The AKM is one heck of a chip. As I was reminded earlier, the 120 db range is the wideband noise specification. If you want to know the range in a 500 Hz bandwidth, the noise (and dynamic range) reduces by 10*log(20000/500) or 16 db for a 500 Hz dynamic range of 136 db. Since the max is 5v, this would represent a maximum signal of +18 dbm. With a 136 db dynamic range at 500 Hz, this implies the receiver sensitivity is -118 dbm.
Thus connecting this A/D converter directly to the detector with no amplification would give an excellent high level blocking capabilities, but you might want 20 db of pre-amplification in order to get down to a more reasonable -135 to -138 dbm MDS sensitivity level, 500 Hz bandwidth. 136 db of blocking dynamic range capability would be quite interesting. - Dan, N7VE -----Original Message----- From: Ahti Aintila [mailto:[EMAIL PROTECTED] Sent: Tuesday, November 08, 2005 2:39 AM To: Tayloe Dan-P26412 Cc: FlexRadio@flex-radio.biz Subject: Re: [Flexradio] Firebox max input signal? 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 > > > > _______________________________________________ > FlexRadio mailing list > FlexRadio@flex-radio.biz > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz
