Why Can't I Hear My Amp?

[The Ballzz]

Hi Guys,
I have an amp that I built and generally love, great tones, harmonic feedbacks, etc, etc, but when playing with my very low volume band, I can't hear it until it is way too loud! The odd thing is that I also have a DSL5C and a Class5, both at 5 watts and I need to gently attenuate to not be too loud, but they are both easily heard.

The amp has an identical clone of the early JMP2203 pre-amp, with a 10-ish watt, cathode biased pair of 6AQ5/EL90's for power. Everything is identical to the 2203 until after the PI, including the semi high, early 2203 preamp voltages.

Built the amp about a year ago, but just recently went back at it to modify the dropping string to address the somewhat low preamp voltages and fiddle with the NFB/Presence circuit. The last step, and where I'm at right now, was too eliminate the NFB/Presence and ground the 10k PI tail. It kinda seems like it may be more "hearable" but has lost all it's magical sparkle, etc.

Voltages as follows, bearing in mind that I actually use V1A as the first stage as opposed to many scematics that show V1B as the first stage:

V1)
1) 211v
2) 0v
3) 1.89v
6) 250v
7) 0v
8 ) 2.72v
V2)
1) 157v
2) -10mv
3) 1.106v
6) 291v
7) 157v
8 ) 159v
V3)
1) 202v
2) 13.6v
3) 23.09v
6) 194v
7) 14.25v
8 ) 23.09v

V4)
1) 16.6mv (Grid)
2) 19.56v (Cathode)
5) 316v (Plate)
6) 310v (Screen)
7) Tied to #1
V5)
1) 11mv
2) 19.55v
5) 316v
6) 310v
7) Tied to # 1

All heaters at 3.27/3.54VAC

PT Taps, Loaded 283 & 283VAC/566VAC B+ 316v
PT Taps, Unloaded, Except For Rectifier Tube) 291 & 291VAC/582VAC B+) 394v.

Any & all help/comments/thoughts will be seriously appreciated!
Thanks,
Gene

[xtian]

I'm guessing the big difference is midrange. In a live band, that's where the guitar stands out. If you have a good "studio" or at home sound that pleases you, it may be heavy in lows and highs, like a Mesa Recto kind of thing, but that can really get lost in a live setting.

[The Ballzz]

I'm guessing the big difference is midrange. In a live band, that's where the guitar stands out. If you have a good "studio" or at home sound that pleases you, it may be heavy in lows and highs, like a Mesa Recto kind of thing, but that can really get lost in a live setting.

You sir, just put it quite well and I'm right there with you! As a lifelong pro sound guy, I'm all too aware of the syndrome of folks getting their "ULTIMATE TONE" at home, all by themselves and then wondering why it just doesn't cut it live!

I guess I'm trying to figure out how to add a bit of that mid range bark, without losing the top end sparkle and low mid grunt. I've already tweaked a few things to make it so that while it is nice and thick and beefy in the low mids, that low end doesn't really extend down into the real "bass" frequency range. As it is, I run the mid cranked, treble at 3 to 4 and bass at 1 to 2! Before defeating the NFB/Presence circuit, I ran it between 2 and 5. And oh yeah, the gain and master must be on 8 to truly cop that glorious first note feedback of Jimi's Foxey Lady! Cranked past that, it gets a bit "ratty" sounding!
Thanks,
Gene

[xtian]

I would try messing with the Mid control to allow more mid boost. You'll see your Mid pot has one leg connected to ground. If you cut that connection completely, you'd have a tone-stack lift, which would give you a whole lot more gain, and a lot more mid. Try replacing that wire with a resistor (like 47k) or a 1M pot as a quick experiment to see if it points you in the right direction.

[The Ballzz]

Here is an interesting Q&A session from another forum regarding this conundrum:

Well,
Let me address the perceived discrepancies/questions individually:

"It is claimed to have lost some high frequency sparkle. Is this after you eliminated the feedback loop as mentioned in post #1?"

Yes, after eliminating the feedback/presence loop, sparkle is gone, but appears that it may be a bit more "hearable" I won't reall be sure until rehearsal tomorrow.

"If you dial the MiniMass down from 9 to 4 on the DSL5 and Class5 do you find they loose high frequency sparkle?"

Neither of these two amps have the kind of clear sparkle that is able to be achieved with an amp with NFB/presence circuit, even when not attenuated at all, although the small loss of highs when heavily attenuated is fairly well compensated for by use of the treble boost switch included on the MiniMass.

"Next it is claimed to have sounded best when increasing, the opposite of eliminating, feedback as described in post #5."

Yes, the apparent sound had much more clarity (not to be confused with clean-ness) the distortion sounds had more definition and when rolling back guitar volume the clean tone were magical. Still the amp was difficult to hear until the volume was excessive.

"Does the overall output voicing concerning the lack of sparkle come back at all with new or newer power tubes?
When playing loud what is the AC voltage readings at the power tube control grid pins as well as the DC voltage readings at the cathodes?"

Power tube changes make little to no difference in overall sound and/or tone.
I have never watched voltage readings while playing an amp, but will endeavor to attempt getting these readings. I must say that I've never seen any posted accounts of such readings for comparison, or how they pertain or relate to proper amplifier functioning. If you have a source for such information, I'm all ears!

I realize that some of my observations/statements seem contradictory, but that is the basis for my confusion, questions and concerns. It just seems so bizarre that an amp can be so loud but not heard! I mean, even though it can't be heard clearly, it is obvious in the room that it is quite loud! This excessive volume becomes even more evident when no one else is playing!

I'm beginning to suspect some sort of higher or lower frequency oscillation that is either above or below the range that is capable of being heard or reproduced by the speakers, and that that oscillation "re-introduced" by the NFB loop may be canceling some of the desired fundamental and harmonic frequencies. I just got an oscilloscope and have only learned enough to make simple readings and must do some more studying to learn how to use it to investigate more fully. As always, any help and suggestions will be truly appreciated.

Still Scratchin' My Head,
Gene

[V2]

I would try replacing the 25k mid pot with a 50k mid pot. Or go crazy and use a 100kA pot. Above noon, it'll act similar to a tone-stack lift. (my preference would be 50kB)

[The Ballzz]

I already had a 50k in the mid and swapped back to a 25k while tracking down a feedback issue that has been otherwise sufficiently resolved. It was not the pot that was the problem and this was before bringing all my preamp voltages up to early JMP2203 ranges. I will give it a quick and easy try.

I did find that by eliminating the NFB/presence loop/circuit the amp is much more "hearable" but has lost a bit of it's sparkle and clarity. Certainly usable for our next little string of gigs. After our mini-tour, I'll dig back in to nail down a properly operating NFB/presence loop.

One somewhat difficult issue is A/B-ing changes, as the amp sounded absolutely incredible, by itself, as it was and didn't point out the "I can't hear it" syndrome until used in a band setting. I guess I need to build a couple of resistance substitution boxes that I can clip into the circuit so that I can try changes, sort of on the fly, as opposed to setting up a mini workbench area at my amp in the rehearsal zone.

I must say that throughout my many years of mixing sound for bands with spiked hair youngsters, playing pointy guitars, I've certainly encountered many Marshall amps that exhibit the same issue I experienced. The really bizarre and confusing thing is that even two seemingly identical Marshalls can have one showing the problem I've had and the other sound incredible. I am endeavoring to discover what that critical, yet magical difference is caused by.

On another note, are you the same V2 who frequents the My Les Paul forum? I'm assuming yes, given your location. Nice to see you, small world!

Thanks,
Gene

[V2]

On another note, are you the same V2 who frequents the My Les Paul forum? I'm assuming yes, given your location. Nice to see you, small world!

Yessir! Nice to see you here too. I haven't posted much here; really try to 'stay away' from too much internet...

But there is a wealth of info here and on some other builders sites, so I read it often. I am also on the FB Tube Guitar Amp Builders group. That one is also highly recommended (Lyle Cadwell, Bruce Egnator, and a tonne of other knowledgeable folks).

[The Ballzz]

On another note, are you the same V2 who frequents the My Les Paul forum? I'm assuming yes, given your location. Nice to see you, small world!

Yessir! Nice to see you here too. I haven't posted much here; really try to 'stay away' from too much internet...

But there is a wealth of info here and on some other builders sites, so I read it often. I am also on the FB Tube Guitar Amp Builders group. That one is also highly recommended (Lyle Cadwell, Bruce Egnator, and a tonne of other knowledgeable folks).

You got a link to that group. Some pretty heavyweight names there. I love to read stuff by knowledgeable folks!
Thanks,
Gene

[The Ballzz]

Never mind, I found it and I am "pending!"
Thanx,
Gene