Older N72's with new PS02

[kid]

I have 4 older N72 in a rack with the PS01 power supply. I would like to build four J99's and house them together in a new CH01 chassis. I understand that I need a new power supplly in order to power the J99's. Will this PS02 power both the N72's and the J99's together? Also will a CH01 from you come silk screened for both four N72's as well as four J99's?

[tpryan]

>Will this PS02 power both the N72's and the J99's together?

The PS02 produces +/-27VDC, which is then regulated down to the appropriate working voltages by local regulators on the amp modules. The original N72s do not have this local regulator, so you have two choices. One is to modify the PS02 to produce +/-24V. This will keep the N72s happy, but will limit the performance of the J99s somewhat. The other choice is to add some circuitry to drop the voltage to the N72s. This could be as simple as a 1N4372 zener diode in series with each N72 module, which will drop the 27V to just about 24V.

>Will a CH01 from you come silk screened for both four N72's as well as four J99's?

The new CH01 has the gain steps labelled "1" through "12" instead of in dBs of gain. This is due to the simple fact that the N72, J99, and A12 have different gains at the same switch position.

-Tim

[kid]

What about the A12 will this be able to be powered by the PS02? Can it live in the same rack as a N72 (with zener diode in series), and a J99?

[tpryan]

Yep.

[kid]

Ok here is another scenario for ya. What about a New N72 board combined with 4 old N72's and an older PS01 supply? Will this work ok? Any power issues?

[tele_player]

Ok here is another scenario for ya. What about a New N72 board combined with 4 old N72's and an older PS01 supply? Will this work ok? Any power issues?

Tim's response on another thread:
---- Begin Quote
Good question. The LM317 style regulator used on the N72 needs a 3V difference between input and output, worst case. That's why the PS01/02 run at 27V. If you have a rack with older N72s without the on-board regulator, you can add new ones to the system simply by not populating the regulator and related components on the new boards. You can also use the new N72s with any 24V supply in the same manner.
---- End Quote

So, if your PS puts out +24v, don't use the regulator on a new N72. If your power supply puts out +27, DO use the regulator.

[otherworldrec]

which boards are without the voltage regulator? I have Version 2.0, which variety is this?

Thanks

Scott

>Will this PS02 power both the N72's and the J99's together?

The PS02 produces +/-27VDC, which is then regulated down to the appropriate working voltages by local regulators on the amp modules. The original N72s do not have this local regulator, so you have two choices. One is to modify the PS02 to produce +/-24V. This will keep the N72s happy, but will limit the performance of the J99s somewhat. The other choice is to add some circuitry to drop the voltage to the N72s. This could be as simple as a 1N4372 zener diode in series with each N72 module, which will drop the 27V to just about 24V.

>Will a CH01 from you come silk screened for both four N72's as well as four J99's?

The new CH01 has the gain steps labelled "1" through "12" instead of in dBs of gain. This is due to the simple fact that the N72, J99, and A12 have different gains at the same switch position.

-Tim

[tpryan]

The first batch with the regulator was screened "N72B Rev 1.0", from August 2003. I dropped the "B" a few minor revs ago, the current boards are screened "Rev 2.6".

[kid]

Hey Tim,

Could you elaborate on just how to install the diodes to reduce the voltage down to 24V for the older N72's? Where do the diodes get soldered to?

[tpryan]

For use with a PS03, you'll need to drop about 6V across the zener diode. The 5.6V 1W 1N4734 is a good choice. Cut the trace on the N72 PCB that supplies +24V from J1 to R1 (270R) and R2 (12R). Scrape the mask off of the trace as needed and tack the diode across the cut in the most convenient spot. Don't forget to install it "backwards", with the cathode toward J1. If this doesn't make sense to you, don't try it yourself. Find a competent local tech, or send them back for modification.

[kid]

Thanks Tim. I have a PS02 so would I use a 1N4372 that you mentioned in the earlier part of the thread? I will look into it and if I feel it's too complicated I will contact you about doing the modification.

[FairDinkum]

I have a newer PS03 power supply and I have found a couple of the older N72 modules - I was told they were assembled by SCA and have attached an image of it. I can't see the version number, but the power connector is the older 4 prong style. I understand I need to lower the voltage with a zener and I'm looking for assurance that I'm modifying the correct trace. Please see the attached photo (in my next post below) - is this the correct trace to connect the zener diode?

n72_top.jpg (199.73 KiB) Viewed 3169 times

[FairDinkum]

Hi Tim,
Could you please verify the trace to cut to add the zener to lower the voltage for this older N72? Please see attached photo.
Just looking for assurance that this is the correct trace.

n72_trace_highlight.jpg (197.24 KiB) Viewed 3169 times

Thanks!