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5150 Circuit Opinions
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 3/9/2000 2:31 PM |
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Ethan |
5150 Circuit Opinions Back to the Peavey 5150 amp, any opinions on what's wrong with this amp? Here's what I hear: it has plenty of gain (too much?) and lots of low end, but something is missing. I think it needs to be more Marshall and less Peavey. So what is the problem? Crummy trannies, cheap caps, or just not a good design? It seems like a good model to modify as they are available pretty cheaply. For what it's worth, I put an adjustable bias in a head once and set it up with EL34's. It didn't do much. It sounded like a 5150 w/a slightly different response. I went back to 6L6 later as I was afraid the power trans couldn't handle the extra filament. -Ethan |
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| 3/9/2000 2:47 PM |
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| A.S |
I agree. It has a buzzy sound that lacks mid and whatīs with that awful treble you canīt get rid of? A.S |
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| 3/9/2000 3:58 PM |
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| Stephen Conner |
TMT Many folks think the problem with the 5150 crunch sound (and with many Boogie rigs!) is TMT... too many tubes. I used to be a gain freak metal shredder and I made up various high-gain designs. I generally found that the more tube stages you stuck in, the worse it sounded! Each stage seemed to make the sound more mushy and flat, and generally sap the dynamics and life out of it. Eventually it sounded just like a transistor fuzz box. I now much prefer the sound of fewer stages driven harder, with tiny coupling caps and no cathode bypass caps to prevent farting. 4 triode stages like this (excluding the PI) still seems enough for beastly shredding, especially when you get the power amp wound up too. So why not try bypassing a few of the preamp stages, and removing some of the components Peavey used to dump gain between stages. The other problem with the 5150 (AFAIK) is that even on the clean channel, the signal passes through all the tube stages! So you get lots of noise and a lack of dynamics. You could probably improve the clean channel a lot by bypassing most of the stages. Or you could trade it for a nice Marshall. Apparently, even though Eddie Van Halen endorses the 5150, he still plays Marshalls live and in the studio. Steve C. |
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| 3/9/2000 4:11 PM |
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| Trace |
Ayyyy mennnn!!! No need to look for the lost scrolls, the truth has been found borthers and sister. I could not agree more with you Stephen. Dymanics go right out window and all the fuzzy stuff comes roaring in. If you want to control the amps dymanics then adding more tubes is the opposite way to go in my opinion.
You are dead on the money! Why bother using extra tubes when a distortion pedal is cheaper? Maybe it's the thrill of the hunt or in this case the thrill of the building. (ha, ha)
This is interesting Stephen. Do you have a schematic of one of the designs you are refering to? I'd love to check it out. I've been able to use bypass caps with out having the amp fart-out at all. Most of the time people tend not to consider the power section and how it will effect the tone when the amp is cranked up (which you touched on a little bit). Trace | |||
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| 3/10/2000 2:28 PM |
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| Stephen Conner |
Hi Trace, I used this overdrive stage philosophy in the Toaster amp I designed lately. It doesn't actually have 4 triode stages with 1nF blocking caps and unbypassed cathodes in a row, only 2, but the gain structure is the same as if it did. The first 2 triode stages are wrapped round a 2-band active tone stack, and when the bass knob on this is turned down (which you need to do for high-gain sounds) it's the same as having an extra 1nF blocking cap. The next 2 triode stages have the small blocking and no bypass caps, and the clean channel bypasses them completely. Then there is a 'dirtier' channel that goes through 1 triode, and a 'crunch' channel that goes through both. Hit http://homepages.strath.ac.uk/~cnbp111/baxeq.html which shows the first 2 stages http://homepages.strath.ac.uk/~cnbp111/overdrive.html shows the last 2. (You might have seen them before though) I did it this way so I would still have some bass left for clean sounds! For the crunch, I tried various 12AX7 tubes in the second position but they were all a bit hard rock. I got a much mellower tone with a 12AT7, and still plenty of gain for my taste. Before that I designed a simple tube preamp for my solid state shred war machine (an old 100 watt PA amp fitted with graphic EQ from an old stereo) It was just 4 12AX7s in a row with the normal values of cathode bypass caps. The second coupling cap was 1nF and the rest were 22nF. To prevent farting I used resistors to throw away 20dB of gain between each stage. I also used 350V B+ and 180K plate load resistors. It sounded like shit, in fact this was the experience which led me to slam 'many stages in a row' type amps. I had to use a compressor pedal to put some dynamics back in! If I had only twigged to remove the cathode bypass caps and gain dumping components - it might have been almost bearable. Steve C. |
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| 3/9/2000 4:03 PM |
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| Trace |
Re: 5150 Circuit Opinions
Now there's a year long thread as to correctly answer this question! (ha, ha) Many people feel it's just a silly design over all. the thing is designed to run on the edge" at all times which it pretty much does. It also does not help that it's built like a tinker toy.
I would say it way too much but that's my opinion. I've seen guys who will not play any other amp so it's mostly personal preferance.
I don't think anything is missing per say, I think they need to take things out of the cicuit in order to help things out a little bit. A couple preamp tubes would be a good start 
It's easier to buy an older Marshall than even consider modding (re-designing) a 5150. The 5150 is mighty close to a SLO-100 so someone would be better off buying a SLO-100 over the 5150. Same goes for the Dual (triple) rec amps. Just my opinion is all.
I think it's easiest to sum it up by saying it's a bad design over all. I'm sure there's people who will disagree with my stance on this but that's what makes the world go round. 
I would disagree on that one. There are a bunch of other amps that are far easier to mod than the 5150. I do not think there's anything easy about modding these amps. All the experienced techs I know hate working on these amps. It's not a lot of fun.
There's too much happening in the preamp for EL34's to make much of a difference at all, or any tube for that matter. I would say a "cleaner" tube would be the way to go with such a hot preamp.
It's better to run these amps with 6L6's. There's far too much gain in the preamp to use a tube that will add more distortion to the tone. Usually this is a good way to make a muddy tone. My 2-cents worth Trace | ||||||||
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| 3/9/2000 5:11 PM |
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| Ethan |
Thanks for the opinions. Now that I think about it, the last one I worked on was a pain in the ass. Oddball board mounted pots, circuit boards hard to remove to get at, etc. I have some old Marshall's that I like a lot, and just sold a SLO-100. Remember that a used SLO is $1500+ and a nice old P to P Marshall is probably $700+. Even a Solo head is about $850, so for a high gain 100 watt amp they're fairly cheap (rightfully so, I guess!). For someone that wants a gainy amp cheaply, I still think they're a good amp. For a well rounded bluesy tone, they're not even in the running. It would be interesting to bypass a gain stage or two and see what happens- Ethan. |
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