Compressor/limiter? Apparently optical's not fast enough for peak protection though... optical compressor and vca peak max limiter?
Design of that module can be your job. I've never used one as an effect, nor needed one for protection.
Wow, so many post reply about this thread.
Actually, i'm very interesting about aguilar preamp, but when i'm googling to search aguilar schematic, i didn't found yet.
I think a good bass preamp should have:
- Built in slap button ( mid scoop eq ), should be enable using footswitch
- at least 4 parametric eq
- Compressor / Limiter
- Presence/ bright
Lets, start stage by stage.
Assume our bass is Fender JAzzbass without onboard preamp, what is a suitable gain stage should be? Buffer+ Inverting? Using TL072 Opamp?or any opamp?😀
Actually, i'm very interesting about aguilar preamp, but when i'm googling to search aguilar schematic, i didn't found yet.
I think a good bass preamp should have:
- Built in slap button ( mid scoop eq ), should be enable using footswitch
- at least 4 parametric eq
- Compressor / Limiter
- Presence/ bright
Lets, start stage by stage.
Assume our bass is Fender JAzzbass without onboard preamp, what is a suitable gain stage should be? Buffer+ Inverting? Using TL072 Opamp?or any opamp?😀
An opamp for the input is good idea.
I suggest OPA2134 ,way less noisy than the antediluvian
TL0xx series, though each one can choose one according
to own his taste.
Stage by stage is a good idea.
I have about 3 dozen basses, some active, some passive, and they all vary in level quite a bit it seems. As this is DIY, best bet would be to direct record your instrument(s) and see what levels that produce with a variety of techniques, then adjust the gain to suit your needs. You could even set it to a mid range value and use a pot or switches to dial it for a particular instrument.
I think the input stage should have sufficient gain to get it to near line level so a balanced stage could also be run from here, independent of any processing as a clean DI.
After the i/p stage, whatever that is, you could split the signal and run a pair of parallel paths, maybe one with a traditional Fender type passive stack and the other with parametric.
If as a group we decide to do modular stages, then individuals can mix and match what they want and need. Or would people prefer to have it resolved to a single design?
In my case at least I'll also be adding a 5pin XLR and PSU for my Alembic.
Now that I've mentioned it, the state variable filters used in the Alembic instruments and pre's can be very powerful tone shapers.
A good Preamp should have active/passive input and Impedance matching at the output.
An active onboard preamp usually generates mid bright sound, my question is, how to keep an original taste of this passive fender bass?
An active onboard preamp usually generates mid bright sound, my question is, how to keep an original taste of this passive fender bass?
There isn't any impedance matching necessary as the high Zin that suits a passive will work fine for an active. My previous point was that differing active systems and pickups give differing output. One of my factory active basses has about the same level as another that uses the same pickups.
Not true in my experience; like pickups they vary.
I assume by 'taste' you mean tone (but correct me if I'm wrong - assume language misunderstanding). A Jazz bass is a couple of inductors with series pots so cable capacitance and input Z of the amp all affect tone. These can be varied to some extent to change the tone if you want, but you still need a fairly high Zin for the amp. A clean gain buffer stage will then keep you closest to the original tone.
I've often heard the statement that active electronics make the instrument too bright, and I personally think that's unfounded. A properly designed preamp means that cable capacitance no longer rolls of the signal. I'd much rather have a knob to determine the high roll-off than be dependent on the used cable and amplifier and used potmeters.
I think poorly designed tone-controls have more to do with bad sound, and you run the same risk when designing them for a preamp (the circuitry of which to all intents and purposes, is not that much different from active electronics).
I'm interested to see Aguilar schematics as well, as well as the Mike Pope preamp and the commercial germanium mike preamp which is also out there, but I have the feeling that they might not be all that special (from a circuit topology point of view).
The OPA2134 someone mentioned sounds excellent, the preamp in my precision bass has one (used as a buffer, the remaining stage is a precision railsplitter).
A compressor is also an excellent addition, it can really "fatten" up your sound.
There are a couple of schematics out there we could use, the Demeter Compulator is one (optical), but a Ross compressor (ancient, OTA based) is also an option. Alternatively, we could use the envelope detector of an envelope filter like for instance the Lovetone Meatball, and use the (LED) output for a optically controlled gain stage. That would leave you with loads of knobs to twiddle.
Edit:
Ah, Brett caught most of it already, serves me right for starting to type immediately!
Filter tone controls would be superb as well, I have made a few for my instruments, not too hard to do and really nice tone-shapers indeed. That would be nice, Fender stack and two filters. That Alembic XLR is a great idea too Brett, means you don't have to mess with that little box anymore, even Alembic hasn't got that on any of their pre's, right?
As for input topology, a discrete opamp could be very nice as well, that's what Glockenklang uses in their preamp.
I think poorly designed tone-controls have more to do with bad sound, and you run the same risk when designing them for a preamp (the circuitry of which to all intents and purposes, is not that much different from active electronics).
I'm interested to see Aguilar schematics as well, as well as the Mike Pope preamp and the commercial germanium mike preamp which is also out there, but I have the feeling that they might not be all that special (from a circuit topology point of view).
The OPA2134 someone mentioned sounds excellent, the preamp in my precision bass has one (used as a buffer, the remaining stage is a precision railsplitter).
A compressor is also an excellent addition, it can really "fatten" up your sound.
There are a couple of schematics out there we could use, the Demeter Compulator is one (optical), but a Ross compressor (ancient, OTA based) is also an option. Alternatively, we could use the envelope detector of an envelope filter like for instance the Lovetone Meatball, and use the (LED) output for a optically controlled gain stage. That would leave you with loads of knobs to twiddle.
Edit:
Ah, Brett caught most of it already, serves me right for starting to type immediately!
Filter tone controls would be superb as well, I have made a few for my instruments, not too hard to do and really nice tone-shapers indeed. That would be nice, Fender stack and two filters. That Alembic XLR is a great idea too Brett, means you don't have to mess with that little box anymore, even Alembic hasn't got that on any of their pre's, right?
As for input topology, a discrete opamp could be very nice as well, that's what Glockenklang uses in their preamp.
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Well I know of a few things but can't find them! I've seen a mega-simple optical comp. using just a LED, LDR and 741, anyone else seen it? Can't find the schematic... Don't know about the limiter though, maybe this?
An externally hosted image should be here but it was not working when we last tested it.
Got a trigger-indicator with it too...
An externally hosted image should be here but it was not working when we last tested it.
Original page here
Well, there are a few compressor schematics out there. Here are a few candidates:
There's the Flatline compressor by John Hollis, but I couldn't get that to work properly, the rectifier portion driving the LED is a bit too simple.
The Ross Compressor, working on this one right now, can be found on the General Guitar Gadgets site. OTA based
Demeter Compulator, very simple optical compressor with a precision rectifier driving the LED in a Vactrol. Mine distorts a bit, will need to do some more tweaking.
Alternatively, we could use the envelope detector part of the Meatball:McMeat.pdf and replace the filter with a simple gain stage.
For a limiter there's this one:
Which is based on a LA-2a limiter.
Edit:
Actually, that's not a precision rectifier driving that LED in the Compulator, or is it? At least there is one in the Meatball schematic.
There's the Flatline compressor by John Hollis, but I couldn't get that to work properly, the rectifier portion driving the LED is a bit too simple.
The Ross Compressor, working on this one right now, can be found on the General Guitar Gadgets site. OTA based
Demeter Compulator, very simple optical compressor with a precision rectifier driving the LED in a Vactrol. Mine distorts a bit, will need to do some more tweaking.
Alternatively, we could use the envelope detector part of the Meatball:McMeat.pdf and replace the filter with a simple gain stage.
For a limiter there's this one:
Which is based on a LA-2a limiter.
Edit:
Actually, that's not a precision rectifier driving that LED in the Compulator, or is it? At least there is one in the Meatball schematic.
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Here are some other interesting schematics:
Silonex Compressor
Silonex Limiter
These are application sheets from Silonex, a company which makes these optocouplers, Uriah here on the forum sells these as they are also used in the Lightspeed attenuator.
Silonex Compressor
Silonex Limiter
These are application sheets from Silonex, a company which makes these optocouplers, Uriah here on the forum sells these as they are also used in the Lightspeed attenuator.
No, I don't know what it is, it's a very strange circuit? - but I don't see how it could be a rectifier?.
Yes, these optical compressors or limiters work with "something" driving a LED (light emitting diode), which is pointed at an LDR (light dependent resistor) which controls an amplifier.
The "something" driving the LED can either kick in at a certain level, which makes it a limiter. Or, drive the LED proportionally accoring to signal level, which makes it a compressor.
Quite often the LED and LDR are mounted in a housing together and sold as a unit, the "Vactrol", "Analog Photoisolator", "Optocoupler" etc. etc.
The "something" driving the LED can either kick in at a certain level, which makes it a limiter. Or, drive the LED proportionally accoring to signal level, which makes it a compressor.
Quite often the LED and LDR are mounted in a housing together and sold as a unit, the "Vactrol", "Analog Photoisolator", "Optocoupler" etc. etc.
An optoacoupler can act as a variable resistor inside a circuit, lets say a feedback loop, and because of no contact points it doesnt have the bad sides of a pot. You regulate the resistance by a led coupled to a light variable resistor. Regulating the led light gets you to control the resistance applied to the signal without distortions and nasty effects.
Look for the lightspeed attenuator for an implementation of it 😎
Look for the lightspeed attenuator for an implementation of it 😎
I would be very interested as well!
By the way, threadstarter, how's about actually contributing something?
By the way, threadstarter, how's about actually contributing something?
SOmetimes i confused about designing something, i don't have a good experience about analog signal processing.
Need a guidance about this preamp design😀
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