Hi Dan,
I was wondering the same specification of the PreSonus Firebox, but did not
ask them. Thanks for doing that.
Obviously Firebox has better dynamic range than Delta 44 (higher max level,
lower noise?). However, the best specifications I have seen is with AKM chip
set as given in your link below (123 dB dynamic range with +23 dBu maximum
input signal ≈ 31 Vpk-pk).
Since the "Tayloe detector" ("QSD" as Gerald says) can handle about 4 Vpk-pk
and we optimally could use gain of 31/4 = 7.75 (+17.8 dB) between the best
practically available sound card and the sampling detector. We should also
find a better amplifier to replace INA163, because it is too noisy at these
low gains. So far I have not found any pin to pin replacement, but I am
experimenting with two OPA2227's as dual balanced output amplifiers
assembled on a small circuit board. Naturally a minor "surgery" has to be
done to the TRX board.
I wonder, why TI suggests OPA2134 together with PCB11804? It has higher
noise than OPA2227.
By the way, my sound card is WT192X that has AKM chip inside and can take 31
Vpk-pk.
73, Ahti OH2RZ
----- Original Message -----
From: "Tayloe Dan-P26412" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Cc: <FlexRadio@flex-radio.biz>
Sent: Tuesday, November 08, 2005 12:41 AM
Subject: Re: [Flexradio] Firebox max input signal?
Here is the information that I got about the PreSonus Firebox line inputs.
It looks like it is good for +18 dBu or about 17.4v pk-pk maximum.
In contrast the Delta 44 is rated to +14 dBu or about 11v pk-pk.
- Dan, N7VE
--------------------------------------
For Line inputs (0dBFS=+18dBu) , we are performing something very similar
to the datasheet you refer to. We attenuate the signal by approximately
5.5x to "fit" into the converter.
Best Regards,
Jonathan Hillman
[EMAIL PROTECTED]
PreSonus Audio Electronics
225-216-7887 x. 117
----------------------------------------
From: Tayloe Dan-P26412 [mailto:[EMAIL PROTECTED]
Sent: Monday, November 07, 2005 2:15 PM
To: jonathan hillman
Subject: RE: Maximum input to the Firebox?
I have looked at the manufacturer (TI, Cirrus Logic, AKM etc)
specifications of several of the best 24 bit A/D devices currently on the
market.
On of the things that I noticed is that although the A/D input is rated at
0-5v, the reference designs of the parts often show an input buffer that
has a gain of less than 1 in order to allow the input to go to a level of
greater than 0-5v (5v pk-pk). Example
http://focus.ti.com/lit/ds/symlink/pcm1804.pdf figure 44 or
http://www.asahi-kasei.co.jp/akm/en/product/ak5394a/ek5394a.pdf figure
13.
The AKM figure 13 above shows an attenuation of about 5.3x (input R=3.3K,
feedback = 620+91 ohms, gain of ~0.188x). I can see that this might be
needed since line level devices such as a mixer board often are capable of
relatively high outputs. A Heath-Allen mixer console
(http://www.allen-heath.com/DL/ml4000ug_ap4314_4.pdf - see page 12) is
rated at an output of +23 dBu, where 0 dBu is 0.775v RMS (1.096v pk or
2.192v pk-pk). Thus +23 dBu translates to ~ 31v pk-pk of audio.
Thus, I might expect the line input buffer to the A/D converter to have
attenuation rather than gain. I am simply trying to find out what the
input buffer stage of the A/D converter looks like (gain and voltage
limits) in order to best match my output to the line input of this box.
- Dan Tayloe
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