New Rocket build sounds amazing but needs some hum reduction

[jkey04]

I mailed the PT off to Heyboer yesterday. Im not sure how long it is going to be before I get it back. They told me they are either going to fix it or mail me a replacement.

If there is still a noise issue once I get it reinstalled, then I will definitely consider rotating the caps. I agree with your explaination rooster.

Again, thanks for all the help. Im ready to get this amp up and running so I can take it to some gigs!

[rooster]

As a practice I take a new PT and plug it into a switched off powerstrip, just raw wires separated, and then fire it up. Yeah, not for the timid.

You can measure the taps, etc., too, but the main reason I do this is to listen to the pot job that was either done well or not. Typically you come to trust your manufacturer, sure, but I hate pulling the PT out of a TW Express, for example. Ive done that twice at this point and for the problem you seem to be experiencing. I learned.

[jkey04]

Just received the PT in the mail from Heyboer. Hopefully I'll have time this weekend to get this amp put back together and running.

Heyboer was easy to deal with, and they handled the situation wonderfully.

I would have never considered this as a problem, so thanks for bringing this to my attention. You learn something new every day!

[jkey04]

I installed the repaired PT a few days ago, and it help with the hum. I still seem to be getting some hiss from the cut control. Using an oscope, i found that i have AC interference on the plates of the PI and the power tubes and on the hot side of C15. What could be my problem?

I replaced the wires on pins 1,6, and 7(both plates and grid2) of the PI with shielded wire, but this didn't help at all.

I plan on rewiring the entire preamp with shielded wire, but i don't think that will completely solve the problem.

[Reeltarded]

Noooooooo! Don't waste your time and strangle your amp.

You have a bad cap looks like. Unfamiliar with the circuit, wait for a better reply BUT shielding stifles any possibility of open topend, and makes for bland congestion down low. Cough cough cough, ect.. Dress not Mess!

I sound like the church lady.

[M Fowler]

I'm convinced that you have a dirty AC line and need to try the amp in another room or another building.

The Rocket does not need shielded wiring and is such a forgiving amp in regards to such things as the noise your describing.

Mark

[jkey04]

I thought the same thing about having dirty AC power in my house, but i took the amp to my parents house before i shipped the transformer back and it sounded exactly the same. I can try that again now to see if it is any better, and I'll also run ithru a Furman to see if that helps.

Another point to make is that my Dr Z amp is dead quiet (unless preamp volume is cranked) when plugged into the same power outlet.

All we can do is keep troubleshooting...thanks again for the input. I'll hold off on all the shielded wire.

[redshark]

You don't need shielded wire and yes, the rocket is a quiet amp. Go through every connection. The hum makes me think you could have some grounding issue. Did you rotate the cap stack like a regular rocket layout? Did you test the heaters?
Just some suggestions....

[jkey04]

Thanks for the input you have given me so far on my Rocket build. Today i have been reading a pdf file written by the valve wizard on grounding and it has me considering redoing my whole ground scheme.

First of all, I used PEC pots like i stated previously; therefore i couldnt solder to them. RJ sold me those washers with them solder lugs on them, but i do not think i have used them correctly. What is the correct way to implement them?

Tonight, my plans are to (in this order) run the amp thru a furman power conditioner to observe how it sounds with cleaner power, rotate filter caps 90 degrees, then adjust grounding scheme to maybe a star ground format.

I want this amp to have a solid ground scheme so i can rule that out as the source of the hum. That is if it doesn't solve my hum problem. My knowledge of proper grounding methods is very little right now, so I am trying to learn all that i can through this build.

Thoughts?

[Tillydog]

I want this amp to have a solid ground scheme so i can rule that out as the source of the hum. That is if it doesn't solve my hum problem. My knowledge of proper grounding methods is very little right now, so I am trying to learn all that i can through this build.

Thoughts?

Add me to the list of people who think your problem is related to grounding.

The layout has been proven to work, so my 0.02p is to spend effort on following it *exactly* rather than inventing some new grounding 'scheme'.

For instance, from your photos on the 1st page there only looks to be one ground connection to your 'stack-o-caps' where the layout calls for 2.

Where things are shown as being grounded to the same place, then that's what needs to be done (turning the caps around might help you achieve this).

No 'extra' grounds, etc...

My 0.02p....

[redshark]

I'm almost 100% sure you have a grounding issue. You should be attaching grounding lugs to everyone of the PEC pots and use a grounding bar to match the 100% proven rocket layout that you can find in the files section. I would do that first than any other thing.

[jkey04]

Alright...my conclusions from last night are:

AC power does not seem to be affecting the amp.

Rotating cap stack and adjusting the cap grounds removed AC bleed in power tubes

I still have hum in the preamp. Each tone control has hum in it; the cut control being the worse then bass a close second. When i place the oscope probe on the tone control side of C2 and C5 the hum is reduced in the treble and bass controls respectively. Could this be filament hum or is it a grounding issue??

Another thing that i noticed last night was that when i turn the mains on with the amp in standby, there is a slight, lowend, audible tone coming thru the speaker. Where could this be coming from? There shouldn't be anything coming thru the speaker when the amp is in standby, so this bugs me.

Thanks again for the help so far!

[PlinytheWelder]

This is one of the better grounding schemes for a wreck type amp.

[img633]http://i1154.photobucket.com/albums/p52 ... -13-09.jpg[/img]


In my case, I moved the power supply grounds from the 120V mains ground lug to the power supply caps ground lug

See here. http://www.aikenamps.com/StarGround.html

[jkey04]

Thanks for the grounding layout Pliny. I like this better than using a buss bar.

I seem to have finally gotten rid of the hum, but i still have a slight hiss in the treble frequencies when the volume is about halfway up. Is this normal? From what I can tell using my scope, there is some AC bleed over that starts on the input plate (pin 6) of V1 then is amplified through each stage after that.

Could this hiss be a bad resistor? Which resistor could cause this?...or is there a chance this will go away when i put the bottom shield plate on and mount the amp in the cab? Shield plate should arrive this week.

Thanks again for all the help so far! I have been playing the amp a lot the past few days...it sounds killer!!!

[Reeltarded]

Hiss?

What is your other amp? What amps have you liked? How does this amp compare in hiss to those amps?