How to make my new Plexi clone louder

[Hardtailed]

Can't keep up with a band??
If I put my 50W Plexi clone on 3, everybody wants to kill me (I'm talking about a JCM800-style MV that I added)
Whether I cascade or parallel the first 2 gain stages (got that on a switch).

Is it really a 50W? With 2 EL34?
What's the voltage on the plates? And the screen?

From what I remember, the October project was not a 50W, but rather a concept to get the Plexi tone at low volume.

Plexis are loud, I've never had such a loud amp

[Gaz]

Chuck,

The Presence seems to be operating normally, and nothing peculiar seems to be happening when I adjust it. The OT leads are not twisted, and I will do so. I followed the layout here (the "Stage" version at the bottom of the page) meticulously.

FWIW, the only thing that troubled me was when I first turned on the amp there was a hum. I cured it by grounding the speaker jack at the star ground, which is located at the input jack. Was this just a hack on my part?

Hardtailed,

It the "Stage" version, which uses 2xKT77s. From what you say, there is something wrong with mine... but it does sound 'normal', I even recorded great clean tones with it that sounded just as good as my band mates Dr. Z Mazerati.

Thanks, All.

[Chuck H]

I followed the layout here (the "Stage" version at the bottom of the page) meticulously.

OOOh... Woah, that's not how I would have done it. All the board and pot grounds are daisy chained, the screen filters are grounded on the same buss in the middle of the preamp board, the NFB and presence leads are shoved up in front of the preamp tone controls and the power supply isn't grounded anywhere near earth. To be honest, IMHO this thing is a layout/lead dress nightmare.

How much quieter does the amp get when you turn up the treble control? and what happens when you turn it up all the way? How about turning up the treble AND presence controls? Do this with the volume on the amp set fairly high so the amp WILL break into oscillation if it's prone to.

FWIW, the only thing that troubled me was when I first turned on the amp there was a hum. I cured it by grounding the speaker jack at the star ground, which is located at the input jack. Was this just a hack on my part?

Kind of. Grounding the output at the input is bad lead dress for sure. I would move that ground as far down the buss and away from the input as possible. If that results in hum then try using isolated output jacks.

Sorry if you find this post insulting. But hate the game not the playa'

Chuck

[Gaz]

I was in the middle converting the cathode follower to a normal gain stage when I made this post, but I'm going to wire it back up normally to do a a bit of troubleshooting.

I can say that the amp does not break into oscillation when the treble and presence are dimed - I know I've tried that at least once when I put all on controls on '10' to see how much volume I could get out of it.

The amp is very quiet, noise wise, but that's not to say the amp's layout is not causing some parasitic as you suggested. And I'm definitely not insulted - I didn't design it! Thanks for the help.

[Chuck H]

If you've used a nice fat buss wire for the grounds it may be Ok. As far as the treble and presence levels go, If you can dime them with the amp turned up loud and the amp remains stable, You probably don't have a parasitic oscillation. But... Just for kicks I would push the tonestack leads up toward the front and away from the presence and NFB controls, and push the presence and NFB controls toward the front and away from the tonestack. Kind of opposite how it is now.

The treble control making the amp quieter MAY be normal when the amp is played clean. The treble pot can increase the voltage division from the low and mid frequencies enough to cause a percieved drop in body and fullness. But once the amp is clipping there should be no percieved volume loss unless something is... OOoops... I almost did it again.

Chuck

[jakehop]

In my band, I use a 50W slightly modified clone on 2 or 3 o'clock on both bright and normal, and that's perfect through 4xG12H30. I also heard the moniker, that 50W will make your ears bleed. I have a pretty good hearing, and yes, after a couple of minutes playing, especially the midrange gets annoying. But in my band we play pretty loud, to make the sound big, and make room for dynamics, turning down to get great clean-tones, etc. so with a couple of ear plugs, it's all good.

Jake

[rathmann]

Too much NFB?

Could there be a power of of ten error in the selection of the NFB pot or series resistor? If the NFB and Presence pots were swapped there'd be a 5k pot in series with the NFB instead of the 100k. That's more than an order of magnitude. Or maybe it was omitted entirely?

Connection to the wrong OPT tap?

Anyway your question of "Would there be any situation that any of you can think where an amp in a new build would sound perfect besides being too quiet?" makes me think there's something wonky in the NFB and/or driver.

Check for something that might cause signal cancellation between each of outputs of the PI and power tubes.

Best of luck

Steve

[daz]

I was just going to say that ! NFB can drop a huge amount of volume depending on the values used. i have my NFB bypassable via a switch. The difference was huge. It was so much louder w/o NFB it was crazy. Of course the difference will vary a lot depending on the value of the NFB resistor as has already been said. And which tap you use.

[DougH]

Some thoughts:

What's the speaker compliment? Are you using the same speakers when you compare it to other amps?

NFB? Wrong resistor value or connected to wrong OT lug?

[Gaz]

Everyone:

Thanks for all the great suggestions and pointers. I ended up bypassing the tonestack and converting the cathode follower into a normal gain stage just to make sure I was clipping the hell out of the power section. the amp was plenty loud then, and I was assured that there was nothing, in fact, wrong with the amp - except for now it could only do 'fuzz'.

The amp is considerably louder with NFB removed, and I really favored the sound until i realized it was nearly the same as having it in and the presence turned all the way up.

I've now rewired the preamp as dual-volume with an anode mixer, and it's sounding better... blah, blah...

JUST WANTED TO SAY THANKS!