Altec 1628a Mods - and 1674 and 1678 .....

@?,*???&? · Post by **@?,*???&?** » Tue Jan 24, 2006 8:09 pm

RodC wrote:Jeff Robinson, I have seen the 1678s for sale before, I have never heard any of that series. Those are post green face units, do you have any examples of how they sound?

I don't have any examples of how these sound, but I would say they are very representative of late 70's solid state. Warm and solid without being 2-dimensional or lifeless and mine both have green faces. I scored 2 of these units for $54 on ebay. In checking, I guess these were selling for +$1700 each new. They'll be worth way more to me if I can do the mod you suggest. It's funny, but I already have the schematic. I'll look into either doing the mod myself or someone locally. Weird, I'll mod a mic on my own, but this seems like much more foreign territory.

RodC · Post by **RodC** » Tue Jan 24, 2006 8:59 pm

SEE BETTER Suggestion in my next post.

Go for it jeff, this would be an easy mod. If you can solder all you would have to do is remove one resistor (R103 or R203 whichever side you decide to mod) , you can even leave the switch in place (Leave it in the -60 positon). Just remove the resistor, solder wires in each of the holes left by the resistor. Run one of the wires to the center of a pot and the other to one of the side connections of the pot. If you want I can draw you a picture.

The worst that could happen is that you will pick the wrong side of the pot to connect to and your gain control will work in reverse. Then just move your side connection to the other side.

I would run the wires and try a 1k, a 5K and maybe a 10K pot (audio taper) and see which one works best.

You may be able to remove the switch and use the hole and a washer to mount your pots.

RodC · Post by **RodC** » Wed Jan 25, 2006 11:03 am

ONE MORE suggestion, I just realized you need a way to control Gain/Volume of each line out, if you look at R105 and R205 that is the Mix level, the pot on the front of the unit. If you connect your line out to the center lug of that pot then the Mix Level control on the front will adjust the output of each line out. You may even want to check the output level of U7 (Pin 1 or 14 depending on the side) if you need more gain.

I wish I had a better pic of the board. If you could locate R136 you could cut the trace leading from it to C108, or lift that side of the resistor, then solder a wire from R136 to the center of the corasponding pot, R105 or R205.

This would make it pretty sweet, you could use R103 as a -10 db cut then use the front pots for your level controls. This would make drilling or midifying the case unnecessary.

chrissss · Post by **chrissss** » Thu Mar 09, 2006 11:10 am

hey guys, i'm trying to figure out how to wire the main outs on the 1628a for a balanced connection into the line in's on my board (it's an old board, but uses LF356 opamps at the input, so is pretty high impedance i think).

the back has 5 lugs labeled 1, 2, 3, 4, 5.
1 and 2 have squares next to them which i think means in phase, 5 is the ground.
it says:
"150 ohm, strap 1-2, 3-4 || 600 ohm strap 2-3"
which should i strap? and what should i connect to a trs jack?

thanks,
chris

bayoucables · Post by **bayoucables** » Thu Mar 09, 2006 11:53 am

For high impedance, strap 2 and 3 together and connect + to 1, - to 4, 5 to ground. For low impedance, strap 1 and 2 together and 3 and 4 together, connect + to 1-2, - to 3-4, 5 to ground.
There's lots of Altec schematics and info at a page I just put up: http://www.choiceestimating.com/altec

chrissss · Post by **chrissss** » Thu Mar 09, 2006 3:20 pm

i'm just getting the hang of this impedance thing.

my impression is that you always want the output to be as low impedance as possible, and the input to be as high as possible (at least when dealing with solid state stuff).

so i just wired it for 150 ohm impedance.

i feel like i'm off somewhere. . .

chris

bayoucables · Post by **bayoucables** » Thu Mar 09, 2006 3:25 pm

A little further down in this forum, Rod C posted a link that has lots of good info on impedance: http://messageboard.tapeop.com/viewtopic.php?t=32491

RodC · Post by **RodC** » Tue Apr 04, 2006 8:03 pm

Awsome update, in my original mods I had this at the bottom:

All the LEDs on the front look cool, but I have considered taking them all out and replacing them with a Pot to use as a gain control. This would be cool, just wire the pot in place of the resistor mentioned in the Adding a ?10db/-20db Pad section above.

Well I did it, I put 25K resistors in the LED holes and wired them as gain controls, now I can drive the pres as hard as I want. I can go from quiet drum OH to Close mic'ed guitar cabs. If you have any altecs with the 1588C or 1588B pres you have to try this.

I used some of the small Ohmite (ASM6668) pots so I didnt have to make the holes bigger. Just be careful when you remove the LEDs. You have to:

Take the black ring off the inside with a small screwdriver, becareful not to break off the lip on the outside.

Push the LED out the back.

Then push the holder out the front.

wkrbee · Post by **wkrbee** » Sun Jul 09, 2006 7:12 pm

Newby here. Great set of mods.for the 1592B and the 1628.
Picked up a 1628 stuffed with 1588Cs.I have some questions.
Is there any difference between the 1588A,1588B,and 1588C?
Rod,are you still using the front panel gain pots as output pots,(ala 1592B mods)?
The 1588 mods.change out a few of the resistors and caps.Has anyone played with the values of the input and output coupling caps?Or gone to all metal film resistors?
Finally,has anyone found a set of schematics for this beast yet?
These mods have got me all fired up.After I'm done with the 1628, I've got a 1592B to mod.
Thanks
Jim

RodC · Post by **RodC** » Mon Jul 10, 2006 6:39 pm

Not too familiar with the 1588a. The B does not provide phantom power and is a different circuit. The C will pass phantom power but only 15V and has a larger input trannsformer.

Yes I am still using the front panel gain pots, this has made these pres very flexable. I like to use a lot of gain on the toms and push them, but turn it down on the kick and snare.

I havent changed any components, whats in there seems to be pretty good quality.

I have some more tracks Ill put up soon, but here is some of the first I recorded with the 1628a. ALL the drums, Toms, Snare Kick OH were recorded with the 1628a. (1 kick, Drummer had click pads, 1 Snare, 2 OH 3 toms.) Im pretty happy with them all, but I like my M7 EF86 stages much better for OHs.

They just lost there singer so they put 2 of their songs up without vox, check out Song 1:
http://www.myspace.com/sevryn

You can check out one more track on my myspace:
http://www.myspace.com/beyondsanity

Check out - Chain of commands

RodC · Post by **RodC** » Mon Jul 10, 2006 6:44 pm

I have a couple of these I want to mod, I've been thinking about sending one to drumsound cause I know he could prob do a better job of recording with it than I can. I would like his suggestions for improvements.

wkrbee · Post by **wkrbee** » Wed Jul 12, 2006 7:59 pm

Thanks Rod.
I've been getting Tape op for a couple of years.First time I've stumbled over this site.Glad I did!

RodC · Post by **RodC** » Mon Jul 17, 2006 2:37 pm

wkrbee wrote:Thanks Rod.
I've been getting Tape op for a couple of years.First time I've stumbled over this site.Glad I did!

If you decide to add the pots for the gain control let me know and I'll PM you a good source.

wkrbee · Post by **wkrbee** » Mon Jul 17, 2006 3:13 pm

Got 'em here @ work for .19 each,(employee price in a discontinued product).Any particular taper used?

RodC · Post by **RodC** » Mon Jul 17, 2006 3:17 pm

wkrbee wrote:Got 'em here @ work for .19 each,(employee price in a discontinued product).Any particular taper used?

DANG I thougt I was getting a good price.

Thats cool, the small ones always cost the most. I used Linear. Im sure audio would be fine. What brand are they?

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Altec 1628a Mods - and 1674 and 1678 .....

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