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Old 20th January 2006, 12:43 PM   #351
AndrewT is offline AndrewT  Scotland
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Hi Quasi,
that revised layout seems better.

to all,
is there any benefit:-
by relocating the bypass caps closer to the outputs?

by relocating the outputs and bypass caps at the extreme far end of the PSU PCB?

making the discharge resistor values higher and drawing less current from the PSU?
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Old 20th January 2006, 04:14 PM   #352
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Default Re[03]: LEDs

Hi Quasi,

Thanks for your reply about the LEDs. For the LED post Fuse I would connect it just after the fuse on amp module near the bypass caps so I believe the existing 0.1uF bypass cap will accomodate. For the pre fuse LEDs I will place near the PSU 0.1uF bypass cap. As these LEDs will need to be chassis mounted their wires could induce some artifacts over and above the LED itself so your suggestion of placing a bypass cap makes good sense.

I asked the question as I had no idea if "innocent" LEDs could introduce some artifact I had no idea about. I know red LEDs are at times used in amp circuits as a strickly a diode, not for status, due to the specific voltage rating red LEDs have. In that case I had no clue if other circuit elements directly or indirectly addressed such possible artifacts.

My my, your wife gave kitty a long name. I will not ask if you have to use a long name when you use your wife's name nor if such long names has your wife decided on for your kids . I had one cat who passed away a year ago October past. Her name was Chicago "White Sox". She was mostly black except for most of nose and the white feet with part of leg from foot all white. Ergo the name. That was her name when I adopted her. I wold often use "Miss" ahead of her full name, of "Miss White Sox". She also had a nickname of "Chico".


Regards,

John L. Males
Willowdale, Ontario
Canada
20 January 2006 12:15
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Old 21st January 2006, 03:38 AM   #353
quasi is offline quasi  Australia
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Default For Zeonrider - Quasi amp using 2N3773

From other thread

Quote:
Originally posted by zeonrider
- what do you think & how to put 2N3773 instead IRFP 240, because I, have 253 pcs original MOTOROLA (new)
This is the schematic modified to take high power bi-polar NPN transistors. Over the next few weeks I'll draft a PCB and post it in a new thread.

The PCB will limited to TO-3 devices because many DIY's seem to have plenty of these laying around.

Cheers
Attached Files
File Type: pdf nchan 300 bp 1v1.pdf (40.2 KB, 1865 views)
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Old 21st January 2006, 03:50 AM   #354
quasi is offline quasi  Australia
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Default LEDS

Hi John,

Sometimes LEDs are used in constant current sources in amplifiers.

The LED forward voltage (approx 1.8v for red LEDs) is used as the reference voltage for ccs transistor.

Cheers

All other members of my family are limited to 2 or 3 names and we generally only use the first name (except when more expressive names are required, like today if the kids don't get off their computer now, ......I mean right now!!!!).

Cheers again
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Old 21st January 2006, 06:54 PM   #355
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Default Quasi for KING !

Quasi for KING ! , Hmm. , not for king for" PRESIDENT" .This is just modern. Thanks Quasi, I am waiting for PCB. For me is beter separate PCB.s . Don't catch all fishis , just leave something for As,
when we came for new season of F1 in Melburn.
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Old 5th February 2006, 07:42 AM   #356
Danko is offline Danko  Hungary
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Default Soma questions about Quazi's amplifier

Hello!


I could buy IRFP260 for a very good price, so I plan to use them in Quazi's amplifier. The problem is, that the Gate-Source capacity of theese FETs is about 5nF.
If I paralell theese devices, the gate-capacitance will be so much, that the previous stage can't drive properly at high frequency. How can I solve this problem? If I "insert" a small current-amplifier stage just before the MOSFETs, will that be OK? Maybe, an emitter-follower?

Just for comparison, if it's required for my question:
IRFP260: Pd=280W, Cg=5.2nF, Id=46A
IRFP240: Pd=180W, Cg=1.3nF, Id=20A
IRFP450B: Pd=205W, Cg=2.9nF, Id=14A

And another Q:
What power ratings should be the "small" resistors? (not the ones series with the Drain, or Source)
I see only 0.6W types on theese pictures:
http://www.diyaudio.com/forums/attac...amp=1100430955
http://www.diyaudio.com/forums/attac...amp=1101456107
Can I use 1206 SMD resistors?
And what about the TO92 case transistors? Can I replace them with their SMD-version? (I hate drilling PCBs.... )

Is it possible, to implement a short-circuit-protection, without too much pain ?


Thanks in advance!
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Old 5th February 2006, 08:30 AM   #357
quasi is offline quasi  Australia
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Hi Danko,

Your problem could well end up being heat. Let me explain.

Whatever you do to drive the output stage harder will mean a lower impedance on the gates and this means more current. I.e. the current through the pre-output stage in the amp is normally around 18mA. With a rail to rail voltage of 150v this equals 2.7 watts, most of which is dissipated by the two transistors.

You could easily increase the current here (lower the impedance) by reducing the value of R20 and R22. Lets say you used 100 ohms. The current will now be about 40mA and the heat will be 6 watts, so a large heatsink is required plus T9 & T10 will need to be upgraded.

Adding another stage will not get away from this problem, you would just shift the heat somewhere else. In any case the second stage has plenty of gain and it could control a few hundred milliamps in the pre-drive stage so you do not need the extra stage.

If I were you I would just build it using the high power FETs and examine the waveform. I think you will be pleasantly surprised.

With respect to the resistors, 0.6 watt types are used throughout the amp except for the output source resistors. To check the actual dissipation for each resistor use ohms law calculations. The main current flows are shown here; http://www.diyaudio.com/forums/showt...662#post818662 ; post #325.

You can replace the TO92 transistors with SMD types, if you can find some with the ratings needed.

It is fairly easy to implement short cct protection. My idea is an optocoupler where the LED is used across an output source resistor and the optocoupler transistor is used to control protection, i.e. second stage shutdown, load disconnection, amp-off etc.


Cheers
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Old 5th February 2006, 09:14 AM   #358
Danko is offline Danko  Hungary
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Thank you Quazi, for the fast reply!


Quote:
If I were you I would just build it using the high power FETs and examine the waveform. I think you will be pleasantly surprised.
I gonna try this! Unfortunately tomorrow will start the spring-semester at the high school, so I will have almost no time for this

I will calculate the dissipation of the resistor's, thanks for the picture! I'm just busy now, with PCB manufacturing...

I will think about using an optocoupler as current-limit-detector. But, to tell the truth I have not seen schematics, using an optocoupler at this place.

Thanks, Quazi!
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Old 5th February 2006, 03:17 PM   #359
Danko is offline Danko  Hungary
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Hi!


I calculated the dissipation of all the resistors. I think, the 1206 SMD-components will be OK.

Here's the PCB layout:
http://sziget.mine.nu/~danko/aramkor...-06_171834.png
The blue line is an insulated wire. The copper is on the component side, so I can easily measure everything, and I can experiment with this stuff.

Here's the PCB:
http://sziget.mine.nu/~danko/aramkor...5/dscn8489.jpg
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Old 7th February 2006, 02:40 AM   #360
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Hi Danko,

Nice PCB you have designed. I see you go for the curve traces and round not square pads.

I have a few questions based on your PCB that are parts related if I may. I am not questioning any part of your decision in the below questions. I am asking in part to learn some things and/or to expand on what I have read/researched.

1) I see the "+" symbol about many of the parts on the silk screen. What is the significance of the "+" on the silk screen?

2) I notice you seem to use two capacitors to do PSU bypassing - 1uF with a 100nF in parallel. May I ask why you added the 1uF in parallel to the 100nF/0.1uF capacitor?

3) For T1/T5 you chose to use MPSA42's rather than 2SC1845s. Basic reason for choice?

4) I see you use two 0R47 resistors in parallel for the output device source resistor per output device. I know quasi has a preference to using 0R47 for these resistors, but indicated 0R33 on the schematic based on many comments. Of course with parallel 0R47 the effect is using 0R237. Why did you choose to use two parallel resistors for source, as opposed to using a single 0R22 resistor? Also, what is your reasoning to use 0R22 vs many who feel 0R33 is lower value to use in such suitations?

5) You have chosen to use 220uF for C11/C13, rather than 330uf? May I ask why? I am inclinded to use 680uF or 1000uF instead.

6) YOu have chosen to use two 1uF capacitors in parallel for C1? Your reason to parallel tow 1uF rather than use a 2uF (or 2.2uF)? Reason you perfer 2uF rather than 1uF?

As FYI I am likley to use APT2045BN's for at least the initial versions I make as they seem to have a nice balance of PD vs Ciss. I have been trying to select output decices with the best Ciss vs PD I can. For this reason I have some IRFP450 so I can benmark the stock design to using devices like the APT4025BN, and as happens mostly TO-220 devices. The latter of which have lower Ciss, but lower power output handling which for some casues is more than enough for the application needs. Like you I look at the overall Ciss loading of the number of parallel devices. I have been using the 3xCiss of the IRFP450 as my benchmark total of the output devices as well as a few other key parameters of a MOSFET to determine what will be on the shortlist to test and see if there is any improvement.

I do not have anywhere the knowledge quasi and others about here have. I do like to dabble in some inventive theory of my own for better or worse. I am patient sort, so I move along at tugboat speed The theory first of my own inventiveness and asking questions is the time consuming part. Then test out what I have learned and wish to validate or invalidate from my theory .

I am at the research/determine/find some parts still before I can do the test out part. The parts of focus for are not output devices, and for all intents are transistors. One major issue is sourcing some of the transistors used and/or alternates. I have already gathered a few different MOSFET types for initial comparison.

Danko, though the IRFP260 has some good Pd ability, but the T(off) time is really slow compared to T(on), about a 4/1 ratio that may lead to cross conduction issues in the upper audio frequency range. Most MOSFETs seem to have more of a 2/1 ratio of T(on)/T(off). The IRFP450 also has this 4/1 ratio Also the rise and fall times of the IRFP260 are about twice of the average MOSFET used for audio purposes, which may or may not be of concern for your intended use of the devices for this amp. The IRFP450 on other hand has rise and fall times about average for most MOSFETs which is twice as fast as the IRFP260. Just some thoughts to think about, not a negative at all to your choice or application/price/performance elements you have intended.

Danko, all the best to your chosen design varient. It will be interesting to hear what your thoughts and experiences are once you have the amp working.


Regards,

John L. Males
Willowdale, Ontario
Canada
06 February 2006 20:43
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