ulysses
Well-known member
Why would you want to do that?
API 312 Thread!
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khstudio
Well-known member
[quote author="BladeSG"][quote author="AnalogPackrat"]
Bigger C3 give better bass response. Not sure what the tradeoff is. I'm using 1000uF. The originals used 250uF.
A P[/quote]
Just wondering about the statement above, I've searched this thread for info about C3 and cannot find anything else about the reason(s) why there are the 3 choices of 220uF, 1000uF and 4700uF.
Any ideas about the 'tradeoff'?
Thanks,
Steve
had to edit, just realised my 312th post is in this 312 thread. LOL![/quote]
I asked this in another thread & the responce was that a higher value would give a more even/balanced frequency responce @ different gain levels. I think I said that right... I tried the 250uf & liked it but haven't had a chance to hear a 1000uf + yet. I'm making 8 channels of a very similar pre & this is one area I keep wondering about.
Have any of you guys actually listened to the different values & what did you settle on? Is higher better & what did you hear?
Thanks, Kevin
Bigger C3 give better bass response. Not sure what the tradeoff is. I'm using 1000uF. The originals used 250uF.
A P[/quote]
Just wondering about the statement above, I've searched this thread for info about C3 and cannot find anything else about the reason(s) why there are the 3 choices of 220uF, 1000uF and 4700uF.
Any ideas about the 'tradeoff'?
Thanks,
Steve
had to edit, just realised my 312th post is in this 312 thread. LOL![/quote]
I asked this in another thread & the responce was that a higher value would give a more even/balanced frequency responce @ different gain levels. I think I said that right... I tried the 250uf & liked it but haven't had a chance to hear a 1000uf + yet. I'm making 8 channels of a very similar pre & this is one area I keep wondering about.
Have any of you guys actually listened to the different values & what did you settle on? Is higher better & what did you hear?
Thanks, Kevin
NewYorkDave
Well-known member
[quote author="ulysses"]"Aside from that, the only drawback would be that a physically larger capacitor will probably have more inductance and therefore less than perfect HF response. If that's something you're worried about, then bypass the electrolytic with a small film cap (0.01 or 0.1 µF)."[/quote]
But consider what happens when you put a small capacitance across a small inductance: you end up with a parallel "tank" circuit that's resonant at some (high) frequency.
I've never gotten into bypassing 'lytics with films, so I can't say if this is an actual problem in practice. But it's something to watch out for.
But consider what happens when you put a small capacitance across a small inductance: you end up with a parallel "tank" circuit that's resonant at some (high) frequency.
I've never gotten into bypassing 'lytics with films, so I can't say if this is an actual problem in practice. But it's something to watch out for.
khstudio
Well-known member
[quote author="NewYorkDave"][quote author="ulysses"]"Aside from that, the only drawback would be that a physically larger capacitor will probably have more inductance and therefore less than perfect HF response. If that's something you're worried about, then bypass the electrolytic with a small film cap (0.01 or 0.1 µF)."[/quote]
But consider what happens when you put a small capacitance across a small inductance: you end up with a parallel "tank" circuit that's resonant at some (high) frequency.
I've never gotten into bypassing 'lytics with films, so I can't say if this is an actual problem in practice. But it's something to watch out for.[/quote]
Dave,
It's funny you said that... I tried to bypass the electro's on my Topaz Console ( master out section) & didn't like it... it seemed very unbalanced to me... it did raise the highs though.
I haven't really done it enough to hear the differences except for that one time but how does it actually work when applied to a power supply as oppossed to in the circuit? Is it the same?
I hope I made sense :?
Kevin
But consider what happens when you put a small capacitance across a small inductance: you end up with a parallel "tank" circuit that's resonant at some (high) frequency.
I've never gotten into bypassing 'lytics with films, so I can't say if this is an actual problem in practice. But it's something to watch out for.[/quote]
Dave,
It's funny you said that... I tried to bypass the electro's on my Topaz Console ( master out section) & didn't like it... it seemed very unbalanced to me... it did raise the highs though.
I haven't really done it enough to hear the differences except for that one time but how does it actually work when applied to a power supply as oppossed to in the circuit? Is it the same?
I hope I made sense :?
Kevin
I just encountered a strange problem with one of my api channels.
The gain seems to "jump" from normal to very high, very quick and unstable (if you understand what i mean). This happens on higher gainsettings. Up to the the last 10-15dB the pre works like it should, then after that, its behaving very strange.
The other channel works fine.
I tried swapping the opamp, same result.
Is it probably the 22k revlog pot that has gone bad?
/Jonas
The gain seems to "jump" from normal to very high, very quick and unstable (if you understand what i mean). This happens on higher gainsettings. Up to the the last 10-15dB the pre works like it should, then after that, its behaving very strange.
The other channel works fine.
I tried swapping the opamp, same result.
Is it probably the 22k revlog pot that has gone bad?
/Jonas
Rob Flinn
Well-known member
I'm experiencing some weirdness with my API made using Fabios boards & Sowter o/p's.
I connect my scope grounds to earth & connect 1 probe to each phase. When I do this one phase is twice the level of the other . If I swap the probes over this swaps channels on the scope.
I can't understand this. Both ch on the scope are set identically & measure the same when fed with identical signal. The output of the API is straight from the transformer.
I can't figure out why this is happening or whether I'm being stupid. Can anyone shed any light on this ??
I connect my scope grounds to earth & connect 1 probe to each phase. When I do this one phase is twice the level of the other . If I swap the probes over this swaps channels on the scope.
I can't understand this. Both ch on the scope are set identically & measure the same when fed with identical signal. The output of the API is straight from the transformer.
I can't figure out why this is happening or whether I'm being stupid. Can anyone shed any light on this ??
3nity
Well-known member
Hi i'm currently working on 2 fabio's 312.
using OEP input and lynx output and A/B 1731 or JH990.
Could somebody please explain me what's th simpliest schem to follow?? without servo??
and what would be the better option? 22k relog or lorlin rotary switch??
what's the Servo function??
using OEP input and lynx output and A/B 1731 or JH990.
Could somebody please explain me what's th simpliest schem to follow?? without servo??
and what would be the better option? 22k relog or lorlin rotary switch??
what's the Servo function??
ruairioflaherty
Well-known member
Hi 3nity,
I am not very experienced so take my advice with a pinch of salt. I'm planning to build some 312s (perhaps with a fabio board or my own) so the other night I sat down with the original 312 schemo (get it from www.danalexander.com), Fabio's schemo and also the 7th Circle A12 schemo.
I drank coffee and looked, drank more coffee and looked some more and before you know it I had a pretty good understanding of what was happening. Referencing the more complex option laden schemo (Fabio) against the bare bones API makes things clearer. I even had fun :grin:
cheers,
Ruairi
I am not very experienced so take my advice with a pinch of salt. I'm planning to build some 312s (perhaps with a fabio board or my own) so the other night I sat down with the original 312 schemo (get it from www.danalexander.com), Fabio's schemo and also the 7th Circle A12 schemo.
I drank coffee and looked, drank more coffee and looked some more and before you know it I had a pretty good understanding of what was happening. Referencing the more complex option laden schemo (Fabio) against the bare bones API makes things clearer. I even had fun :grin:
cheers,
Ruairi
enthalpystudios
Well-known member
how are peoples group buy cinemags working out? or just people using the cinemags in general... because i'm f-ing digging these....
finally got one channel going, fabio card with cinemags and fabio melcor amps.
forgot the tiny jumper on the melcor, and that was *bad* news. so if anyone is stuffing a melcor board, and hears a ton of f-ed up noise and 1khz and up oscillation stuff, thats probably why ;]
right now i'm trying to listen for the difference with a melcor board that has 100nF decoupling caps on the voltage rails to ground..... its on the melcor, and right next to the sockets as well on fabios board.
and also realized i had to jump pads or solder in the line relay to make a 'normal' connection for the mic input... but once i hammered through these things, i'm finding that my melcors dont like more than +/-18vdc whatsoever, and really respond better to +/-15. But for some reason I recall people running at 24 bipolar!
when i did this, i had breakup at a certain input level, and a distortion that onset regardless of gain setting.
but once i dropped the voltages down, this thing sounds really really nice, i gotta say.
also, regarding the gain capacitor, must it be a lytic? I have some cool film caps i wouldnt mind experimenting with, but i'm at a loss as far as where start, and if thats even 'ok'
hope people are stuffin those cinemags up!
thanks to everybody who posted in this thread, others, and especiially the melcor deconstructed (long one to read when you're impatient to stuff your little guys)
billy
finally got one channel going, fabio card with cinemags and fabio melcor amps.
forgot the tiny jumper on the melcor, and that was *bad* news. so if anyone is stuffing a melcor board, and hears a ton of f-ed up noise and 1khz and up oscillation stuff, thats probably why ;]
right now i'm trying to listen for the difference with a melcor board that has 100nF decoupling caps on the voltage rails to ground..... its on the melcor, and right next to the sockets as well on fabios board.
and also realized i had to jump pads or solder in the line relay to make a 'normal' connection for the mic input... but once i hammered through these things, i'm finding that my melcors dont like more than +/-18vdc whatsoever, and really respond better to +/-15. But for some reason I recall people running at 24 bipolar!
when i did this, i had breakup at a certain input level, and a distortion that onset regardless of gain setting.
but once i dropped the voltages down, this thing sounds really really nice, i gotta say.
also, regarding the gain capacitor, must it be a lytic? I have some cool film caps i wouldnt mind experimenting with, but i'm at a loss as far as where start, and if thats even 'ok'
hope people are stuffin those cinemags up!
thanks to everybody who posted in this thread, others, and especiially the melcor deconstructed (long one to read when you're impatient to stuff your little guys)
billy
[quote author="NewYorkDave"][quote author="ulysses"]"Aside from that, the only drawback would be that a physically larger capacitor will probably have more inductance and therefore less than perfect HF response. If that's something you're worried about, then bypass the electrolytic with a small film cap (0.01 or 0.1 µF)."[/quote]
But consider what happens when you put a small capacitance across a small inductance: you end up with a parallel "tank" circuit that's resonant at some (high) frequency.[/quote]
But wouldn't the parallel capacitance of the electrolytic mean the total capacitance would still be high?
...or am I the one who's high?
But consider what happens when you put a small capacitance across a small inductance: you end up with a parallel "tank" circuit that's resonant at some (high) frequency.[/quote]
But wouldn't the parallel capacitance of the electrolytic mean the total capacitance would still be high?
...or am I the one who's high?
Greg
Well-known member
hi Billy:
I used Cinemag iron in a pair of Eisen Audio 312 type preamps with the John Hardy 990C. I built them and bench tested them. Shortly after, I loaned them to a friend of mine and he's had them ever since. He loves them on percussion... snare and toms the most.
I used Cinemag iron in a pair of Eisen Audio 312 type preamps with the John Hardy 990C. I built them and bench tested them. Shortly after, I loaned them to a friend of mine and he's had them ever since. He loves them on percussion... snare and toms the most.
3nity
Well-known member
Hey i might pass for a fool after this question but i have to ask it...in Fabios 312 could i connect the togle switches at the relays place?
this would avoid any relay use ????
and would avoid the 5V at the PSU.
i started thinking of this when i saw the aromat price. :green:
thanx
this would avoid any relay use ????
and would avoid the 5V at the PSU.
i started thinking of this when i saw the aromat price. :green:
thanx
smallbutfine
Well-known member
3nity,
yes, this is completely possible. Solder the switches to the relays switching pads and there you are.
You can even bridge the toggle options to avoid relay and switch, e.g. if you do not need pad or phase or st like that.
But the use of relays is preferred to the use of switches nevertheless - because switches do need long runs to the frontpanel, while relays keep the audio path short and clean (this is why they are used...)
So, if you use switches, take care of where you run your wires to the switch, be sure to drill them to minimize pick-up of noise and hum.
I think about an intermediate solution like this for mine, too.
Kind regards,
Martin
EDITED: Sorry, replaced 'phantom' with 'pad'...
yes, this is completely possible. Solder the switches to the relays switching pads and there you are.
You can even bridge the toggle options to avoid relay and switch, e.g. if you do not need pad or phase or st like that.
But the use of relays is preferred to the use of switches nevertheless - because switches do need long runs to the frontpanel, while relays keep the audio path short and clean (this is why they are used...)
So, if you use switches, take care of where you run your wires to the switch, be sure to drill them to minimize pick-up of noise and hum.
I think about an intermediate solution like this for mine, too.
Kind regards,
Martin
EDITED: Sorry, replaced 'phantom' with 'pad'...
enthalpystudios
Well-known member
i can't remember what i paid, but i got some very nice tyco dip8 relays for fabios boards from an ebay seller called 'mwrenton'
also have gotten some good caps of different variety's, and a ton of 4-40 nuts, and etc, just different surplus stuff.
looks like right now he's only got some 48v dip16 for .35
but regardless, the price i got on the 5v for fabios boards was awesome.
so, worth looking around imho... also, i lucked out an found exactly 6 C+K pc mount toggles for fabios board surplus for only a few bucks. non-threaded unfortunately....
hopefully i'll be very exact on my frontpanel drills.
regarding the film bypass, I think I may try it just to see what happens, i'd like to experiment with that cap on my units, especially since the opamp isn't a stock 2520... with a melcor, i wonder if the requirements change for that part.
also have gotten some good caps of different variety's, and a ton of 4-40 nuts, and etc, just different surplus stuff.
looks like right now he's only got some 48v dip16 for .35
but regardless, the price i got on the 5v for fabios boards was awesome.
so, worth looking around imho... also, i lucked out an found exactly 6 C+K pc mount toggles for fabios board surplus for only a few bucks. non-threaded unfortunately....
hopefully i'll be very exact on my frontpanel drills.
regarding the film bypass, I think I may try it just to see what happens, i'd like to experiment with that cap on my units, especially since the opamp isn't a stock 2520... with a melcor, i wonder if the requirements change for that part.
I was not being a smartass above. I'm truly wondering if there is a reason that the small inductance of a large electrolytic could create a problem whereby it could overcome the effect of the capacitor (to become a 'short' as the frequency increases). Or if there is a situation where the small inductance of the large electrolytic could interact in a serious way with a small parallel capacitance. I guess they are really the same questions.
Also I've tried to find out what the typical inductance of large electrolytics is - maybe my googling is getting rusty...
Also I've tried to find out what the typical inductance of large electrolytics is - maybe my googling is getting rusty...
smallbutfine
Well-known member
Just a question about C1, C2 and CPP1...
The opamp supply caps are originally as low as 12µ what seems definately an oldschool pricebreaking decision, Fabio's boards use 220µ what some people call 'overkill', so i'm a little bit confused...
I planned to make 2 very fine elna starget powered apis, but couldn't find 220µ's so i decided to go with what i have - would you bother paralleling two 100µ's or do you think this is not worth the trouble at all, as the original was 10 times smaller?
For the phantom power, it's even worse...how critical is this cap concerning sound? How low may i go with capacitance before i will notice a quality loss on condensers? Would it be worth the trouble to parallelize a bunch of good nichicons to get the capacitance?
(OK, i really want to finish these babes, i'm very excited and only have a few holidays left...so want to work with what i have - :razz: )
Maybe someone already experimented 'real life' and could drop in with his thoughts...
Any opinions welcome.
Kind regards,
Martin
The opamp supply caps are originally as low as 12µ what seems definately an oldschool pricebreaking decision, Fabio's boards use 220µ what some people call 'overkill', so i'm a little bit confused...
I planned to make 2 very fine elna starget powered apis, but couldn't find 220µ's so i decided to go with what i have - would you bother paralleling two 100µ's or do you think this is not worth the trouble at all, as the original was 10 times smaller?
For the phantom power, it's even worse...how critical is this cap concerning sound? How low may i go with capacitance before i will notice a quality loss on condensers? Would it be worth the trouble to parallelize a bunch of good nichicons to get the capacitance?
(OK, i really want to finish these babes, i'm very excited and only have a few holidays left...so want to work with what i have - :razz: )
Maybe someone already experimented 'real life' and could drop in with his thoughts...
Any opinions welcome.
Kind regards,
Martin
therecordingart
Well-known member
If I were to construct the R312 from Fabio's BOM "word for word" what are the odds of running into problems?
I'm looking to build a preamp with no frills.
I'm looking to build a preamp with no frills.
I' have realay boards for switching dual primaries (fits cinemag APC7501APC - other xfmrs can be mounted off board) and other Preamp utilities here
http://www.groupdiy.com/index.php?topic=214402#214402
http://www.groupdiy.com/index.php?topic=214402#214402
