Optical units are fine -- most of them are not absolute encoding though, and we definitely do not need high resolution. However, perhaps a Bourns ACE (absolute contacting encoder) can be used instead?
I kind of like having an absolute volume control that by definition knows what the level is set at even if changed when unit is off.
Another alternative is to use only a remote, as this would save on costs provided Dork is already set up with remote. I like to have a manual override though.
I also propose that Dork stage 1 has 5-6 inputs with pre-scaling to calibrate each in level with one set of double outputs.
Dorkstage 2 also could add compound 8 in + 8 out for HT.
I also propose that we make a design which can fit in one box as complexity and hazzle of connectors (not to mention those extra cabinet(s) will drive costs and thus reduce participation.
Petter
I kind of like having an absolute volume control that by definition knows what the level is set at even if changed when unit is off.
Another alternative is to use only a remote, as this would save on costs provided Dork is already set up with remote. I like to have a manual override though.
I also propose that Dork stage 1 has 5-6 inputs with pre-scaling to calibrate each in level with one set of double outputs.
Dorkstage 2 also could add compound 8 in + 8 out for HT.
I also propose that we make a design which can fit in one box as complexity and hazzle of connectors (not to mention those extra cabinet(s) will drive costs and thus reduce participation.
Petter
then we lose remote control capability.
don't worry about keeping level settings. i've gotten that taken care of. my microprocessor will have an SRAM (static memory) which will retain all values even if the unit is unplugged.
the input trimming memories will take care of that. i'm planning on having at least 5, probably 6 inputs. one of the inputs will be pre-programmed to be "direct", e.g. the volume control will not affect it. this is for surround sound processors.
on the contrary, the modular nature of the thing is exactly what will increase participation. by making things interchangable we have far more flexibility with prototyping and implementation. fitting everything into a single large chassis can actually be more expensive, because it forces us to have to build the whole darn thing at once to have a functional unit. on the other hand, let's say i build 6 preamp modules, my control unit, and power supply. someone else wants to try my stuff out. i can very easily send him or her 2 of my preamp modules (for stereo), along with a very rudimentary control module that can be constructed very cheaply. it wouldn't have all the fancy display and interface functions but would be like a development kit of sorts, to allow other people to listen to the preamp in basic form. they could also use their own power supply. the re-usability of modules will save everyone money in the long run IMHO.
actually, now that you mention it... it is quite possible to implement this in as few or many chassis as the user desires. the preamp modules will be a single board each. the power supply is flexible, up to the individual to implement. the control module will need to be a separate unit but again the implementation is flexible. it's quite conceivable that the same preamp PCBs that i use in separate chassis could be stacked into a single chassis. my preamp modules will hopefully be very compact, e.g. 6x6 or somethign like that. you could stack these up into a tall chassis to have all channels together, or put 2 side-by-side in a standard rack mount chassis to have a simple stereo unit. again, the final implementation should be extremely flexible.
cheers,
marc
OK, I give up on the player onboard card.
Yes, the preamp should be modular. But as you figured out,
that means modular boards. You can't force people to use the "correct" number of boxes.
Actually, the Boulder IS worth studying, they do address a lot of these ideas. I don't know the price, but it is sure to be astronomical- which should make us all feel better even with cost overuns! I have to admit-this seems to be catching fire!
Yes, the preamp should be modular. But as you figured out,
that means modular boards. You can't force people to use the "correct" number of boxes.
Actually, the Boulder IS worth studying, they do address a lot of these ideas. I don't know the price, but it is sure to be astronomical- which should make us all feel better even with cost overuns! I have to admit-this seems to be catching fire!
level matching on input
Hi guys,
first some OT:
I am very new on DIY but have actually started on the road to building a scratch Grounded Grid.
Now on T:
One feature I don't see mentioned is a way to level match inputs. In my current setup, different components have their own special settings.
Hi guys,
first some OT:
I am very new on DIY but have actually started on the road to building a scratch Grounded Grid.
Now on T:
One feature I don't see mentioned is a way to level match inputs. In my current setup, different components have their own special settings.
More Specs
Hello Dorkus and All,
I feel these additional specs are required to build a serious multichannel preamp system -
1 - 0.5 dB or better volume steps
2 - Stereo/Reverse/L+R mono/L mono/R mono switching as per older preamps.
3 - Polarity switching of each channel in unison, or independantly - This is useful for finding channel to channel differences.
4 - Volume Up/Down buttons - These work well in conjunction with a digital display of attenuation. (Rotary encoder not required)
5 - Logic output to remotely control power switching of individual sources.
Some other suggestions that come to mind are -
Standardised connector layout modular construction (or multi-option pcb) that allows plug-in connection of different types and topologies of individual stages - eg-
optional tube type or semiconductor output module with options of electronic or transformer balancing,
optional plug-in motorised pot or VCA or electronic attenuator module, or
optional rotary switch or relay matrix or electronic switching module,
optional series regulator or shunt regulator module, etc......etc.
This approach could be implemented with a motherboard and plug-in modular circuit stages. (This is not a new idea).
This would allow upgrading according to budget and easy comparison of different topologies, and optimising to the target system.
Eric.
Hello Dorkus and All,
I feel these additional specs are required to build a serious multichannel preamp system -
1 - 0.5 dB or better volume steps
2 - Stereo/Reverse/L+R mono/L mono/R mono switching as per older preamps.
3 - Polarity switching of each channel in unison, or independantly - This is useful for finding channel to channel differences.
4 - Volume Up/Down buttons - These work well in conjunction with a digital display of attenuation. (Rotary encoder not required)
5 - Logic output to remotely control power switching of individual sources.
Some other suggestions that come to mind are -
Standardised connector layout modular construction (or multi-option pcb) that allows plug-in connection of different types and topologies of individual stages - eg-
optional tube type or semiconductor output module with options of electronic or transformer balancing,
optional plug-in motorised pot or VCA or electronic attenuator module, or
optional rotary switch or relay matrix or electronic switching module,
optional series regulator or shunt regulator module, etc......etc.
This approach could be implemented with a motherboard and plug-in modular circuit stages. (This is not a new idea).
This would allow upgrading according to budget and easy comparison of different topologies, and optimising to the target system.
Eric.
hi eric,
i like your suggestions a lot. i originally wanted to specify 0.5dB steps but i thought this might be impractical. the Wolfson IC part does have this sort of precision but any home-brew scheme may have to be a little coarser. i still prefer a rotary encoder over up/down buttons though, as i like the tactile feeling and direct control of a knob. the remote control will have up/down buttons.
i'm not a big fan for building in channel mixing/switching as each channel will be entirely independent. i do not want any dependencies whatsoever between the channels. polarity switching is very useful though, and something we can implement very easily if we go with a balanced topology.
the plug-in boards are neat also, particularly for prototyping, although i think the final channel module will be a single PCB to optimize the layout. i would really like one channel of the preamp to be contained all on one very compact, neat, and tidy board. this board would include input switching, attenuator, active circuitry, and local supply regulation. i think an optimized preamp design must synergystically combine all these elements into a tightly integrated whole. but again, for prototyping purposes, subdivision would be useful.
from some of your suggestions it sounds like you might be into good ol' tube/analog stuff.
that is cool, but to reiterate i think the goal of this preamp should be to help integrate the most modern of systems. this is a multichannel preamp after all. there are plenty of minimalist stereo preamp designs to go around, but what i (and i suspect some others) need is something to tie together my home theater, traditional CD, and multichannel SACD/DVD-A playback systems.
anybody want to start suggesting some gain stages?
cheers,
marc
i like your suggestions a lot. i originally wanted to specify 0.5dB steps but i thought this might be impractical. the Wolfson IC part does have this sort of precision but any home-brew scheme may have to be a little coarser. i still prefer a rotary encoder over up/down buttons though, as i like the tactile feeling and direct control of a knob. the remote control will have up/down buttons.
i'm not a big fan for building in channel mixing/switching as each channel will be entirely independent. i do not want any dependencies whatsoever between the channels. polarity switching is very useful though, and something we can implement very easily if we go with a balanced topology.
the plug-in boards are neat also, particularly for prototyping, although i think the final channel module will be a single PCB to optimize the layout. i would really like one channel of the preamp to be contained all on one very compact, neat, and tidy board. this board would include input switching, attenuator, active circuitry, and local supply regulation. i think an optimized preamp design must synergystically combine all these elements into a tightly integrated whole. but again, for prototyping purposes, subdivision would be useful.
from some of your suggestions it sounds like you might be into good ol' tube/analog stuff.
that is cool, but to reiterate i think the goal of this preamp should be to help integrate the most modern of systems. this is a multichannel preamp after all. there are plenty of minimalist stereo preamp designs to go around, but what i (and i suspect some others) need is something to tie together my home theater, traditional CD, and multichannel SACD/DVD-A playback systems. anybody want to start suggesting some gain stages?
cheers,
marc
More ADHOC Thoughts
Hiya Dorkus,
To fill you in a little I work 5/40 in my own shop repairing all manner of audio, video, pro audio and lighting gear.
Ancient, classic, state of the art consumer, pro and audiophile are all part of the day to day stuff, and I've been doing this for 25 years.
You get to see a lot of engineering ideas and techniqes this way !.
It's my own shop, so if I feel like it I am able to crank it to the max on the bench on my monitoring system, and so I have done many a truckload of A/B comparisons in my time.
With such practice it now takes me about 10 seconds to determine sonics and if I could stand living with it for any period.
If it inspires my interest, I can even get to take it home and soak test for a day or two.
Anyway to reply,
I have not met any digital rotary controls that I like.
Any less than 1dB steps is inadequate IMO - I notice the Boulder has 0.1dB volume steps.
IMO - Polarity switching is MANDATORY.
I'm not thinking minimalist - I agree that multi-channel is very appropriate.
Call me from the old school, but to compensate for errors in both source material (especially vinyl) and replay system and listening room, equalisation is most desirable, more especially when playing at lower levels.
My favorite amp for general and social listening situation, is an old (20 yrs) Denon dual power transformer, dual power supply integrated amp that has all the pre-amp fruit including a pre-out 0dB/10dB/20dB attenuator and switched tone controls featuring switchable bass and treble turnover points with solid polypropylene caps (values up to 10mF), L/R/M switching, and even more.(no steak knives)
Although this amp is not SOTA ultra-fi, it holds it's own very well indeed, and gives much more fun than most systems that I have heard/experinced/lived with.
Musicality and toe tapping is about pleasant flavour, and not just sterile measured accuracy IMO.
Therefore, compromises on signal path lenghts are ok, and pcb-pcb connectors are ok so long as good pin connectors are used,
and don't do so much damage as some would believe.
The more important things are correct input and output and interstage loading and matching and driving.
So long as techniques that avoid IMD are used, it should not be too hard to build a pre-amp box that is very acceptable.
IME discrete component stages are more friendly sounding .
Perhaps a little more food for thought for you.
Regards, Eric.
Hiya Dorkus,
To fill you in a little I work 5/40 in my own shop repairing all manner of audio, video, pro audio and lighting gear.
Ancient, classic, state of the art consumer, pro and audiophile are all part of the day to day stuff, and I've been doing this for 25 years.
You get to see a lot of engineering ideas and techniqes this way !.
It's my own shop, so if I feel like it I am able to crank it to the max on the bench on my monitoring system, and so I have done many a truckload of A/B comparisons in my time.
With such practice it now takes me about 10 seconds to determine sonics and if I could stand living with it for any period.
If it inspires my interest, I can even get to take it home and soak test for a day or two.
Anyway to reply,
I have not met any digital rotary controls that I like.
Any less than 1dB steps is inadequate IMO - I notice the Boulder has 0.1dB volume steps.
IMO - Polarity switching is MANDATORY.
I'm not thinking minimalist - I agree that multi-channel is very appropriate.
Call me from the old school, but to compensate for errors in both source material (especially vinyl) and replay system and listening room, equalisation is most desirable, more especially when playing at lower levels.
My favorite amp for general and social listening situation, is an old (20 yrs) Denon dual power transformer, dual power supply integrated amp that has all the pre-amp fruit including a pre-out 0dB/10dB/20dB attenuator and switched tone controls featuring switchable bass and treble turnover points with solid polypropylene caps (values up to 10mF), L/R/M switching, and even more.(no steak knives)
Although this amp is not SOTA ultra-fi, it holds it's own very well indeed, and gives much more fun than most systems that I have heard/experinced/lived with.
Musicality and toe tapping is about pleasant flavour, and not just sterile measured accuracy IMO.
Therefore, compromises on signal path lenghts are ok, and pcb-pcb connectors are ok so long as good pin connectors are used,
and don't do so much damage as some would believe.
The more important things are correct input and output and interstage loading and matching and driving.
So long as techniques that avoid IMD are used, it should not be too hard to build a pre-amp box that is very acceptable.
IME discrete component stages are more friendly sounding .
Perhaps a little more food for thought for you.
Regards, Eric.
hi eric,
thanx for the info. you obviously have a lot of experience with gear and i appreciate your input very much.
i too would like very high resolution volume control, .5dB would be good and .1dB would be fantastic but i'm worried about how we will implement it practically. the #1 criteria of the volume control must be minimal degradation of the signal. i still would like a rotary control on the main panel though - i think if we get the resolution of the attenuator high enough, i can up the software to get a very analog-like feel to it. remember, with software, we can fix anything. that's assumming we have a rotary encoder with high-enough resolution (which is why i specified a more expensive part earlier).
i agree with you that the "degradation" caused by things as small as board connectors is often exaggerated. i'm not saying that they don't affect the sound at all, but the change in sound from a single connector is often far too small to be worth fussing over. perhaps several of them in series could become a problem, but i'm not too worried about a couple of them to get our circuits to be more modular.
i am all for toe-tapping musical enjoyment. i was an EE in college but before that i spent my entire life training to become a professional musician... played violin for 15 years, including 5 years of study at a prominent conservatory, only to decide i probably wasn't going to "make it," so i switched to engineering specifically to pursue my next passion, audio. i wound up working in the dot-com sector cuz the pay's better than engineering. in any case, i like to take a balanced perspective on things. i take engineering seriously but in the end i'm still a musician at heart; i have the sound of live acoustic music burned into my brain and that is what provides the ultimate reference for me. thus my system is geared to that - i have an ME amp, Merlin TSM-M speakers, MSB Link DAC (modified), various homebrew and commercial cables, all of which i choose to help me enjoy the music more, not to obtain that sterile "ultra-fi" sound that some audiophiles seem to covet.
as for the tone controls, i'm afraid i'll have to take a rain check on that one. having some HF trim can be useful with bad recordings i suppose, but to be honest i really find the sound of an absolutely pure audio system preferable in the end to an equalized one, even with very poor recordings. yes it may end up sounding obnoxiously bright but if i use a tone control to reduce that it'll come at the cost of some other part of the signal that i didn't want to lose. in fact, i've even found that the more transparent my system becomes, the more some of my "bad" recordings improve. i have plenty of RCA Victor recordings of Jascha Heifetz that are pretty poor quality, but took leaps forward in musical enjoyment when i upgraded my gear - things i never thought could be buried in those distorted soundtracks come alive now.
anyway back to the preamp! someone suggest some gain stages! i guess i should outline some spec though eh? let's say between 10dB and 20dB gain, and very low noise, i'd say an input noise figure of at least -106dBV is desirable. (incidentally that is the noise figure Pass specifies for BOSOZ.) we might actually want two active stages, an input buffer and an output stage. or we could make both input and output stages have gain in a distributed-gain arrangement like Bryston uses. this would work very well as long as we have high enough supply rails, e.g. +/-30V or so. thoughts?
cheers,
marc
p.s. the Boulder stuff looks pretty close to what i am trying to do so i'll go take a look. although i've heard that Boulder gear sounds rather dry... anyone hear it?
thanx for the info. you obviously have a lot of experience with gear and i appreciate your input very much.
i too would like very high resolution volume control, .5dB would be good and .1dB would be fantastic but i'm worried about how we will implement it practically. the #1 criteria of the volume control must be minimal degradation of the signal. i still would like a rotary control on the main panel though - i think if we get the resolution of the attenuator high enough, i can up the software to get a very analog-like feel to it. remember, with software, we can fix anything.
that's assumming we have a rotary encoder with high-enough resolution (which is why i specified a more expensive part earlier).i agree with you that the "degradation" caused by things as small as board connectors is often exaggerated. i'm not saying that they don't affect the sound at all, but the change in sound from a single connector is often far too small to be worth fussing over. perhaps several of them in series could become a problem, but i'm not too worried about a couple of them to get our circuits to be more modular.
i am all for toe-tapping musical enjoyment. i was an EE in college but before that i spent my entire life training to become a professional musician... played violin for 15 years, including 5 years of study at a prominent conservatory, only to decide i probably wasn't going to "make it," so i switched to engineering specifically to pursue my next passion, audio. i wound up working in the dot-com sector cuz the pay's better than engineering.
in any case, i like to take a balanced perspective on things. i take engineering seriously but in the end i'm still a musician at heart; i have the sound of live acoustic music burned into my brain and that is what provides the ultimate reference for me. thus my system is geared to that - i have an ME amp, Merlin TSM-M speakers, MSB Link DAC (modified), various homebrew and commercial cables, all of which i choose to help me enjoy the music more, not to obtain that sterile "ultra-fi" sound that some audiophiles seem to covet.as for the tone controls, i'm afraid i'll have to take a rain check on that one.
having some HF trim can be useful with bad recordings i suppose, but to be honest i really find the sound of an absolutely pure audio system preferable in the end to an equalized one, even with very poor recordings. yes it may end up sounding obnoxiously bright but if i use a tone control to reduce that it'll come at the cost of some other part of the signal that i didn't want to lose. in fact, i've even found that the more transparent my system becomes, the more some of my "bad" recordings improve. i have plenty of RCA Victor recordings of Jascha Heifetz that are pretty poor quality, but took leaps forward in musical enjoyment when i upgraded my gear - things i never thought could be buried in those distorted soundtracks come alive now.anyway back to the preamp! someone suggest some gain stages! i guess i should outline some spec though eh? let's say between 10dB and 20dB gain, and very low noise, i'd say an input noise figure of at least -106dBV is desirable. (incidentally that is the noise figure Pass specifies for BOSOZ.) we might actually want two active stages, an input buffer and an output stage. or we could make both input and output stages have gain in a distributed-gain arrangement like Bryston uses. this would work very well as long as we have high enough supply rails, e.g. +/-30V or so. thoughts?
cheers,
marc
p.s. the Boulder stuff looks pretty close to what i am trying to do so i'll go take a look. although i've heard that Boulder gear sounds rather dry... anyone hear it?
boulder = yuck
i took a look at their high-end preamp, and while it superficially looks similar to what i'm trying to accomplish i did not like the idea of 9 (!!!) op-amp modules per channel. granted they are not all in series and at least they are discrete-based, but i dunno if i would like the sound of that many stages, particularly op-amps which use a lot of feedback. one or two stages maybe (e.g. Bryston BP20) but 9??? but hey, i shouldn't hold a grudge based on looks alone, i'd be curious to hear what it sounds like. i imagine it can't be all that bad (for that much money it better not be) but i'd still put my money on BOSOZ anyday. i'm curious how they accomplish their attenuation though.
i took a look at their high-end preamp, and while it superficially looks similar to what i'm trying to accomplish i did not like the idea of 9 (!!!) op-amp modules per channel. granted they are not all in series and at least they are discrete-based, but i dunno if i would like the sound of that many stages, particularly op-amps which use a lot of feedback. one or two stages maybe (e.g. Bryston BP20) but 9??? but hey, i shouldn't hold a grudge based on looks alone, i'd be curious to hear what it sounds like. i imagine it can't be all that bad (for that much money it better not be) but i'd still put my money on BOSOZ anyday.
i'm curious how they accomplish their attenuation though.
high resolution volume encoder
the biggest challange for volume control is going to be to find a chip/circuit with good resolution... the encoder is still easy, even without a high resolution encoder - the price on this thing is going to be insane if even the encoder is expenseve. there are two possibilities I see for cheap high-rez encoders:
1. use a lo-rez encoder and require several revolutions for full volume range... although some people might not like the feel because its too slow
2. use a pot with a constant voltage across the ends.. many ucontroller boards have an a/d converter (although I'm not familiar with the one you want to use), and you can use it to measure the voltage of the brush on the pot... so now you have an absolute encoder which resolves as well as the a/d converter on the controller.
the biggest challange for volume control is going to be to find a chip/circuit with good resolution... the encoder is still easy, even without a high resolution encoder - the price on this thing is going to be insane if even the encoder is expenseve. there are two possibilities I see for cheap high-rez encoders:
1. use a lo-rez encoder and require several revolutions for full volume range... although some people might not like the feel because its too slow
2. use a pot with a constant voltage across the ends.. many ucontroller boards have an a/d converter (although I'm not familiar with the one you want to use), and you can use it to measure the voltage of the brush on the pot... so now you have an absolute encoder which resolves as well as the a/d converter on the controller.
again, an absolute volume control would prevent the use of remote control. although a pot feeding a ADC would give the most "analog"-like feel by far.
i think a high-res encoder, with fine attenuation steps (0.5dB or better) and a "smart" algorithm that takes encoder acceleration into account will yield a very ergonomically-pleasing control. the beauty of using a microcontroller is that we can tweak the control algorithms endlessly to taste.
i think a high-res encoder, with fine attenuation steps (0.5dB or better) and a "smart" algorithm that takes encoder acceleration into account will yield a very ergonomically-pleasing control. the beauty of using a microcontroller is that we can tweak the control algorithms endlessly to taste.
not enough precision.
it will feel nice but we need precision and repeatability. it will also mess up our input memories scheme, unless we make a "servo" of sorts that will adjust the control automatically as needed. but that's way too much trouble for such a minimal gain in ergonomics. i'm fine with a optical encoder, the one on my Denon surround sound unit is not great but pretty usable, and it is a pretty low-res control. with a little more resolution, i think it'll feel just fine.
it will feel nice but we need precision and repeatability. it will also mess up our input memories scheme, unless we make a "servo" of sorts that will adjust the control automatically as needed. but that's way too much trouble for such a minimal gain in ergonomics. i'm fine with a optical encoder, the one on my Denon surround sound unit is not great but pretty usable, and it is a pretty low-res control. with a little more resolution, i think it'll feel just fine.
Motor Pots & servos
Dorkus, the idea of a dc pot feeding an ADC is standard practice in digital mixing consoles, with a motor to make the knob follow remote signals. ALPS have some low-cost rotary pots designed specifically for this job. The control system is fairly simple, and can easily be handled by a PIC or AVR processor.
If we have a linear pot fed from dc, into an ADC, apply a log or pseudo-log law through an algorithm or look-up table and produce a level control number, that can control a VCA, digital attenuator IC or relay/ss switched attenuator. When a remote signal is received the level is altered and the pot turned to match it, otherwise the level setting tracks the pot.
I've been looking at these ideas since starting to work with the D&R Sirius radio broadcast console, which uses this technique.
Colin
Dorkus, the idea of a dc pot feeding an ADC is standard practice in digital mixing consoles, with a motor to make the knob follow remote signals. ALPS have some low-cost rotary pots designed specifically for this job. The control system is fairly simple, and can easily be handled by a PIC or AVR processor.
If we have a linear pot fed from dc, into an ADC, apply a log or pseudo-log law through an algorithm or look-up table and produce a level control number, that can control a VCA, digital attenuator IC or relay/ss switched attenuator. When a remote signal is received the level is altered and the pot turned to match it, otherwise the level setting tracks the pot.
I've been looking at these ideas since starting to work with the D&R Sirius radio broadcast console, which uses this technique.
Colin
ok, that sounds reasonable. i guess we can leave the choice of control flexible, since it is just software and a single piece of hardware after all. i still prefer a optical encoder just because it has absolutely no dependence on position whatsoever, which is what i want, but that is a design decision we can leave up to the individual implementer. it's a pretty moot point right now anyway, given that we don't even have an attenuator design to control yet.
Encoders & volume control
Optical or mechanical, both can be incremental, with no position dependance. I use mecanical ones with absolutely no problems (3 years of daily service). I've used Bourns ECW series ( http://www.bourns.com/html/encoders.html ) and Alps ( http://www4.alps.co.jp/2002pdf/pdf_e/encoder/ec11.pdf ), with a preference for Bourns, which has a very nice tactile feeling, despite of its low price
Concerning the attenuator, I've posted here a relay based one (http://www.diyaudio.com/forums/showthread.php?s=&postid=19490#post19490 ). But for a 256 step attenuator (8 bits), you will need 32 (!!) relays per channel, thus 160 relays for 5 channels.... A little bit unrealistic
I daily use this 6 bits version, and IMHO the 1.25dB steps are quite fine for my hearing tastes
Just my two cents...
Optical or mechanical, both can be incremental, with no position dependance. I use mecanical ones with absolutely no problems (3 years of daily service). I've used Bourns ECW series ( http://www.bourns.com/html/encoders.html ) and Alps ( http://www4.alps.co.jp/2002pdf/pdf_e/encoder/ec11.pdf ), with a preference for Bourns, which has a very nice tactile feeling, despite of its low price
Concerning the attenuator, I've posted here a relay based one (http://www.diyaudio.com/forums/showthread.php?s=&postid=19490#post19490 ). But for a 256 step attenuator (8 bits), you will need 32 (!!) relays per channel, thus 160 relays for 5 channels.... A little bit unrealistic
I daily use this 6 bits version, and IMHO the 1.25dB steps are quite fine for my hearing tastes
Just my two cents...
inputs anyone..?
What about an USB port and an INet module, so that we can monitor the state of the pre-amp over Internet..???
No-no.. over to something more serious..
This project can become quite interesting. Maybe I overlooked it, but I cannot recall seeing anyone mention input selection anywhere ...
Maybe the number of inputs, and attenuator steps could be set as values in a declaration field for the uP program before compilation.
This would make it easier for people to adapt to their own needs.
Personally I think I would support the idea of integrating an AD within the preamp, but this is really a matter of personal taste, and anyone can adapt to ones personal needs, given that the AD should not be remotely controlled except for a single input line...??
Someone said that the best interconnect is no interconnect, ( except for a short piece of wire...??)
Someone said balanced....
I have been tumbling with the idea of using the X driver as a preamp..
what do people think..??
What about an USB port and an INet module, so that we can monitor the state of the pre-amp over Internet..???
No-no.. over to something more serious..
This project can become quite interesting. Maybe I overlooked it, but I cannot recall seeing anyone mention input selection anywhere ...
Maybe the number of inputs, and attenuator steps could be set as values in a declaration field for the uP program before compilation.
This would make it easier for people to adapt to their own needs.
Personally I think I would support the idea of integrating an AD within the preamp, but this is really a matter of personal taste, and anyone can adapt to ones personal needs, given that the AD should not be remotely controlled except for a single input line...??
Someone said that the best interconnect is no interconnect, ( except for a short piece of wire...??)
Someone said balanced....
I have been tumbling with the idea of using the X driver as a preamp..
what do people think..??
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