diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Pass Labs (http://www.diyaudio.com/forums/pass-labs/)
-   -   Single ended solid state amplifiers? (http://www.diyaudio.com/forums/pass-labs/127806-single-ended-solid-state-amplifiers.html)

fotios 9th August 2008 12:01 AM

Single ended solid state amplifiers?
 
Because i haven't any reply, yet, about my query what is the single ended solid state amp. then i can proceed in my assumption that is an amplifier with single supply rails. Obviously is the old fashioned method and it needs a big cap in output for blocking the dc part.
Maybe my thought it is foolish, but if we implement two single ended output channels each one with opposite supply and driven by opposite voltage gain stages, then by bridging them, we can obtain an output with eliminated dc part. The gnd node also it is not used in the load return path.
Sorry if my input has nonsense.

Fotios

Jeb-D. 9th August 2008 12:47 AM

Yes, approaches like that have been taken. Look up circlotron, it has mostly been applied to vacuum tubes, but the concept will work for transistors as well.

Of course, bridging two single ended amps means you no longer have a single ended amplifier ;) It is horizontal push-pull.

The benefit is that you don't have to use any complementary or quasi-complementary devices.

woody 9th August 2008 03:43 AM

Fotios, look at the Passdiy web page and read his articles this
should explain single ended amps. Many single ended amps
do use + and + voltage supplys and no output caps for example
look at the Pass Build a class a amplifier article or one of the
Alph amplifiers they are single ended yet have no output caps.

fotios 9th August 2008 06:35 AM

Quote:

Originally posted by woody
Fotios, look at the Passdiy web page and read his articles this
should explain single ended amps. Many single ended amps
do use + and + voltage supplys and no output caps for example
look at the Pass Build a class a amplifier article or one of the
Alph amplifiers they are single ended yet have no output caps.

Hi woody
Thanks for the suggestion. A have looked already the articles in fast, and i know the method for eliminating the output cap. proposed from Nelson Pass. My query in reality is around the symmetrical gain stages reffered by Nelson Pass in my other thread - about merging single and balanced input signals in the same stage - where there is a brief explanation from Nelson about his approach.

Fotios

fotios 9th August 2008 06:58 AM

Quote:

Originally posted by Jeb-D.
Yes, approaches like that have been taken. Look up circlotron, it has mostly been applied to vacuum tubes, but the concept will work for transistors as well.

Of course, bridging two single ended amps means you no longer have a single ended amplifier ;) It is horizontal push-pull.

The benefit is that you don't have to use any complementary or quasi-complementary devices.

Also the need of the output capacitor it is eliminated.

Thanks for your lights

Fotios

Jeb-D. 9th August 2008 04:37 PM

Quote:

Also the need of the output capacitor it is eliminated.
Oh, of course :D I forgot the best part.

fotios 10th August 2008 08:52 PM

Quote:

Originally posted by Jeb-D.


Oh, of course :D I forgot the best part.

You know something Jeb?
I start to understand an inexplicable thing to me for many years. I have seen many monoblock amplifiers builded with double heatsinks, one left and one right as in stereo amplifiers. My query was why the constructors shared the PNP transistors in the one heatsink and the NPN transistors in the other heatsink because i consider the thermal coupling of output devices in symmetrical designs indispensable. How they can obtain this coupling in so much distance between the heatsinks? Maybe the answeer it is found in the single ended - bridging of the two independend pcboards (that you reffer as horizontal push-pull). I don't know if my thought it is correct, and i ask your comprehension for my ignorance if exists.

Fotios

woody 11th August 2008 11:57 AM

I haven't ever seen this but here is a thought. If the heatsinks
were insulated from the chassis the transistors could be mounted
without insulators. Mounting the output transistors directly to the sinks without insulators would let the transistor run cooler at the
expense of having those sinks electricaly hot!

fotios 11th August 2008 07:29 PM

Quote:

Originally posted by woody
I haven't ever seen this but here is a thought. If the heatsinks
were insulated from the chassis the transistors could be mounted
without insulators. Mounting the output transistors directly to the sinks without insulators would let the transistor run cooler at the
expense of having those sinks electricaly hot!

Hi woody
You may consider as a syntax error in my previous post where i said "many". I meant "some".
As for those you refer; Indeed there are amplifiers in which the heatsinks used also to supply the output transistors mounted on them without insulating wafers. An example are the Peavey CS-400 to CS-1200 series of amplifiers. In these, the PNP and NPN TO3 output transistors are mounted in seperate heatsinks which of one provides the + Vrail and the other the -V rail, but the heatsinks are arranged in series and very close the one to the other. Of course these amplifiers are for P.A. use and unrelated with Hi-End devices. Because their output it is fully complementary and biased in class AB, there is the need of simultaneous thermal track of both sides from the bias network to keep the iddle current equal per each side. For this purpose, it is used a smart arrangement of some double and simple diodes connected in series between the bases of predrivers. Half of diodes are mounted in one of the two heatsinks and the rest in the other, but the distance between them it is very small, less than of 1". This scheme it is very effective and can be realized also with transistors.
I think that this bias arrangement would be defective if the distance between heatsinks was big such as in each side of the case.
Instead in the mode of two single ended - bridged channels, this can be done with succes because each channel has its own bias network.
Also, we must not forget that the bias network don't offer only the appropriate quiescent current for the corresponding class of operation; it also offers thermal compensation of the current to keep the output devices safe from thermal runaway.

Fotios


All times are GMT. The time now is 10:14 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