Ampeg svt-vr---fan too loud???!

[nevetslab]

Every once in a while, I'll find something sent over from our Guitar Dept that seems silly. That Department is no longer across the street, but now down the block and around the corner, eliminating the ability to walk over and fetch gear with a dolly. This time, it's one of the seven Ampeg SVT-VR's with the complaint that the Fan is TOO LOUD.

I plugged it in, once I hefted it up to the check-out bench, and didn't notice anything obnoxious about it. SVT-CL's are usually noisier, their nominal pitch being higher, and mounted to a resonant front panel helps increase the acoustic noise on them. Not so on the SVT-VR. I looked around the shop to see what I had on hand. I had a couple dual-fan cooling boxes that I used in my ventilating dark room windows, now work great for cooling down power tubes. EBM ball bearing fans, but 115CFM so too much for this application. The existing Fan in the amp is an off brand...Jamicon 2400 RPM 67CFM, 42dBA rating. I found I had a rack-mount fan panel using three NMB 110CFM fans, same size, thicker.

I removed the Jamicon fan, plugged it back in to listen to it unmounted, then having removed one of the NMB fans, listened to that as well. Noticeably noisier, but, all I had. This morning, I made SPL measurements of the amp, near-field but out of the air stream (6 inches behind the power xfmr with the fans mounted on the grille at the opposite end. Got the room measurement, then that of the stock fan, then with the higher speed fan, it being all I had for comparison. A bit over 4dB difference overall, with a different frequency spectrum, sounding noticeably higher in pitch and louder.

So, I searched to see what I could find in the 50CFM range for 120mm AC fans. Not much available, as it turns out, in stock. EBM makes a nice fan for $48, NMB made one for around $14, but what will be delivered from Mouser is a question, since the company that owns NMB has eliminated the lower CFM fans from their catalog. Mouser has inventory, but, the data sheet they provide doesn't agree with their published details. Sunon was the only other option they had, for $21. So, I bought one of each, knowing we're not about to start buying EBM fans.

Now, if this amp is being used in a recording session, then yes, the fan WOULD be too noisy. ANY of the SVT amps (SVT-CL, SVT-VR, SVT2-Pro) would be objectionable. I could always install a switch to turn the fan off. Which would long term increase maintenance issues in the preamp.



The first screen shot of my CEL-500 Series hand-held spectrum analyzer shows the room with nothing turned on, and the studio next door quiet. The second shot is the stock Jamicon Fan (70CFM), and the last shot is the NMB 110CFM fan.

I'm not sure who made the complaint, but......hey, I'm in need of labor hours right now, so if they want it, they got it.

[nevetslab]

Revised SVT-VR Fan Panel w/50CFM fan

The two slower speed fans arrived today...a Sunon SP103AT1122LBTGN, being a 54CFM 1900RPM fan, metal frame, ball bearing and an NMB 4710PS-12T-B20 53CFM sleeve bearing (new data sheet doesn't show RPM). I listened to each unmounted, and the NMB sounded louder and felt like higher CFM than was stated, so I mounted the Sunon fan.

Major improvement over the 67CFM Jamicon fan that came in the amp. SPL measurements on my CEL 551 SPL meter, 1/3 Oct Leq mode:



In looking at the two images with the fan running, last image being the stock Jamicon fan, I had selected Linear for the top right corner reading while having selected A-wtd for that top right corner reading. But, you can see the difference on the left side of the spectrum (Linear, A-wtd, 1/3 oct bands 12.5Hz-20kHz centers. Looks like the A-wtd level dropped down about 12dB, and huge difference in the overall spectrum.

The Sunon fan, having ball bearings, I was hearing cyclic noise from the bearings, which might be that peak in the spectrum @ 1.25kHz. So, the Sunon fan was $21.09 + shpg. It won't move as much hot air out of the cabinet, so I'll have to keep an eye on the maintenance cycle.

[Leo_Gnardo]

So, the Sunon fan was $21.09 + shpg. It won't move as much hot air out of the cabinet, so I'll have to keep an eye on the maintenance cycle.

The first complaint I'd expect would be "amp mysteriously shuts down after xxx minutes of loud continuous playing." If that doesn't happen, you're home free.

[TomCarlos]

I remember dealing with fan noise in a couple amps. I bought two or three just to experiment. It was a tradeoff - the CFM vs Noise. In the end, I chose the "ADDA" brand sold through Jameco. The come in a variety of sizes, voltages, CFM, etc.

[SimTech]

I just replaced one of the Jamicon fans with an NMB fan that is quieter, runs slower, and moves more air than the Jamicon original. The only thing is it is almost too thick to fit behind the transformer with "almost" being the operative word here. If you use screws that are the exact length so as not to protrude beyond the nuts on the back (or easier just to put the s rew heads inside) the fan fits perfectly and DOES NOT touch the transformer. It's flow is only slightly obstructed by the transformer but so is the original but it's a little thinner but not much.
No, I don't have dB meter screenshot but the difference between the one I removed and the NMB is drastic and readily apparent to even the most casual observer.
Again, screw length MUST be EXACT. DO NOT let the fan hardware contact or cause the fan to contact the transformer when installed . The fan's grille still fits on the inside of the rear grille but be careful adding thick washers or nuts to secure the fan. The NMB fan has the exact same connector as the Jamicon so it's plug and play electronically.
Note this is for a 120v amp if that matters. I'm not sure if the otherwise wired amps use 115-120 on their fans or what.
https://nmbtc.com/parts/4715ms-12t-b20-a00_60hz/
or (Same fan new number)
https://nmbtc.com/parts/11938mb-a1k-ea-00_60hz/