Getting DoZ to work - 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 27th December 2003, 08:02 PM   #1
rchua77 is offline rchua77  Singapore
diyAudio Member
 
rchua77's Avatar
 
Join Date: Jul 2003
Location: Back in Singapore
Unhappy Getting DoZ to work

Hello all,
apologies for the probably often asked question regarding the DoZ amplifier.
I hope someone would be able to help me.

I have a working power supply delivering 60V to the amplifier, but i'm unable to get the full voltage across the 10ohm safety resistor and ground. And when I measure the voltage of the output pin(speaker out), I'm unable to get the 1/2 supple voltage despite tinkering with VR1 and VR2.

I would appreciate any help rendered and apologies again for this often asked query.
  Reply With Quote
Old 27th December 2003, 11:30 PM   #2
diyAudio Member
 
Join Date: Jul 2001
Location: The Netherlands
There is a excelent forum of Rod Elliot at the website www.sound.au.com. Maybe you can try to get an awnser there too?

I think 60V is a very high supply. I wonder if the output transistor can handle that kind of power .. you need about 3.75A quensent current so the transistor dissipate 112Watt argggg that a lot!

If you can't get it to work, post again and I'll five you some DC-values to comparein your circuit. I'm sure we can get it to work,

Greetings,
Thijs
  Reply With Quote
Old 28th December 2003, 05:53 AM   #3
rchua77 is offline rchua77  Singapore
diyAudio Member
 
rchua77's Avatar
 
Join Date: Jul 2003
Location: Back in Singapore
New Update, solved the 1/2 voltage at the output pin and managed to get a 1V across the 1ohm resistor.

Now I'm wondering how to get about calculating the quiescent current for a supply voltage of 58.9V and with 29.5V at the output pins.

Anyone knows the calculations for a load of 4 ohm?
  Reply With Quote
Old 28th December 2003, 10:26 AM   #4
diyAudio Member
 
Join Date: Jul 2001
Location: The Netherlands
Hi,

Good to hear you got it to work! Can you tell us when was the problem?

Now tp calculate the the Iq

You will have about 28V peak in 4 Ohm, that's 7 ampere. But being a push-pull amplifier, Rod Elliot advises 0.75x the peak current: 0.75 x 7 = 5.25 Ampere..

Now beware: you are dissipation 315 Watts by now.. are you sure have you designed your amp to copewith that?

Goodluck,
Thijs
  Reply With Quote
Old 28th December 2003, 02:09 PM   #5
rchua77 is offline rchua77  Singapore
diyAudio Member
 
rchua77's Avatar
 
Join Date: Jul 2003
Location: Back in Singapore
I have two heatsinks each rated 0.52 deg C/W to mount each amplifier. I'm not sure if thats enough but they were the largest I could find.

Perhaps I should limit the voltage? By using zeners to regulate the voltage down to 20V ?? Any suggestions on how to do it?
  Reply With Quote
Old 28th December 2003, 02:23 PM   #6
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
You can use a capacitance multiplier as shown at http://sound.westhost.com/project15.htm
but add zener diodes to cut down the voltage.
This just spreads the heat across more transistors, as the heat you reduce from the amplifier transistors just goes to the power supply transistors.
Your power supply voltage is too high to run 4-ohm speakers with this amp. Not that it won't work, but the bias current will have to be set low enough so that your transistors don't get too hot. With a 60V supply, and say a 30C temperature rise, you will need to limit the bias current to about 1 amp given the heatsink you're using: 60V * 1A = 60W; 60W * 0.52C/W ~ 30C.
  Reply With Quote
Old 28th December 2003, 02:57 PM   #7
diyAudio Member
 
Join Date: Jul 2001
Location: The Netherlands
NO, those heatsink are far too small..

Your 60V is far too high to be practical. If I were you I use a different transformerand would go for a Vsupply of 24 Volt at about 2 Ampere Iq.

Goodluck,
Thijs
  Reply With Quote
Old 28th December 2003, 03:39 PM   #8
rchua77 is offline rchua77  Singapore
diyAudio Member
 
rchua77's Avatar
 
Join Date: Jul 2003
Location: Back in Singapore
A thousand apologies to all! My speaker load impedance is 8ohms. Duh silly silly me! I apologise for the mistake.

With a supply of 58.9V, and having it halved to 29.5V by VR1 and 8ohm load. What kind of Iq should I look at to produce 20watts or somewhere around there?

Would the increased load impedance make it easier to have a lower Iq with 58.9V? Whats the optimal Iq to bias the quiescent current for 58.9V considering my two pieces of 0.52deg C/W heatsinks?

The transistors i'm using are MJ15003 if it helps any. I would like to get a smaller transformer but my budget overstretched and this transformer was from a salvaged project.
  Reply With Quote
Old 28th December 2003, 07:37 PM   #9
diyAudio Member
 
Join Date: Aug 2002
Location: Farmington, CT
Send a message via AIM to Mattyo5
Ok....heres what I did. I had a DOZ w/ 8! output transistors in parellel PER channel. PS voltage was 52-53v. I had heatsinks that dissipated 150 watts of heat PER CHANNEL. quiescent current was about 3A. So, I had about 150wpc of heat ...and 50wpc into 8 ohms ...or thereabouts. If you are going to run that high of voltage...I suggest you get more transistors than just the pair you have there....and BIG heatsinks. You might also want to have higher voltage driver transistors. Actually, for the driver transistors I used the same output transistors...I was using 2sc5200's I think. Worked pretty good. Make sure the driver transistors are heatsinked. they'll get hot. Later!

-Matthew K. Olson
  Reply With Quote
Old 28th December 2003, 07:40 PM   #10
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
I would say that you will not get this thing to work long term with such a high voltage. For one thing my understanding is that the quality of the result increases with the quiesent current, so by reducing the current to at least half of its optimal value, it will decrease the quality of the output by half. If you are doing this type of amp for its audio benefits, then that got to be an unacceptable compromise. I run my Zen amp off a 12V AC transformer, and these are very similar amps. 24V would be a much better bet for you.

I would also guess that unless these 60V transformers are massive they might not have the VA rating for the job.

I got my 12V AC transfomer off ebay for about 10, so cost shouldn't be a real issue.

I hope this helps.

Shoog
  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
Would this work ? LesPaulStandard Instruments and Amps 3 4th May 2006 02:14 AM
Will This Work? sousmielie Class D 6 27th December 2005 05:53 PM
It Should Not Work ! f4bok Solid State 3 6th September 2004 05:33 PM
Would this work? JoeBob Solid State 5 18th July 2003 03:40 PM


New To Site? Need Help?

All times are GMT. The time now is 04:47 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