I am building a DI similar to the "Full Featured Direct Box" application from Jensen:
http://www.jensen-transformers.com/wp-content/uploads/2014/08/as066.pdf
I understand that tying pin 1 to chassis is best practice. However, as can be seen in the schematic, there is a parallel output labeled "to amp" that uses a mono signal at the chassis potential as well. When connecting an instrument through a DI to a mixing board as well as to an on-stage amplifier, the possibility exists of incompatible grounds.
The schematic shows a ground lift using a resistor and capacitor in series from pin 1 to chassis, and even indicates "preferred position". Is this a solution that will prevent most cases of buzzing? If I were to exclude the option of a ground lift switch, would it be more wise to leave the resistor/capacitor connection, or just connect pin 1 directly to ground?
http://www.jensen-transformers.com/wp-content/uploads/2014/08/as066.pdf
I understand that tying pin 1 to chassis is best practice. However, as can be seen in the schematic, there is a parallel output labeled "to amp" that uses a mono signal at the chassis potential as well. When connecting an instrument through a DI to a mixing board as well as to an on-stage amplifier, the possibility exists of incompatible grounds.
The schematic shows a ground lift using a resistor and capacitor in series from pin 1 to chassis, and even indicates "preferred position". Is this a solution that will prevent most cases of buzzing? If I were to exclude the option of a ground lift switch, would it be more wise to leave the resistor/capacitor connection, or just connect pin 1 directly to ground?
if you have to ask these questions (don't understand what these part do and why)
it would be wisest to build the device as per the schematic.
Hi Guys
The trend is away from the use of ground-lift switches.
In the DI schematic linked, the unbalanced connection to the guitar amp provides a ground for the guitar and for the primary of the transformer.
You do not include an expensive transformer unless you want to separate the grounds of the various pieces of equipment. It is there to isolate the second piece whether it's another amp or a line to the PA. The preferred wiring of pin-1 is to have it tie to the chassis right at the XLR. You can buy XLRs that do this in their mounting.
With every pin-1 grounded to chassis at both ends there is an obvious ground-loop appearance, but none of these pin-1 connections are for the signal, rather it is to extend the shielding provided by the chassis. This improves immunity to RF ingress.
The modern alternative to a ground lift is to use a parallel R,C and anti-parallel diode pair.
Have fun
The trend is away from the use of ground-lift switches.
In the DI schematic linked, the unbalanced connection to the guitar amp provides a ground for the guitar and for the primary of the transformer.
You do not include an expensive transformer unless you want to separate the grounds of the various pieces of equipment. It is there to isolate the second piece whether it's another amp or a line to the PA. The preferred wiring of pin-1 is to have it tie to the chassis right at the XLR. You can buy XLRs that do this in their mounting.
With every pin-1 grounded to chassis at both ends there is an obvious ground-loop appearance, but none of these pin-1 connections are for the signal, rather it is to extend the shielding provided by the chassis. This improves immunity to RF ingress.
The modern alternative to a ground lift is to use a parallel R,C and anti-parallel diode pair.
Have fun
Bill Whitlock and Deane Jensen's circuit is a good overall solution. Often I omit the G/L switch and leave things permanently lifted with just the R/C circuit there as an RF ground for shielding purpose. Normally, if thee is a G/L switch I leave them engaged (open) all the time unless I really need them closed for some weird situation occurring.
Bill Whitlock, of Jensen, went through the how and why of all this at a seminar he gave at BC Place on Vancouver last fall at an AES meeting.
When I design gear here at Radial, we still put G/L switches (with RF bypasses) all over the place as one never knows when one may be needed. 90% of the time it does not matter if they are in or out but there are times they make one look like a miracle worker.
Bill Whitlock, of Jensen, went through the how and why of all this at a seminar he gave at BC Place on Vancouver last fall at an AES meeting.
When I design gear here at Radial, we still put G/L switches (with RF bypasses) all over the place as one never knows when one may be needed. 90% of the time it does not matter if they are in or out but there are times they make one look like a miracle worker.
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