with an extra switch. That wouldn't help the RIAA stage when recording from it, though.
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sp16
doing tests on my turntable place one capsule MM drodujo not my fault connected with the REC but when the disc hear the oscillation started again and I had to put the mute to avoid breaking the speakers.
I had commented that when you do this varies the high voltage going to the plates of the valves phono 300v the FET Q6 so I wanted to change but as color which is not, could be a BUX 84, I think I could be wrong
If I can help I would not like to leave it like this.
Cheers
doing tests on my turntable place one capsule MM drodujo not my fault connected with the REC but when the disc hear the oscillation started again and I had to put the mute to avoid breaking the speakers.
I had commented that when you do this varies the high voltage going to the plates of the valves phono 300v the FET Q6 so I wanted to change but as color which is not, could be a BUX 84, I think I could be wrong
If I can help I would not like to leave it like this.
Cheers
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