Help repairing Ampeg 1540 Crossover

[J M Fahey]

Hi, I have this dead Ampeg 1540 crossover , the one in the "fridge size" box with 1x15"/4 ohm spk and 4x10" + Horn ; which can be biamped (2 x 4 ohm separate inputs) or run full range (two parallel 8 ohm input/link jacks)
It´s been messed up beyond repair, no pad switch, missing pads, rusty worn jacks, the works, but the components themselves (power resistors, capacitor, coil, even the lamp) are healthy.
If I can have the Xover schematic I can draw, etch and build a new board using available switching jacks and those old components.
Thanks.

[Enzo]

Here you go. I can make a gray scale copy if this is too dark.

[J M Fahey]

Hi Enzo, thanks a lot.
Can´t believe it, I thought : "well, I´ll check in a week or so ....", but you answered in 26 minutes !!!! (twenty-six, no kidding).
And that includes searching your undoubtedly vast library, scanning and posting exactly what´s needed.
The scan is fine, I just needed the schematic.
Although relatively simple, tracing it "from the board" was very frustrating, because the complex switching: in/out , series/parallel, joining/separating grounds, etc. was made through unreliable cracked rusty contacts, and, besides, I can´t get those same jacks in Argentina, so the next best solution was making a new board using pin-incompatible plastic "Marshall jacks".
The 6-pin connector pinout wasn´t clear either, because the cabinet is unavailable for me to test (long story).
Again, thanks a lot.

[Enzo]

26 minutes? Darn, I'll try harder next time.

[brash]

Ampeg 1540 he Straight wire

Any ideas how I can just straight wire the 4 10's and one 15 straight at 4 ohms?

Thanks,
Jeff

[Enzo]

I can think of no way to wire five drivers for 4 ohm total. At least not if the drivers are of common impedances like 4 ohms or 8 ohms.

[52 Bill]

I can think of no way to wire five drivers for 4 ohm total. At least not if the drivers are of common impedances like 4 ohms or 8 ohms.

If the four 10's are 8 ohms, series parallel them to give you 8 ohms, then parallel them with a single 8 ohm 15 inch.

[Enzo]

Duh...

Having a senior moment, I guess.


You are right, but the speakers would then not share power equally. I was trying to come up with some way they would see equal power. But I guess that arrangement would electrcally be the same as a 4x10 cab and a 1x15 cab stacked.

His drivers are already 4 ohms though. Can;t get 4 ohms from five 4 ohm drivers.

[trudgemetal]

similar problem, less expertise

I also have a 1540 cabinet, with the 4x10s working & installed, but missing the 15" speaker and the xover switch. I own as a 15" ampeg speaker from a BA115 that I want to install in the 1540, but I also need to figure out how to replace the xover. Any idea where on of these can be gotten? I looked all over the internet but couldn't find any for sale. And then, assuming I was able to get my hands on an xover, is the repair very involved? Do you think an attentive amateur could install the 15" speaker and the xover? Thanks!

[J M Fahey]

This cabinet, like most things trying to make 1000 different things, is a mess.
"Master of all trades, master of none".
FWIW I still have the X-Over I asked about and pictured above, I just hardwired the original cabinet into 8ohms and that was it.

Starting from the beginning, what do you have now?
What head? (brand/model/power/impedance)
Are the 4x10" wired for 4 ohms?
Does the tweeter work?
15" speaker impedance and power handling?

[trudgemetal]

Ampeg 1540 HE repair

This cabinet, like most things trying to make 1000 different things, is a mess.
"Master of all trades, master of none".
FWIW I still have the X-Over I asked about and pictured above, I just hardwired the original cabinet into 8ohms and that was it.

Starting from the beginning, what do you have now?
What head? (brand/model/power/impedance)
Are the 4x10" wired for 4 ohms?
Does the tweeter work?
15" speaker impedance and power handling?

I have a Sunn Beta Lead, it's 100W & 2Ohms.
The 4x10s are rated 4Ohms & 200W as half of a Bi-Amp setup or the cabinet says the full setup (4x10 & 1x15) is rated 400W & 8 Ohms.
As far as I know, the tweeter works.
The 15" speaker is 4Ohms but I can't figure out the power handling. It is a stock 15 from an ampeg BA-115 combo, and has this written on the speaker itself:

15614B 4 Ohm
67-000700s3 G1
86-118-04

not sure if that's helpful.

The other issue is that the knob for the High Frequency Attenuator (crossover switch) is missing.
Let me know if there is other info you need to know! Thanks for responding so quickly.

[J M Fahey]

I just checked and the Sunn Beta Series (Lead/Bass/Power Plus) is 100 (very solid) Watts into 4 ohms.
So you can drive *either* the 4x10" (+ tweeter) at 4 ohms total, *or* the 15" , also at 4 ohms, but not both .

Problem is, they are not 2 stacked cabinets (in which case you could use one or the other) but a single very large, heavy and unwieldy cabinet, not quite justified if driven by only 100W .

Personally, and considering what's available, I would build a simple 4x10" cabinet (visit some local lumberyard) , sized, say, very practical 24" x 24" by , say, 12" to 15" deep, fill it with those 4x10" (and the tweeter if you wish) and use it.
I'm quite sure the Sunn will kill the single 15" , that's why I suggest the 4x10" .

In the future, if I get a >300W head, I'd fill the 1540 cabinet with 4 x 10" "Ampeg type" speakers "wired for 8 ohms" plus some beefy 8 ohms 15" speaker (your choice: EV, Pro Eminence, etc.) and have a large "fridge" type cabinet compatible with most big heads out there (Ampeg/Peavey/Sunn/Hartke/etc.)
It will require roadies, a van, etc. but at least will justify the mess.
But driven with only 100W ..... żżż???