Lab Series L4 Bass Head 200 watts, IC sub for CA3094ae Op Amp

[1ampman]

I've been working on why my amp has low output and breaks up. This op- amp is NOT amplifing to the proper gain according to the schematic. I have a signal generator (1kz) and scope which helped me find the problem. It's an 8 DIP. Are these availible or have a sub of equal specs??? Hopefully I can get this old beast singing again......

[Gtr_tech]

Out of production for years. I may have one....lemme have a look around. No guarantees tho...

Since it is an OTA hald a CA3080 may work. Or half of a LM13700.

[Gtr_tech]

Brain fart....the 3080 is a single OTA. Stuck in 13700 mode I guess....

[Gtr_tech]

Scratch that. I don't think either would drop in and run due to the darlington output that has. Reading the datasheet it states that its basically a 3080 with the darlington on the output. So if yer brave you can use a 3080 and add the missing parts/repin as needed.

Sounds like a hassle, but I've had to jump through some hoops to functionally replicate unavailable ICs. Sometimes ya gotta do what'cha gotta do to get it back in service.....

[1ampman]

I've been seaching the net and Ebay is the only place that has them. BUT they're all from China. So I don't know if they meet original specs or will work in this circuit? Will they blow out after 15 minutes?? Do I chance it?

[1ampman]

Small Bear Electronics has the CA3094 for $6.75.... Has anybody ordered from Small Bear? I'm guessing it's Chinese. Opinions??

[jrfrond]

I might have them in stock. I can check tomorrow.

FWIW- I've ordered IC's from many Asian sellers on eBay and haven't gotten screwed once. Most times, they are the ONLY source for defunct IC's.

[truth_hz]

Small Bear Electronics has the CA3094 for $6.75.... Has anybody ordered from Small Bear? I'm guessing it's Chinese. Opinions??

Steve@ smallbear is a stand up guy. Just be warned, the ca3094 "E" is a 24v part, the "AE" is a 36 volt part according to the datasheet.

[Gtr_tech]

Ok...I don't have any. That number sounded familiar for some reason.....thought I may have come across some while looking for 3080s. Mus have been the 3140s....

Anyway....NTE don't cross it. Ebay has several listings for the 3094, but they're all Hong Kong phoo-ee and likely fakes. Not worth the gamble. Maybe a post in the usenet group sci.electronics.repair might scare one up.

[1ampman]

15 volt bipolar supply is hooked to the IC. It's the last gain stage before the Master Volume which then it goes to the power amp section. Let me know if you have one, otherwise I'll order from Small Bear.... This is a great forum!

[1ampman]

This is really going down hill... So I ordered from Ebay (quanity 5) CA3094AE from Hong Kong. I tried 2 of them and they DIDN'T WORK. The amp sounded like an earthquake with 60 cycle hum with nothing plugged in. Obviously wrong for this circuit. The SCHEMATIC calls for the same chip (AE) BUT the original I pulled from the circuit is CA3094 E (RCA) ... Are these the same? Was the chip swapped out on the production line (parts change)??? If I ever get this fixed a bottle of Bourbon is called for... Anybody close by is welcome to join me.....

[Enzo]

Or the old IC was burnt out, and new working ones reveal the rest of the circuit still has problems. Possible?

Disconnect the speaker and turn down the master or whatever. Are the DC levels around this IC close? Does it amplify signal?

[1ampman]

Enzo... Yes you are correct. The new chip is working fine. I hooked up my signal generator and followd it thru. Made the trimpot adjustment that sets the preamp output. Followed it right to the Power amp board. A nice clean 1kz sine wave. But now the power amp PUTSOUT a Chopped TOP SINE WAVE (almost a square wave) with 1volt of DC. What would be the first step? Pull the outputs and test them? .... This is some nice progress.... I actually bought some Bourbon today but won't open till it's fixed.

[Enzo]

I doubt it is the outputs. You have a super clipped output? CLips both sides evenly? Or just one side of the wave is clpped?

Are we talking output into no load? If there is a load, get rid of it. If the amp cannot make a good waveform with no load, then it won't clear up when the load is applied. On the other hand if it makes nice withno load and collapses when load is applied, then that does direct us towards the final stage.

There are a few DC vltage refernces on the drawing, you got those? Is that 33v on the right side of the diffy pair?