SVT 3 Pro fan replace

[tchristian]

Just a quick FYI: I used some rubber dampeners to reduce fan noise in my 3 Pro. Here's an informal soundtrack with 1) old fan with rattling bearings, 2) new fan with stock mounting, and 3) new fan with isolators.

- I couldn't find a sleeved 24V fan so I ended up with a bearing fan from McMaster-Carr (part # 1939K14).
- I used the smallest sandwich mounts they had (part # 9119K111).

The isolators gave less improvement than I hoped.

 

[cornfarmer]

Hard to tell on the recording, but what kind of dB improvement do you think it made? Or percentage?

I got my bias fixed on mine finally and the only other thing it could use is a new fan, though mine doesn't sound as bad as yours.

 

[tchristian]

Yeah, I recorded it on a GoPro - lots of background hiss. I should have used a proper setup.

I don't think the dampeners got me more than maybe 10 or 15% reduction. Probably not worth the effort for most. If I think of some other way to decouple the fan or reduce the noise I'll post it. (That fan is pretty quiet when just held in hand.)

I searched pretty hard online for a sleeved fan. I read on TB that Ampeg chose that type because the bearing fans transmit bearing noise through the chassis. I agree. Couldn't find one though.

 

[tchristian]

I went back in and added some thin, self-adhering foam. Used an SM57 into a high end console this time, but I still have a ton of background noise. (I don't know enough about gain staging to have done a nice job of recording this.)

Still, underneath the noise I hear the foam getting me a little quieter. Maybe forget the isolators and just use foam? Either way, my "used-to-be-a-perfectionist" side is giving up now.

 

[beans-on-toast]

All fans aren't created equal. Some are ultra quiet, others are noisy. The mcmaster carr listing is missing a number of specs. Holding the fan in free air will give you some indication as to how quiet it can operate. When mounted in a chassis, it can produce additional noise due to the moving air.

What I normally do when replacing a fan is look for a manufacturer and model number of the original one. Then look up the specs. I use those as a reference when looking for a quieter model. It's usually a good idea to look for a fan that moves the same amount of air. Better performing fans tend to cost more. Isolation mounts can help in some cases but it is more about how quiet the fan is and how the air is moving.

Check out electronic suppliers such as mouser, newark, digikey, and allied. There are many good makes such as ebm-papbst and Orion.

Some fans come with wire leads, others require a plug in cord so check for that. Some fans have temperature sensors built in, not normally something that you would require as amps wth DC fans usually have circuits already serving that function.

 

[tchristian]

Thanks for the input. In fact, I've been using Mouser, Newark, Digi-Key, Allied Electric and a host of other suppliers for many years. As an empirical atmospheric chemist I spent most of my time designing, building, and deploying mobile and airborne platforms for FTIR spectrometers and a variety of less complex science equipment. Some of that work was with simple electronics to control instrumental functions e.g. power supplies, valve switching, mass flow sensors, etc. On two of our instruments we employed one of the same shock and vibration isolation systems used by the military for mounting missiles to airborne launch platforms. I've used sandwich mounts on a number of different instruments; that's why I thought of them here in the first place.

I tried for a couple solid hours to locate a 24 volt fan with the same specs as the sleeved Rotron fans that Ampeg used originally and that are no longer available. In fact, Rotron offers a bearing fan with those exact specs (Comair Rotron ST24B3). I installed one in our other 3 Pro and it's loud. In all the years and all the times I've ordered from McMaster or used their products I have yet to find "cheap". They stock quality goods. So I'm confident the fan I installed will last a good long time. It's not as loud as the ball bearing Rotron and it's specs are close enough for me.

cheers, theo

 

[beans-on-toast]

It never hurts to add details to a thread for others that may come across it.

The fans that Ampeg used/uses aren't the best. Rotron goes way back with them. The old Rotrons in SVT's for example had a small rubble nipple that you removed for oiling. What a good idea, now they want you to buy a new one.

Searching for parts can be a time consuming. What's worse, I can seldom buy everything that I need from one supplier which means multiple shipping costs.

Sounds like you have a very interesting job.

 

[cornfarmer]

What is the make/model of the orig fan, if you remember or have that info handy? Wouldn't mind looking it up to match the specs. Yes, I'm too lazy to crack open mine!

Looking on McMaster, I noticed fan #1939K49 was slightly quieter and had higher airflow, only 1/4" less deep.....

 

[tchristian]

The original sleeved fan was Comair Rotron Sprint ST24A3 (blurry pic but that's the #). The replacement is ST24B3. That's my understanding anyway. I bought mine off ebay for $25. Thinner should be fine. Let us know if you go with a different fan.


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