Noisy Ampeg SVT VR re-tubing and fan upgrade

[magic papa]

Hi All,

Just got my brand new Ampeg SVT VR. Made in Vietnam, but the tone is great so I don't care. The only issues are operating noise and hiss.

Basically when I flick the standby switch it feels like airplane taking off. It's the fan, when I disconnected it the noise went away.

It uses pretty standard 120mm 120V AC fan, so I ordered a new one online which I hope will be quieter. The specs said 38dbA, so I guess this is less than the airplane. If anybody had experience with silencing the fans in these Ampegs please share it.

The other issue is hiss. Rather huge hiss; not a biggy at high volumes becasue the hiss doesn't increase with volume, but it precludes using the amp in quiet environments at low settings. It sounds like I have a waterfall inside my cab.

I think I can attribute it to preamp tubes, I was also getting crackling noises, but I fixed it by replacing one of the preamp tubes with a spare Tung Sol marked as low microphonics. I also think that helped a tiny bit with the hiss.

The original ones are Sovtek and I probably don't like them already. Would it be a feasible thing to replace all preamp and driver tubes in order to reduce noise? If so - what tubes would you recommend. It costs some $$$, but I splashed out already on the amp so might as well get it to sound best.

Can power tubes also be responsible for noise?

Many thanks

MP

PS. I know I shouldn't have to do anything on a new piece of equipment, but I guess when the prodution of these things went cheapo the quality of some of the stock parts just isn't acceptable.

[johnk_10]

IME, most, if not all of the hiss in a VR comes from the preamp tubes. (i've never heard a power amp tube cause hiss).

i changed all the pres in mine with NOS ones and it dropped the noise level by more than 50%. for the 12AU7's, i can highly recommend NOS 5814A's if you can find them at a reasonable price, but most EH (sovtek) and JJ 12AU7's are usually pretty quiet.

for the 12AX7's, i put a telefunken, an amperex and an RCA (all NOS) in mine and it sounds exactly like my '69 SVT.

[magic papa]

Originally Posted by johnk_10

I(...)
i changed all the pres in mine with NOS ones and it dropped the noise level by more than 50%. (...)

Thanks, that's encouraging. I was on the right track then

Perhaps silly question - how do you get to the other tubes? After removeing rear cover I can only see the driver tubes and one 12AX7 (which is the one I replaced). There should be some more 12AX7s.

[johnk_10]

they're up top inside of the preamp chassis.
you have to pop off the front grill panel and remove the four philips screws on top to remove the chassis. then you remove the screws that hold the cover plate. then you'll see the 5 preamp tubes inside.

[JimmyM]

they're up in the preamp...you have to unbolt the upper section and look inside it.

[magic papa]

Originally Posted by johnk_10

they're up top inside of the preamp chassis.
you have to pop off the front grill panel and remove the four philips screws on top to remove the chassis. then you remove the screws that hold the cover plate. then you'll see the 5 preamp tubes inside.

Cheers, I was also wandering whether they need to be any special ones? By default I would pick low noise and microphonics ones, but do they need to be matched/balanced? I'd imagine the driver ones should be balanced and matched.

[JimmyM]

the little tubes bias themselves so plug them in and go.

[slick_tu]

I don't have any personal experience, but I've read posts that recommended using fans with ball bearings rather than sleeve bearings:

Originally Posted by beans-on-toast

For your reference, this is the fan (Jamicon JA1225H1SON) that came with a Vietnamese VR that I had: http://www.jamicon.com/spec/AC/JA1225-0N.pdf

You can compare the specs with other models. Basically it is an AC fan, sleeve bearing, 120X120X25mm(4.75x4.75X1") dimension with 4.125" mounting centres, 60CFM air flow rate, 41.8 dbA noise rating.

You want to look for something with a ball bearing as opposed to the sleeve bearing, similar CFM flow rate, with a lower noise spec.

I haven't tried this one but it looks good: part number 670-OA125AP112TB (http://www.orionfans.com/112007/m0_oa125_series.pdf) at www.mouser.com.

Note that there is a difference in 120 vs 220 VAC specs. The 50 HZ 220 VAC models tend to be a bit quieter. They turn a little slower.

[ampegfuzz]

Has anyone used the fan fliptop sells? Is it quiet?

[Soverntear]

get a nice pc fan with some leds in it :P

[Jerrold Tiers]

Ball bearing fans last longer.

ball bearing fans can have a nasty knocking sound to them. Sleeve bearings are quieter as long as they are good.

So the more expensive ball bearing fan can make annoying noises longer than a sleeve bearing fan does...............

But BB fans vary..... some are quiet, some are not.... it's the luck of the draw.

[PolkaHero]

I replaced all five preamp tubes in my VR with various GE/Sylvania/RCA tubes from one of my Hammond A100 organs. I never had a hiss problem with the stock tubes in mine, but it sounds a lot warmer now.

I also replaced the stock fan with one from Mouser Electronics that is about 12 dB quieter. It's better, but I still wouldn't use it in a recording studio without isolating the amp.

[magic papa]

Originally Posted by slick_tu

I don't have any personal experience, but I've read posts that recommended using fans with ball bearings rather than sleeve bearings:

Thanks for that. I ordered the 670-OA125AP112TB fan. Let's see whether it is any good. I post the results once it arrives.

I read somewhere that the noise coming from the bearings is almost immaterial because it is the air flow that causes the most of it.

Well, this certainly is not the case in my amp. The air flow noise is significant (and is probably here to stay), but the fan itself has a nasty whizz. Perhaps it's faulty, but I don't want to take chances with warranty repairs here in Perth. Just bought the amp, don't want to give it away for 3 months to just to be told that there's nothing wrong with it

[magic papa]

Just my own followup for those interested.

I replaced the stock fan with 670-OA125AP112TB from Mouser Electronic and it did cut the noise substantially. It is actually quite bearable now, even at low volumes.

The fan costs $21, so it is beyond me why the cheapskates from Loud didn't do the same on the $3000 piece of equipment (this is how much it costs in AU).

Anyway, it's a worthwhile upgrade for those annoyed by the fan noise.

[JimmyM]

Originally Posted by magic papa

The fan costs $21, so it is beyond me why the cheapskates from Loud didn't do the same on the $3000 piece of equipment (this is how much it costs in AU).

i'm sure the $21 you paid is a lot more than the bulk rate they pay for the cheaper fans. doesn't make it right, but that's how it goes.

[magic papa]

Originally Posted by JimmyM

i'm sure the $21 you paid is a lot more than the bulk rate they pay for the cheaper fans. doesn't make it right, but that's how it goes.

Sure, but I reckon my fan costs way less in bulk too. I wonder what is the difference between the two if you buy both in bulk then. Probably not more than a couple of dollars.

It's not the price that's an issue - it's the attitude.

[slick_tu]

Originally Posted by magic papa

Sure, but I reckon my fan costs way less in bulk too. I wonder what is the difference between the two if you buy both in bulk then. Probably not more than a couple of dollars.

It's not the price that's an issue - it's the attitude.

The General Motors rule was if they could save 1 mil (1/10 of a cent) on one part over another, they would do it. How did that work out for 'em?

[Groover]

Things to check... Make sure the volume on the channel you are not using is completely all the way down. This is something that got me in the beginning with these amps as far as the hiss goes (I used channel 1, but had channel 2 turned up and was making a constant hissing sound)

Also... the fan on my amp (SVT-HD) blow inwards and sounded like an airplane taking off when starting up. If you reverse the fan (not recommending that, just saying here...), the airplane noise drops significantly.

The solution in reducing the fan whirling noise in my case while keeping the fan blowing inwards, was to put 1/2" spacers at the mounting bolts spacing the fan a little bit away from the perforated rear grille.

I think the newer amps have the grille cutout differently where the fan is to eliminate this, but maybe you still need to space it out?

Anyway... sounds like the new fan worked in your case

[Groover]

And something like this would be awesome:

http://www.dyson.com/fans/

[magic papa]

Originally Posted by slick_tu

The General Motors rule was if they could save 1 mil (1/10 of a cent) on one part over another, they would do it. How did that work out for 'em?

I rest my case