Express Hiss Issues

[camden_guitarist]

Hi there everybody, yesterday was the big day, I fired up my Express for the very first time.

Being a newbie and all I called in the help of a good friend of mine who teaches me the ropes on the tube amplification (even though he thinks it's a 'dead' science; he builds lots of hi-end SS bass and guitar amps).

He soon figured out that I'd been relying too much on visual inspection of photos and there for not really 'looking' hard enough. I had 'forgotten' 3 connections : the ground on the first cathode, a plate connection to the powersection and I had also forgotten to hook up the 25W power resitor to the rest of the chain to the B+ voltages. Pretty stupid mistakes but hey, I may have been very enthusiastic taking on this project.

After setting the bias for 2 EL34's we hooked it up to a Soundcity cab (loaded with the famed FANE drivers) and had a test drive...not bad at all...

But, and here come's the subject of my question/query : there was no hum but a lot of hiss mixed in with the signal. My pal explained that it must be the 3rd triode that is not actually doing anything but 'enhancing' the hiss that comes from the preamp. So, we removed it and it cut the hiss considerably. Kinda weird though coz it doesn't show on Geetarpickers vids that it's kinda hissy. Might I have made another mistake which we missed which explains the hiss? It's really apparent when playing at low guitar volumes, to get that nice warm clean sound that Geetarpicker uses.

We also replaced the second cathode cap to 1mF which cut a bit of low end coz it was very bassy to our taste for a guitar amp.

Last but not least we tried a few variations of output tubes and I stuck with a pair of 6L6's which were a good compromise between the EL34's and 6v6's in output power.

Well I'm gonna test it extensively at home through another cab (Marshall VST100, loaded with Celestion Golds, I don't have the luxury yet of owning a vintage cab ) and I'll post some more detailed info lateron. I'll try and do some soundclips but since I live in an apartment I'll have to keep the volume down

Thanks for any info/help you can offer.

Cheers,

Paul.

[sliberty]

Let me preface my comments by saying that I am not an expert, so your mileage may vary.

If you like the tonal results of removing the 3rd stage and changing the bypass cap, so be it. But that stage is an integral part of what makes an Express sound like an Express, as is the bypass cap value. The 3rd stage is not "just adding hiss" as your SS friend suggested. If I were in your shoes I would return the amp to stock, and look for the real causes of your problems.

Hiss is a fact of life with bright gainy amps, and the Express is a very bright amp. If the hiss is very extreme, it might just be a crappy V1 tube. Try several nice 12ax7's in V1 to see if the hiss improves.

As for the bass-heaviness, that one surprises me. I find that the Express is a little light on bass compared with, say, my (sold) JTM45 - now that was a bass-heavy animal. There may be something else at work here, but I am not really sure what.

If you have heard and liked other Express amps, I would say that you should return your amp to stock and look for either lead dress / wiring mistakes, or component problems (incorrect cap values, or caps that don't measure properly. But modding the circuit actually just leaves the inherant problems un-resolved, and works around them.

Some photos might be helpful. Maybe one of the gurus here will notice a problem.

Steve

[camden_guitarist]

Hi Sliberty,

Thanks for the input, I've already thought about putting it back to stock and check with other 12AX7 or maybe even a less gainier 12AY7. It hasn't gotten a lot less gainy on the other hand, and I'm quite pleased with the result as it is at the moment, I just wanted to check on the forum about what other people with more Trainwreck experience think.

I hope some of the gurus will offer some help, I'll try to upload some pictures soon, I've already got them on my Facebook profile.

Take care and I'll catch you guys later

Cheers,

Paul.

[sliberty]

Paul,

By the way - my own personal pref is to use a 12AT7 in the Phase Inverter. Some will call that an aweful choice, ubt I find it cleans the amp up just a tad without reducing the punch and touch sensativity. I have done the same thing in my AC-15 with simlar pleasing results. I prefer to keep V1 as a 12ax7 though as I think it is an integral part of the touch sensative nature of the amp.

Good luck!

Steve

[Kregg]

http://www.geofex.com/ampdbug/hiss.htm

http://www.geofex.com/ampdbug/ampdebug.htm

[geetarpicker]

Sounds a little odd to me too that the amp was bassy, which makes me somewhat question the spec of this build? The noise shouldn't be all that bad. But when you have an amp probably capable of 110-120 sound levels yes you are going to notice some noise when it idles. If you attenuate it down that really does help judge things. When I attenuate down to conversation levels it's hard to hear ANY noise with my Express or my two clones of it.

I've found that when I take a 4 input style Marshall and set the gain and EQ to match my Express (The Marshall probably all dimed maybe with the treble/presense a tad back, and the Express all on about 1/2 with maybe the volume on 1-2pm) the Marshall is actually noiser, quite noisier.

Keep in mind on most of my videos I mute the audio right up until I play and fade out at the end, though I don't use any gates during the tracks. I recently did a Youtube video of a song from my CD using my Gretsch Silver Jet playing "New Mexico". That one is worth checking out to judge the expected noise on less than an optimum gain settings with a sparse dynamic backing track albiet full band. I had the amp with basically everything on just about 1/2 w/500pf bright ON, then I backed the guitar way down to about 2-3 to get a clean tone. On that video I never change the guitar knobs from this low setting. I was playing right on the edge of clean/distortion and it's a pretty delicate track so you would think the noise would be a problem. Still it wasn't really that bad, though I guess if I was cutting it for a CD I'd probably swap out tubes for lower gain ones like 12AY7s. However I should mention in this video I was simply using 12AX7s the same as my other videos where I turn up the guitar more.

http://www.youtube.com/watch?v=-U36Uxwi ... annel_page

[camden_guitarist]

Hi people,

I'll solder it back to stock and swap some tubes to test it more fully, already today putting it into the VST100 through my 8Ohm hotplate tamed the hiss ratio considerbly, I'll have to try that as well with the 3rd gain stage added.

I'll keep you guys posted.

Cheers and thanks for your input.

Paul.

[Rimy]

glen, you said a while ago that your original express had something like 50mv of noise coming out of your speaker with the settings on 12.
i measured mine and i had something like 42mv. after the measuring i tried the grounding scheme as in the 80W wreck from allyn
https://tubeamparchive.com/viewtopic.ph ... c&start=45
finnaly the noise went down to 19mv.
thanks to allyn!!!

camden, maybe you should give it a go on this grounding scheme for your noise.

ralph

[Rimy]

i did some tweaking and research again.

i tried allmost every resistor combination (carbon film, metal film, metal oxyd) in the amp.

conclusion:
the 100k plate res in v1+v2 hiss a lot. even with metal oxyd resistors.
i tried all sorts of different settings. i tried v1a 68k, v1b 56k v2a 82k and the hiss improved a lot.
so i tried all plate res with 56k and 47k in series = 103k on the plate and the hiss was still better than ever before.

i finally reduced the noise level to about 11ma on the speaker out with a 8ohm cab.

in case anyone is going to try this, please let me know if it works?


ralph

[tubedogsmith]

As for the bass-heaviness, that one surprises me. I find that the Express is a little light on bass compared with, say, my (sold) JTM45 - now that was a bass-heavy animal. There may be something else at work here, but I am not really sure what.


Steve

Try bypassing the third stage like he did and see what you think about the bass.

[Roe]

I'm considering changing the grounding scheme and see if that reduces the hiss a little. just to make it a little more p90 friendly

[rooster]

Camden - OK, I agree with you on trying something different at pin 3 of V1. I think 1uf is a bit extreme, try something like 5uf at lowest value maybe just to keep it more in the KF park

As to the idea that the circuit is too bassy for gtr, if we are talking the same language, then I would agree. The odd part is that I have a friend who built one and it has no bass pretty much. ?? I haven't really researched his build yet but I have played his amp and it is without the bass that mine have. And don't misunderstand, my versions have plenty of treble, as well. So this kind of language from you can be confusing because you didn't say whether you had more than enough treble? My comment then is based on this being the case.

A further comment regarding Ken and the choices he made in his circuits would be that, unfortunately, he had gtrs and speakers that most of us do not have. Glen DOES have those things so he is the one to listen to in regards to the REAL DEAL time warp scenario. But again, UNFORTUNATELY, most of us are not going to own those PERFECTLY MATCHED combinations of things - and this then is where the alteration of the circuit becomes a consideration. Dealing with my wallet, I really have to take a good look at altering things. Sorry Ken and Glen!!!!!

Any, the Komet amp thing was sort of an attempt to do something like this, modernize the amp for newer tubes and speakers, etc.. Whether it succeeds in this I would not be the one to ask. (The sadder truth on this note to me is that Ken's family has not reaped any benefit from this association, yet another story.) But it does say to me, this Komet amp thing, that Ken was willing to consider something 'new' maybe, and maybe because of the dumbing down of all things gtr.

.....Which ultimately means to me, that, given what we might find to plug in with (gtr & pickups) and play out of (speakers) these days, even Ken would be forced to alter his original designs. And here I think it is probably more a matter of moderation - because - you either agree that Ken nailed something very beautiful, or you think he was just another amp guy fumbling around. If you believe the former, and I certainly do!!!, then think about what you change, that's what most here are saying.

[Roe]

here's some info on grounding schemes:
http://forum.metroamp.com/viewtopic.php ... 83#p249183
http://forum.metroamp.com/viewtopic.php ... ng#p137708

I've implemented most of larry's suggestions to great effect. she's much more p90 friendly now.. still has a little work left

[LOUDthud]

The .002 cap (in conjunction with the 150K) between the second and third stage does quite a bit to balance the bass. When you removed the third sage did you eliminate this cap. If hooking that cap to the phase inverter, it might not do as good a job of balancing the bass because the phase inverter has a very high input impedance.

[Roe]

larry's grouding sheme worked great on the express! much less noisy.
"star" ground 1: heater CT, v1 w/filtering, volume, eq
"star" ground 2: v2 w/filtering
"star" ground 3: v3 w/ filtering AND output jacks
"star" ground 4: screens filtering and bias circuit
"star" ground 5: just about everything else, I even included the el34 catodes
"star" ground 6: wall power earth ONLY

on my amp ground 1-5 form a straight line but 6 is placed in the corner where the power cord comes into the amp

I removed the ground buss bar on the pots with great results but somehow the presence pot needed to be grounded on the back