DCAudioDIY.com

DC Area Audio DIYer's Community
It is currently March 28th, 2024, 8:48 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 41 posts ]  Go to page 1, 2, 3, 4, 5  Next
Author Message
PostPosted: October 11th, 2015, 8:20 pm 
Offline

Joined: October 21st, 2013, 6:53 pm
Posts: 270
Hey All,

I was just curious what determines the exiting voltage at my speaker terminals on my EL34 Ultra Linear tube amp.

Are there any relatively easy mods that I can use to experiment with the voltage going to my speakers?

I was just puzzled why crossover caps come with 250V and 600V ratings, when it appears to me that most audio equipment doesn't produce that kind of voltage. Or does it, and I have just never seen that?

Wouldn't a change in voltage going to my speakers create a change in sound quality in some meaningful way?

Thanks,

Chris


Attachments:
001.jpg
001.jpg [ 528.81 KiB | Viewed 25096 times ]
Top
 Profile  
 
PostPosted: October 11th, 2015, 9:14 pm 
Offline
User avatar

Joined: July 24th, 2015, 4:17 pm
Posts: 1701
Location: Parkville, Maryland
Hey Chris!

The turns ratio of the output transformer determines output voltage. Having said that -- you might try trial listening comparing taps since the tubes are really more interested in the load on the plates. Sometimes say a speaker system with a nominal impedance of 4-ohms (typical) may perform better connected to the 8-ohm taps giving the tubes a plate load that better suits the tubes and enables better sound.

Further -- crossover capacitors with much higher dielectric working voltage for some reason sound better than their lower voltage peers. you can certainly use caps with a 50wvdc rating without a problem, but caps with say a 250wvdc rating from the same manufacturer can sound better in an audio circuit.

_________________
Walt


Top
 Profile  
 
PostPosted: October 11th, 2015, 9:49 pm 
Offline

Joined: October 21st, 2013, 6:53 pm
Posts: 270
Thanks Walt!

So you can't change the voltage by adding or subtracting anything before or after the transformer?
I kind of thought that's how it worked.

I have tried the 4 ohm taps but I like the 8 ohm taps better. An overused word, but better "fidelity", which to me means "sounds more delicate".


Top
 Profile  
 
PostPosted: October 12th, 2015, 6:47 am 
Offline
User avatar

Joined: July 24th, 2015, 4:17 pm
Posts: 1701
Location: Parkville, Maryland
The output transformer is just that -- a transformer. It isolates the high impedance high voltage (including the D.C. plate voltage) power tubes from the speakers and "transforms" the high voltage high impedance signal down to a low voltage high current signal suitable for your speakers. You are limited to the designed power output of your amps. You want more power? Bigger amps. will get you there.

Just keep in mind that if yo have a 50-watt/channel amp. now -- 100-watts only gets you another 3-db -- only a noticeable change in loudness. You want another 3-db? Say 6-db more than what a 50-watt amp can get you -- you are talking 200-watts. Get it?

_________________
Walt


Top
 Profile  
 
PostPosted: October 12th, 2015, 6:56 pm 
Offline

Joined: October 21st, 2013, 6:53 pm
Posts: 270
Hey Walt,

So the transformer lowers the voltage for the speakers. I wouldn't have imagined that. The bias on my output tubes is 300mV. Is the voltage higher somewhere else in the circuit?

This is where I break from other audiophiles: I'm looking for "richness", not SPL . It's kind of an elusive quality I have invented myself for something that doesn't seem to be explained by common audiophile knowledge.

When you think of sound as a combination of Frequency and Magnitude, I like to add another qualifier I call intensity, which is neither a change in magnitude or a change in frequency, but a change in "richness of the signal quality.

I'm not sure how to explain it in any other way, but I have developed it ALMOST as much as possible in my speakers, and I seem to think the next magic manipulation falls somewhere in the amplification stage.


Top
 Profile  
 
PostPosted: October 12th, 2015, 7:56 pm 
Offline
User avatar

Joined: December 14th, 2013, 2:19 pm
Posts: 948
Hey Chris. I am loathe to post here fire fear is I've again having it pointed out to me what a fucking moron I am.

But it seems you are getting bits and pieces of information.

Here goes. The voltage at your speakers is a function of the power you are putting into them.

The power formula is W = E x I or volts times amps. Substituting values from Ohm's Law, we can also say that W = voltage squared divided by the impedance of your speakers. And, Wattage equals Current squared times your speakers impedance. Apologies for errors here, I'm on a cell phone.


Top
 Profile  
 
PostPosted: October 12th, 2015, 8:01 pm 
Offline
User avatar

Joined: July 24th, 2015, 4:17 pm
Posts: 1701
Location: Parkville, Maryland
Hi Chris!

Pardon me for saying this, but you really should dig into some books on the subject. That said, what you are measuring is nothing more than voltage drop across the 10-ohm cathode resistors which represents 30-ma cathode current. You might try 38-ma for better sound. Your schematic shows that the plate voltage is 455-vdc. The primary circuit of your amp., which is typical, is a high impedance, high voltage circuit and the high voltage audio signal needs to be converted to a lower voltage and higher current signal for your speakers use plus the transformer blocks the high voltage DC from you speakers. Another thought. i have no clue why we call them tubes. The British call them valves and that better describes what tubes do.

_________________
Walt


Top
 Profile  
 
PostPosted: October 12th, 2015, 8:02 pm 
Offline
User avatar

Joined: December 14th, 2013, 2:19 pm
Posts: 948
So, if you have eight ohm speakers and you are putting sixty ways into them, then 60 x 8 = 480. The square root of which is 21.9. So you are putting 21.9 volts RMS into your speakers. Peak to peak voltage is 2.828 times that value or about 62 volts. That is the voltage the caps must withstand.


Top
 Profile  
 
PostPosted: October 12th, 2015, 8:04 pm 
Offline
User avatar

Joined: December 14th, 2013, 2:19 pm
Posts: 948
I completely agree with Soundmods. Pick up Morgan Jones' Valve Amplifiers. It's not an easy read but every moment reading that wonderful book is a revelation!


Top
 Profile  
 
PostPosted: October 12th, 2015, 9:35 pm 
Offline

Joined: October 21st, 2013, 6:53 pm
Posts: 270
I can look for that book, but as you can probably tell, I really need basic electricity first. The more elementary the better!

I have seen some good illustrated videos on Youtube. Any other suggestions?


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 41 posts ]  Go to page 1, 2, 3, 4, 5  Next

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 35 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group