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Old 5th March 2013, 07:18 PM   #1
ke4mcl is offline ke4mcl  United States
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Default need help choosing between two amp schems

i'm working on a project and have two schems to choose from. i am only interested in using one of these two.

http://diyaudioprojects.com/Technica...-Schematic.jpg

or

http://www.tremolo.pl/Firmowe/FENDER...-5c1-schem.gif

the first one has no caps in the audio path. what are the advantages and disadvantages of such a design? the project is a simple guitar amp using junk on hand. again i am only interested in picking the best of these two designs but not sure which to pick. help?
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Old 5th March 2013, 07:55 PM   #2
Ketje is offline Ketje  Belgium
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The first one is rather original but very low power and you have to calculate all the resistors yourself.
While the other one,well let's say it will function (more or less)
Mona
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Old 5th March 2013, 07:57 PM   #3
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Champ is simpler, stages are independent, and its a proven design for guitar. The DC coupled circuit has minimal tolerance allowed on a number of parts. Can you recalculate the resistor values if your output transformer ISN'T 250 Ohms DCR as specified?
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Old 5th March 2013, 08:09 PM   #4
ke4mcl is offline ke4mcl  United States
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i found that 250 ohm DCR on the OPT to be interesting. i have tons of OPT's here so i might get lucky but whats the advantage to that capacitor-less circuit?
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Old 5th March 2013, 09:14 PM   #5
DF96 is offline DF96  England
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Capacitor-less circuits can be helpful for people who suffer from faradaphobia, an irrational fear of capacitors. They may be able to cope with a few caps in the power supply, but any more than this brings them out in a cold sweat. There is no known cure at present, so sufferers need our understanding and sympathy.
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Old 5th March 2013, 09:23 PM   #6
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You building a guitar amp or a hifi amp?

The champ is NOT a hifi amp.

The DC coupled schematic looks interesting. It is Cathode coupled, and is a bit odd, since there is no low Z return to ground that I could see... doubt it makes much power. There are other ways to do a cathode coupled output stage that work better, imo.

The 250 ohm DCR is for biasing the 6V6, you don't need to be that exact...

Quite frankly I wonder if it really works. Where did the circuit originally come from?

Bottom line, pick something else to build.

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Old 5th March 2013, 09:47 PM   #7
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I'd build the Champ.

1. It's a known and highly regarded design from a tonal point of view. In fact I've built one. You can get a Jensen speaker for it. You will get that sound. If you don't like it, somebody else will.

2. Caps in the signal path are perfectly acceptable in a guitar amp, they are desirable to a degree. A DC coupled amp always risks getting DC on the input and then goodbye Jensen speaker.
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Old 5th March 2013, 11:31 PM   #8
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It is a *transformer* coupled amp - cathode coupled transformer - no possibility whatsoever of DC on the output.

The question is what is the application??

Neither amp is particularly good, for their presumed applications, respectively, imho.

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Old 6th March 2013, 01:00 AM   #9
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Of course, it should have occurred to me that it would be transformer coupled.

It seems, however, that I'm not the only one that something escaped...

Quote:
Originally Posted by ke4mcl View Post
the project is a simple guitar amp using junk on hand
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Old 6th March 2013, 01:29 AM   #10
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You will get more help on the Instruments ans Amplifiers forum.
The Champ is a known design and is therefore RECOMMENDED.

But I would recommend::::

I have recently completed a restoration of the following amp. It is "Champ-like" but is higher gain. (and therefore you might think more modern but is a 1942 design). It was originally used for Harmonica but is great for guitar too.

Here it is :
Historic Harmonica Amplifier

It has 2 off 6J7 one of them triode strapped (just use 6SJ7 if you want to go octal, same tube but without the top cap of a 6J7). 6V6 Single Ended Output with a very interesting and effective tone control based on feedback around the output tube, 80 rectifier, sub a 5Y3 if you want to go octal.

This amp is truly stunning with my Telecaster, better than any Champ I've used, some of the amp's lovely sound with guitar may be due to the electrodynamic speaker.

Cheers,
Ian
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