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Re: Uli Behringer of The Music Group Q&A

Mr. Behringer:

Since you are redesigning the ADA8000, please also address these issues:

1. The outputs are designed to drive pin 3 (inverting output) first, then invert it for pin 2. This output stage topology gives rise to problems in a couple of different scenarios. One of the most common is if you are converting the XLR output into a 1/4". If this 1/4" is mono, then pin 3 will most likely be tied to ground. When this cable is plugged into the ADA8000, the signal is shorted, and nothing is present on the Tip (pin 2). This is a fairly common configuration, especially for those hooking into consumer grade equipment with unbalanced RCA inputs.

Some possible solutions would be:
A. Drive the hot (pin 2) output only, and impedance balance the cold (pin 3) like you do with many of your mixers.
B. Add sufficient resistance (perhaps betweek 500 ohms and 1k) between the driver's outputs and the pins on the output connector. That way, if pin 3 is shorted to ground, there is enough resistance that the driver won't go into current limiting, and you will still have undistorted output on the hot pin 2.

2. The gain adjustment jumps very quickly as you approach the full clockwise position... This change is around 15dB for that last step! There also is a 10dB gain jump at the very start of the rotation. Also, the gain at the full clockwise position is a bit too much.

Some possible solutions would be:
A. Use a better pot that has better correlation with gain changes. I know this is difficult in a reverse (C) taper pot, but it can be done well.
B. Change the value of the series resistor to 47ohms, up from the 22ohms it is currently. I typically do this mod in my ADA8000s to help with the gain jump.

3. There seems to be a clocking issue when using ADA8000s with MOTU interfaces. Clicks and noise occur on ADA8000 inputs, that really aren't there. It gets worse when you use the BNC clock input signal. It can be very random, and can usually be solved by power-cycling the ADA8000, or even just disconnecting and reconnecting the optical input. Some units seems to have more of an issue with this than others. Other 8-channel preamps do not have this same issue with the MOTUs - only the Behringers.

Possible solution: there must be something in the muxing chip that is causing this. I've noticed that none of the other units I've tested use the Wavefront chip, so I'm guessing it has to be something with it.

Thank you for your time.

Bob Puff
New Life Electronics
Rochester, NY

<blockquote data-quote="Bob Puff" data-source="post: 59278" data-attributes="member: 2030">Re: Uli Behringer of The Music Group Q&amp;AMr. Behringer: Since you are redesigning the ADA8000, please also address these issues: 1. The outputs are designed to drive pin 3 (inverting output) first, then invert it for pin 2.&nbsp; This&nbsp; output stage topology gives rise to problems in a couple of different scenarios.&nbsp; One of the most&nbsp; common is if you are converting the XLR output into a 1/4&quot;.&nbsp; If this 1/4&quot; is mono, then pin 3 will&nbsp; most likely be tied to ground.&nbsp; When this cable is plugged into the ADA8000, the signal is shorted,&nbsp; and nothing is present on the Tip (pin 2).&nbsp; This is a fairly common configuration, especially for&nbsp; those hooking into consumer grade equipment with unbalanced RCA inputs. Some possible solutions would be: &nbsp; A. Drive the hot (pin 2) output only, and impedance balance the cold (pin 3) like you do with&nbsp; many of your mixers. &nbsp; B. Add sufficient resistance (perhaps betweek 500 ohms and 1k) between the driver&#039;s outputs and&nbsp; the pins on the output connector. That way, if pin 3 is shorted to ground, there is enough&nbsp; resistance that the driver won&#039;t go into current limiting, and you will still have undistorted&nbsp; output on the hot pin 2. 2. The gain adjustment jumps very quickly as you approach the full clockwise position... This change&nbsp; is around 15dB for that last step!&nbsp; There also is a 10dB gain jump at the very start of the&nbsp; rotation.&nbsp; Also, the gain at the full clockwise position is a bit too much. Some possible solutions would be: &nbsp; A. Use a better pot that has better correlation with gain changes.&nbsp; I know this is difficult in a&nbsp; reverse (C) taper pot, but it can be done well. &nbsp; B. Change the value of the series resistor to 47ohms, up from the 22ohms it is currently.&nbsp; I&nbsp; typically do this mod in my ADA8000s to help with the gain jump. 3. There seems to be a clocking issue when using ADA8000s with MOTU interfaces.&nbsp; Clicks and noise&nbsp; occur on ADA8000 inputs, that really aren&#039;t there.&nbsp; It gets worse when you use the BNC clock input&nbsp; signal.&nbsp; It can be very random, and can usually be solved by power-cycling the ADA8000, or even just&nbsp; disconnecting and reconnecting the optical input.&nbsp; Some units seems to have more of an issue with&nbsp; this than others.&nbsp; Other 8-channel preamps do not have this same issue with the MOTUs - only the&nbsp; Behringers. Possible solution: there must be something in the muxing chip that is causing this.&nbsp; I&#039;ve noticed&nbsp; that none of the other units I&#039;ve tested use the Wavefront chip, so I&#039;m guessing it has to be&nbsp; something with it. Thank you for your time. Bob Puff New Life Electronics Rochester, NY</blockquote>

[QUOTE="Bob Puff, post: 59278, member: 2030"] Re: Uli Behringer of The Music Group Q&A Mr. Behringer: Since you are redesigning the ADA8000, please also address these issues: 1. The outputs are designed to drive pin 3 (inverting output) first, then invert it for pin 2. This output stage topology gives rise to problems in a couple of different scenarios. One of the most common is if you are converting the XLR output into a 1/4". If this 1/4" is mono, then pin 3 will most likely be tied to ground. When this cable is plugged into the ADA8000, the signal is shorted, and nothing is present on the Tip (pin 2). This is a fairly common configuration, especially for those hooking into consumer grade equipment with unbalanced RCA inputs. Some possible solutions would be: A. Drive the hot (pin 2) output only, and impedance balance the cold (pin 3) like you do with many of your mixers. B. Add sufficient resistance (perhaps betweek 500 ohms and 1k) between the driver's outputs and the pins on the output connector. That way, if pin 3 is shorted to ground, there is enough resistance that the driver won't go into current limiting, and you will still have undistorted output on the hot pin 2. 2. The gain adjustment jumps very quickly as you approach the full clockwise position... This change is around 15dB for that last step! There also is a 10dB gain jump at the very start of the rotation. Also, the gain at the full clockwise position is a bit too much. Some possible solutions would be: A. Use a better pot that has better correlation with gain changes. I know this is difficult in a reverse (C) taper pot, but it can be done well. B. Change the value of the series resistor to 47ohms, up from the 22ohms it is currently. I typically do this mod in my ADA8000s to help with the gain jump. 3. There seems to be a clocking issue when using ADA8000s with MOTU interfaces. Clicks and noise occur on ADA8000 inputs, that really aren't there. It gets worse when you use the BNC clock input signal. It can be very random, and can usually be solved by power-cycling the ADA8000, or even just disconnecting and reconnecting the optical input. Some units seems to have more of an issue with this than others. Other 8-channel preamps do not have this same issue with the MOTUs - only the Behringers. Possible solution: there must be something in the muxing chip that is causing this. I've noticed that none of the other units I've tested use the Wavefront chip, so I'm guessing it has to be something with it. Thank you for your time. Bob Puff New Life Electronics Rochester, NY [/QUOTE]

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