reliable tube/mosfet hybrid amp - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 8th November 2002, 12:48 PM   #11
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Default Re: another try

Quote:
Originally posted by JAZZ2250
Oops. The link to an image didn't work. Here's the full address.

http://www.geocities.com/Tokyo/5913/hybrid.gif
I could not get the site to open. Then I tried

www.geocities.com/Tokyo/5913

From there you can pick the page you want.

Cheers.
__________________
AM
  Reply With Quote
Old 8th November 2002, 01:36 PM   #12
diyAudio Member
 
stokessd's Avatar
 
Join Date: Nov 2002
Location: Grantham, NH
I used to own a counterpoint SA-100 which sounded quite good on the right set of speakers. But it was very fragile. I blew a set of output FETS, sent it to counterpoint to have repaired, got it back, plugged it in (without anything hooked to it), and blew the same fets again. I then traded it for a VTL amp.

It had power supply rail fuses too, but the fets were faster fuses than the fuses.

Good sound yes... Relable no... (not really fair; it used it for years with no problems before the failure)

So it is possible to make a good soundning hybrid, and I'd postulate that with a good quality bipolar output stage it would be quite reliable too. Or a fet stage with a better design would probably do the trick.

Sheldon
  Reply With Quote
Old 8th November 2002, 04:12 PM   #13
diyAudio Member
 
Join Date: Jun 2002
Location: Bangalore
What I heard from another forum is - Counterpoint' Hybrid amps blow the Fets - surprisingly large number of people do not seem to be aware of-
Is it a design fault and fets blow due to Oscillation ?
When we discus Hybrid amps Moscode Tube / Mosfet hybrid amps have cult following entirely due to their excellent design and reliability.
Bythe way I am looking for Moscode schematics - does anybody have them?
K.S

Quote:
Originally posted by stokessd
I used to own a counterpoint SA-100 which sounded quite good on the right set of speakers. But it was very fragile. I blew a set of output FETS, sent it to counterpoint to have repaired, got it back, plugged it in (without anything hooked to it), and blew the same fets again. I then traded it for a VTL amp.

It had power supply rail fuses too, but the fets were faster fuses than the fuses.

Good sound yes... Relable no... (not really fair; it used it for years with no problems before the failure)

So it is possible to make a good soundning hybrid, and I'd postulate that with a good quality bipolar output stage it would be quite reliable too. Or a fet stage with a better design would probably do the trick.

Sheldon
Moscode Tube / Mosfet
  Reply With Quote
Old 9th November 2002, 03:13 AM   #14
diyAudio Member
 
stokessd's Avatar
 
Join Date: Nov 2002
Location: Grantham, NH
Quote:
Originally posted by kayes
What I heard from another forum is - Counterpoint' Hybrid amps blow the Fets - surprisingly large number of people do not seem to be aware of-
Is it a design fault and fets blow due to Oscillation ?
I think it's more of a design flaw than a characteristic of MOSFETs. After all if FET's were fragile, then Nelson Pass' designs would be puddles of molten silicon. The Counterpoint amps don't have any small emitter resistors for load balancing. So if the output is shorted, the FET itself dissipates all the power by itself If I remember correctly, it's an avalanche type of failure too). According to Mike Elliot, the amps sound much better without them (If I recall correctly, there are provisions for them on the circuit board). I did find the amp to be a good sounding (a bit warm and soft; which was nice).

Sheldon
  Reply With Quote
Old 10th November 2002, 04:31 AM   #15
JoeBob is offline JoeBob  Canada
diyAudio Member
 
JoeBob's Avatar
 
Join Date: Nov 2001
Location: Montreal, Canada
I said I'd soon have some input, and I just finished off one of my amps (it's in pieces, needs the chasis to be assembled, will do tomorrow) but it really does sound nice, the tubes add their sound and the MOSFET power follower (Class-A) is indeed rather neutral (very nice sounding on it's own though) and blends well with the tubes. All and all I'm very happy with it, and will probably stick with that setup for a while to come. So MOSFET/Tube hybrids can indeed sound superb, give it a try, but with all things, a bad design will sound bad.
  Reply With Quote
Old 10th November 2002, 05:50 AM   #16
diyAudio Member
 
JAZZ2250's Avatar
 
Join Date: Mar 2002
Location: Seoul. Korea
A good tube/SS design is what I need. I'm so happy that you have made a success cause it will be my next project. I just didn't wanted to spend my time and money for what would never happen. BTW, could you provide some preliminary info before you prepare a full review of your work? I'm eager to know what you have made. Thanks.
  Reply With Quote
Old 10th November 2002, 04:02 PM   #17
JoeBob is offline JoeBob  Canada
diyAudio Member
 
JoeBob's Avatar
 
Join Date: Nov 2001
Location: Montreal, Canada
I made a simple source-follower circuit with IRFP044Ns, only one in the signal path, as well as one for the ccs (just slight variations on the power follower 99c design by Andrea Ciuffoli). Andrea reccomended a tube stage to drive it (he reccomended his headphone amp, but that sucker was a little on the expensive side to build). So I built a simple tube stage composing of a 6922 tube doing the voltage gain followed by a 6AS7G wired up as a cathode follower. The tube stage must have a low output impedence so as not to take off the high end due to the MOSFETs high input capacitance. I'm really happy with it, I'll probably tell you more when it's broken in, but for now I have to finish my second stereo unit, for these are meant to biamp with.
  Reply With Quote
Old 15th November 2002, 02:03 PM   #18
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Default NFB on the Hybrid

You should be careful about the negative feedback on the hybrid amp. The Nfb going to the cathode of the input tube. This and the inter coupling capacitor ( to the MOSFET stage) can cause a bass lift of several db in the low frequencies - below 10 hz. It shows up as increased bass and is not good as it causes very low frequency (damped) oscillation. If you control this with a low value inter coupling capacitor , the bass lift disappears and the low frequency instability seems to be controlled. It is easy to simulate this with a simple program like ECAP or if you are familiar , with Spice.
I tried this circuit and it sounds very good. I made many changes to it get rid of the oscillations. I am still not sure if it is unconditionally stable. Sounds good in any case.
cheers.
__________________
AM
  Reply With Quote
Old 15th November 2002, 03:11 PM   #19
halojoy is offline halojoy  Sweden
On Hiatus
 
Join Date: Nov 2002
I think it is better to use the MOSFETs
as a separate output buffer

only to have eventual feedback in the voltage ampl tube

I have seen this design, with 2 caps as a coupling between
  Reply With Quote
Old 15th November 2002, 03:35 PM   #20
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Default Feedback

I tried this circuit with no negative feedback. I liked it. Mid range was nice - I cannot explain easily but it was good. Bass was a bit floppy as the output impedance was high -around 1 ohm or so. But if you crossover to a sub- or have a very well damped sub ( Q less than 0.6 ? ) it will probably be good. I plan to make an amp with no nfb with an active sub . I think this may be the ultimate answer. Without nfb I find that portions of the music that tend to 'shout' seem to be very well controlled. In addition the voice seems to be very well reproduced - more natural .
It is certainly a very good idea to try a Valve voltage gain stage with a unit MOSFET stage. You can try many configurations.
The no NFB one is good and maybe you can start with that. This is an area where 'low distortion figures' are to be largely ignored. They are probably just under 1 % or so ! The sound is worth it.
I am just hoping I get enough time to work on a no nfb design for my active Tannoy603 project.
Note that I tried the ECC series and also the 6SL7 and 6SN 7 series. The 6SN7 beats the rest hands down. For higher voltage output and more output stages you will have to use a power voltage stage. I think maybe you have to use the power pentodes in triode mode. I have bought several pentodes just for this. Haven't got time yet to try them out.
cheers.
__________________
AM
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
MOSKIDO - Hybrid Tube/MOSFET Amplifier Kashmire Pass Labs 7 22nd September 2011 08:30 PM
24V Tube IRF610 MOSFET Hybrid HPA lineup Solid State 10 23rd October 2008 02:36 AM
Hybrid Tube / Mosfet Amplifier poynton Tubes / Valves 8 10th August 2007 05:32 PM
bass guitar amp hybrid Tube/mosfet ?? partyjups Instruments and Amps 1 19th April 2004 01:08 PM


New To Site? Need Help?

All times are GMT. The time now is 09:34 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2