Is this possible?

[daz]

Again, my 18 watt build. Yeah, i'm as tired of asking as i am of EFF'ing with it, but here goes. Those who've followed my saga of electronic ignorance know i've had issues with the tone being rather hard especially in the mids. The bass issue is no longer a real problem. But after a incredibly stupid amount of experimentation i have come to believe with almost no doubt that my problem is that this amp, for whatever reason, has a abundance of a frequency that is one that most amps have little of, or at least it's not peaking like mine seems to be. So the question is this....is there a way to filter out a specific mid frequency by setting up a filter and a pot so i can sweep the mids and figure out what parts i need to create a cut at that harsh frequency that has me pulling my hair out? all the filters and such i have been told to try over the course of weeks do nothing more than add or cut highs, and thats not what it needs. i don't know where this freq is coming from, but i cannot seem to figure it out, so the only thing i can imagine that is left is to find a way to cut it. So i'm asking...is there a way to do this? By the way, if i had to guess where this peak is i'd estimate probably somewhere between 700Hz-1kHz, maybe 2k at the highest. but it seems to be very high in volume above the rest of the range and very narrow.

[Enzo]

Are you sure it is the amp and not the speaker resonance? Have you played the amp through a different speaker and enclosure?

[Earl]

I would have guessed a speaker as well.... Personally, I've found that some (especially ceramics) can sound very harshish with a no "tone stack" amp.

In my case replacing a C12Q with a P12N made all the difference! :-)

[daz]

EV12L, celestion 100 watt, reverend alltone, jensen/fender, fender blue. I think it's my output section. heard a sorta "click" at one point and the tone changed for the worse instantly. Tried new 84's after that, and they sounded a lot better. And i had tried those same tubes (sovteks, yuck!) a week before and they weren't as good as my now apparently shot JJ's. Theory....the output section was pummeling the tubes at some point and i killed them. i have tried various cathode resistors and i'm sure went too low at one point. (120 to 150 R) But i'm unsure as to how to choose the right resistors for the cathode and screen and whether my plates are too high. (355v) So i'm thinking i might need to tweak the power supply but have no understanding of what to look for and how to rectify any problems.

this is just a theory. But one thing i do know is that in the maybe 2 weeks or so i've been trying to tweak this amp's tone, those tubes went from sounding best of 3 sets to now sounding worse and displaying a lot more of the negitive tone i described. I don't think it's 100% why it sounds like this, but i do wonder if the p/s is in need of adjustment because those tubes sure went south fast.

[d95err]

How about recording a few simple clips with the amp and take them into some kind of recording software. Then you can play with the software EQ's to try to figure out what the problem frequencies are.

[daz]

That would be good if it helped rectify the issue, but unless theres a way to do it i have no use in knowing the exact frequency. I suspect there IS no way, after all if there was why wouldn't tubes amps have more versatile tone sections like mid sweep pots and such like a lot of SS amps have. But i had to ask.

[d95err]

That would be good if it helped rectify the issue, but unless theres a way to do it i have no use in knowing the exact frequency. I suspect there IS no way, after all if there was why wouldn't tubes amps have more versatile tone sections like mid sweep pots and such like a lot of SS amps have. But i had to ask.

It can be done of course, but it would probably require adding one or more triode stages. Tubes are expensive, so typically guitar amps have very simple EQs. I guess the trick is to design an amp that sounds good right away, with little need for advanced EQ-ing...

Trying to EQ away your problem is probably not the right solution anyway. It seems that there's something more basic that is wrong. Either something in the amp or, as others suggested, the speaker.

[daz]

It seems that there's something more basic that is wrong

Thats always been my first thought, but i've had a lot of people look at the schematic in it's various forms it's been thru, and no one seems to see anything wrong that i have not tried changing. The wiring is right because i have been over it since i built this thing several years ago more times than i care to mention. I know every component like the back of my hand and i know it's wired right. The ot and pt are a 18 watt heyboer set, and i've tried 5 different speakers, 3 sets of 84's and several different ax7's and even a at7. But i still think there is some basic thing thats not right. I just can't find anything tho after a insane amount of investigation and asking truckloads of questions here and elsewhere. I keep getting the speakers and tubes questions but haw many speakers and tubes do i have to try?! I mean, i've had maybe 50-60 amps and i have yet to find one that sounds wrong like this and could not sound right till i found one particular speaker thats the only one it sounds right with. They all sounded good with MOST speakers. Best with one particular one, yes. But not FLAWED with all but one particular one. So i tend to think like you, that there is something not right. But it's like i'm playing hide and seek in a 3 room house.....you can only look thru those 3 rooms so many time before it becomes apparent that if you can't find the person you're never going to by continuing to look in the traditional way. Thats why i'm looking at something like this....notching out the freq.

[Steve Conner]

It could have a jinx. You might need to can it and start from scratch with all new parts and a different design...

I have built tube amps with mid sweep EQs, and they are nice, but not as essential as you'd think. Mostly just good for getting that modern Mesa crunch tone, or the "Jaco" bass tone. The old Fender-style treble and bass knobs work remarkably well for everything else.

What cabinet did you try all these speakers in? The cabinet affects the speaker's response. As an extreme example, if you take the speaker out of the cabinet and play it just sitting on the bench, it'll sound incredibly nasal and midrange-y.

Also, are you using feedback, and is it wired right?

What kind of music do you like, and whose tone are you trying to nail?

[daz]

The speakers are in various known good cabinets aside from one, which sounded like a$$ and i then put the speaker in a known good one.

No NFB

general blues and classic rock tones. ZZ top to SRV and such. But those sort of tones to me are also versitile and work fine for all sorts of music. if i can get reasonably close to those tones out of an amp and it's quality tone, i can also get Brad Paisly to EVH too. One GOOD tone can do it all with the right guitar and in how you use it.

[6267]

ok, so if you have a resistor in series (i.e. in line with the signal, say after the coupling cap, you can put another capacitor between this resistor and ground. This will shunt some of the sound to ground, but if you use the right size of cap, it will improve the highs mids. I'm assuming it's not the mids but higher harmonics of the mids which are unpleasing. Try a .0047 or smaller either as I said earlier or between anode and cathode of a normal gain stage. Too large a cap will cut the sound volume, but just right should voice it more pleasantly. Google or wikipedia RC filters. Also, my 18w amp which was commercially designed has a big 47k(? not exactly sure) in series with a .01 cap (1kv) across the primaries of the output transformer. This is called a zobel network and it lets the amp drive into a more even impedance. In addition to my earlier comment, you could look up zobel networks and try to tune one which will work across your primary. The values are somewhat dependent on the tubes and speaker (more the speaker).

[daz]

It's not so much that the mids are bad, it's that there is just too much mid, and in a frequency that makes the sound hard. I could recreate on another amp i'm sure just by putting a graphic in the loop and boosting probably 1k by about 3 or 4 DB.

[6267]

A notch filter is what you're looking for then. It could also be an impedance issue somewhere, first grid resistor, speaker...dunno

[daz]

I made some changes today that changed the map for the better in a big way. removed one of the gain post and in it's place a 220k/220k voltage divider. tried them on both stages when i had 2 gain pots and it did nothing. Don't get it, but it's worlds better. But the midrange persists, however now i can dial it out with the mid pot and it goes away. problem is, then it's too scooped. So i need the mid pot to work at a different frequency because it not only removes or adds that hardcore midrange that was killing me, but when it removes it, it removes a lot more of the mid frequencies too. Any way to change that besides the mid and bass caps? (can't seem to fix it that way...tried many caps both directions)

[PRNDL]

Have you considered a Matchless Spitfire?

It's an identical circuit to the 18 Watt light, with some value changes in the cathodes:

Preamp = 1.5K / 25µ vs. 820 / 47µ
PI = 1.2K / 1M vs. 820 / 470K
output = 120 / 25µ vs. 130 / 100µ

The tone stack is also different, which may have more of an impact on the tone.