the title of the tread says all...
i have 10 opa2134 so i want to use it
in my PA soundsystem i have this problem:
the output voltage of the electronic 4way crossover is not enough to bring the power amplifier near the "clipping region"(full power),neither if i make all its input and output gains to the max.
so i think that a preamp with a +15dB gain is what i need.
for an unbalanced preamp i was looking at the project88 of sound whesthost, but i need a balanced one,so i need some help.
some question:
i really need a differential opamp like the opa1632 after the two stage of the preamp?
cause i don't need of volume or balance pot between the two stage, i really need of two stage for the preamp?
thanks in advantage for your reply!
i have 10 opa2134 so i want to use it
in my PA soundsystem i have this problem:
the output voltage of the electronic 4way crossover is not enough to bring the power amplifier near the "clipping region"(full power),neither if i make all its input and output gains to the max.
so i think that a preamp with a +15dB gain is what i need.
for an unbalanced preamp i was looking at the project88 of sound whesthost, but i need a balanced one,so i need some help.
some question:
i really need a differential opamp like the opa1632 after the two stage of the preamp?
cause i don't need of volume or balance pot between the two stage, i really need of two stage for the preamp?
thanks in advantage for your reply!
if you don't need extreme CMRR then you can roll your own with several op amps and ratio matched resistors
"instrumentation amplifier" is another name, can be done with 2 or 3 op maps:
Building a differential amplifier : OPERATIONAL AMPLIFIERS
Doug Self has a book on preamp design
some info in http://www.douglas-self.com/ampins/balanced/balanced.htm - fig 13 is a 2-op amp hi-Z differential reciever
"instrumentation amplifier" is another name, can be done with 2 or 3 op maps:
Building a differential amplifier : OPERATIONAL AMPLIFIERS
Doug Self has a book on preamp design
some info in http://www.douglas-self.com/ampins/balanced/balanced.htm - fig 13 is a 2-op amp hi-Z differential reciever
Last edited:
yes,but in the schematics i've seen for balanced preamp,there was (after the preamp stage) opa 1632 that is a fully differential opamp and has 2 different output, (out+/out-)
the instrumentation amplifier has just 1 out...
or i've missed something?
i'm studying something like this schematics,but i would not required the opa1632..
the instrumentation amplifier has just 1 out...
or i've missed something?
i'm studying something like this schematics,but i would not required the opa1632..
Last edited:
strictly speaking "balanced" in audio interfaces only refers to balanced impedance in the +,- lines source's output, and differential receiver with balanced (or very high) Z inputs
the differential receiver gives common mode rejection - breaks gnd loops, often cures hum
if your amps have balanced inputs then you only need to match the series Z in +,- lines of your pre's output and can use the instrumentation amp output gnd as the negative line out "source"
or you can invert the instrumentation output with another op amp if you think you need bipolar drive of the +,- balanced amp inputs
the differential receiver gives common mode rejection - breaks gnd loops, often cures hum
if your amps have balanced inputs then you only need to match the series Z in +,- lines of your pre's output and can use the instrumentation amp output gnd as the negative line out "source"
or you can invert the instrumentation output with another op amp if you think you need bipolar drive of the +,- balanced amp inputs
Last edited:
i'm trying to do a preamp similar to this schematics, preferably without using the opa1632 (that i have to buy).
i have balanced output at the crossover and i have balanced input at the power amplifier,i have to rest balanced even in my preamp.
i have balanced output at the crossover and i have balanced input at the power amplifier,i have to rest balanced even in my preamp.
I can't get excited over "eye candy" symmetry when there is little reason to belive in a audible difference - much less clear "better"
instrumentation amp diff receiver > volume pot (or not) > output buffer/amp (skip this too if you have enough gain in the front end)
put the same value R in series with the pre's buffer/amp output and the local gnd and be done
do look through Doug Self's balanced audio page - some of his diff amp cicuits can be changed to have fixed gain by changing the R ratios
for instance his fig 12 R3,4 can be upped to give gain, fig 4b shows the balanced impedance output
instrumentation amp diff receiver > volume pot (or not) > output buffer/amp (skip this too if you have enough gain in the front end)
put the same value R in series with the pre's buffer/amp output and the local gnd and be done
do look through Doug Self's balanced audio page - some of his diff amp cicuits can be changed to have fixed gain by changing the R ratios
for instance his fig 12 R3,4 can be upped to give gain, fig 4b shows the balanced impedance output
Last edited:
OK
yesterday i have not seen your edit and i didn't understand your post.
the circuit in fig12 is very interesting
i can up r3 and r4 to 47K to have a 4.7voltage gain (it's right?) letting all other resistance to 10K.
the input resistance of the amplifiers is just 10K for the hot and the cold input.
you think it will be fine?
thank you for helping me!
yesterday i have not seen your edit and i didn't understand your post.
the circuit in fig12 is very interesting
i can up r3 and r4 to 47K to have a 4.7voltage gain (it's right?) letting all other resistance to 10K.
the input resistance of the amplifiers is just 10K for the hot and the cold input.
you think it will be fine?
thank you for helping me!
at least use 1% metal film which are pretty cheap nowdays, should keep CMRR over 24 dB without sorting
but even a cheap digital multimeter can sort R to much better than 1% match - if not absolute accuracy
the formula for diff input Z is a little more complicated but it is balanced, and higher than the input R
but even a cheap digital multimeter can sort R to much better than 1% match - if not absolute accuracy
the formula for diff input Z is a little more complicated but it is balanced, and higher than the input R
Attachments
Last edited:
ok, i have several 10K and 47K 1% metal film resistor at home
i can sort it with a digital multimeter
in your design i think i have to add a R from hot input to gnd and one from cold input to gnd,something like 47K or less,to set input resistance,or not?
a CMRR low as 24dB could be a problem?
this pre is connect with the xover and with the amp via 50cm shielded cables so noise on common mode should be not so a real problem,or i 've do't understand the meaning of CMRR?
sorry for my newbie question😛
i can sort it with a digital multimeter
in your design i think i have to add a R from hot input to gnd and one from cold input to gnd,something like 47K or less,to set input resistance,or not?
a CMRR low as 24dB could be a problem?
this pre is connect with the xover and with the amp via 50cm shielded cables so noise on common mode should be not so a real problem,or i 've do't understand the meaning of CMRR?
sorry for my newbie question😛
input R to gnd is a good idea if you have DC blocking caps in the path, a floating xfmr output or don't know if you do
they also have to match well to not upset the balanced interface
they also have to match well to not upset the balanced interface
PuccioQM
i'm curious to know what x-over and amps you have in your P/A system and what console/mixer your using also what sort of cabling you have to interconnect it all?
i'm curious to know what x-over and amps you have in your P/A system and what console/mixer your using also what sort of cabling you have to interconnect it all?
Hi turk
xover is T.racks ds2/4 (4way digital xover from thomann.de)
amp is T.amp proline 3000 for 2X1500WRMS subwoofer
another amp is camco DX12 for 2X900WRMS kick bass
i use a consolle Vestax VCI-300MKII for djing
i connect consolle with jack mono cable (50cm) with a DI-box (ultra DI-20)
from DI to xover I use xlr cables (usually 5mt or 10mt)
from xover to amps xlr cables (50cm)
that's all
xover is T.racks ds2/4 (4way digital xover from thomann.de)
amp is T.amp proline 3000 for 2X1500WRMS subwoofer
another amp is camco DX12 for 2X900WRMS kick bass
i use a consolle Vestax VCI-300MKII for djing
i connect consolle with jack mono cable (50cm) with a DI-box (ultra DI-20)
from DI to xover I use xlr cables (usually 5mt or 10mt)
from xover to amps xlr cables (50cm)
that's all
well all this stuff seems resonable gear
i couldn't find any info on the Vestax mixer and thomann's website does't seem big on giving very detailed info on the t. stuff but if that t.racks x/over is anything like other driverack units i've encountered you should go through the initial configuration and setup to determine if any limiting or compression is engaged a few caught me because instead of output level the where controlling attenuation (kinda backwards) so without being there to hear what kind of spl your getting out of your rig you may have more head room than you realize just because your not lighting up clip indicators on the amps doesn't mean your gain structure is bad. the only thing i'm wondering about is the di your using ,is this to convert an unbalanced rca or 1/4 inch output on your mixer to the xlr input on the x-over if so rather then use a di you can make a cable with the appropriate pinning for this purpose
i couldn't find any info on the Vestax mixer and thomann's website does't seem big on giving very detailed info on the t. stuff but if that t.racks x/over is anything like other driverack units i've encountered you should go through the initial configuration and setup to determine if any limiting or compression is engaged a few caught me because instead of output level the where controlling attenuation (kinda backwards) so without being there to hear what kind of spl your getting out of your rig you may have more head room than you realize just because your not lighting up clip indicators on the amps doesn't mean your gain structure is bad. the only thing i'm wondering about is the di your using ,is this to convert an unbalanced rca or 1/4 inch output on your mixer to the xlr input on the x-over if so rather then use a di you can make a cable with the appropriate pinning for this purpose
vestax vci300 is a "all-in-one" usb consolle with an integrated soundcard.
Its master output is from 2X Jack 1/4" stereo (balanced).
I use the DI box only for practical reasons (I'd change the termination of xlr longer cables),but it's a unity gain DI...
Its master output is from 2X Jack 1/4" stereo (balanced).
I use the DI box only for practical reasons (I'd change the termination of xlr longer cables),but it's a unity gain DI...
well if your output is in fact balanced you should not need the DI
you did say that your using a 50 cm mono plug from the output of your console to the DI ?
once again before building a preamp i'd find a 1/4 inch stereo plug (Tip Ring Sleeve) and wire Tip to xlr pin 2 Ring to xlr pin 3 Sleeve to xlr pin 1 you would need two for L/R outputs
i might be wrong but i think what's happening is your grounding one half of your balanced line which would reduce your gain
most DI's are intended to change a high impedance unbalanced line to low impedance balanced line in your circumstance you may be further reducing your gain
you did say that your using a 50 cm mono plug from the output of your console to the DI ?
once again before building a preamp i'd find a 1/4 inch stereo plug (Tip Ring Sleeve) and wire Tip to xlr pin 2 Ring to xlr pin 3 Sleeve to xlr pin 1 you would need two for L/R outputs
i might be wrong but i think what's happening is your grounding one half of your balanced line which would reduce your gain
most DI's are intended to change a high impedance unbalanced line to low impedance balanced line in your circumstance you may be further reducing your gain
hi turk
using DI my gain not reduce,i've try with and without it.
using it the sound it's a little more "controlled",so i think i'll continue using it.
i've no time these days for make some test....but in the next week i'll make some test at the voltage output amplifier,mainly for set up my limiter treshold (and not burn loudspeaker!)
i'll update here whatever the situation and solution i'll find!
behaving differently is not correct for people who helped me and for the forum!
thanks
using DI my gain not reduce,i've try with and without it.
using it the sound it's a little more "controlled",so i think i'll continue using it.
i've no time these days for make some test....but in the next week i'll make some test at the voltage output amplifier,mainly for set up my limiter treshold (and not burn loudspeaker!)
i'll update here whatever the situation and solution i'll find!
behaving differently is not correct for people who helped me and for the forum!
thanks
- Status
- Not open for further replies.