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Old 8th May 2008, 01:12 PM   #1
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Join Date: Jun 2007
Smile mosfet output for my tube preamplifier

hello.
i maybe will build tube preamplifier later
i am looking for a power output for such tubeamp
thinking of using mosfet, something like firstwatt f4 maybe

found a attachemente in another topic
http://www.diyaudio.com/forums/attac...amp=1162677844
Anybody knows this amplifier? what mosfets and descriptione
not can be found anything information in the post:
http://www.diyaudio.com/forums/showt...83#post1048283
(SEWA - Seven Watt Amplifier)

thanks, jacma
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Old 8th May 2008, 02:12 PM   #2
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Location: Columbia, SC
I confess that I'm a little confused. Are you looking for:
1) A solid state amplifier?
2) A hybrid amplifier?
3) A tube preamp that somehow uses a solid state output stage?

Grey
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Old 8th May 2008, 04:29 PM   #3
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Default Re: mosfet output for my tube preamplifier

thanks Grey for your reply

Maybe I eksplain better now my topic here
I reading this advise from Mr Nelson, in 'First Watt model F4 Operation and Service Manual'
Quote:
Nelson Pass:
"... so you should find it easy to drive
with tube equipment if you like."
Now, this is my topic posted:
Quote:
Originally posted by electrofan

...... something like firstwatt f4 maybe

found a attachemente in another topic
http://www.diyaudio.com/forums/attac...amp=1162677844

Anybody knows this amplifier? what mosfets and descriptione
not can be found anything information in the post:
http://www.diyaudio.com/forums/showt...83#post1048283
(SEWA - Seven Watt Amplifier)
1. All comments welcome and I want to know about mosfets Amplifier in attachment in other topic
2. Is different or is same also as F4 ampifier?
3. What is better for suitable drive of one Tube preamplifier?

thanks
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/jacma
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Old 9th May 2008, 12:50 AM   #4
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Join Date: Jan 2007
Location: Iowa
"1. All comments welcome and I want to know about mosfets Amplifier in attachment in other topic"

-The schematic in the background that you posted is the output section of a Elektor Hybrid amplifier. Here is the front end that is missing from the schematic taken from another thread:

http://www.diyaudio.com/forums/attac...amp=1162413419

The tread:

Nishiki hybrid amp

"2. Is different or is same also as F4 ampifier?"

-Quasi similar I guess (?). Basically it is just the current output...back end... of an amplifier, the above tube schematic is the voltage amplification...front end. I am sure you could tweak it a bit and drive it with your own tube line stage, but I am willing to wager that the F4 would do it better.

"3. What is better for suitable drive of one Tube preamplifier?"

-Are you more or less just looking for a power follower or power buffer, an amplifier that has no gain or little gain? Because this is what the F4 is, more or less an over-grown buffer. For that I would try searching around the forum and the internet for "Power Follower" and/or "Power Buffer"

http://sound.westhost.com/project83.htm

http://www.audiodesignguide.com/my/Hot_Follower1.GIF

http://www.audiodesignguide.com/tra/...r_follower.jpg

Zero Feedback Impedance Amplifiers

^^^Maybe this

http://www.diyaudio.com/forums/searc...der=descending

^^^Searching "Power Follower" all forums, titles only...little leg work for you, I am having a slow day

I assume this is what you mean, though I am a little confused. You can really drive anything with a tube line stage, it is just like any other pre. In essences with a well designed power follower you will hear the sound of the pre, there isn't really an amp per-say to color the sound. Though it would sound great too driving a Zen amp or an Aleph 3/J...or a 300B (sorry Mr. Pass).

Power follower 99c Vs Zen

^^^ May be of interest

BTW, what pre are you planing on building?

Cheers

James

edit: Keep in mind too that all power followers (that I know of) need an ACTIVE pre that can swing enough voltage, no place for passive pre's.
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Old 12th May 2008, 12:15 AM   #5
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Thumbs up thanks JPeitzman


thanks James, I love you!
so many info for me!
you must have work more then '10 minutes' to find good stuff for me

i have visit those links and will do more read now in week
then i hope i will make mind what power follower to build
i am not sure which voltage amplifier to make
if make tube or maybe some nice jfet preamplifier

firstwatt F4, may be my power, because much info here in forum for this
the other 'hybride' is in my mind very much same principe follower as F4
but too little to know about that other one

again, many thanks my friend
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Old 12th May 2008, 06:22 AM   #6
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Quote:
you must have work more then '10 minutes' to find good stuff for me
A few, but like I said, a slow day...just trying to help.

Quote:
i am not sure which voltage amplifier to make
if make tube or maybe some nice jfet preamplifier
If you consider JFET's I can throw out a couple of ideas. I have built a ESP Audio Project 88 Op Amp Line Stage, a JFET Bride of Zen, and just recently a JFET Aikido. The P88 was the first line stage I built and it was in a pinch, I needed a pre bad and the project was simple. Since then I have improved the power supply a bit and switched the op amps for top grade LM4562's. This amp is what I still use for movies and some music, for now at least...read on.

Later I stumbled across a thread on a JFET version of the Bride of Zen pre. It was so simple it would almost be dumb NOT to build it. I can honestly say that when it comes to music, especially jazz/blues/acoustic guitar/most live recordings the JBOZ walks all over the P88. It is so warm and life-like, at the same time it is almost like it is not there. For a single JFET this is a magical little line amp. It is however very dependent on the power supply. Such a simple circuit has a very low PSRR and the PSU can really effect the sound and speed of the amp. I feel though that after all the bugs have been worked out that a very good implementation of this little amp can go toe-to-toe with almost any line stage and at least hold it's own. It does have some faults to my ears, it can be a little bass shy for instance, but it is hard for me to find faults in it.

Then about four days ago I built the JFET version of the Aikido or Tubecad fame. This little amp has really surprised me. The initial impression was not overly favorable, but I have since been able to do some more listening with it. This is the little pre amp that could...could kick the s*** out of quite a few other amps. Fast, clear, detailed, and bass that heavy, controlled, and able knock your face in with the right amp! Listening to this with my JLH it really became a different amplifier. I still like my JBOZ of jazz, blues, live, etc... but for rock, techno, movies, this may be my new weapon of choice. Here is a link to a short and not over good review I did of the JFET Aikido.

http://www.diyaudio.com/forums/showt...69#post1506269

If you decide to go tubes, which I strongly suggest you do, I can throw out just a few of hundreds of different options.

1. The DHT 26, 10Y, ect... with either a choke load or transformer output. This would be considered by some, I included for now, the tops for tube lines. Open, rich, detailed, pure liquid music, when designed right a DHT line can be pure magic. This and option 2 will soon be gracing my basement. One thing to consider since these are directly heated is that hum reduction can cause many a headache. If you decide to go this route though you will have much help and many examples.

2. A simple 12B4A, enough said, very simple. Many people recently have built this simple line amp and been quite impressed. Many have said that it beat many consumer line amps and many high quality home designs too. Most people that have built this one say the the level of detail has to be heard to be believed. A big plus, it is kind of like the JFET BOZ of the tube amps, just a handful of parts and one tube. A second plus is that the 12B4A is not a mainstream audio tube, you can find them for about $8.00 USD give or take a little.

3. The Aikido line stage with tube instead of JFET's. This seems to be a very popular design that I never liked until I built one with FET's. I can say that what you read about the tube version is almost the same for the FET version. FAST! Detail is very good....well I wrote about it above. I am really wanting to build the tube version now to compare them directly. A couple pluses with this design, it by design negates a lot of hum, it has a good PSRR. Good if you don't fully have designing very quiet tube supplies down yet. Second is that it can use almost any tube under the sun with a little bit of modification.

4. To many others here to list, it is really crazy how many tube line amps are out there. Grounded grid could be an option, VTV has a simple 6SN7 line amp out there, SRPP with triodes or pentodes, a single pentode, the list goes on and on.

If you decide to build JFET's I would look at the JFET BOZ just to get a taste of the sound. A very simple project and sounds incredible. If you want a design to really drive the F4 or similar to it's peak and back you should look to the Pumpkin preamp.

For tubes, I would say just pick something an jump right in. Beware with tubes of a few things. 1. Iron can be expensive to very expensive! Check around at surplus stores and yard sales, you never know what you may find. Heck just a couple weeks ago I picked up a NOS 7729 (top quality 12AX7 variant, gold pins, low noise, tight matching, sort of rare) for $0.50USD! You can find some cheap but sometimes high quality iron for projects. 2. Beware of high voltage and high voltage caps! Even 250v with a few hundred uF of caps behind it can hurt a lot at best, it however can kill. Don't fret to much though, just be safe and respectful at all times and you will be fine. Where you really have to watch out is in high voltage for big tube amps like the 845. Funny things can start happening at 1kv if the proper measures are not taken. 3. Remember always, when you are done building and testing, take pictures! Tube amps are far to beautiful not to be shared with the world!

Here are some links for you again:

1. The Jfet BOZ
Jfet BOZ
JfetBOZ mods
2. Just one of many 12B4A links
Yet another 12B4 line stage, or is the 12B4 better than the Grounded Grid.....
3. LOTS of good info on tubes and home of the Aikido. Of note also is that PCB's can be ordered up for the Aikido, just something to consider.
http://www.tubecad.com/

Just search around too for "DHT" , "26" , "10Y", "JFET" , whatever else, there is lots of information on the forum on JFET pres and tube pres.

Quote:
again, many thanks my friend
Just hope that some of it helped. I like Grey at first was kind of confused but I think I figured out what you where looking for. If not then I am sorry to make you read so much . No matter what you build you will always find help here and may you be happy with what ever you end up with. I think you would be very happy with a F4 and a good pre, but as always happy building!

BTW, I almost forgot, this could be VERY useful, here is the Pumpkin. Don't skip over this one, it was designed to dance with the F4.

Pumpkin Preamp - Perfect for F4

Although sometimes a Choky is a very nice person willing to help, and reading some of his posts can be very Zen . This is a great little line amp that he has put together. Good stuff on his website too. He also mentions the UGS in his first post, you might want to try searching for this, just search titles only first, just another design to consider.

Cheers

James
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