SVT fan noise

[selloutrr]

I was thinking while i was on my way home about an Ampeg SVT 1987 anniversary head i bought a couple years ago. when i first got it the fan was really noisey so i called ampeg and they tracked down a direct NOS fan i swapped them and it was the same loud fan. The amp sounds beautiful but the fan noise is so loud it can at times over power the amp. I haven't looked at the schematic yet but i can't imagine that they designed the fan to run this loud. Must be a voltage issue, to high? and is the fan even needed? maybe i could just unplug it, or if it completes a circuit make a dummy plug or add a switch that completes the circuit with out the fan or with? I would like to try my options before i drill.

Just curious if this is normal and anyone else has experienced this?

[drhulsey]

... is the fan even needed?

Our bass player has an SVT head, and he's plenty loud enough that I don't recall hearing the fan. With the army of power tubes in an SVT, I would be reluctant to do away with the fan. I would check out the fan voltage and see if you can find a quieter replacement.

[billyz]

I had an Eden SS bass amp and the fan was pretty loud when it came on.
First ,I reversed the fan and it helped. Then I put a 5w 120 ohm resistor in series with one lead and it slowed enough to be quiet.

[selloutrr]

Thanks I'll dig it out and give it some love!
I agree it's not safe to turn the fan off entirely. i'd hate to burn up the amp from removing the fan.
good idea's i'll try flip the polarity of the fan first if that's not enough i'll put a 500K pot on it 2 or 3W and briefly test how low i can take it and still get air flow.
Meter the result and divide it by 1/2 - round up and put that value in and live with some noise to make sure the tubes stay cool.

I love the tone so i can live with some fan noise It's not bad cause i know what it is and that it's helping keep the amp safe. What kills me are the noises you can't pin point or give a possitive use.

Thanks Again i'll let you know what i end up with.

[Phil_S]

I don't know what the fan looks like, but you might think about getting a 240v computer fan. Run it on 120v at half speed. I think the proper thing to do is to use it as an exhaust fan.

[selloutrr]

great idea but i'm to anal to alter it from stock. I need to finish up a pedal board i'm building that's taking up the whole kitchen island cause my shop is full of boxes and is being redesigned. After this board is done (nightmare of a project!) I'll get on the SVT and take pics so you can see what's up and how it turns out.

[rfgordon]

The AC powered fans out there are fairly loud. If you look them up in the Mouser catalog, you'll see the quieter ones rated at about 33 dB.

The DC powered fans made for pimped out computer chassis are a very different story! There are several models out there rated as low as 15 dB for a 120 mm diameter fan. I can't recall if the back of the SVT chassis has a convenience outlet--if it does, you would use a wall-wart powered DC fan in an aggie-engineered attachment, and just disconnect or remove/save for later the stock AC fan.

Check the fans at www.xoxide.com

I put a super quiet fan that lights up blue into an amp last winter. It ran a pair each 6V6 and 6L6 cathode bias, so it made some serious heat. The blue fan was really cool--pun intended!

[David Root]

I have a '75 SVT but its fan isn't that noisy. Yes, you can hear it if you turn the volume way way down, but it only takes a small chunk of 300W to obliterate it entirely.

Perhaps your '87 has a smaller diameter fan running faster?

[selloutrr]

the fan is about 6" ~ 6.5" and really #$*& Loud you can over power it but if you where to play it live and pause between songs it would be heard in the first 4 rows. I'm still waiting to get the Pedal board off my bench it stopped being fun about 2 years ago when the guy couldn't make up his mind what pedals to use then after two years finally decides (20+ pedals talked down to 14? with options to plug more in) and expects it to be built over night, the same guy that buys an amp from guitar center at full price plays it for a month and expects to get more then he paid for it when he sells it... Oh yeah and he punishes his ears everyday sitting infront of a 100W Marshall Plexi set at 8 or better and then wonders my he can't hear treble... I kid you not he's def above 6Khz... Completely Gone!!! and wonders why i don't want to come over and sit in front of it with him. Anyway I can't wait to get that board off my bench and back to the things i love... Tube Tone! (by September) I'll do the SVT first then finish up the Risson LTA120 and I'm going to see how long it will take to knock out TW express going non stop with all parts sorted and holes drilled I'm going to guess 18-26 Hrs.

Thanks for letting my vent I feel better this pedal board has me all bent

[selloutrr]

I finally got a chance to put the SVT on the bench it's # 062 of 500 made in 1987. On further inspection the fan is powered on 115V. The vent grill is embossed to house the fan to blow air into the cabinet. I made a jumper that switched the polarity but the result was no different so i put it back to stock. The ground wire is attached to the vent screen and disn't make a strong ground. I moved the ground it to the chassis and was able to calm down about 20% more fan noise it's liveable now and still has all the SVT thunder! If it still kills me i'll rip the whole power section out and add a resister so i can turn the fan on and choose the speed. but for now i'm happy. here are a few pics. I totally forgot the output tubes are Phillips, that was a nice surprise! Thank you for all the input, it was the motivation i needed to get this project on the bench.

[leaveitalone84]

That's a nice SVT. I have a '74 that has been a good friend to me for a while. Needs some work though.

[selloutrr]

I love the tone! This is one of the best I've heard but I believe it has more to do with the tubes used in the Preamp ( brimar and Bugleboy ) then the circuitry. I voice it to have a growl in the low mids and a very smooth top end. But the Huge Iron and Phillips Output tubes don't hurt.