45 into an 845 parafeed circuit - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 3rd September 2006, 01:18 PM   #1
diyAudio Member
 
Join Date: Dec 2002
Location: dry ol Melbourne Australia
Default 45 into an 845 parafeed circuit

Hi guys

Iíve read just about all the posts on 845s here (and at AA). Iím interested in doing an 845 SE power amp, and just now have some funds and time. I'm after designs not too complex or too expensive.

I was going to say a two stage amp is preferable, but a three stage with not too much complexity is fine. I will probably use a TVC, but can add a good preamp if I need more gain.
Iím a way off being able to design a circuit, and with three kids and other audio projects too, I wonít have time for a lot of tweaking ..

Iíd like to go for a 45 into an 845 parafeed. Who has a circuit for such an amp?

If using an IT, Iíd lean towards not too much up or down; but I prefer to build cap-coupled first and maybe try IT later.


Thanks
  Reply With Quote
Old 3rd September 2006, 02:14 PM   #2
Gluca is offline Gluca  Italy
diyAudio Member
 
Gluca's Avatar
 
Join Date: Nov 2004
Location: Back to Italy
Default just an idea that works fine

tubelabs 45 into 845

Not a parafeed amp but you can mod the power stage. 845 needs a couple of stages to be driven properly.

Ciao
  Reply With Quote
Old 3rd September 2006, 06:32 PM   #3
diyAudio Member
 
Join Date: Nov 2004
Location: Charlotte
Default Parafeed 845 into 845

Check out this amp out. Even though it is not a 45 into 845, you may get some ideas or mod it to use the 45.

http://www.cognitivevent.com/av_monstro.html
  Reply With Quote
Old 4th September 2006, 10:06 AM   #4
diyAudio Member
 
Join Date: Dec 2002
Location: dry ol Melbourne Australia
Gluca

I was for a while very keen on tubelabsís approach, but I think the PCBs are not available yet, and Iím now likely to go P2P with an exact circuit.

quinnling

il Monstro (282 pounds) is the maybe the King Kong of 845s . . alas adaptations are beyond me at this stage.
I will look further for a circuit that Iím after, or closer to it.

Thanks

Richard
  Reply With Quote
Old 4th September 2006, 03:58 PM   #5
diyAudio Member
 
Join Date: Dec 2002
Location: dry ol Melbourne Australia
www.tubelab.com/845SE.htm

On further thought, I like the idea

IMO not attractive as laid out & shown (but easily changed). Apart from the extra power (which may or not be a benefit, depending on your speakers, dB needed), Georgeís claim:

Ďthe A2 amp does a much better job of recreating highly dynamic music which contains a lot of transients. Snare drums, rim shots, the sound of a cello being smacked sharply with the bow.Ē

Should really suit my primary musical taste (rock).

But "no free lunch" . . if dynamic music sounds better, I wonder what disadvantages might or do accrue??

Cheers
  Reply With Quote
Old 4th September 2006, 07:18 PM   #6
Gluca is offline Gluca  Italy
diyAudio Member
 
Gluca's Avatar
 
Join Date: Nov 2004
Location: Back to Italy
The driver capable of pushing the grid into A2 doesn't come for free ... tubelabs approach seems to be easy, cheap and strong enough to master an 845 in A2. A CF (or a step down IT) would probably not do the same job.

Ciao
Gianluca
  Reply With Quote
Old 5th September 2006, 03:33 PM   #7
diyAudio Member
 
Join Date: Dec 2002
Location: dry ol Melbourne Australia
Default Gluca - your thoughts?

I am considering a small ďreverse experimentĒ on tubelabsís amp:

Have the two MOSFET stages switchable in or out, preferably seperately, to compare the sound (see if they sound preferable in or out) and have control over output for different speakers (and probably tone).

The two MOSFET stages (to my reading) join the existing circuit at seven points. So a switch that moves the MOSFETs in or out would need to join to all seven points - would this work?

Are switchable stages feasible?

Cheers
  Reply With Quote
Old 5th September 2006, 05:34 PM   #8
Gluca is offline Gluca  Italy
diyAudio Member
 
Gluca's Avatar
 
Join Date: Nov 2004
Location: Back to Italy
GAH!? I dont know. I dont like the idea of having switches hanging around in a 1KVish amp. Maybe George (tubelab) can pop in and say more.

Usually I build two different amps (left+right) and listen to them at the same time without switches. At the end I choose the one I like more (actually my left ch is always different from my right ch ... I keep on modding them -LOL-)

Ciao
  Reply With Quote
Old 5th September 2006, 10:29 PM   #9
diyAudio Member
 
Join Date: Dec 2002
Location: dry ol Melbourne Australia
Yes, I intend to build two different amps (left & right) and listen to them at the same time,
one a tubelabs 45 into 845, and
one a ďconventionalĒ cap coupled 45 Ė 845, likely a 6P5GT input, 45 driver 845 v3.jpg here: http://world.std.com/~doyle/

Both with a good 10 K OPT (that I have) and 1000V B+.

I was thinking of having a switch on the tubelab design, but you are right a switch on a 1 KV amp would require great care.

Cheers
  Reply With Quote
Old 6th September 2006, 02:26 AM   #10
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
Quote:
Maybe George (tubelab) can pop in and say more.
I finally have a few minutes (too many people hanging around my office at work to be on the forums)....

Yes, I built a breadboard version of my 845SE, but I was nowhere near it when the power was on. 1100 volts generally will not give you a second chance, and death is rather irreversible.....

I tend to set up the whole circuit, then listen and measure, then move on to the next circuit. This makes A-B comparisons hard. My workbench, and the Tubelab 3 breadboard does not have the space to accomodate two 845 sized channels simultaneously.

For simpler amps, I do build two (usually identical) channels and try any experiments on one of the channels. Use a switch (suitably grounded) that allows switching the two speakers. Differences become obvious when they swap sides. Sometimes it helps to use a mono input signal. This is absolutely the way to audition different OPT's, the "reference" transformer in one channel, and the "test" transformer in the other channel.

I have not had the time to tinker with my 845 amp in a while, but I did discover that the power supply is very important to the sound in this amp. This is true for all SE amps, but this one is seems to be more critical (or my last two power supplies were just lousy).
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  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
Parafeed Circuit cdeveza Tubes / Valves 25 27th February 2011 10:13 PM
2a3 parafeed alexg Tubes / Valves 2 17th November 2007 11:47 AM
to parafeed or not to parafeed that is the question nhuwar Tubes / Valves 63 28th February 2007 01:29 PM
6V6 Parafeed? G Tubes / Valves 13 8th June 2004 02:05 PM
Parafeed Brett Tubes / Valves 14 7th April 2003 01:53 PM


New To Site? Need Help?

All times are GMT. The time now is 03:14 AM.


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