Aguilar amps

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Good day,

Can anyone help me with an issue with an Aguilar DB751 bass amp?

When turned on the status led blinks for the normal 45 seconds and goes steady
But the operate led is off. There is no input or output. Unit worked fine when powered up before transport for a gig and when powered up for gig this occurred. Anyone came across this issue with this amp? All voltages good and relays are enabled.
Your question is somewhat vague :)

What is your actual problem?

And this is a Bass amplifier , so some moderator should move this to the proper Musical Instruments section or you open a thread there.

Also update the "Country" data on your user profile, answers depend stongly on that.
I´m attaching DB750 schematic, which should be close enough for troubleshooting.

It´s a BEAST of an amp, but specially has a *very* complex self protection section, see page 5 , which complicates servicing.

In principle, since it happened after normal transport but not rolling downstairs or similar, most probable is that some of the myriad connectors and cable harnesses unplugged, or anything seated on a socket (tubes or relays) did the same.

With amp OFF and unplugged from mains for 1 hour, pull and firmly reseat each and every cable harness connector, any plug in sub board (if any), relays (if in sockets), etc., then plug into mains, no instrument or speaker connected, all controls set to 0, pray a little and turn it on.

There´s a high probability it starts normally.

If not, troubleshooting is complicated, maybe the shortest path is to ship it back to Aguilar factory, freight will be expensive but you have a guarantee it will be solved.

Not so sure about an "independent" Tech, if anything because Factory will not help him or sell him parts if needed.

Just as a side note: when "outside" North America or Europe, or far away as we are here in Argentina, I always suggest Musicians to buy less glamorous and simpler amplifiers, in this case suggest older Peavey or Ampeg, not the latest Class D versions either.

Popular, easy to find schematics, lots of Techs worked with them so many can offer advice, Mother Companies take care of users , keep replacement parts (in case of Peavey, for up to 30 years) , you feel backed up.
In other examples, you are not.

Won´t name names, but some amplifiers have to be sent back to Mother Company to Italy, Sweden , Denmark or good old USA to be serviced at original factory .

Consider this for your next purchase.


  • aguilar DB750 schemos080409.pdf
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Thanks JM

JM thanks so much for posting that schematic! I’ve had an intermittent issue for years on my DB750. The company would not release it to me, they said they would give it to a tech they approved. So, it finally failed hard I found this post and fixed it. One shorted diode in the Vc supply.
Hi JM,
It's the firsy time I see what technicians know for a long time:
"I always suggest Musicians to buy less glamorous and simpler amplifiers"

Long before manufacturers changed the proven designs of simple amplifiers into a collection of chips, relays, hundreds of parts;
only to make noise?

At the end, and any musician must agree on that, it's the guitar player that makes the mood.

These modern money sucking amps are very hard to service due to the lack of schematics, parts etc. And if you dare to ask what you think is correct for a repair, they think you're ripping them off.

After more then 50 years of servicing amps, I'm disillusioned in both the manufacturers and the musicians.

The heart of making music is transformed in a digital monster. The soul is gone...
(appart of a few good and rare musicians. Yes, they still excist...)
I really doubt that there are many of the high class guitar players how do really care much about fancy equipment. But for the beginners it is easier and more fun to brag about 1956 guitars, matched Russian tubes salvaged from Sputnik prototypes, pickups wound per hand personally by Leo Fender and other nonsense than learning to play the instrument. This is not really new, all my life I met such guys.
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Only >50 guys like us like old simple amps; newer generation love Engl, Diezel, etc. Ever looked inside one of them?

Wall to wall tightly packed PCBs with computer like thin tracks , 24 relays, a dozen ICs, ribbon cables all over the place, the works.

Even a Mesa Boogie may have 18 relays inside.
Yes, I know what you are talking about. Just have a VOX Nightrain aka VOX Nightmare on the bench. Loads of relays as well and occasional dropouts that I could trace finally to the potentiometers. These must be the cheapest stuff you can buy worldwide, as a private customer I pay 0.38€/each at a reputable dealer (TME.EU) for this crap. And they use a tandem master volume pot each channel driving one of the power tubes. Considering some channel imbalance of these al cheapo potis this certainly gives some nice asymmetric distortion in the power stage - individual per amp and changing over the rotary angle. Hey, this is genius!

The 12AX7 tubes go through some rubber shock absorbers that makes it nearly impossible to replace them without bending the pins.etc ppp.

All in all an over-featured boutique amp that I would not trust for a single gig.
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I am not that intrigued by real old stuff that I generally consider too bulky. But some old ideas concerning sound reproduction are worth to be transformed into newer and smarter hardware. And with some efforts DIY solid state technique outperforms DIY tube technique in size, weight, cost and RELIABILITY. No doubt this has taken a long learning curve. To illustrate what I am taking about I append two 3D-views of my latest modules that make up for a complete, simple amp outperforming 2xEL34/6L6GC stages.


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