Lego's spin on Sluckey's spin of Hoffmans Revibe

[EL34]

Modify your post
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[lego4040]

  is that better?

[EL34]

looks much better


You can separate the two pictures that are side by side also and they will be on their own line

[lego4040]

Will seperate that, thanks Doug. Any ideas on my hum noise?

[lego4040]

How would you insert a video or link to a yout tube video on this forum? I took a short clip of revibe and vox head, I have a loud hum and its there weather I have vibrato on or off(louder with it on) I took voltage readings and here is my readings from the schematic

[EL34]

Will seperate that, thanks Doug. Any ideas on my hum noise?

No ideas on the hum, I am knee deep in my build and other stuff at work
The guys here are your best bet


Just paste a youtube url in your post and the forum will take care of the rest

[lego4040]

Got it, thanks Doug. I'm stoked about your Princeton Reverb. Im uploading to youtube now but wifi is at snail speed

[lego4040]

Did some trouble shooting, I put smaller standoffs for board too. The other ones had jacks way to close. The resistors all checked out good but I don't know why I had some minute DC volts on the pins that should read 0 per schematic. I left shop so I won't get back to it till Monday but will think and chew on anyone's thoughts and inputs. Have a good weekend folks.
Oh Steve, aside from the hum that combo Revibe/vox is wicked

[sluckey]

Oh Steve, aside from the hum that combo Revibe/vox is wicked

The Revibe should be wicked in front of any amp.

As for hum....

Connect the revibe to another amp. Got hum?

Disconnect the power cord green wire from chassis ground. (A ground buster adapter works well, or just unbolt the wire.) Got hum?

Turn the MIX control to zero. Got hum?

Pull V4. Got hum?

I'm trying to narrow down where the hum is coming from so please answer all four of the above questions.

As for voltages... I don't see any. Did you write them on that schematic? If so, we can't see them on that tiny pic! We need a big hi rez pic to read them. You could always just type a list or chart. We need voltages for all B+ nodes and all tube pins, even if zero.

Wiring errors are a common problem with new builds. Are you sure it's wired correctly?

[EL34]

As Steve said, Lift the ground on the revibe plug, you don't need it.

The two chassis are connected together via the guitar cord shield
You have a ground loop if you are using the 3rd prong on both power cords

That's two paths to ground
power cords connecting both chassis and guitar cable connecting both chassis

Also, plug both units into the same wall receptacle or power strip

When I plug an amp into one wall socket and the revibe into a power strip on my work bench, I get a hum
when they are both plugged into the same power strip, all is dead quiet

[lego4040]

I put the Revibe into normal channel and got hum, I put it into virbrato channel and got much less hum. I lowered the board from 5/8" standoffs to 1/4". The jacks were way to close to board. I thought about pulling the center tap ground but ran out of time and didn't feel like hanging around shop anymore.  Yeah I wrote  them down on schematic next to the voltages that are there already from print out. I shrunk pictur down to not take up space. If you look at the schem volts in red mine are next to it in pencil.

[lego4040]

I just did a 8 hr shift for core drilling holes from one floor to another and dealt with a leaking expansion tank which flooded out a corner off a floor. Now I'm home and I'm getting the things to do list thrown at me. I will do all those things Monday

[sluckey]

I don't see any red flags with your voltage readings.

I thought about pulling the center tap ground but ran out of time and didn't feel like hanging around shop anymore.

Just to be clear, we ain't talking about pulling any "center tap" grounds. We're talking specifically about disconnecting the green wire in your power cord. If you used an IEC connector, then disconnect the wire from the ground lug of the IEC to chassis.

FWIW, I have the green wire of my power cord connected to chassis. So far I've had no ground loop hum issues. I've had my revibe connected to six different amps without any hum issues. But I'm prepared to use a ground buster adapter if need to. Fingers crossed.

[terminalgs]

In Merlin's excellent grounding chapter ( http://www.valvewizard.co.uk/Grounding.html ), see 15.11 "Ground Lift".   I  built many tube preamps and struggled with hum issues and ground loops via instrument cables and the safety grounds on the mains.   until I started using this style of ground lift.   It might be easy to adapt to your circuit if you used hoffman's board (i.e. easy to insert this between your chassis and circuit ground).  this ground lift scheme is also used on lots of modern tube amps (Vox, Marshall, etc) as well as studio pre-amps and th the like.

you can also play with the chassis location of your filament supply's center tap with a jumper wire and alligator clip.

You'll need to use isolated input jacks, so the "sleeve" of the inst. cable is circuit ground.   With these, you can put a .01uf cap from the sleeve lug on the jack to an immediately close-by chassis ground. This shunts any RFI that might be on the outside of the instrument (although you are searching for the source of hum.,, RFI is usually more buzz than hum).

[EL34]

This is what we are talking about as far as lifting the power cord ground wire

[lego4040]

Steve, on the schematic it shows what the voltage reading around the amp should be for checking purposes. They are shown in red, I wrote my readings in pencil next it

[sluckey]

See reply #112.

[EL34]

You can just use one of those 3 prong to prong adapters to do a quick check on the power cord thing

[lego4040]

Here is my quick and crappy video of Revibe. I do not get a hum when I plug guitar straight into amp but I noticed a high pitch squeal for a couple of seconds and if you listen when I throw switches on Vox clone I get a clink on glass sound
http://youtu.be/uHNQL6nwKTw

[lego4040]

Update, I removed the ground on the plug and it got ALOT quieter, but not silent. I put mix on Zero and that did not of anything. I put sensitivity to 10 and it got even quieter. I pulled V4 and I it was dead silent, I had no guitar coming thru amp but it was as quiet as if it'd been off. I took a vid of it and will post as well. Should I lift ground on amp?

[EL34]

Leave the amp grounded for safety


You can lift the ground on the revibe and it will not do any harm

[lego4040]

I thought that would be an issue if I did that with the amp ground.  I'll go thru amp again, check things. I'm not a tech with this stuff but can follow instructions. Trouble shooting pedals drive me nuts cause of size of parts but I usually got it solved

[lego4040]

Here it is today after ground lift. I also changed the little blinking led to a glass jewel.

I used a compression fitting to lock jewel, it fit threads perfectly. I used a small grommet in back then bulb
http://youtu.be/2YSSq8gw4Y0

[sluckey]

The hum level changes with the intensity pot? It almost sounds like a bad Intensity pot or the pot has a bad ground connection. Something interfering with V4 grid path to ground. Measure resistance from V4-7 to chassis. Should be about 320K with intensity pot set to minimum. And should be about 1.7M with intensity at maximum. And resistance should vary smoothly as you SLOWLY rotate the pot.

Do you have hum if you pull V5?

Have you tried another tube for V4?

I'll do some checks on mine tomorrow and I'll have some more questions for you then.

[lego4040]

I've put different 12ax7 in v4 and had same hum. The hum doesn't ramp up or down when I turn intensity, when I move off of Zero it's more pronounced and when I put to 10 it almost goes away. I will pull v5 steve

[sluckey]

when I move off of Zero it's more pronounced and when I put to 10 it almost goes away.

I was able to repeatedly duplicate that behavior on mine. I discovered it while removing the shield from V5. All of a sudden I had your hum! Touching the tube or wiggling the tube would make the hum go away but I could make it return by just wiggling again. Reseating V5 was the cure. So I rolled several tubes into V5 socket, even tried a couple 5751s. I had a couple tubes that had that hum and I could not make it go away by wiggling the tube. Some of the other tubes were always quiet no matter how much I wiggled them or thumped on them.

So, grab a few 12AX7s and try different tubes in the V5 socket. Cross your fingers.

[lego4040]

Ok Steve, I took reading from V4-7 to chassis and I got 384K with sensitivity on 0. With it on 10 I got 1.7m ohms. I poked around checking for anything out of the ordinary. I swapped V4&V5 with a matched pair of JJ's and it did not like it at all. I put the NOS Bell & Howell's and left tube covers off and it was perfect. No noise at all, I turned all dials in every direction playing thru amp and it was perfect. Will see what happens tomorrow when I plug it back in

[sluckey]

I'm not satisfied with just rolling tubes until I find one that works.

I'm wondering if the LED mod is causing the circuit to be picky about which tube is plugged into V5. Tomorrow I'll put the original cathode resistor/cap in and see if it behaves better. I'll stay in touch...

[lego4040]

I never thought about that with the led. I will button up amp and see if it stays happy. If it does my next step is to make some pine cabs for both

[sluckey]

Bet you're itching for a Princeton Reverb now! 

[lego4040]

  before I built these two I was Jonesing for one. I almost bought AllenAmps version since I built one of his amps already. Then Mojos version next. Now Doug's got his in the works, damn. I would like to build it in a tweed style instead of a Blackface, not sure what size I would need but I would guess a big 5E something. A 2x12 Princeton reverb in a tweed cab would be Heaven