Gallien-Krueger Backline 110

[GHRock]

I need a schematic for the Gallien-Krueger Backline 110 bass amp.

It is a very small and clean designed 70watt bass amp.

Channel B is not working.

I'm also looking for any info at all about a Sound 90C amp head. This is a tube amp that was manufactured in Mineola, New York.

[Enzo]

Hmmm. I just requested schematics for the Backline 115 a week or so ago, to no response. I'll post it if I get it in case they share some similarity. I should take my own advice and call them on the phone.

The GK here blew a couple small e-caps to pieces.

Never heard of Sound. Is it a complex amp? COuld draw your own schematic maybe.

[GHRock]

I hope you have better luck than me. I requested schematics for the Backline 110 over a week ago and have heard nothing from them. I am afraid some companies are laying off product support people that really sucks!

The Backline 110 amp is very little, but is beautifully built. Tracing schematic is almost impossible since it is a multi-layered PCB with few traces on the outside. All the parts are in single line, perfect for automatic insertion, but give no indication by position what hooks to what. The "B" channel is not working.


I have never heard of the Sound Model 90C either. It was manufactured in Mineola, New York. It is just a head and must be at least 15-20 years old. It has two 6V6's for power output with a 12AU7 splitter/driver. It has 4 12AX7s for the preamp and reverb. This circuit is traceable, I will have to do that for a couple of areas of the circuit to be modified.

Any info would be greatly appreciated. I will insert a couple of pics, if you are interested

[GHRock]

Here are some pics of the Sound Model 90C

Here is the Sound Model 90C:






Made in Mineola New York. I have no other info and can find none on this amp. It has two 6V6s for output power, a 12AU7 and 4 12AX7s

Does anyone have any info on this amp?

[Enzo]

I assume the B channel is only in the preamp section?

WHen I face a dead channel I usually go down the row of op amps looking at the output pins. If I find one slammed over to one of the rails, I can usually assume it is bad or driving an LED. The LED thing is easy to determine.

Those Marshall AVTs like to eat a particular op amp in the preamp. I can never remember which one, so a quick trip with the voltmeter finds it.

And the SOund? Doesn;t look like a repackaged something familiar. Beats me.

[GHRock]

Thanks Enzo.. That's exactly right and what I have done. Problem is this little amp has a preamp with 7 TL072 opamps. I've got it down to 3 candidates of possible bad opamps.
A problem for me is the PCB and whole amp is absolutely pristine. I hate to change any parts and make it "not perfect", but I am going to change those three out one at a time and put in sockets while I do it. Hope I get lucky and don't change any parts I don't have to.

Thanks for your good comments!

[Enzo]

And just for grins I googled "Sound AMplifiers" Wow, the original exercise in futility.

As to changing parts, a little alcohol or commercial flux remover will remove the evidence of a changed out chip, assuming you solder well.

One thing I tell my trainees and anyone else who cares - parts are cheaper than labor. I can buy an op amp for 22 cents. How much time should I put into deciding if one of those is good or bad with labor at $1 a minute or more?

I don't replace parts willy nilly, but if I suspect one, I replace it and find out.

[GHRock]

Your comment that "parts are cheaper than labor" is perfect for me at just the right time.

Some how I was thinking "if I changed out a part that was not bad, it would be a sin".
When I think appropriately my customer just wants his amp back and probably doesn't care if I blow off a couple $.22 parts.

I have adjusted my approach to be more pragmatic. Once again, Enzo, you hit the nail on the head.

Thanks for your comments, they are appreciated.

Now, the Sound 90C:

I have looked for a few days for info on the Sound 90C and absoulutely nothing, same a you. Inside it looks like any old point to point wired amp by a professional manufacture.
This is kind of unbelievable.....

If you have ever seen a Holland inside, this is not what the Sound 90C is. So why no info? This is an interesting puzzle to me. My customer has asked me to mod it extensively. If it was worth anything as a vintage amp, we should just restore it.
What do you think about a chance it worth more than just an amp?

It is hard for me to value since it is not in any of my blue books or anywhere.

Thanks for your interest!

[Enzo]

I appreciate a vintage piece, and respect its vintage value. If it has any. I have a Fender Vibroverb that came in tonight, and the guy mentioned about 50 times he didn't want the amp changed and didn;t want it made non-vintage, and look at the lack of rust and did I mention I didn;t want it changed? SO I will just fix what is wrong and stop.

On the other hand, when a customer brings me an amp, it is after all HIS amp. I might recommend not doing something, but if he insists, I either go ahead and do it, or in severe case, I can always decline to take the job. I may appreciate an amp as a vintage piece, but the customer may simply see it as his amp to do with as he pleases.

I've never heard of the Sound brand, but that doesn;t mean ther are not people out there seeking them. ANy on ebay? But if the customer wants it messed with, it is his amp after all.