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harrygrey382 25th June 2007 02:16 PM

Guitar amps
 
Hi,
I'm mainly a hifi man myself, however, I've offered to help my little cousin out with a guitar amp project. So, can someone give me a little hand here?
Firstly, if there is a better place, I'm sorry, mods could you move it.
Why are tube amps percieved to be louder than SS? Do they always use more sensetive drivers? If so, why don't they make low powered SS amps with sensetive drivers?
Secondly, I'm helping him build a new one (keep the old amp unit), what sort of drivers are considered good? What sort of sensetivity am I after, is 100dB sensetive, or normal?
If someone knows of a good DIY guitar amp forum I'd be interested, but haven't found any

PB2 25th June 2007 02:25 PM

https://taweber.powweb.com/store/kits.htm


https://taweber.powweb.com/weber/

el`Ol 25th June 2007 03:02 PM

http://www.eighteensound.it/index.as...roduct&pid=240
http://www.hypex.nl/
plus a guitar preamp depending on his taste,
and he`s got a portable PA.

FastEddy 25th June 2007 03:08 PM

" ... Firstly ... Why are tube amps percieved to be louder than SS? Do they always use more sensetive drivers? If so, why don't they make low powered SS amps with sensetive drivers? ..."

The answer here is usually summed up: Tradition and Clipping. Tube amps are preceived as being "better" by professional musicians, mostly because old habits die hard. Marshal and Fender amplifiers from the '60's were and are all tube type amps. Most musicians learn on and buy tube type amps that their guitar heros have bought and once a musician learns to "handle" the sound of a clipped and distorted tube amp, they don't want to switch, feeling they have mastered what the masters have mastered ... Check out: "Crossroads Guitar Festival" / http://www.amazon.com/Crossroads-Gui.../dp/B0002Y4T92 ... every budding guitar player should see this ... Note that every lead guitar performer on this video has a tube amp micked up to the master festival PA ... even James Taylor, Dan Kominski (acoustic guitars) and that steel slide guitar guy, what's his name.

There is definately something to the sound of a tube type amp run at maximum gain into clipping. Tubes (valves) do sound different at clipping levels than do solid state transistors, having a completely different distortion pattern when viewed on test equipment (like oscilloscopes and spectrum analysizers). This "tube sound" can be reproduced by carefully built solid state amps, but not to the satisfaction of the traditionalists. Generally, because solid state distortion is quite different than tube distortion, the preception is that tube amps are "louder" than solid state, but the reality is that the distorted tube amp sound is "better" at higher sound pressure levels than the distorted solid state sound because the guitar player has the tube distortion "under control" at these higher levels. (Also, speakers / drivers do not fail quite as rapidly when driven to clipping by tube amps, partly because the tube amp distortion is "easier" on the speaker cones.)

" ... Secondly, I'm helping him build a new one (keep the old amp unit), what sort of drivers are considered good? What sort of sensetivity am I after, is 100dB sensetive, or normal? ..."

100 db is quite sensitive, but about "normal" for the built in, unbaffeled, ventilated, "all in one", higher efficiency guitar amp driver / speaker cabinets.

There is a nice active guitar / musician DIY forum right here ... http://www.diyaudio.com/forums/forum...php?forumid=30 ... and plenty of tube amp support at ... http://www.diyaudio.com/forums/forum....php?forumid=5 :smash:

(Personally, I build power MOSFET amps that are intended to be driven by a tube pre-amp ... the tube pre-amp sound satisfying the traditionalists, the MOSFET output transistors supplying large amounts of power without distortion, the distortion being entirely within the tube pre-amp ... = longer lived speakers, better audience response to the sound = IMOP.)

Geek 25th June 2007 08:02 PM

Re: Guitar amps
 
Hi,

Quote:

Originally posted by harrygrey382
Why are tube amps percieved to be louder than SS?
Because of their distortion characteristic. Tubes "compress" while transistors hard-clip. Discussions for similar HiFi effects in the "Tubes" forum.


Quote:

Do they always use more sensetive drivers?
Usually. Even the el-chaepo Epiphone Valve Jr. uses a 99dB driver.


Quote:

If so, why don't they make low powered SS amps with sensetive drivers?

Cheap power. Partswise, a 1 watt SS amp costs the same as a 10 watt one and a 10 watt one costs nearly the same as a 100 watt one to make overseas.


Quote:

Secondly, I'm helping him build a new one (keep the old amp unit), what sort of drivers are considered good? What sort of sensetivity am I after, is 100dB sensetive, or normal?
100dB is normal. They can go 115dB for the more costly ($150+ range) Eminence.

Though this guy has great drivers I hear at insane prices:
Warehouse Guitar Speakers


Quote:

If someone knows of a good DIY guitar amp forum I'd be interested, but haven't found any
Brand new :)

http://tonegeeks.sicomm.us


Cheers!

harrygrey382 26th June 2007 09:14 AM

brilliant, as ever a great source of info guys. I'll get some more info about his current amp and start investigating replacement drivers. BTW, do the same principles re box design with hifi speakers apply to guitar amps e.g. bass ports etc.?

sreten 26th June 2007 12:13 PM

Quote:

Originally posted by harrygrey382
brilliant, as ever a great source of info guys. I'll get some more info about his current amp and start investigating replacement drivers. BTW, do the same principles re box design with hifi speakers apply to guitar amps e.g. bass ports etc.?
Hi,

Re cabinets yes and no.

You don't really want to go much below bottom E on guitar ~ 90Hz.

Higher Q guitar drivers are used in "half" open backed cabinets, good
for "lead" guitar. Heavier style guitar is best suited to lower Q drivers
in sealed cabinets. Open backed combo with a sealed extension is a
possible option.

Vented is generally only used for bass guitar cabinets.

There are loads of possible guitar drivers .......

:)/sreten.

FastEddy 26th June 2007 02:55 PM

" ... do the same principles re box design with hifi speakers apply to guitar amps e.g. bass ports etc.? ..."

Certainly they do! Same, same ... Acoustics is acoustics and electronics is electronics. One thing that you may wish to consider is reliability as much as quality. If the amp is going to be lugged from concert to concert, then the drivers should be sourced from generally accepted professional grade speaker sources ... or at least these "pro" resources should be considered. (Several musicians I know use speakers / drivers that are speced for use in mobile automotive "boom box" systems = able to take abuse from road travel and extra loud, extra powerful amps, etc.) :smash:

" ... You don't really want to go much below bottom E on guitar ~ 90Hz. ..." Unless you plan on hooking a bass guitar to it as well. Many budding musical talents start out playing bass first, then graduate to lead guitar .... so

" ... Higher Q guitar drivers are used in "half" open backed cabinets, good for "lead" guitar. Heavier style guitar is best suited to lower Q drivers in sealed cabinets. Open backed combo with a sealed extension is a possible option. ... Vented is generally only used for bass guitar cabinets. ..." ... True

alan-1-b 29th June 2007 01:35 PM

bottom E is 82 Hz ...
 
Quote:

Originally posted by sreten



You don't really want to go much below bottom E on guitar ~ 90Hz.

Higher Q guitar drivers are used in "half" open backed cabinets, good
for "lead" guitar. Heavier style guitar is best suited to lower Q drivers
in sealed cabinets. Open backed combo with a sealed extension is a
possible option.

Vented is generally only used for bass guitar cabinets.

There are loads of possible guitar drivers .......

:)/sreten.

Bottom E on 6 string guitar is 82 Hz.

One problem numerous electric guitarists have complained about is getting a balanced, or even response, across all the bass range.
This is a drivers' problem which cannot be compensated for by changing bass tone setting on one's amp.
Too many supposed Guitar speaker drivers have Fs higher than 82 Hz - I see on manufacturers' spec sheets Fs ranges from 89Hz to 110Hz !
110 Hz is the A string.
Yes, there were otherwise good sounding guitar drivers years ago with above 82 Hs Fs, but there were also more with below 82 Hz Fs then than is currently the case.
Problem is the combination of the high output impedance of almost all guitar amps combined with the high impedance spike at the speaker's Fs causes effectively higher volume for the 1 or 2 notes' bass fundamentals that happen to be very close in pitch to the Fs, and often somewhat lower bass oomph for the next few notes above, and almost no bass response from the bass notes with fundamentals below the Fs.
This effect is more noticed with amps without heavy distortion effects applied from high gain preamp controls, as when there is a lot of distortion present much of the signal is 2nd ; 3rd ; and higher order harmonics and proportionally less of the bass fundamentals, thus heavily distorted amps signals make use of the speakers' bass response above its Fs .
Playing with a cleaner sound, or even with medium distortion, we get un-even bass response, and some of us simply turn down the bass tone pot. a bit more than we'd prefer to, to get a bearable tone.

In an open back cabinet, including half-open, response is usually OK down to the driver's Fs.

In a closed cabinet, the Fs is raised in frequency, and quite a lot if the cabinet is small -{small relative to the number of drivers in it}, thus though the closed back cab. does give more bass oomph, such is only for the upper bass region, unless one uses a large cabinet and significantly lower than 82 Hz Fs drivers.
This is one of the reasons the Celestion "Vintage 30" driver is popular - Fs is 75Hz, as were the Celestion guitar speakers of the late 60s to 70s.
Similarly, one reason for the popularity of the re-issues of Celestion's G12M Greenback and G12H in the "Heritage" series.
Apparently the H version has the original option of a 55Hz Fs, thus making it very suitable for use in a closed cabinet.

For the combination of 2 cabinets as one open and one closed, try Celestion G12-75 in the open backed, and Vintage 30 in the closed cab. , {or G12-65 + G12H-Heritage for each you can afford them !}.

Eminence in the USA similarly have only very few models with Fs below 82 Hz in their electric guitar drivers' range.

Yes, I know of the re-issues of vintage spec. Jensen speakers, with their high Fs, but remember those were originally used in open back cabinets, and their signature sounds were not even bass response - there are other determinants of likeable guitar-amp-speaker tone which various players give priority to above even bass response.

Another advantage to low Fs drivers is we can get a decent low end tone when we tune down to open D.

Bottom E on basses is 41Hz, and for the 5 sring basses with a low B string the B is just about 30 Hz, though a lot of such bass players simply make use of the extra weight this gives to the 2nd harmonic at about 60 Hz.

harrygrey382 30th June 2007 05:49 PM

ok thanks, good starters there.
His amp is a Peavy Studio Pro 112. It has a Blue Marvel 12" driver rated at 96.5dB, 70 Hz ~ 6.5 kHz useful range.
His main priorities are increased volume of sound. So I think the plan is to get new driver(s). Will an increase to 100dB make a noticeably difference, or shall I go higher? Is choosing drivers purely on sensetivity ok?
I notice the Vintage 30 is 100dB, whereas the G12-75 is 97, so may try the closed back route. What about other makes?


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