50W 12xxx spec preamp, not enough gain

[darkbluemurder]

Anyway, with a linear 50k pot you have all the sounds of the 25k plus added mids.

Fully agree with that.

I also second the recommendation to look to the negative feedback circuit - 39k from the 8 ohm tap is way more than 100k from the 4 ohm tap. That makes the amp more tame.

Cheers Stephan

[fhn_lopes]

Anyway, with a linear 50k pot you have all the sounds of the 25k plus added mids.

Fully agree with that.

I also second the recommendation to look to the negative feedback circuit - 39k from the 8 ohm tap is way more than 100k from the 4 ohm tap. That makes the amp more tame.

Cheers Stephan

We had an unespected gig last weekend and I didn't have the time to tweak the NFB but will do , thanks. Actually my amp is starting to sound thin and less punchy, even with a Les Paul, I think I will need a retube soon

BTW, something weird is going on.... after I put the .68/820 combo in v1b making two bright channels, a strange noise started when one of the channels is cranked... sounds like a bird singing very fast... never had this issue, I just made normal channel to a kinda 12xxx birght channel and this started to happend... what could be wrong?

[neikeel]

The high pitched chirruping is parascitic oscillation (you increased the gain slightly). Try chopsticking the grid and plate wires in the preamp, if that does not work you may need shielded wire or grid stoppers.
Do you have a recent pic?

[jnew]

Do you have a 5000pF on volume I pot?
50K mid never worked for me tone wise but it does add a little more gain. Some like it, some don't. NFB loop is important too. 100K should grease things up, as mentioned. Also, are you running a variac and lowering voltage? What's interesting about the early EVH tone is that it really isn't as much amp distortion as most think (with the exception of some songs) but the starving of voltage, for lack of better words, makes an amp sassy and gritty sounding which is the magic texture and smear of its distortion characteristics.

[fhn_lopes]

Thanks Neikeel! But I have a language problem here by chopsticking you mean twisting the wires in 90° angles like we do to the heaters? Or making them shorter? Sorry, I'm Brasilian and I couldn't find any reasonable translation for that

[fhn_lopes]

Oh BTW, important info, I had a cascaded configuration before and didn't have this problem. I just reversed it to dual bright channels... I'm using a shielded wire from the volume pot to the grid in channel II (the 12xxx spec one). no pic yet but will upload soon

[fhn_lopes]

Do you have a 5000pF on volume I pot?
50K mid never worked for me tone wise but it does add a little more gain. Some like it, some don't. NFB loop is important too. 100K should grease things up, as mentioned. Also, are you running a variac and lowering voltage? What's interesting about the early EVH tone is that it really isn't as much amp distortion as most think (with the exception of some songs) but the starving of voltage, for lack of better words, makes an amp sassy and gritty sounding which is the magic texture and smear of its distortion characteristics.

No 5000pf on the volume pot, just the 500pf acros the 470k mixer. now both mixer have 500pf acros them.
Another thing, I'm not using a Variac yet.

Here's a pic of her BEFORE any mod was done.

[jnew]

What he meant by chopsticking is taking a wooden chop stick and physically moving some of those wires around to find where the parasitic oscillation is coming from. Chop sticks being made of wood will prevent you from getting your tail lit up with any voltages because you will be doing this with the amp "ON".

Double check a plexi spec layout and place a 5000pF cap on VOL I's pot. You should realize some gain changes. This is very effective if you come off 10 on VOL I. In other words, A MUST TRY.

[fhn_lopes]

now I got it thanks James, sometimes the language is a barrier and when things like 500V @ 3A are involved we need to know exactly what to

That been said, I think I know where the parasitic oscliation is coming from now, I did some crapy soldering last time and my iron touched the end of the wire that comes out of the vol II whiple, making a small portion of it without the plastic cover other than that there's no reason for that to happend (at least nothing that I have caused )

Will try the 5000pf across the pot and the 100k nfb.. time has been an issue these couple weeks... thanks guys, as soon as I try the stuff I'll let you know if that worked out.

[jnew]

[fhn_lopes]

Finaly did the mods and did a small rehearsal with my band yesterday... I feel a HUGE difference in the low end now, maybe too loose but I'm using a BKP VHII in a les paul Classic so maybe that's why. I assume this is the 100k @4ohm NFB that I'm running now. Also put a 4n7 (didn't have a 5n -5000pf) across Vol II (the 12xxx channel) and I can feel a slight gain increase, but still a bit far from what I hear in your clips.

The overall tone now is good and the oscilation is partially gone, it only happends if I jump the inputs with my guitar plugged at channel I... If I do the other way I can crank both volumes and there's no oscilation. Actually I found out it sounds like a capacitor charging bc when I hit a note and mute it imediately, the oscilation stops for a small time and then comes again, increasing the frequency as the time goes (like a beep getting faster). Using only one channel per time makes no difference at all so I gave up looking for the source for now. Can it be a bad cap?

Even though I'm not using a EVH guitar, I can hear some nuances that I couldn't hear before so I"m happy. I can hear the "smack" in the high end and the 'thump' in the low end (when I say thump thnik of the palm muted low E in the intro of Dance the night away). I'm broke now but I can see that a variac and EH 6CA7s will do a lot more here .. also a DSD in my HSS strat... Think I'm on the right track, thanks guys!!

[Carbia]

but still a bit far from what I hear in your clips.

When you record an amp, it has a lot more gain than when you hear the cabinet in front of you.

Last time I recorded in a pro studio I took my 50 watter to record. I used to play live with the volumes totally dimed (lar/mar master at half) and recording... I recorded the tracks at volume FOUR to get the same gain I used to hear playing live.
So... big difference.

[jnew]

My clips don't have a lot of gain at all, to be honest. It sounds like more than there actually is.

[dnkhoward2]

I agree with you guys completely. Last time I was in the studio my sound was way over distorted to me and the engineers. Kind of blew me away since I thought I had a moderately distorted tone.

I think I chase sustain and try to get it with distortion. Haven't figured that one out yet.

but still a bit far from what I hear in your clips.

When you record an amp, it has a lot more gain than when you hear the cabinet in front of you.

Last time I recorded in a pro studio I took my 50 watter to record. I used to play live with the volumes totally dimed (lar/mar master at half) and recording... I recorded the tracks at volume FOUR to get the same gain I used to hear playing live.
So... big difference.

[fhn_lopes]

I really have no experience in recording my amp with real mics... only impulses, from the line out in my attenuator... probably here's the point, but as far as I can say the gain is pretty much ok for me with tons of sustain and grit, but it's not VHI if you know what I mean.... but tonewise, I'm happy with this latest results even though I feel the amp a little too bright, but it's not interfearing in my playing and with the band it's sounding ok, cutting real nice as any marshall should, and the overbrightness is not bothering.

Can't wait to record my amp but really don't know when I'll be able to.

I'll send a crappy cellphone clipe as soon as possible

thanks guys