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Old 21st April 2009, 06:21 AM   #11
chrish is offline chrish  Australia
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Thanks Ian. Just tried to look at that site, but would not allow viewing without registration and then would not allow registration with a gmail account Will have to find a workaround later as I am just stepping out the door...

I thought the output sounded a little "baby huey" ish

Regards,

Chris
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Old 21st April 2009, 06:45 AM   #12
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"One specific question to begin with is, why are most guitar amplifiers build PP?
Is that only because of the extra output power?"

I think it's mainly because push-pull is required to operate in class AB
for high output power and/or anode efficiency. Guitar amps are heavy
as it is... Cheaper for mass production also, as already pointed out.
But it's not just PP, it's class AB that is the big win in efficiency.

SE output stages do have inherent 2nd harmonic production, but
typical guitar amp circuits have SE front ends and somewhat
asymmetric phase splitters that generate a lot of 2nd harmonic.

Having said that, there are a lot of very popular class A botique guitar
amps on the market and it is a popular mod for class AB amps to run
in class A.

IT would be interesting to explore SE guitar amps. One may get away
with a limited bandwidth OPT, which could help with the weight issue.
I would think a 20 watt SE amp could be built without going to
heroics. Just think, no phase splitter to design ;-)
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Old 21st April 2009, 06:52 AM   #13
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As mentioned the reason for PP amps owning the guitar amp market is most bang for buck. The amps out there get 60watts out of a pair of 6L6s, and you don't get that with tubes running in anything but class-B. The main reason is buyers always look at specs first, and everything else second. Besides in the old days they did not use miked cabs and huge PAs like today. But time they are a changing...a bit... Small class-A guitar amps are coming out of the woodwork like there's no tomorrow. Some music styles actually work best with PP class-B amps, so class-A is not always the best for guitarists.
I started building guitar amps some 8 years ago, and at first I was confident my amps would blow those old textbook designs out of the water. hehe...I can tell you right now if you build a guitar amp with the same design specs as a HiFi amp it will sound like crap. I did that mistake and made sure all details in the amp was high-end HiFi quality. The fun part regarding guitar amps is they are just like an instrument and should have it's own character and personality, which it wont have if made like HiFi amps. I finally got the tone right when a guitarist friend of mine told me to make it so bright it hurts. The trick is getting the brightness without the harshness.
Anyhow, good luck and have fun trying crazy ideas. I desided to offer something different and therefore build OTL guitar amps. you can see some here, tho this website is old and I havent had time to update anything for about a year...www.devildogamps.com
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Old 21st April 2009, 06:55 AM   #14
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Btw. A guitar has very little notes, or energy, below 100Hz. This means your output transformer can be much smaller than a similar powered HiFi amp.
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Old 21st April 2009, 07:01 AM   #15
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Quote:
IT would be interesting to explore SE guitar amps. One may get away
Hi Michael,
As parttime/longtime producer of boutique amps, www.revintage.se , I have been there. Can not understand the SE hype. The really nice sounding solution is selfsplit PP( reVintage Prince). No splitter needed, always Class-A and better sound for guitar.

My next track to explore is 6B4G PP for guitar, maybe with triode/antitriode, selfsplit with 6B4G and 6V6........

I can recommend 7591 as output tubes together with custom wound Heyboer OPTs. And don´t forget to use rectifier tube.
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Old 21st April 2009, 07:04 AM   #16
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Quote:
Originally posted by b_force
I don't know exactly, I know a few OT's for PP and Se that you can buy for almost the same price. I didn't looked at the weight.
You pay for the iron. Lowest note in guitar, E at 41Hz doesn't require an output transformer to be designed any lower than this,saving weight and copper so you will find a HiFi amp transformer designed for 20Hz cutoff double the size, better quality often quadruple the cost. In saying this there are quitar amps used for HiFi. SOme are astoundingly good. I use a HiFi amp for trumpet as sound levels can be awesome high requiring higher power without clipping distortion caused by power/ B+ sag.
My other 807 p-p amp I use for guitar is also a near HiFi amp. It sounds too clean. To make it sound rough I use zener diodes with a double pot across the grid leak resistors in the output stage with series caps so clipping can be gradual and a very loose global nfb loop, perhaps 6dB NFB. That tactic is an old one not seen anymore. It isn't a quality arrangement, and alot of quitar amps were/are fudged around surplus WW2 /TV tubes and forced into work. 1-10% thd was quite the norm, whereas a true HiFi amp is looking at less than 0.1% 3rd harmonic thd at rated output and masses of global nfb to keep it quiet. BIG difference.

richy
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Old 21st April 2009, 07:20 AM   #17
AuroraB is offline AuroraB  Norway
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This site has a LOT of info, including fully spec'd instructions, layout etc. for several of the mythical (?) Dumble and Trainwreck amps..
You'd have to register here too, though, to get to the nuggets.....

www.ampgarage.com


This one , www.hoffmanamps.com , also have a lot of info and projects.

www.ax84.com also have a lot of projects, mainly on the slightly less ambitious side, but still lots of good info.

As for SE vs PP, I don't think I'd bother with SE for guitar, except maybe for smaller practice amps of say 2-5 W, but then I'm no guitar guru....
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Old 21st April 2009, 07:37 AM   #18
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Quote:
Originally posted by b_force
But I've read that SE amplifiers are have more second order harmonics (distortion). Can that not be a extra point to go for a SE design?
When a string decay we expect to hear softer sound than when it is loud and bright. It is natural.
PP may produce harder sound on low levels, while SE amp sound the softer the softer is the sound. Well made PP amps may behave the same, but it is easier to get wrong, artificial, sound from PP than from SE amp.
I still remember sound of a small German amp called Regent - 30. It was PP, in class A. Fantastic sound.

Edit: hum was the biggest minus, but the sound was fantastically musical. Here is the info: http://www.el-me-se.de/pdf_files/Regent%2030%20H.pdf



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Old 21st April 2009, 07:40 AM   #19
b_force is offline b_force  Netherlands
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What a reply's


But keep discussing, I think it would be very interesting to talk about difference tastes and how they can be accomplished.

No time to reply now, but I'm already thinking of a specific tube guitar book.
The problem is that there are many books and my opinion is that they are not al that great. Mostly I'm missing the deep story's and theoretical side.

Does anyone know if "O´Connor, Kevin - Principles of Power" is a good book to have?
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Old 21st April 2009, 07:53 AM   #20
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Quote:
but it is easier to get wrong, artificial, sound from PP than from SE amp.
This may be true for hifiamps, but for guitar it is all about tone. Here it is usually easier to get it right with PP.

PP, pentode, Class-A and cathode-bias is a sure way of getting it right.


b_force,

Of Kevins books, I suggest you start with TUT3.
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