Tube Pre Amplifier for SEWA 7 Watt ClassA MOSFET

Status
Not open for further replies.
Jump to Latest
lineup

lineup

Member
Joined 2005
#1
Hello people.

I hardly ever find a chance to start a new topic in Tubes.
Tubes are nice and interesting!

This Project is about build a Pre Amplifier
to match the input of SEWA 7 Watt Class A MOSFET Power Amp.

If you post here, please RESPECT OUR TOPIC.
And find out some basic knowledge about SEWA MOSFET amp
before you make your posts and suggestions.
The SEWA thread is GIGANTIC, so try the last pages
for uptodate information about latest version of The Circuit.

Thank you.

/lineup


Reference link:
Pass Labs >SEWA - Seven Watt Amplifier
SEWA - Seven Watt Amplifier
:spin: :spin: :spin: :spin:
 
#2
Great idea to start a topic here 😀

I have a design in mind, but without an actual SEWA present, I can't say if it will work to perfection.

If I am correct, we need 25V P-P driving some fairly hefty Cin on the MOSFET. Driving the capacitive load isn't an issue for what I have in mind, but keeping it stable with no feedback loop.

If there is a SEWA owner within reasonable driving distance of Chilliwack, BC, I'd like to meet up with you 🙂

Cheers!
 
#3
Geek said:
Great idea to start a topic here 😀

I have a design in mind, but without an actual SEWA present, I can't say if it will work to perfection.

If I am correct, we need 25V P-P driving some fairly hefty Cin on the MOSFET. Driving the capacitive load isn't an issue for what I have in mind, but keeping it stable with no feedback loop.

If there is a SEWA owner within reasonable driving distance of Chilliwack, BC, I'd like to meet up with you 🙂

Cheers!
Click to expand...

Thanks Geek.

My own thinking, based on what little i have seen and read about tupe preamps, is 6922 / E88CC / 6DJ8
Not a very original thought, yes,
but this these tubes has made a lot of good and many people happy.
And is easy to find and buy, to a resonable price in most countries.
-------------

This article have a very valid title:
THE SUITABILITY OF THE 6DJ8 FOR AUDIO
Russia’s Best
Today I see many premium numbers with exactly the same internals as their commercial version, sometimes with a gold "flash plate," which the marketer adds to the pins after the fact. Since the gold rubs off on the narrow line of contact with the first insertion, its value is questionable. With a superior beefy structure, the 6922s I have recently bought from Russia are the best I have ever seen from that country, and certainly deserve a premium label.
Click to expand...

About The Author ROGER MODJESKI

Roger Modjeski received a BS in Electrical Engineering in 1973 from the University of Virginia and was a teaching assistant while studying for his Masters at Stanford in 1975.
He has been active in electronics since the age of five watching his dad build a Heathkit Williamson.
Prior to starting Ram Tube Works and Music Reference in 1980, he opened a high-end retail store where he met and later worked for Harold Beveridge.

His other interests are music theory, piano, singing, building musical instruments, solar energy, architecture, and understanding how things work.

This article attempts to correct a few misconceptions
about some of the popular dual triodes
used in audio amplification.


With comparison of diffeent variations of 6DJ8. Original Article Link ( recommended! )

THE SUITABILITY OF THE 6DJ8 FOR AUDIO
http://store.electron-valve.com/suof6dforau.html


/lineup 😎
 
#4
Geek said:
If there is a SEWA owner within reasonable driving distance of Chilliwack, BC, I'd like to meet up with you 🙂
Click to expand...

Gregg... you are a SEWA owner... one of the things we didn't get aeound to talking about enuff... i have (most of) the parts for 4 monobloks (need Mosfets & thru hole passive parts) -- 2 are yours. All part of the toob-i-fication project. We did talk about using the Al tube for chassis & heatsink which was the missing ingredient...

dave
 
#9
Hi Guys,

planet10 said:


Gregg... you are a SEWA owner... one of the things we didn't get aeound to talking about enuff... i have (most of) the parts for 4 monobloks (need Mosfets & thru hole passive parts) -- 2 are yours. All part of the toob-i-fication project. We did talk about using the Al tube for chassis & heatsink which was the missing ingredient...

dave
Click to expand...

...

Uhhh.. I think I remember what I forgot to pack it in the scramble to make the Greyhound? :zombie: :blush:


Mad_K said:



Cin is typically 250pF 😉
Click to expand...

Very cool. I assume this takes into consideration Mr. Miller's contribution?

Anyway, this is what will drive it. Yes, it's an ECC88 and if you want to use a 6922/E88CC, it'll need changes.

I haven't done the gain stage yet... backed up on projects.

It uses lower voltage and higher current. I've used this as a straight buffer and is stable into a 4.7uF load, as well as complex weired inductances. It'll also drive fair good. Not as good as two trioded 6EJ7's in mu-follower, but it'll swing 25V P-P across 2K resistive+capacitive okay.

So, three tubes. One 6DJ8 for each channel and a third dual-triode for the gain stage. I'm thinking 6CG7.
 

Attachments

  • modified_wcf.gif
    modified_wcf.gif
    6.8 KB · Views: 4,402
#12
This Project is about build a Pre Amplifier
Click to expand...
In that case why not specify the requirements first.

Ok you've given us low impedance. But what else? Should it be cheap? Or a cost no object preamp? Or somewhere in between.

Simple or complex? DHT or IDHT. Classic or modern. Kit or complete DIY?

Would you like to develop it from scratch in this thread here or would you like a proven design.? From the Sewa thread I gathered that you would want some gain.
 
#13
Hello
Bas Horneman

This thread is mainly for 'The SEWA People'.
Some SEWA owners has been requesting suitable tube pre amp
for their power endstage amp: SEWA.

You can of course join in, too, even if you have no SEWA 🙂
We could use all good advices from really experienced valve builders, like you.

Thanks for reading and posting. Everything is most welcome.
Many of us are just beginners in tubes.
But we can learn - like you could.
I would imagine, you were not born a valve circuit designer ??
😉


Regards
lineup
 
#14
This thread is mainly for 'The SEWA People'
Click to expand...
I understand... 🙂 But what I am curious about is what do you trashy people want? 😉 Just to try anything with valves? Or the best valves have to offer?

We could use all good advices from really experienced valve builders, like you.
Click to expand...
I'm not really experienced at all...it just looks that way 🙂 But before someone can give you good advice you have to know what you want. Hence my question...must it be cheap or expensive? Transformer coupled or cap coupled...etc., etc.

I'm experienced enough to know that it is easy to make a valve pre-amp. To make something outstanding is a whole different ballgame.
 
#15
IMHO it should follow the lines of simplicity like SEWA and the suggested BOZ frontend. It should be in the same (or better) quality/price range as BOZ/SEWA.

It boils down to a single (/dual) tube and some resistors and caps. I presume the work/money would have to be spent on the PSU


Requirements:

+/-20V voltage swing
Able to drive 47K, 250pF
10-20X Gain
Volume control
Source selector
Low noise


Wishlist:

-Uses available parts
-Transformerless (or readily available)
-Easy to build
 
#17
My suggestion based on those requirements would be to build something like Douglas's (Sector7G' or Bandersnatch on diyAudio.com) Guinevere but with (a minimal reactance psu - not shown here yet). And instead of the relatively hard to get depletion mode mosfets use that IXYS 10m something part. Tube could be 5687 or the 2 dollar supertube 6n6p. (Or many other tubes for that matter)

:cop: Compromised URL removed by Moderation

One tube socket. One dual tube. 3 Single chip CCS's. (If using the IXYS jobbies and the MR psu.)
 
Last edited by a moderator:
Status
Not open for further replies.
Top Bottom