How common is hiss in an Express build?

[dms]

Thought it deserved its own thread -

Trying to get a sense of how many Express clones have turned out to be hissy, and what construction tips might make the difference. I haven't listened critically to my hiss to see if it swells and tails off like a compressor, as was mentioned in a previous thread on Orphan Annie.

Care to share your express build results?

Davids

[ampdoc1]

dms,

I've built two amps, and they were both "hissy" with the standard tube compliment. I don't think there is anything wrong with this, but rather a result of the impressive amount of gain that is available. I replaced the two gain stage 12AX7s with 12AT/U/Y7s, and almost eliminated the hiss. The gain is less, but the amp still has great dynamic response and ability to produce lots of harmonics and feedback when called upon.

David Hicks

[rhinson]

hello, i've had just excellent luck with using 5751's in either or both of the first two preamp tubes---haven't tried one yet in the p.i. these tubes give a more solid, smoother/even sort of frequency response and tone down the gain just a bit (comparing them to current production 12ax7's that is). folks should give them a try, esp. in amps you think are a little brighter or more gainy than you would like. rh

[geetarpicker]

Yes my Express does hiss. However I did an AB comparison once with my '68 Plexi 100 watt Marshall. I set the Marshall on 10 (all knobs) and then set the Trainwreck cut back to about 12:00 where the two amps had very similar gain. I then recorded the amps in the studio and listened to the playback of both amps at the same level. In that comparison it was apparent the Express had a little bit better signal to noise ratio than the Marshall, all else being equal. Still, the Express is noisier all the way up, but it also has way more gain. Considering the gain the Express has it has a pretty decent signal to noise ratio.

[doctord02]

I'm beginning to wonder if the hiss is coming from the volume pot itself, or perhaps the tone controls... I have a wreck clone built from the Kelly '90/A1a schematic using Alpha pots and Sozo caps/metal film resisters and it's quiet as can be. Really, it's very quiet.

I have another amp that mated a wreck preamp to a Moonlite power amp (6SN7 wired push-pull for about 2.5 watts). It screams just like my other wreck, but it also is very hissy. I just went thru it and pulled out every single carbon comp resistor and replaced them with metal film. A hair quieter, but still too hissy. Then I went and tried both 5751's and 12AY7's. Different, but still too hissy. So now I suspect the pots, 'cause they are no-name and cheap... Just wondering if anyone else has run into hissy pots...

[dms]

Thanks guys - I guess that's what is needed: a reference point. It's just that when you play it for the first time, you don't necessarily think in terms of fair comparison. My JTM45 build is pretty quiet, but it has nowhere near the gain. By the way Geetarpicker - heckofa potential caption comes to mind... "The Trainwreck Express: less noise than a Marshall 100 watt with everything on 10 (11)." My God - how did you survive that?!

I remember running my 135 watt ultralinear Twin wide open with the master/gain pulled in a studio for a recording, and having to stand almost motionless with the p90 single coil Les Paul- there was about a 5 degree angle within which the noise could be managed. This was just a 2x12 openback... I shudder to think about that Marshall through even a single cab...

My Ruby runs on Alpha pots for now too - no carbon comps in this build, but a few 1/4 watt metal films (where K&M used them). The Chinese 12ax7a-s are apparently pretty high gain (who would be surprised if those were noisy); I will have to try the couple of Mullards that I have, and the 5751s.

Thanks to all who responded - helps keep things in perspective. I'm just itching to put this thing next to a K&M-built Ruby to see how it matches up.
Davids

[geetarpicker]

I use to practice in a 20'x20' carpeted room with a full Marshall superlead 100 stack on 10 with two 4x12 cabs stacked with 30 watt black backs. Yep, I have the tinitus to show for it. However since about 1985 I've worn earplugs. Still from about 1978-1985 I did some damage but not too bad. I have a friend that would practice in a darn small bedroom with a 100 watt non-master stack when he was a kid. Now that's nuts!

These days attenuators are a wonderful thing. However sometimes in the studio I like to wear 30db cut earplugs, crank the headphones up, and track right infront of a ton of volume to get all the sustain and feedback interaction. I have some gun muffs with the guts of some Sony headphones inside. They help isolate things so you can hear the mix, even with a blazing amp right there.

Keep in mind my hiss comparison was done in a studio, where the amp heads were in the control room and the cabs out in the main room with plenty of isolation. Did the listening test on the control room monitors, so as to level the db for an honest comparison.

[Robert]

Doctord02,
In my Ruby build, I used mil-spec PEC 2watt pots, from Digikey $7-10 ea, and have hiss. When experimenting with the Fast-Gradual switch, taking the signal off of the junction between the 22k&82k resistor eliminated the hiss at the expense of some sensitivity and gain.

[doctord02]

Thanks for the tip Robert, I'll investigate there...

[Robert]

At the time I tried that mod, I was focused on what the hell Fast Gradual could be. I just noted it took away the hiss and felt it decreased the touch sensitivity. I didn't think I would use it so I just remove it. In hindsight, I should have realized it was worth investigating. You could try varying the resistors, say 70/30, 60/40, 50/50,40/60, etc. and see if you can eliminate the hiss while retaining all the other aspects we love about the circuit. The mod is on the Trainflex schematic in the files section here.