Fender TBP-1 a little noisey

wamalot · #1 01-23-2012, 01:55 PM

I got a used Fender TBP-1 and it is a little noisey when the Drive is engaged, but not when clean, even with tube engaged. It is low frequency, but not 60 or 120 hz hum I have heard before. I have never heard 'motorboating', but this might be that, since that is a fair description of the sound. It is low in the background, but still there.

Some sites I visit talk about checking the grounding and several kinds of caps. Also how to ground them before exploring (not my first rodeo...)

I have changed tubes and no difference... I am handy with a soldering iron but don't have enough info on this preamp, so:

1) I have looked a dozen places for the schematic, anyone have an idea?

2) Any listing of mods to quiet a tube preamp in general?

3) Anyone with experience modding or fixing this to be quiet(ER)?

Any help is appreciated!

wamalot

Deepwoods · #2 01-23-2012, 02:38 PM

Maybe the power source? Try a different circuit or outlet to see if that helps.

BassmanPaul · #3 01-23-2012, 02:43 PM

motorboating is often caused by leakage through the B+ line. You should check your power supply filter caps.

JimmyM · #4 01-23-2012, 03:44 PM

I'm wondering if that isn't normal operating sound. When you crank the drive, you're also going to increase background noise. You telling me it sounds fine when clean makes me think it's likely OK, though I'm not familiar with that preamp enough to tell you one way or another.

popgadget · #5 01-23-2012, 04:24 PM

I was thinking the same thing. Drive increases gain, and noise along with it. Is the noise there with the input shorted?

aledeville · #6 01-23-2012, 04:38 PM

The TBP-1 has a drive circuit, but it's an overdrive and only capable of this. That shouldn't be noisy.

How have you set your preamp?

wamalot · #7 01-23-2012, 05:27 PM

Good suggestions, all! Thanks!

I was using a bass that needs some switch work, so I will first try the preamp with a more solid instrument. It makes no difference how I set any of the preamp's other settings.

In the house I was running the preamp into a JBL EON 15 for practice.

I have a good power conditioner so I will try that. It wasn't my first suspicion because of the quiet clean channel, but I do need to eliminate all suspects!

I do have a very quiet tube I want to try also. Usually the quiet ones don't tremble and vibrate. True for preamps, too!

I have not shorted the input to see if there is noise yet.

MOST interesting about the power supply filter caps. I will look at that, too.

I hope this isn't just normal, but maybe...

I'll be back with reports!

again, thanks!

vivifiction · #8 01-23-2012, 05:43 PM

I have a TBP-1. First, the schematic is painted on top of the unit. At least, for mine it is (and this was done by fender).
My overdrive circuit doesn't make any unexpected noise when engaged. One of the pots seems a bit scratchy and so it makes some noise when I adjust, but once it's set, nothing. It doesn't make any sort of hum. I'm assuming that since the issue was bothersome enough to come to TB, it's probably not the natural noise.
I'd recommend fiddling with your settings with the overdrive engaged. The TBP-1's tone circuit is a little peculiar (flat is at 2-10-2, I think) and it might have tricked you. Also, the bass and treble pots have a boost feature by pulling the knob out, and maybe a boosted high end is the culprit.

wamalot · #9 01-23-2012, 08:59 PM

Thank you vivifiction! I have loooked that over, and it seems to be a block diagram, but maybe it will tell me enough. I will look more closely. Especially thanks for letting me know it is quiet when the drive is on. This is supposed to be for recording, so I expected quiet, so I will keep looking.

craig.p · #10 01-24-2012, 03:33 AM

Quote:

Originally Posted by wamalot

I have never heard 'motorboating', but this might be that, since that is a fair description of the sound. It is low in the background, but still there.

Just FYI, motorboating is a bup-bup-bup-bup sound that happens about 8 times a second (more or less) and is usually fairly prominent. Sounds like a trawler at idle. My experiences hearing it over the years prompt me to say that if there's any doubt that what you're hearing is really motorboating, then it's probably something else. That's how accurately the "motorboating" moniker matches up with the audible symptom.

BassmanPaul · #11 01-24-2012, 10:47 AM

Quote:

Originally Posted by craig.p

Just FYI, motorboating is a bup-bup-bup-bup sound that happens about 8 times a second (more or less) and is usually fairly prominent. Sounds like a trawler at idle. My experiences hearing it over the years prompt me to say that if there's any doubt that what you're hearing is really motorboating, then it's probably something else. That's how accurately the "motorboating" moniker matches up with the audible symptom.

Motorboating can vary from one pulse every ten seconds into the ultrasonic. it just depends on what is causing the instability. If the OP has a scope he can work his way through the pre-amp to find the root cause.

craig.p · #12 01-24-2012, 03:49 PM

Wrong. Motorboating is what you hear, and it's typically only a few Hz, notwithstanding what some online sources that appear to have expertise in the matter state.

wamalot · #13 01-25-2012, 09:19 PM

Partial report, the diagram on top is a block diagram of signal flow, it is not a schematic that will list parts: capacitors and transformers, etc. So I am still looking but that may not appear according to what I am reading online about Fender's newer designs.

I tried it out with the quieter bass, and it is quieter, but I jiggled the cable and heard a different scratching, so I clearly need a different cable. I have a white coily Bullet cable, so I will break that out. It may clear up other noise.

Getting an oscope this weekend, I have a multimeter only. The probes will be up to 600v so that is covered.

Step by step. Thanks guys!

Son of Bovril · #14 01-26-2012, 02:24 AM

I have a TBP-1 that I have used for recording plenty of times, but haven't used the OD so I can't comment on that...

Depending on how you are setting the drive settings, pushing up the gain might cause a bit of hiss, does it reduce when you turn the blend all the way to the clean signal?

It could just be a bad tube in the OD channel and hopefully it's not something serious. I can't say I have experienced any problems with mine, in fact it has proven numerous times to be shoulders above my other pre's... In recording I constantly have hiss issues with my eden nav. The Fender has always been dead quiet

I'm guessing the hiss is pretty loud if it is bothering you. Hope u find a solution soon, I will check if mine does the same as soon as I get a chance and report back

Son of Bovril · #15 01-26-2012, 02:25 AM

PS. it could also be that your tweeter on your cab is turned up quite high or is it noticeable on a direct recorded line?

rodl2005 · #16 01-26-2012, 03:43 AM

+1 on the tweeter. Not the same, but I thought the overdrive on my SVT 7 PRO -Berg AE cab rig sucked, then realised the horn was on, only 1/4, but still on.
Sounded great after I switched it off.

anotherlin · #17 01-26-2012, 04:27 AM

By the way, if you can, can you post pictures of the inside of a TBP-1 ? Thank you. I'm curious.

BassmanPaul · #18 01-26-2012, 09:09 AM

Quote:

Originally Posted by craig.p

Wrong. Motorboating is what you hear, and it's typically only a few Hz, notwithstanding what some online sources that appear to have expertise in the matter state.

I'll bow to your superior wisdom. you obviously know so much more than I.