SEWA - Seven Watt Amplifier

[Ryssen]

Quick question - what VRMS input is required to bump this amp (bare) up to full tilt?

You meen just the SEWA without the tubes?

With tube I would like about 1,5-2v.
Will try it with just the ECC86 when I get all the parts,jleaman and Geek plaese post schematics for new ideas, Im not realy sure when or where I can use Direct copling.

 

[Tyimo]

Hybrid SEWA

Hi!

Quick question - what VRMS input is required to bump this amp (bare) up to full tilt?

+/-12-15V! So, you need a lot of gain from the line stage.

I am afraid that a simple CF with ECC86 or 88 will be not enough to drive the SEWA because the Mosfet's high input capaticantes.

Ryssen, you should try the Swedish REMUS preamp!

Greets:

Tyimo

 

[Geek]

Re: Hybrid SEWA

Hi Guys,

You meen just the SEWA without the tubes?

Yup!

With tube I would like about 1,5-2v.

Oh, at most. I usually aim for 0.7 VRMS with 1V max.

Will try it with just the ECC86 when I get all the parts,jleaman and Geek plaese post schematics for new ideas, Im not realy sure when or where I can use Direct copling.

Schematics for sure from me. I'm an open-source type guy

Hi!



+/-12-15V! So, you need a lot of gain from the line stage.

Thanks!

Not much gain really, +/- 15V is 30V P-P which is dozing for a tube

I am afraid that a simple CF with ECC86 or 88 will be not enough to drive the SEWA because the Mosfet's high input capaticantes.

Pump up the current, pump up the current, DANCE!

Fortunately most of the totem designs I've used I have tested as stable into moderate capacitances. Knowing these plasti-tubes though, I should test for as high as 10nF maybe?

Cheers!

 

[Ryssen]

Ryssen, you should try the Swedish REMUS preamp!

He,he I built that one about 16 years ago..But where I am going to use/test this amp is with my computer-modded audiophile 2496,allright I post a pic so you can se for your self.it has a "Brute force" linestage
maybe it could drive the SEWA direct.But now I decided to make SEWA a hybrid.

I am afraid that a simple CF with ECC86 or 88 will be not enough to drive the SEWA because the Mosfet's high input capaticantes.

well if I use a ecc86 as voltamp and ecc88 as CF it might work.or
comments, schemas..
Computerstereo...

 

[Ryssen]

The subwoofer Isobarik ofcorse...

 

[Ryssen]

Commenst on this please.

 

[tinitus]

I think the beauty of SEWA lies in its simplicity, and I think you loose it along the way

All it needs is preamp with gain

If you build a tube into the SEWA you will need a pre anyway

So why not simply build a nice tubed preamp with the needed gain

 

[Ryssen]

So why not simply build a nice tubed preamp with the needed gain

I think I have it in the "brute force" but I want a hybrid amp.

 

[Tyimo]

Hi!

I think the beauty of SEWA lies in its simplicity, and I think you loose it along the way. All it needs is preamp with gain

Yes! I agree!
Unfortunately I have never listened a realy good Hybrid power amp ( yet....)

Tyimo

 

[Babowana]

I think the beauty of SEWA lies in its simplicity, and I think you loose it along the way

All it needs is preamp with gain

If you build a tube into the SEWA you will need a pre anyway

So why not simply build a nice tubed preamp with the needed gain

Some people leave for a long distance to find gold, and return
back home with no finding. Next day, suddenly find lot of gold
at home ground.

But, the journey itself is a fun.

 

[Ryssen]

I think the beauty of SEWA lies in its simplicity, and I think you loose it along the way

Ofcorse I will try the SEWA whitout any tubes,As I have 2 holes for 9 pin socket in my top,sure would like some glowing tubes there.
Maybe try if I can run the SEWA direct from the soundcard wihtout the
"Brute force" simplicity...

Not much gain really, +/- 15V is 30V P-P which is dozing for a tube

How much is needed in RMS?My sound card puts out 2v...maybee just a litlle tub in SEWA..

 

[tinitus]

What are your speakers like ??

 

[Ryssen]

The sub is 2 x CA21REX SEAS,and PX17-LTS and Gamma ribbonspeakers,the sensitiviy is about 90db/w.Deepbass and clear top end.I used to power it with 6B4 SE and it sound fine.

 

[Fuling]

I´ve spent the whole night experimenting with ECC86 and mosfets. I tried BJT CCS loading with and without Jfet buffer, hybrid Mu-stage with Jfet on top, choke loading with and without buffer and nothing seems to be able to push a simple Mosfet power follower past 20kHz!

I guess ECC86 simply isn´t a good candidate for the job, and it´s a shame cause I came up with some really neat direct coupled hybrid amp topologies last night...
Since I have everything set up I´ll try PCC88 in the same circuits, it might or might not work better. I have my doubts though, tubes seems to like voltage and Mosfets require some current in the driver stage.

 

[Zen Mod]

I´ve spent the whole night experimenting with ECC86 and mosfets. I tried BJT CCS loading with and without Jfet buffer, hybrid Mu-stage with Jfet on top, choke loading with and without buffer and nothing seems to be able to push a simple Mosfet power follower past 20kHz!

I guess ECC86 simply isn´t a good candidate for the job, and it´s a shame cause I came up with some really neat direct coupled hybrid amp topologies last night...
Since I have everything set up I´ll try PCC88 in the same circuits, it might or might not work better. I have my doubts though, tubes seems to like voltage and Mosfets require some current in the driver stage.

88 like current,but you'll not have much of current with this sissy voltage......

 

[Fuling]

I noticed that, yes.
I gave up on the whole thing, but right now I´m prototyping something involving mosfets, Jfets and chokes but no tubes.

 

[planet10]

All it needs is preamp with gain

But where do you put it? The last one Ryssen posted is a SEWA with a CCS loaded Foreplay-style (CC direct coupled to a CF) preamp in front.

dave

 

[Tyimo]

inductor versions

Hi Fuling!

Could you simulate and/or calculate how big inductor would need for the original SEWA amp instead of the 10R 100W power resistor? (Now it is called OTA7) I would like to try an inductor loaded version.

Greets:

Tyimo

 

[Geek]

Commenst on this please.

I think it's worth a try!

Not much gain really, +/- 15V is 30V P-P which is dozing for a tube

How much is needed in RMS?My sound card puts out 2v...maybee just a litlle tub in SEWA..

10.62 VRMS (sinewave)

I recall seeing somewhere (another forum?) someone saying 7 VRMS. Close enough in the dBV scheme of things

 

[Fuling]

Tyimo: I use surplus chokes rated 112mH/2A DC. Seems big enough, but bigger would be better.