building Single Ended amps - 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 7th January 2007, 12:37 AM   #1
diyAudio Member
 
Join Date: Jan 2007
Send a message via AIM to akimball442
Default building Single Ended amps

Hi, I am new to this forum, although I've been looking at it for a while now. It looks like one of the better, if not the best places on the internet to gain knowledge.

I first fell in love with tubes as a guitar player, in fact, the only solid state amplifier I own anymore is the one my dad bought me as a kid, and only because I can't part with it for that reason.


I later figured out they made audio equipment out of tubes, and got my first Eico ST70 and rebuilt it, and I still use it to this day.

Since then, I've collected a garage full of goodies, amps from old consoles, record players, you name it, if it had tubes in it, I bought it. I've rebuilt lots of magnavox and zenith amplifiers with good success, some of them sounded good, others sounded not so good.

Right now, I have 2 amps I would like to make an attempt at turning into REALLY good amps. I have lots actually, but would like to start getting ideas for two.

One is an RCA 6v6 (with black plate tubes in it) unit out of a suitcase style stereo record player which had 3 speakers. The wiring for the speakers was a joke, and this unit had two dissimilar output transformers. I don't even know what they were trying to do there. I simplified it and put in a pair of zenith OPTs from some SE el84 amp I had laying around that had a burned up power tranny. I also eliminated the common cathode on the 12ax7, and added a little feedback. The amp sounds ok. Much better than it did, but I would like to find a schematic for a REALLY good SE 6v6 amplifier that I can build on a new chassis using the iron I have here.

The second project was a really interesting disaster from the past, an el84 SE stereo amp with 3 OPTs.

Somehow they powered up three speakers by making a hybrid-- combining both sides into one larger P/P OPT and supplying the sound to the single bass speaker that way. Each channel has a tiny SE OPT that powered the left and right HF speakers. These speakers were apparently (on purpose) wired out of phase. Perhaps the different phase is how they powered up that P/P OPT for the bass channel. I followed a schematic I found online and converted it to a regular SE stereo amp. I added a small amount of feedback, this amp sounded HARSH (read: horrible). The feedback made it sound good. This one sounds good, except for some bass distortion, and a general poor low end. I'm certain that's because the output transformers are so tiny.

I know there are a million single ended EL84/12ax7 amps out there. Which one is the best?

Any schematics/links would be appreciated, as well as personal experience... ie.. has anyone on here actually built a 6v6 SE amp?

Furthermore... I keep reading here and elsewhere that people are against negative feedback for whatever reason.... But in the cases of both these amps that didnt have any they sounded horrible until I added it. Why is that?

I know this is a long winded post, and future ones should be shorter.

I'm interested in anything anyone has to say.. or suggestions.

Thanks...
Aaron Kimball
  Reply With Quote
Old 7th January 2007, 03:35 AM   #2
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Quote:
One is an RCA 6v6 (with black plate tubes in it) unit out of a suitcase style stereo record player which had 3 speakers. The wiring for the speakers was a joke, and this unit had two dissimilar output transformers. I don't even know what they were trying to do there.
Sounds like what was called a "matrix amp": it's a way to do stereo on the cheap. The results can be pretty good, if the design is done right. More often than not, the results weren't so good.

Quote:
This one sounds good, except for some bass distortion, and a general poor low end. I'm certain that's because the output transformers are so tiny.
That would be correct.

Quote:
Any schematics/links would be appreciated, as well as personal experience... ie.. has anyone on here actually built a 6v6 SE amp?
Try this: Power amp / integrated 6V6SE (DIY) The schematics - a design process walk-through

Quote:
Furthermore... I keep reading here and elsewhere that people are against negative feedback for whatever reason.... But in the cases of both these amps that didnt have any they sounded horrible until I added it. Why is that?
There's a whole bunch of audiophool nonsense out there, and this is but one example. NFB is not "evil". It may have gotten such a reputation due to the tendency of the "Big Box" designers using it to compensate for fundamentally poor designs. Used properly, NFB will improve any design.

As for your situation, pentodes almost always produce more of the nasty sounding third and higher order harmonics. SE amps that use low-u triode finals can sound pretty good with no NFB applied at all since triodes tend to produce mainly second harmonics, which aren't so objectionable as third and higher harmonics. Also, pentodes have higher r(p)'s, and so worse speaker damping. These require NFB if they are to sound good. However, even adding a few db's of NFB to a triode SE design can improve its sonics. (Of course, there is always the possibility that some folks like the effect of the added second harmonics that SE triode amps produce.)
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 7th January 2007, 06:28 AM   #3
poynton is offline poynton  United Kingdom
diyAudio Member
 
poynton's Avatar
 
Join Date: Mar 2005
Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)
Default Re: building Single Ended amps

Quote:
Originally posted by akimball442




These speakers were apparently (on purpose) wired out of phase. Perhaps the different phase is how they powered up that P/P OPT for the bass channel.
HI.

Usually, it is to give the impression of a wider soundstage and is quite common on 'BoomBoxes'. [Mono centre and anti-phase L/R]

Andy
__________________
If it ain't broke, break it !! Then fix it again. It's called DIY !
  Reply With Quote
Old 7th January 2007, 07:07 AM   #4
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Triode wired 6V6s sound VERY good. The O/P trafos you already have are quite suitable.

Simple circuitry along the lines of the DECWARE SE84 using a 5965 for voltage gain and triode wired 6V6s will work very well. High efficiency speakers are essential, as power O/P will be about 2 WPC.
__________________
Eli D.
  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
Building an ECL82 Single Ended Amp ... oodi Tubes / Valves 12 3rd June 2011 03:42 PM
System distortion and Single Ended Tube Amps Gerrit Boers Tubes / Valves 25 14th April 2010 10:55 PM
Creating a differential signal from a single-ended signal for bridged amps Peter Daniel Chip Amps 45 8th November 2004 12:47 PM
How to use single ended inputs with X power amps? Petter Pass Labs 4 27th February 2003 08:06 PM


New To Site? Need Help?

All times are GMT. The time now is 04:04 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