audio board and +4db connection
- Thread starter danixdj
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Theremingenieur
Senior Member+
I'd use a passive ca. 1:20 voltage divider before sending +4dB signals into the sgtl5000, something like either a 47k : 2.7k.
Or use a logarithmic 50k pot
Or use a logarithmic 50k pot
PaulStoffregen
Well-known member
You're going to need an amplifier to increase the output beyond the roughly 3Vp-p maximum output. The SGTL5000 simply can't create a higher voltage signal.
Thank you Paul, any suggestion for amp circuit?
PaulStoffregen
Well-known member
The basic non-inverting gain circuit should work.
http://www.radio-electronics.com/info/circuits/opamp_non_inverting/op_amp_non-inverting.php
You will also need a resistor between the input to ground, because the audio shield has a capacitor in series. This extra resistor is need for stable DC voltage, because the capacitor only passes AC signals.
Or you might use the "Non-inverting amplifier using single supply" circuit shown ;later on that page. The capacitor C1 is already present on the audio shield. If using that circuit, you'll probably also need a capacitor in series with the output, to block the opamp's DC voltage offset.
http://www.radio-electronics.com/info/circuits/opamp_non_inverting/op_amp_non-inverting.php
You will also need a resistor between the input to ground, because the audio shield has a capacitor in series. This extra resistor is need for stable DC voltage, because the capacitor only passes AC signals.
Or you might use the "Non-inverting amplifier using single supply" circuit shown ;later on that page. The capacitor C1 is already present on the audio shield. If using that circuit, you'll probably also need a capacitor in series with the output, to block the opamp's DC voltage offset.
PaulStoffregen
Well-known member
This circuit connects to an 8 ohm speaker. Earlier you said you wanted to "connect +4db instruments".
yes for +4db instruments... it's not for me?
Sorry for a question that may not solve the OP's problem.
Apart from the fact that dB without reference is simply useless, reading the web on +4/-10 dB instruments I deduce they are referenced to 1 V,
but I do not get it why there is talk about 1:20 voltage divider or factor 20.
The 14 dB difference correspond to my knowledge to a voltage ratio of 5, as 14 = 20log10(5)
Or do I miss something?
Apart from the fact that dB without reference is simply useless, reading the web on +4/-10 dB instruments I deduce they are referenced to 1 V,
but I do not get it why there is talk about 1:20 voltage divider or factor 20.
The 14 dB difference correspond to my knowledge to a voltage ratio of 5, as 14 = 20log10(5)
Or do I miss something?
This is max x20, there is a regulation pot, x5 it's possible i think..
the board you were referencing, yes, but I got impression you should adapt voltage by a factor of 20 when switching from -10dB to +4dB instrument as asked for in OP. But anyhow...
PaulStoffregen
Well-known member
Pure dB units (without an extra letter appended) are merely ratios. There are several different physical dB units used in audio: dBA, dBu, dBm, dBV.
This page has a great conversion script:
http://www.sengpielaudio.com/calculator-db-volt.htm
@danixdj - You've been asking for "connect +4db instruments", but so far you've not specified which physical dB units. Let's do that and get this translated into actual peak-to-peak voltage, ok? Please, visit that page and use the calculator. Then reply with the actual peak-to-peak voltage your application actually needs.
Please, everyone, for this thread let's start talking about signal levels as peak-to-peak voltage. The settings on the SGTL5000 documentation are all in terms of peak-to-peak voltage.
This page has a great conversion script:
http://www.sengpielaudio.com/calculator-db-volt.htm
@danixdj - You've been asking for "connect +4db instruments", but so far you've not specified which physical dB units. Let's do that and get this translated into actual peak-to-peak voltage, ok? Please, visit that page and use the calculator. Then reply with the actual peak-to-peak voltage your application actually needs.
Please, everyone, for this thread let's start talking about signal levels as peak-to-peak voltage. The settings on the SGTL5000 documentation are all in terms of peak-to-peak voltage.
when
sgtl5000_1.lineOutLevel(13); (max) 3.16 Volts p-p
sgtl5000_1.lineInLevel(0); (max) 0: 3.12 Volts p-p
when teensy audio board works at -10db, input and output have the same volume.
if the switch on the mixer is set to +4db i have a clipping input when the mixer goes to 0db. I must to use the output faders at max -4 or -3.
with a resistor the input and output aren't the same, the volume is different because i must to amp the output (for input resistor compensation).
So because some mixer haven't -10db or +4db and works at +4db only, i can't use a audio board correctly.
PaulStoffregen
Well-known member
Did you use that website to learn the actual peak-to-peak voltage you need?
I don't know because it's not specifically dbu or dbv, we have only -10 +4 and i can use only my ear
the max for audio board are:
sgtl5000_1.lineOutLevel(13); (max) 3.16 Volts p-p
sgtl5000_1.lineInLevel(0); (max) 0: 3.12 Volts p-p
for +4
I need to reduce for a clear input signal and i must to amplify for the same output volume
PaulStoffregen
Well-known member
Why are you asking people to help you with circuit details when you don't even know the peak-to-peak voltage you need?
From searching the internet I deduce the +4 and -10dB are really +4 and -10dBV
@danxdj
+4 dBV is ALWAYS 1.58V_RMS (dB IS first of all ALWAYS ratio of POWER, therefore RMS, independent of reference)
but 1.58V_RMS is 4.48 V p_p, overloading the SGTL5000
ok it can be true! it happens this i think
in this case how can reduce input v p_p and amp output v p_p with a good sound quality?
PaulStoffregen
Well-known member
Typically +4 dB professional audio means +4 dBu, which is 1.23 Vrms (for a sine wave), which is 3.47 Vp-p.
But even if you don't know what voltage you really need, even if you want to design a circuit that has adjustable levels, at the very least you need to actually specify what your circuit will do before you can design it.
Now we're at 20 messages and to OP *still* hasn't figured out what he really needs. It's fine to not know. But it's not good to start talking about what circuit will or won't work until you have a good idea of what it needs to actually do.
But even if you don't know what voltage you really need, even if you want to design a circuit that has adjustable levels, at the very least you need to actually specify what your circuit will do before you can design it.
Now we're at 20 messages and to OP *still* hasn't figured out what he really needs. It's fine to not know. But it's not good to start talking about what circuit will or won't work until you have a good idea of what it needs to actually do.
PaulStoffregen
Well-known member
Look, if you're using professional quality mixers, just feed the signal into your mixer and turn the channel's gain up (or down) to amplify (or attenuate) the signal to the required levels.
Easy, right?
I prefer to say: which is 1.23 Vrms, which is 3.47 Vp-p (for a sine wave).
Anyhow, the relation V_pp = 2*sqrt(2)*V_rms is only valid for sine waves.
[parenthesis] I do not know about music, there is a lot of confusion concerning dB in environmental noise discussion [/parenthesis]
I use ONLY professional quality mixer like RANE, UREI, BOZAK ecc
Not, loop connection need same output volume from the efx that mixer send to input of efx... loop connection haven't a gain...
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