6V6 Plexi with Crossover Distortion [Problem Solved]

[dbharris]

Josh, thanks for the advice! I only had 1/2 watt zeners in my parts stash (for pedals) and wasn't sure what was needed for this. I stocked up on extras and other values too in case I wanted to use them to drop some voltage too.

Geoff, Trinity recommends scaling the whole amp. So, that was what I did. It looked like with a couple extra 1n4007 diodes you could choose to scale just the power tubes or power and phase inverter. But I was not sure if that meant changing the dropping string for the preamp to keep voltages where they should be. I'm going to play it like this for a while and if I end up not being happy with the tone, I may try the power amp and PI only.

I'd say my speakers are on the way to being broken in, but probably only have about 10 hours on them. Hoping that will help settle things in too as they relax a bit.

[JMPGuitars]

Josh, thanks for the advice! I only had 1/2 watt zeners in my parts stash (for pedals) and wasn't sure what was needed for this. I stocked up on extras and other values too in case I wanted to use them to drop some voltage too.

I'd say my speakers are on the way to being broken in, but probably only have about 10 hours on them. Hoping that will help settle things in too as they relax a bit.

For voltage dropping, look at the link in my signature.

It's interesting the PR mod helped at all, that's usually only for EL84s.

Please take my advice on the output jacks. It can help with both noise issues and safety. And it's absolutely not optional if you add a NFB.

Thanks,
Josh

[dbharris]

Hi Josh,

I think I have some isolated jacks somewhere, they might be pc mount that I ordered for a pedal, but I can still make that work. And thanks so much for mentioning it is a safety issue with NFB. The ground wire would go back to the star ground for the power amp and PI, right?

On the Ruby mod, I was at the point where I was willing to try anything that was reversible to see if it helped. My problem was not "fizziness" which I understand is why a lot of people add them with EL-84s. I was reading up more on the mod here http://www.paulamps.com/18watterbuzz.ht ... Distortion where it was explaining more or less that under certain operating conditions the coupling caps were getting charged up. I thought/hoped that the same could be true with my 6V6s.

Thanks again for the advice!

-Dan

[JMPGuitars]

Hi Josh,

I think I have some isolated jacks somewhere, they might be pc mount that I ordered for a pedal, but I can still make that work. And thanks so much for mentioning it is a safety issue with NFB. The ground wire would go back to the star ground for the power amp and PI, right?

On the Ruby mod, I was at the point where I was willing to try anything that was reversible to see if it helped. My problem was not "fizziness" which I understand is why a lot of people add them with EL-84s. I was reading up more on the mod here http://www.paulamps.com/18watterbuzz.ht ... Distortion where it was explaining more or less that under certain operating conditions the coupling caps were getting charged up. I thought/hoped that the same could be true with my 6V6s.

Thanks again for the advice!

-Dan

I would order new jacks. You want solid mechanical connections in addition to a good soldering job.

I just took a look at your schematic/layout because of that question. If I ever tie a part of the PI to the power amp star ground, it's only the part where, in your case, the 220K grid reference resistors connect to ground (but not the LTP portion). There's a couple issues with the layout, but the easiest fix would be to snip the ground bus between the 300R resistor and 33uF cap, and connect the other end to the preamp bus wire. Take a look at the ground scheme thread in my signature.

That 33uF filters the preamp, and should not be tied to the power amp ground. That could lead to noise and other issues. If that's not clear enough ask any questions you may have, or take a look at some of my layout designs and you'll see the correct way to implement this.

Thanks,
Josh

[geoff 1965]

another area of safety is you don’t have a bleed resistor,if you fit a 220K 2W metal film between the first positive and negative terminals of the can cap when you switch off the voltage in the capacitors will drain to ground.

[dbharris]

Josh, thanks for pointing that out. I did catch a few errors between layout and schematic, but I did not even think to double check the star grounds. I see the schematic is correct and the layout is wrong. I also looked at your post on grounding. I will rework that this weekend when I'm back inside the amp.

Geoff, that's a great idea. I do have a heavy duty alligator clip lead that I soldered a 220K in the middle of and I use that to discharge the caps before working on the amp or if it is staying outside of the head cab.

[geoff 1965]

Which output transformer and 6V6’s are you using Dan?

[dbharris]

They are Heyboer, but Trinity's take on a clone of the Radio Spares. They are 290-0-290. I am running JJ 6V6S output tubes.

I have another question on grounding and the VRM. I have attached the VRM instructions for clarity. But essentially you move the 1M pull down resistors to the V1 socket and add a cap between the grid stoppers and grid to block DC passing back to the input jack. The instructions say to ground the 1M resistors on the middle tab of the terminal strips that connects to the chassis.

Wouldn't it be better to run a wire back to the preamp star ground? If so, does it matter if I run 2 wires back or tie the ground side of the 1Ms together and then run 1 wire?

[dbharris]

Quick update...I fixed the grounding scheme, it made no difference to background noise.

I finished the wiring for the VRM. I had only briefly tested it before. It definitely works but it noisy and creates some strange noises/unusable settings. So, I've ordered an 8uf and 16uf cap to add a filtering node at the VRM ahead of the B+ filter. I also ordered some marshall style cliff jacks for the speaker jacks.

IMAG1969.jpg

I'm hoping that settles everything out and I'll be able to box the amp up for a few weeks to play it before deciding on whether to add GNFB.

The power at my house is a little wonky too. Still all of the original wiring (house built in the late 1940s) and there is no dedicated earth connection here. Just hot and neutral. Lately it has been intermittent a couple times a day too.

-Dan

[JMPGuitars]

Quick update...I fixed the grounding scheme, it made no difference to background noise.

I finished the wiring for the VRM. I had only briefly tested it before. It definitely works but it noisy and creates some strange noises/unusable settings. So, I've ordered an 8uf and 16uf cap to add a filtering node at the VRM ahead of the B+ filter. I also ordered some marshall style cliff jacks for the speaker jacks.

IMAG1969.jpg

I'm hoping that settles everything out and I'll be able to box the amp up for a few weeks to play it before deciding on whether to add GNFB.

The power at my house is a little wonky too. Still all of the original wiring (house built in the late 1940s) and there is no dedicated earth connection here. Just hot and neutral. Lately it has been intermittent a couple times a day too.

-Dan

Do you have any grounded outlets at all? Your amp should be grounded.

If the electricity has issues, I recommend getting a filtered power strip and/or using a filtered inlet. I use both. I use a Furman SSB6. There's lots of other options too.

I assume correcting the outputs should help. If you still have issues, post a demo video so we can hear the noise.

[dbharris]

Unfortunately, none of the outlets in the house are grounded. They are all 3 prong, but the earth is not connected.

The VRM noises were nasty. The background hum is not a big deal for me, once you start playing it isn't noticeable. If I am touching the bridge or strings of the guitar it gets much quieter too. That happens with all of my amps.

Hoping to be changing houses in the next 1-2 years anyways.

[geoff 1965]

that's an amendment i made to the schematic i worked from,there was no filtering pre VVR so 1st half of my dual can filters the VVR & preamp.
reading through the notes in the VRM link you posted it says on the schematic "B+ in from the standby switch or after the 1st power supply filter cap if noisy" but on the layout it says after "additional" filter cap.
same principal here as zener's working more efficiently with filtered B+.

[crgfrench]

Unfortunately, none of the outlets in the house are grounded. They are all 3 prong, but the earth is not connected.

This is a real safety issue. I would spend whatever to have a qualified electrician come out, pound a copper stake into the ground outside the house and connect your grounds. You can't play guitar from the grave.

[dbharris]

I totally understand the safety concern and I will call around for a few estimates.

[dbharris]

Alright, I forgot to take pics before loading the chassis back in the head cab. But I added a 16uf F&T cap at the vrm as the first filter node. Grounded to the power amp star. Cured all the weird noises. I also placed a 2W 220K metal oxide resistor in parallel with that cap to drain power when turning the amp off.

I changed the speaker jacks to Marshall style Cliff isolated jacks. Ran a ground wire back to the power amp star. Maybe lowered the background hum a bit.

Lastly, I added the 2 470K resistors as a voltage divider after the gain pot. No treble peaker cap. Since I tend to run that pot fairly high I am considering adding the same network after the volume pot too.

I think I will still add global negative feedback and make it switchable. But going to enjoy playing the amp as is for a month or so.

Thanks again to everyone that helped me out!

-Dan

[dbharris]

Somebody on the Trinity forum asked for a clip. I still feel like I have some tweaking to do for this amp. Going to add GNFB in January and then go from there.

Please excuse the sloppy playing...

https://youtu.be/h20X0cRYa1w

The Ocean is Neck/Bridge (LP), Middle (Strat)

Sunshine of your Love is Neck (LP) with volume rolled down to 8 for main riffs and and 10 for solo with tone on 0 for solo only, Neck (Strat) and same vol/tone changes on guitar

Pawn Shop is Bridge (LP) Bridge (Strat)

Then I play some open chords and roll the volume back on the guitar to clean up the tone

Last, is playing each channel separately and then jumpered together.

-Dan

[crgfrench]

That amp sounds pretty sweet to me, nice job!

[dbharris]

Thanks! I'm still getting used to the Marshall thing coming from fender style amps. It's a lot of fun getting to know this amp.

[ViperDoc]

More of a question than a recommendation: is it not advisable to separate the preamp and power amp grounds? They appear to be all soldered together.

[crgfrench]

More of a question than a recommendation: is it not advisable to separate the preamp and power amp grounds? They appear to be all soldered together.

In the image download/file.php?id=12858&mode=view they look separate. There is a physical overlap of the sections but they don't seem connected. Power ground appears to go to the left star and pre goes way over to the right.