Low End Missing with my Express

[Robbie]

My express seems not to have very much low end. I am running it into a 4 X 12" cab. I have tried Greenbacks, G12T75 and Vintage 30s. The Vintage 30s have the most low end, but don't get there. Has anybody run into this? I was wondering if it had anything to do with the hi-pass filter (.002uf/150k)

Thanks,

Robbie

[doctord02]

The Express doesnt have the same kinda low end 'whump' that say a Marshall has... What kinda lows are you expecting?

[pureoldsound]

what tubes do you have in it? The amp can be fairly bright, but I guess they were built to cut through in band situations...IIRC the 75s are bright speakers...I used to own an Express clone and used it with G12Ms in a 2x12 and wasn't terribly bright...Heck I even had the 500pf cap on all the time....

[rooster]

Robbie - If I were you I would look to replace the two 25uf caps attached to V1. Possibly your brand is off spec? My versions have quite a lot of bass, more in fact than I can use. ?? I am assuming that you used the TS tranny set? No possibility that you are running a wimpy OT? Anyway, these two caps determine the cutoff for bass freqs entering and moving through the preamp at this juncture. In other words, reduce these stock values and the bass will be reduced. For that matter, your V1 could have a problem - have you swapped with other 12AX7s? (FWIW, many early Fender amps used really big values at the first gain stage. 250uf in a 59 Bassman, for example. ...And then most of this was rolled off by the alnico Jensen 10s.)

Going further, did you check all of your voltages against the build guide voltages? And then your pwr tubes could be weak. Are they new and known to be operating as they should?

Anyway, if you were asking, bass should not be a problem in a well built Express.

[Robbie]

Thanks guys for your feedback. Here's a couple thoughts:

1. Expectations: I listened to Glen's videos many times and there seems to be a low end thump that I'm not getting. Maybe this is where I am getting deceived. His tone is great, full bandwidth in nature. I get a lot of mids and highs.

2. I have cross checked the caps and voltages and everything seems in order.

3. I am using a traynor 4x12 cab. It is straight front and I thought it would be similar to a Marshall cab... maybe not?

4. I am using a power soak, but it is still pretty loud, (> 90db). Maybe it needs to be full out to really drive the cab?

Thanks,

Robbie

[leleduke]

Robbie - If I were you I would look to replace the two 25uf caps attached to V1. Possibly your brand is off spec? My versions have quite a lot of bass, more in fact than I can use. ?? I am assuming that you used the TS tranny set? No possibility that you are running a wimpy OT? Anyway, these two caps determine the cutoff for bass freqs entering and moving through the preamp at this juncture. In other words, reduce these stock values and the bass will be reduced. For that matter, your V1 could have a problem - have you swapped with other 12AX7s? (FWIW, many early Fender amps used really big values at the first gain stage. 250uf in a 59 Bassman, for example. ...And then most of this was rolled off by the alnico Jensen 10s.)

Going further, did you check all of your voltages against the build guide voltages? And then your pwr tubes could be weak. Are they new and known to be operating as they should?

Anyway, if you were asking, bass should not be a problem in a well built Express.

What 25uf caps at V1?? Do you mean .022uf??

[dave g]

The cathode resistors for both triodes of V1 are bypassed with 25uF electrolytic caps. If you used .022 film caps there by mistake, that would explain a lot

[leleduke]

The cathode resistors for both triodes of V1 are bypassed with 25uF electrolytic caps. If you used .022 film caps there by mistake, that would explain a lot

The layout on this site shows two 22uf caps on the v1

[dave g]

22uF and 25uF are often considered interchangeable for cathode bypass caps - you won't notice any difference in sound between the two (in fact, 10uF will even sound basically the same, since 25uF is a much larger value than is necessary anyway). On the other hand, if you saw 22uF and accidentally used .022uF, that would definitely cause the type of problem you're describing.

[pureoldsound]

I have tried a 10uf and a 25uf and they sound different. IMHO

[Robbie]

I'm using 22uf cathode caps on the first and second stage. The .002uf /150K combo I was referring to was the filter connected to the grid of the 3rd gain stage. It has a corner frequency of 532Hz. I'm using 6V6's and the TS transformer suite. Its not like I have no bass, but compared to Glenn's video, I just don't hear the low end kick around 100 - 200 Hz. I keep thinking its the cab / speaker combo?

[pureoldsound]

speaker/cab and tubes..What tubes are you using?

[Buschman]

The Express seems to be more of a very thick midrange sound. It is not going to have the bottom of a Fender twin At the same time that's what makes it such a great lead amp.

[rooster]

Robbie - Yeah, OK, I see where you are coming from. Glen needs to address this, tell you about his cab there and how dark it actually is relative to that Traynor cab you are running with.

Glen?

[Robbie]

Here's the breakdown:

> Tubes: RCA 6V6
> Cabinet: Traynor 4 x 12 straight face
> Speakers Tried:

- Greenback (weakest bottom)
- G12T75 (better bottom with crispy highs)
- Vintage 30 (best bottom with lots of low end mids)

> Power Soak used to drop 6db out. Have played briefly full out (trying to save my ears), but don't detect a huge difference in bass

I thought I read somewhere that Glen used PRE-Rola G12 XXX, I just can't remember now. I don't know much about these speakers or where you could get them.