Topic: da-p1 modification for mic-in

[crakt]

i recently bought a used da-p1 and my understanding is that sooner or later i'm going to be in a situation where brickwalling occurs on the mic-in.
i'm going to be running oktava mk012s(-10db pad) and audix 1245s mic-in(both with -20db pad on the da-p1). the mk012s may not brickwall? but the 1245s(which i dont have yet) i'm guessing will brickwall more often? can anyone take a guess on the chances of brickwalling at a loud show? because if there's a high chance, then i'll try and organise to get a mod done now BEFORE any shows get ruined. otherwise if there's less chance then i'll wait and see if i do need the mod.

has anyone here had the following modification done? are there any warnings i should know about or is it pretty straightforward? i'm not going to do it myself but instead take the da-p1 to a repair shop along with these instructions.

http://www.xs4all.nl/~fjkraan/digaud/dap1/MicrophoneCircuit.html
partial quote from page:
=============================================
For 6db mod (reduces mic pre gain by about 6 db)

Need 2 0805 (size) 1.34k 1% resistors if you have a bunch of them hand match them with a VOM to the closest value.

Open the DA-P1 case.. In the Mic Pre section
Remove R529 and R629 These are 110 ohm resistors.
There are two 110 ohm resistors in parallel for 55ohms.  Removing one leaves it at 110 ohms which is a 6db difference.
This is the Pad off gain.

Remove R516 and R616. Replace with the 1.34k resistors.  This is the Pad on setting
Note changing R516 and R616 to 2.23K makes a 10db mod.
=============================================

thanks

Luke

[crakt]

i wonder if anyone can shed any light on this - i tried to get the 'pad on' modification done by replacing Resistors R516 and R616 but the guy who did it reckoned that did not work(tho he only simulated the mod by bridging the resistors). anyone know why it wouldnt work? he then tried to allow phantom power on line-in which did not work either(it gives phantom power initially but then drops off during the next minute).

does anyone have a DA-P1 circuit diagram scan that they could send me?? otherwise i'll have to use xlr attenuators, which i dont really want to have to do.

thanks

Luke

[heath]

hey luke,

found this today with a google search, and thought it might help.  old Dat-Heads post.  This guy might be able to help, if you can track him down.  If you can find a schematic, or come up with any cool mods, please share!!!!   




From: Hawker <Hawker@Connriver.net>
Subject: DA-P1 mods and upgrades
Date: Fri, 05 Nov 1999 11:21:32 -0500

Howdy all.
I have been perusing over the DA-P1 schematic and it looks VERY ripe for mods, improvements etc.  I was wondering if anyone here has played with this b4 and am interested in some feedback.  Since I no longer have regular access to an AP1 (Audio Precision System 1) I have no way
to PROVE that my mods make a difference other than my ear.  So I am looking for thoughts on where to focus my energy.

I have already made some mic-pre gain structure mods with good results.
Wondering if anyone else has mad any other mods and with what results.
Areas I see for mods,

General Audio Mods
1) add the missing .1uF Bypass caps,
2) Change Electrolytics to Tantalum caps,
3) increase size/quality of DC coupling caps,
4) change Ru02 0805 resistors with Mini-Melf (like Apogee uses).
5) Upgrade NJM2115 op-amps (Any ideas what has enough headroom to use here, can't us a OPA2604, OPA2134, NE5532, NJM 2114 etc here)

Some of the bypass caps shown on the schematic are not actually on the PCB (cost reasons?), add those back in.

Ideas to Improve 48V and -5V switching regulator,
1) substitute RC filters with LC filters,
2) Add snubber caps/resisters
3) Linear Post Regulation?
4)  add the missing .1uF Bypass caps,
5) Change Electrolytics to Tantalum caps.
6) Upgrade the ADC (Anyone got data on a AK5340 it was not a US AKM release)

Mic Pre ideas
1) Add complementary Pairs to the Transistors on the mic pre,
2) Add better constant current source
3)  Change Volume control to change gain of stage rather than attenuate
4) Of course change the gain level of the first stage to be more what we really need (lower).

[jk labs]

i wonder if anyone can shed any light on this - i tried to get the 'pad on' modification done by replacing Resistors R516 and R616 but the guy who did it reckoned that did not work(tho he only simulated the mod by bridging the resistors). anyone know why it wouldnt work? he then tried to allow phantom power on line-in which did not work either(it gives phantom power initially but then drops off during the next minute).

does anyone have a DA-P1 circuit diagram scan that they could send me?? otherwise i'll have to use xlr attenuators, which i dont really want to have to do.

thanks

Luke

Just follow the instructions you posted in the first posting:   

• Remove R516 and R616 (MIC PAD) .
• Insert a pair of 0805 2k23 ( "-10 dB MIC PAD MOD") . 

The value is not critical. (And forget matching them. 1% is just fine).
This will work just swell.

Jon

[creekfreak]

wow, those look like some fun traschcan mod's.....+T