Grateful Dead Music Forum

A place to talk about the music of the Grateful Dead 

 #156699  by Erbacher
 Wed May 24, 2017 10:39 am
Hi I'm wondering how I can increase tightness in the bass frequencies? It's a '72 vibrolux and I've modded the tonestack as per the usual stuff (.022 orange drop 225 series caps, tants, dale metal film output resistors, and carbon film resistors in the cathode section, I also added a solid state rectifier to the amp and rebiased) I run it into an mc50 and either into a hard trucker style Baltic birch cabs with jbl k110's in one and e120's in the other...sounds pretty great but the low end still doesn't have the hardness that I'm desiring...I'm wondering in the preamp if there is something I am missing that will help? Or maybe a value change somewhere in the circuit? Is this just the difference between the vibrolux and a twin? How important are the Dimarzio's? I've got a highly modded frankencaster with a Duncan antiquity 1 in the bridge and a Duncan hot stack in the bridge with a 5 way switch...I'm also using the Waldo buffer...thanks in advance for's been interesting to add all the pieces and components over time to get a good idea of what each thing does to the overall sonic signature
 #156700  by tommybo
 Wed May 24, 2017 10:57 am
different guitars and different pickups will react differently- different pickups can either add or decrease bass response -just as different guitars can either be bright or bassy - also experiment with pickup height -
 #156702  by playingdead
 Wed May 24, 2017 11:22 am
Try heavier strings, or just go a little heavier on the lower strings. The amp can only reproduce what the guitar is giving it.
 #156706  by waldo041
 Wed May 24, 2017 8:44 pm
Erbacher wrote:Or maybe a value change somewhere in the circuit?
Yes, see the next questions answer.
Erbacher wrote:Is this just the difference between the vibrolux and a twin?
Sorta, Choke, Filter Capacitors and Power Transformer ALL play a part. There is more to it but the Twin Reverb is the place to start. I am sure Jerry had many Fender options to choose from, to include a Vibrolux, but for the most part used a modified Twin Reverb, MC2300 and 12" JBL's as his base rig.
Erbacher wrote:How important are the Dimarzio's?
For the late seventies to the end, Very important.

 #156710  by Erbacher
 Wed May 24, 2017 9:38 pm
Yeah thanks for all the replies...surprisingly enough tonight I figured out part of the low end tightness issue being related to the impedance mismatch I had been messing with and when I returned the mc50 to the 8ohm tap, the low end got tighter and was immediately noticeable...I may go ahead and gut my twin and do the mods to it and buy a bunch of new parts...a few years ago before I bought the vibrolux I took the twin to a guy who totally screwed it up haha and at one point I sent a pic to brad and he was like WTF happened in there? Haha so I pretty much just put it away knowing sometime down the road I would go back and dial it in...I've learned a lot in the last few years so maybe soon the twin will be resurrected properly...
 #156719  by Erbacher
 Thu May 25, 2017 10:08 pm
My settings on the vibrolux vary from gig to gig depending on the room...bass never gets over like 2.5 or so and treble may run all the way up depending upon how it sounds...reverb 3-3.5 unless I'm going for some kind of huge sound...I play pedal steel as well so depending on the song and situation the reverb may change but for 6 string it's usually right around 3.5...
 #156720  by brbadg
 Fri May 26, 2017 1:50 am
"sounds pretty great but the low end still doesn't have the hardness that I'm desiring".

I guess I'm having a hard time with your explanation.What do you mean by "hardness""?
 #156721  by Searing75
 Fri May 26, 2017 4:11 am
In regards to "tight" lows. You are using the wrong amp man. In your mind, you are looking for a certain tone, and that tone came from certain equipment. Simple. Go get "certain equipment", and you will be golden.

The Twin will get you close, but a good high power solid state power amp with the Twin will get you even closer.
 #156731  by tatittle
 Fri May 26, 2017 8:37 pm
It sounds like he has the amp preamp tapped to a MC50 already. The 10" speakers are going to give you significantly different response than a 12" single/pair. They have more low-mids I think, which can make the low end sound lower in relation. There is also less low end response in 10's naturally (JBLs included). Also, the neck pup will give you looser bass than the middle/bridge. My notion is the ceramic pups are a bit quicker/stiffer sounding than Alnicos, but I don't think it is significant if other factors are compensated appropriately; and find the trade off in sweetness too big and prefer alnicos.

I don't have the tech knowledge or experience to really say, but in my mind the Mac always seemed to really tighten up the low end in that Jerry type way that wasn't possible in standard Fenders etc. Finally, you gotta turn the bass pot up and give it a good audition if u haven't. Don't set controls where you've read they should be despite things not sounding right. I know it is hard to get certain reliable info out of my perceptions in cases like yours, but the rules on pot positions are not as reliable as other things bc they can vary so greatly amp to amp/room to room. Use your ears. Wont tighten it up but should make it more promounced relative to other freqs. Much of tone is ratios of 1 freq level to others, more than mere levels of objective frequencies alone.