Need some help tuning my unstable wreck please

[declan]

Removed cheap test tubes and now have a set of winged C El34 and Brimar preamp tubes which have definately improved the tonal quality. I also managed to pick up an old beaten marshall slant 4X12 last night loaded with 3X Rola Greenback 55hz cones and one Goodmans audiom.

at 1 oclock on the volume I am getting a lot of squealing and feedback when not playing, I know some of this is normal but it seems a little excessive.

Also the feedback seems to take over and shorten the sustain on all but a few notes on the neck. 12th fret harmonics are also pretty dead, again they seem to be overpowered by the feedback.

In short I dont think the notes are blooming like they should. However the tone is there, chord work and on clean settings with the guitar vol rolled back are sounding pretty much like i think they should

Any advice for the best approach, or order of things to look at to improve her.

thanks in advance

declan

[declan]

After re-reading some posts i had bookmarked, I am going to try and use the standard arsenal of tips to deal with instability and see how that affects tone and note sustain/bloom.

Im just realising ....the build only really starts now

[rooster]

Hey. Just one question: When it is at 1 oclock, as you report it is, how loud is the sound? With mine at that setting things are totally solid with no feedback - but also very loud. Loud as in, 'Where the f am I going to play this?'. I mean, this can be heard up an down the street, with me being in my garage, which is totally buttoned up, BTW.

[geetarpicker]

"at 1 oclock on the volume I am getting a lot of squealing and feedback when not playing, I know some of this is normal but it seems a little excessive."

Is this pickup feedback, or does the amp squeal with the guitar knobs turned off?

In other words is this a guitar issue, a string muting issue, or the amp?

FYI I have all my guitar pickups wax potted, including the PAFs in my original '59 LP. I even repot the Fralins in my strats, as they can feedback a little stock but take well to a 2nd treatment. I also had to repot the burstbuckers in my reissue historic LP, even taking them down to the untaped coils to dip them to truly get the wax to penetrate the coils. Then I put the covers on tight and potted a second time. Nothing else worked short of this on my PAFs originals and repros. I like to be able to stand right in front of a cranked Trainwreck amp into a 4x12 without the pickups going crazy. Also the guitar can sometimes squeal when it is too close to the amp head itself, so stacking the amp on a 4x12 puts it right about at guitar height so that is not good. Same goes for any attenuator, you also have to keep these away from the guitar pickups. I can only stack the amp if I keep an extra distance away from the thing. The best is to keep the amp head away from the guitar and the cab, and possibly lower to the floor than either.

Check out my latest "Trainwreck amp" video of the song "The Clipper". The amp and cab placement is not for looks. The cab is elevated to help with sustain, and the amp is placed farther away and lower to keep the noise issues down.

[rooster]

Glenn - Hey there, YOU ROCK!!!, BTW! I love showing your videos to folks that come into our store - people who haven't seen or heard a TW. They always sound great and always make a toneful point about KF's TW design. I didn't know this about your pups, BTW, and thank you for sharing this. I assumed that some of the feedback was actually from unpotted pups, interesting to learn otherwise....

FWIW, I run Fralins and Burstbuckers and Classic 57s, too, and actually dig that most are either stock or purposefully unpotted, in the case of the Fralin Strat pups. Well, except the Strat bridge pup, I always pot that. Well, not to bore you.... Oh, and no, Sir, I do not own any REAL PAFS like you do.

Anyway, I wanted to ask you what tone stack you are using here on your 3 Wrecks? Are they- all 3 of them - 1meg Treble, 25K Mid, and 1meg Bass? Or did you try anything else? Here I refer to a 250K Treble, 25K Mid, and a 500K Bass pot layout shown on one site. I am thinking now that this is not actually stock, but I also know that it reduces gain somewhat, too. I guess I'm curious since you have 3 of them, did you vary from your original? Thanks for the info in advance, Glenn.

Oh, yeah, BTW, I totally get the tranny thing being right in the gtr as you play an Express. In fact, as soon as I fired my little clone up I had a flash back to your 6 minute video where you are off to the 'Input' side of the amp. Good times..........

[declan]

Thanks for the replies Glen and rooster,

Rooster ,Yes without the airbrake she is "where the F*** am i going to play this2" loud.

Thanks for the tips Glen, I will experiment with those placement ideas, I probably should also give my LP PUPs another dip, i dipped them last year but they were only in for about a minute or so and I didn't remove the covers. If you are potting your 59 PAF's, I think you have just convinced me to be more adventurous with my Dry Z's

However, I found the culprit tonight, I rechecked the layout for the 100th time and realised I forgot to solder in the 47pf cap betweeen the PI plates. I had to use the airbrake on 3 or 4 clicks tonight, but she is now quiet , even on full volume, and sounds 100 times better.

I think I have hit that 90% mark, to be honest im not sure if there even is another 10%, but she is now miles ahead of earlier today.

I may experiment with a few different PI plate caps to tame some of the highs and tweak the lead dress to see if i can hear any favourable changes, but i want to hear how she sounds with the band first. I also switched the winged C for Siemens and I think the C's are going ebay.

thanks again guys

[rooster]

declan - Well great, you may have taken care of things then. I did want to add that I am running an LTD into mine and it sounds very very good. Be advised, the LTD is not thick and midrangy for an 808 clone, but this is what seems to work in the amp, at least mine. Honestly, to my ear, it can make the amp sound like its on 1 oclock when I'm only on 8 oclock-ish, which is very cool for the dinky places I play. You might check it out if you haven't.

One other thing? Pull the first preamp tube and turn the amp on. Is it super quiet? Mine is. In fact, all the blow-by or 'rush' noise in my amp comes when the first preamp tube is in place. Further, although Glen(sorry about the xtra 'n', Glen!) suggests adding a grid stop resistor to V1 and V2, small values, I took both of mine out without issue BECAUSE they were generating extra noise. At last glance, I am somewhat baffled by what blow-by is left. Hey, all that's left in the circuit is pots (carbon PECS), tubes, caps and wire!!! Are these pots and caps actually noisy? And yes, I run shielded wire from the input AND to V2. But it is, afterall, a high gain design and is still way quieter than a JCM800 in the 'high gain' input, plus it sounds way way better, of course!!!!!!!

Anyway, further, I don't even have the 47pf cap in the circuit. The amp is incredibly stable but I get that KF used this so I may add it someday. The fact that your amp seemed to come around by adding it makes me think that your problem may still exist. I can turn all my controls on '10' without an instrument plugged in and there are no issues. Can you do this on your build? Oh, I am running the new laydown PT from Tonesluts. I seriously doubt whether it has helped the noise floor or with the build issues you are having but it might, you never know.... Let me know how the gig goes?

[geetarpicker]

I did experiment with the PI cap in one of my clones, but in time I put it back to stock. My original and two clones are all stock values. My clone does seem to be mellowing with time. Also on my cabs with the new Scumbacks I put about 4 layers of felt in front of the cones (stapled to the baffle cutout) to tame the top end just a tad. That trick works surprisingly well.

I usually pot pickups for about 10-20 minutes. Some say that is too long, but I didn't have any luck with shorter times actually doing the job well.

[declan]

You know when you dont know exactly what to expect when hearing one of these live for the first time it is easy to be bowled over by the sheer loudness and thump, I know I was, .... with each improvement I think it takes the ears a little time to hear any new faults or areas which could be improved so I refuse to say the job is complete, in fact im sure i will be tweaking and experimenting for some time to come.

Last week she was not really fit for a practice with the band. I A/B'ed her with my Marshall DSL last night and I can now say with confidence that the Marshall is somewhere in a cloud of wreck dust so every improvement from here on is icing on top of the icing on the cake.

Rooster I will try the all controls maxed with no instrument on wednesday to see how she behaves.

Glen that felt over the speakers trick sounds promising, I was reading how basketweave grill cloth is best for taming some of the highs.

....Before stumbling across the 4X12 I was considering building a 4X10 with those new 10" greenbacks, which according to celestion are a little darker and smoother than the current 12" greenbacks. I am not sure how they would compare to 30 year old Rolas but the portability would be a real ++++ .

thanks again guys, the support here, as always, is much appreciated.

[strato17]

So is the general consensus that airbrake is ok to use with the wreck? I shouldnt do an ohm mismatch with the cab and amp when using the airbrake, correct?

[Fischerman]

So is the general consensus that airbrake is ok to use with the wreck? I shouldnt do an ohm mismatch with the cab and amp when using the airbrake, correct?

The Airbrake doesn't show a constant load to the amp across all settings. At just one or two clicks down from full volume you'd prefer to use a 16ohm cab and set the amp to 8 ohms. But at full attenuation you'd want the amp set to 16 ohms (with pretty much any cab). Somebody made a chart showing the load at different settings but I can't find it right now. Maybe check TGP and search for Randall Aiken as the author (I can't remember his exact screen-name...do a search on Aiken amps and I'm sure he'll turn up in one)...I know he has had some great info about Airbrakes.

[declan]

this is the one i think you mean fischerman, the way i see it if it does not work with the express then what was Ken doing????

http://www.thegearpage.net/board/showth ... t=airbrake

I put the DMM on the amp input to the airbrake with a 4ohm cab and true enough there is a wide variation in impedance especially on the rheostat, my thought was to make a note of these and adjust the impedance switch on the back of the amp accordingly. I will probably use mainly the 3 & 4 positions which works out close to 8 ohms.

Not sure if this is even necessary as there is debate that as the the airbrake is resistive load it is more forgiving of mismatches, which as KF points out varys with frequency anyway

[rooster]

declan and Glen - OK, I am back to back up. With no instrument plugged in, I CANNOT turn all my controls to '10', at least not with the Presence control turned up to max, without a squeal. No way. If I do, with the Input turned to ten with no instrumant plugged in, then either the Mid control or the Treble control will make the amp squeal when you turn either to around 3/4 or more.

Said another way, if I turn all controls to '10' first, and then turn the Presence control up from 'off' - I can turn the Presence control to about 2 o'clockish before the amp will squeal. And it is a high pitched piercing squeal, BTW, not pleasant.

Sorry, I wasn't thinking about the Presence control when I said what I said. And actually I don't turn the Presence control up to anything higher than 12 o'clock so I hadn't tried this.

Anyway, hearing the squeal, as I assume anyone will if they should do this, too (????), I am reminded that KF would always say that his amps were on the edge of instability. I really don't like this in an amp, but then I love this amp. And actually, Glen, since you have an original, can you confirm this event in your amp? If I were to now learn that my amp is actually alone in this behavior....... But I haven't put the 47pf cap in, maybe this is why it is there? Glen?

[declan]

i will certiantly try mine tomorrow night and see what the results are, in the meantime solder in the 47pf and see what happens, its there in Kens circuits so no real reason to leave it out IMO

[Fischerman]

declan, I remember that thread...I'm ChickenLover on TGP.

The 47pF cap across the plates of the PI is there purely for stability reasons. I wouldn't remove it...I usually put a 100pF there anyway. It's there in Fenders/Marshalls and just about everything else...nothing unique there. IIRC, Glenn originally increased that cap in his clones because the clones were a little brighter and that was a way to make them sound closer to his original.

IMO, if you want to tweak the top end then there are other places to do it.

Gut shots would be necessary to suggest layout changes. Just remember that grid wires are very sensitive to picking up stray signals (i.e. they are the 'receivers') and plate wires and OT wires are the ones that emit the biggest stray signals (i.e. they are the transmitters). If a transmitter and a receiver that are in-phase with each other are too close you get positive-feedback and often instability. If the transmitter and receiver are out-of-phase with each other and close to each other then you have negative-feedback which tends to cancel. The earlier in the signal path it is...the more amplification it will see along the way so it's more susceptible to causing instability. Throughout the Express preamp...each grid/cathode pair are in-phase with each other and each grid/plate pair are out-of-phase with each other (each gain stage inverts the phase). The treble wire, from board to treble pot, is another sensitive wire.