new here...a few questions bout my 1st amp

[iknowjohnny]

I read thru the archives and i gotta say this is about the most informative forum of it's type i've been to ! read for about 2 hours straight !

This may be a bit longwinded, but i like to make as much clear as possible to avoid a lot of unnecassary questions. Anyways, i built a 18 watt a few years back and recently revamped it. Put in 6V6's in place of the EL84's and cascaded the pre. i have spent endless hours fighting certain tonal issues and hoped i might get some better results here than i've gotten elsewhere. The pre is very simple really. 2 stages in the 1st triode with grid blockers on all stages, 1 meg gain pot, voltage divider at stage 2, then into the V2 tube as the typical cathode follower and marshall tone stack. all couplers ate .022 mallories. Tried endless cathode R and cap arrays on both sides of v1. The power amp has a 1k shared screen, (want to change to 2 470's but out of them) a 265ohm cathode R with a bypass cap at 47uf, but have tried all the way up to 2200uf.

anyways, i'm trying for a somewhat hi gain (think JCM 900 dual reverb or a bit less) with a squishy transparent midrange, tight bass, and a round full clean sound when the guitar is turned down and a harmonically complex squishy sound/feel when driven. I want this at low to medium levels before the output starts grinding much so that i'm using mostly preamp drive with just some compression in the PA. I've tweaked the PI/PA so it stays clean pretty loud. I ve accomplished the complexity at times but it comes and goes as i tweak.

My main problems are that the high end is just too much and the bass is sorta farty sounding. It doesn't have the tight soft feel like a good marshal preamp. The high end is such that i cannot put the tones above maybe 9:00 or it's overkill. I have no brightening filters or small caps, yet it's much too bright. It was like this with the EL84's too, but they were much worse even. Problem is, if i try and cut high end like putting caps across plate R's and that kind of thing, it rolls off at a certain point that of course rolls off more as you go up in frequency. So therefore you lose too much sparkle.

Finally, the post tonestack master changed the tone a bit too much. once i get past bedroom volumes it begins to get hard in the mid/hig range. The transparency in the mids become more rigid and in your face. I prefer the tone at bedroom levels and would like to retain more of that as i crank the volume to just before where the PA is about to start getting distorted which is where i intend to use it. It's not the type of master...i've tried a crossline and the ganged post PI type too.

Ok, i know there is no simple answer to any of this, and i know i loaded the plate to where it's falling off the sides. But any thoughts that come to mind when reading my story i'd be interested to hear if for nothing more than to spark some ideas. I'm starting to finally get close, so i'm not trying to say and of these issue is horrifically bad. But they keep the amp from being what i was hoping, which in a nutshell is a spongy, harmonically complex marshallish tone with balanced frequencies that aren't too bright or farty. Thanks for listening.

[Phil_S]

Two thoughts:
1) Post this at www.18watt.com where they live and breathe your particular amp and it's variants. I notice some crossover between ampgarage and 18watt, but you will tap other specific expertise there, in addition to what you find here.

2) If you are thinking that you can use the MV to get plexi crunch at bedroom volume out of an 18W, I think you are mistaken. I recommend you build a 1.8W amp, not an 18W amp if you are looking for that.

Sorry for not making specific comments, but much of the content is a bit beyond my comfort range.

[iknowjohnny]

I do post at 18watt, and the amp is cascaded and gets more drive than i even need at bedroom volumes.

[Lonely Raven]

Reading between the lines, I get the feeling that IKJ is saying that he's not finding help at 18watt and was hoping he might find some suggestions here.

I'm no help since I'm a newb, and only just picked up my first 18watt a few weeks ago.

[Alexo]

There is no simple answer to your questions, as you said.

You hear something in your head and you want to bring it into reality, that is an admirable pursuit! But it's also no easy task.

I'm imagining a composition student trying to figure out how to revoice his harmonies to get his first symphony to sound more like Beethoven's Ninth.... This is impossible. If said student wants to reach that level of composition, he needs practice and experience, writing many pieces, experimenting, learning what works and what doesn't.

Keep up the good work and take your time. It's easy to get too close to your problems in building and it can be immeasurably helpful to put a frustrating project on the back burner for a while, build something else (which always teaches you much more than you expect) and then come back to it.

I'm also reminded of what one of my composition teachers said - musical works are like children, you can try to raise them a certain way and push them in a certain direction, but eventually they'll do what they want to do and you have to let go to a certain degree. The best composers listen to what their pieces want, rather than trying to force their pieces to listen to them.

Hope this helps, best of luck.

[Firestorm]

If you had a schematic to post I could be more specific, but just off the top of my head I'd suggest playing with the values in the tone stack (maybe model it first using Duncan's TSC tool); play with the values of the coupling caps going to the output tubes (make 'em smaller probably); add a feedback loop or modify it if you have one -- this is one area that can be adjusted to be very frequency selective; try adding a pot to the voltage divider at V2 to have another "gain" control; and try different speakers.

[Andy Le Blanc]

voiceing can be endless.... I usually get going by trying some old scheme
then play with it until it sounds ok in the shop .... then I play it out
its the playing out that guides futher tweaks.... an amp that sounds
fantastic at bedroom levels most likley wont cut the mustard out at the jam
in the worst room, under much less than ideal playing conditions.....
play out and listen to what others think... then tweak some more

[iknowjohnny]

Ok, i guess i should have kept it to a minimum. how about the bass issue. let me elaborate. The bass has a fuzzy loose sound to it. It is NOT a product of tone shaping gone wrong. i have tried every single tone shaping idea thruout the amp from input to output. RC networks and every tone stack change imaginable. Turn the bass all the way down and the bass still has that fuzzy cardboard sorta sound. it's obviously something deeper than just tone shaping. Something like voltages, tho i have tried a few things there too such as dropping voltages of the B+ and also tried dropping at preamp nodes only.

It's not a matter of too much bass, or even bass thats too low in frequency as i once thought. It's just fuzzy and loose. What are some things that can cause this/ the trannies are a heyboer 18 watt set, and the bass sounded the same with EL84's as it does now after i changed to 6V6. The rest is basically a 18 watt TMB with the stages cascaded.

if i can just fix this issue i can deal with the rest because i've already come very close, but no matter how close i get, with the bass like this it just not happening.

[Andy Le Blanc]

the last bass issues Ive had were the caps and bad speaker..
I had used a ceramic cap.... it was a not so good choice
it didnt fart out at hi volume, it just sounded bad
.02 caps should be ok... the caps where the pre is cascaded into a
cathode follower and if your using a long tailed inverter, the input cap
to the phase inverter can be reduced to tighten things up.....
double check that the speaker is the correct impeadance
and the opt is wired correctly..... and the bias, to cover all the bases
if its a persistant thing then its something thats been overlooked.....

[iknowjohnny]

Yeah, done all that to death. Most things i've tried numerous times to see how they fare in different configs. Like i said, it's not a typical tuning thing like couplers or filters or any of that. I've tried tons of couplers, small to big and things change but the bass is always the same. Speakers....tried 5. Tubes...tried to many to list. cabs, cables, guitars, etc etc. it's none of that. It's definately something deeper. As o said, something like wierdness in the PSU or some such thing. I'm just hoping someone with the same issue who went thru what i have and found it will post with the answer because i'm not far from junking this thing. i could have built a new home with the time i spent on this thing.

[John_P_WI]

IKJ,

What is your power supply filtering scheme and how much?
Tube or SS recitification?
Do you have feedback around the power amp?
Are you overdriving / grid blocking the PI? Kind of a sticky phasey sound?
What value of cathode bypass caps are on V1?

As a reliability point, my gut feeling would be to put at least 1k individual sceen resistors on the output tubes, higher if switching back to EL84's.

Hope these ideas help.

John

[iknowjohnny]

What is your power supply filtering scheme and how much?

32/32 with a 1.5k in between them. then a 20uf and 8.2k for the PI, and a 16uf and 2.2k for v1 and v2. (had a 20uf there as well at one point...no diff) Have also bumper up the 2.2 to as high as 20k just to see what lower v1 and 2 voltages would do.

Do you have feedback around the power amp?

No. Tried it, didn't like it, nor did it cure the bass.

Are you overdriving / grid blocking the PI? Kind of a sticky phasey sound?

I stuck a grid stopper there and that helped the overall tone, but not the bass. No phasey sound or anything like that with or w/o it.

What value of cathode bypass caps are on V1?

name any 2 combos of R/C and i've tried them on both. From 820 to 10k and from .1 to 22uf.

[John_P_WI]

IKJ,

Sometimes the multi-cap cans can cause a little grief. If you are using a SS rectifier you could try paralleling another cap to the first stage of the power supply (you could try another 20u or 30 u). If you have a tube rectifier only add another ten u.

How does it sound with the master on 10 or out of the circuit? Maybe rewire to values similar to the 2204 / JCM 800. (I hate master vols).

I have also found to increase the tightness of bass, I have had to remove mid and treble frequency in the tone stack. Removing them gives an appearance of more bass. As mentioned above, play with the duncan tone stack calculator and watch the attenuation of the mids and highs with diff. values.

With no FB loop, it can be hard to control the tightness of the bass without using other means like triode mode or UL connections, both of which change the tone. Your power amp is running wide open and you may wish to take a little gain out of the PI too.

Just a few more thought to add to the stew...

John

[iknowjohnny]

I tried more uf at the preamp stage and it sounded worse. Not PA tho. But I don't think 10uf will fix this. in fact i'm sure. (EZ81)

Sounds the same with or without any of 3 different masters i've tried or w/o. I can't do w/o a TMB, so removing any of it is out of the question and should need to be done in a properly working amp anyways. i don't want to put a bandage on the symptom, but fix the problem.

As to NFB, i have tried that and it didn't help, but it was EL84 based then. So maybe i'll give that another try. thanks.

[John_P_WI]

IKJ,

I wasn't suggesting removing the treble and mid pots, but was suggesting attenuating the higher frequencies, giving the appearance of more bass.

A mistake made frequently is people try for too much gain in the preamp and think it can be pushed all the way through. Good distortion is built up gradually through multiple stages. I'd suggest getting a solid thumping clean tone and then progress into the master world. Once all of that is working, try out power scaling instead of relying on master vols, your tone will change less.

John