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How hissy should this guitar preamp (Art Power Plant) be?

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How hissy should this guitar preamp (Art Power Plant) be?

Postby DC-Choppah » Sun Feb 26, 2017 1:06 am

I would like to try using a rack-mount guitar preamp in my rig so I can route the guitar signal around. I need something quiet for recording to act as a buffer. I picked this up for trade in recently: Art Power Plant (black and gold). I thought it would be a basic preamp.

It is just like this one: https://reverb.com/item/105037-art-powe ... black-gold

I am not sure what to expect with this, but it has very loud hiss in both the clean and drive channel, and the drive channel seems to be very ugly to me, like a cheap fuzz box. Not very musical and chopped up and thin. Since it says 'studio' preamp I thought it would be quiet at least in the clean channel. But the one I have isn't.

So does anyone know if this thing is just broken and needs to be repaired, or are they all like this?
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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby zenguitar » Sun Feb 26, 2017 2:20 am

I don't have first hand experience with that Art pre-amp but I went through the late 80's / early 90's fashion for rack pre and power amps. Still have my Marshall 9001/9005 combo.

From all the Art units and other makes I tried at the time, I would not expect any hiss as the norm. So definitely worth handing over to a decent tech for some TLC.

Andy :beamup:
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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby ef37a » Sun Feb 26, 2017 8:50 am

This guy..http://jvmforum.com/phpBB3/viewtopic.php?t=8907

Seems to know what he is doing and is not suggesting any excessive noise? Might be worth lifting the lid and seeing if it uses op amps (741s?) and if so, if they are socketed. If so, tell us the numbers and we can suggest replacements if they are no longer available.

Do ALL this with the unit disconnected of course! There will be no dangerous remnant voltages on capacitors as I assume no valves?

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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby Wonks » Sun Feb 26, 2017 10:53 am

Yes, all solid state. Being around 30 years old, there could also be capacitors needing replacing by now.
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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby Folderol » Sun Feb 26, 2017 4:27 pm

Some good points above, also at that age there were still a lot of carbon resistors around (cheap, see) so some of these could have been used around the inputs. Modern metal/oxide ones are much quieter. As a point of interest there was a low noise 741, designated 741N. They cost over twice as much but they weren't that much quieter.
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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby ef37a » Sun Feb 26, 2017 4:39 pm

Folderol wrote:Some good points above, also at that age there were still a lot of carbon resistors around (cheap, see) so some of these could have been used around the inputs. Modern metal/oxide ones are much quieter. As a point of interest there was a low noise 741, designated 741N. They cost over twice as much but they weren't that much quieter.

Yes indeed, Metal Film will be much quieter but carbon comps can just GO noisier than they normally are! They can often be diagnosed with a can of freezer spray.

Re the 741s they can probably be replaced with TL071 or TL072 (single or dual amps) although my choice would be the NE5534/32. Should be a drop in?

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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby DC-Choppah » Sun Feb 26, 2017 5:37 pm

Some picture of the circuit board:

https://dl.dropboxusercontent.com/u/218 ... nt%201.JPG
https://dl.dropboxusercontent.com/u/218 ... nt%202.JPG

The ICs are:

IC # (Count)
---------------------
TL072CP (15x)
55320 (4x)
CA3080E (1x)
MC1458P (1x)

The circuit board says it was made in 1996.
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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby ef37a » Sun Feb 26, 2017 5:53 pm

My guess is a TL072 is in the front end and although usually very reliable have been known to go noisy. The freezer spray could prove that.

Looks like fairly good quality printed board, a good tech should have no trouble replacing a chip. If you go to one, I would get him to fit a socket.

If you CAN prove a chip noisy and you want to have a crack yourself DO NOT attempt to de solder the IC from the board. Instead chop each leg using fine cutters (jewellers side cutters are great. Hobby Craft!) then remove each pin in turn using tweezers. Clean the holes with solder removing braid, I find suckers cause damage.
The advantage of fitting a socket is that IF you bork the print it can be more easily repaired and you never have to touch it again! Also, there are better Jfet IC than the TL0s now.

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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby Folderol » Sun Feb 26, 2017 5:57 pm

OK, so mostly 20 years old, although I don't recognise the 55320 ones.
Unless I'm much mistaken those resistors are almost entirely carbon ones, so Dave's suggestion with the freezer would probably be a good idea. Also, transconductance amps (CA3080E) have been known to go noisy. They are also getting hard to find :(
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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby DC-Choppah » Mon Feb 27, 2017 4:12 am

Unexpected success?!?? :lol:

I got a can of freeze spray and and a can of contact cleaner.

With my guitar plugged into the pre-amp and the preamp output connected to my amp, and making a lot of hiss, I started freezing components while playing. Nothing changed until I got to the front where the pots are. Spraying the pots and the wires from the pots made it go crazy and get really loud in bursts!

Lightbulb

So I cleaned all the pots. Everything got louder and less crackly on the drive channel. So I turned the preamp down and the hiss went down. Then I played the heck out of it and it seemed to get louder and cleaner in a few bursts. So I turned it down further and the hiss kept going down.

Seems I had this thing cranked before. The freezer, the cleaner and just playing it seemed to open the preamp up. I am not sure exactly what I cleaned that made the difference.

Now I realize how loud this thing is. When you turn it down so that it gives the same level as a bypass, the extra hiss is very small. Before, I had to crank it to get it to that level.

And now the drive channel sounds like a Marshall stack! WoW!!! Rock and Roll.

Cool!!!

Thanks guys. Thanks Mr Dave.

The freeze spray sent me in the right direction.
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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby ef37a » Mon Feb 27, 2017 9:58 am

"I love it when a plan comes together!"

Even if not quite as you had expected...But, that's fixin' fings for ya!
It might at some point be worth having the whole PCB out and checking for dry joints in the area that reacted.

You are very welcome DC.

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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby DC-Choppah » Wed Mar 01, 2017 4:54 am

Darn :cry:

Now the eq controls on the clean channel do nothing.

Turning the knobs on the bass, mid or treble of the clean channel has no effect on the sound at all. Nothing. No change. Sounds good. But no eq control at all. Sounds like it is set at mid position.

Gain on the clean channel works and all the knobs on the drive channel including eq work.

Something is still wrong. But eq worked yesterday on the clean channel?!?
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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby ef37a » Wed Mar 01, 2017 10:42 am

Sure there is no push-pull pot switch EQ bypass function?

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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby DC-Choppah » Thu Mar 02, 2017 12:56 am

ef37a wrote:Sure there is no push-pull pot switch EQ bypass function?

Dave.

No.

But since you got me looking, how about a button I found on the back called "Clean Channel EQ bypass" that must have gotten turned off as I mounted this unit into my rig.

Once again, you have pulled me from the fire. Thanks Mr. Dave.

I was going to take it to my tech to fix since I thought it was still broken!
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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby Hugh Robjohns » Thu Mar 02, 2017 11:06 am

I hate those kind of traps. The ones where you convince yourself something is massively broken, and then some smart Alec pokes a button you didn't know existed and magically fixes it! Glad you found it first! :-D

H
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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby ef37a » Thu Mar 02, 2017 1:24 pm

Hugh Robjohns wrote:I hate those kind of traps. The ones where you convince yourself something is massively broken, and then some smart Alec pokes a button you didn't know existed and magically fixes it! Glad you found it first! :-D

H

Hah! Ha! I used to get to do that ALL the time! Peeps would claim there was ABSOLUTELY no way to clear the timer programme memory on a certain VCR then I would rock up and say "Page 5 of the manual" Bish, bash, bosh. Thank you madam!

Dave. (and people are STILL not reading manuals! Mind you, here is a line from an IP camera manual I have just bought...", double-click the left mouse button, the device will automatically in order to enter the prison depending on the window." And that is verbatim. It seems nothing has been learned from way back when we had Japanese imports! )
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Re: How hissy should this guitar preamp (Art Power Plant) be?

Postby Martin Walker » Sat Mar 04, 2017 12:22 am

ef37a wrote:Mind you, here is a line from an IP camera manual I have just bought...", double-click the left mouse button, the device will automatically in order to enter the prison depending on the window."

Sounds like one of those old text-based adventure games Dave :beamup:


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