Hi Chris,
I have no clue how much less overload capacity the 3 x 2W carbon film/oxide source resistors will be. I assumed the wirewound would have a better overload ability. I am not sure how the 5W dimensioning was arrived and the consideration factors. The use of 5W has generally been standard for most Class AB amps of similar designs. I am not 100% sure, but I seem to recall once about a year or two ago running across a design that used 10W source resistors. I am not sure if this was needed per se or just a design being overbuilt. I cannot even recall if it was a Class A design or not, but my hunch is not.
I cannot order from Newark, but I have a look so I know what the specs are and make in case a surplus store happens to have some. One store I was in about 6 months ago had some Dale 5W non-inductive resistors, but not enough to make a module or two. That said I suspect the 5W non-inductive woudl not have the same overload capacity as the common wirewound.
The most demanding music I will listen to will likely be organ music, though older light pop and soft rock compressed dynamic range on the recording might be one other type of music that might cause greater demands on the source resistors. That said in the interest of safety margins maybe it is worth me using 4 or 5 2W carbon film/oxide resistors to cover some of the overload capacity a wirewound 5W resistor could handle. The cost will not really be all that more and in total not really that much different to using the wirewound 5W type. The modification to the PCB for 3-5 parallel source resistors will really not add much time to effect. Most of the time is effecting the change from 1 to 2. Beyond that it really only adds a small amount of time to the editing of the PCB with a graphics program. So one more edit to do on the ToDo list for the PCB. Some edits have been made as single edits to see if could be done. These single edits need to be merged into the base PCB collectively in hope will not take alot of time to merge.
Suffice to say when I have had the time to edit the PCBs there have been many hours spent keeping me form making comments on the thread
I can hear the chuckles and applause of many a happy diyAudio members!
To marus and all,
And for those wondering how the ressearch is going for the thread question on spec's for the quasi amp? It is going, but I had some technology problems the last couple days that did not allow me to spend any time continuing the thread reasearch. Just be aware this request requires me to quickly read each posting to see if proper reading is required to determine if there is related information. I am almost at Post 400 now. I take a summary of the information and put it in a text file I can later quickly edit and convert text to links for people to look back. I convert the text file as the last step once the research is complete.
Regards,
John L. Males
Willowdale, Ontario
Canada
08 February 2007 19:35
I have no clue how much less overload capacity the 3 x 2W carbon film/oxide source resistors will be. I assumed the wirewound would have a better overload ability. I am not sure how the 5W dimensioning was arrived and the consideration factors. The use of 5W has generally been standard for most Class AB amps of similar designs. I am not 100% sure, but I seem to recall once about a year or two ago running across a design that used 10W source resistors. I am not sure if this was needed per se or just a design being overbuilt. I cannot even recall if it was a Class A design or not, but my hunch is not.
I cannot order from Newark, but I have a look so I know what the specs are and make in case a surplus store happens to have some. One store I was in about 6 months ago had some Dale 5W non-inductive resistors, but not enough to make a module or two. That said I suspect the 5W non-inductive woudl not have the same overload capacity as the common wirewound.
The most demanding music I will listen to will likely be organ music, though older light pop and soft rock compressed dynamic range on the recording might be one other type of music that might cause greater demands on the source resistors. That said in the interest of safety margins maybe it is worth me using 4 or 5 2W carbon film/oxide resistors to cover some of the overload capacity a wirewound 5W resistor could handle. The cost will not really be all that more and in total not really that much different to using the wirewound 5W type. The modification to the PCB for 3-5 parallel source resistors will really not add much time to effect. Most of the time is effecting the change from 1 to 2. Beyond that it really only adds a small amount of time to the editing of the PCB with a graphics program. So one more edit to do on the ToDo list for the PCB. Some edits have been made as single edits to see if could be done. These single edits need to be merged into the base PCB collectively in hope will not take alot of time to merge.
Suffice to say when I have had the time to edit the PCBs there have been many hours spent keeping me form making comments on the thread
I can hear the chuckles and applause of many a happy diyAudio members!To marus and all,
And for those wondering how the ressearch is going for the thread question on spec's for the quasi amp? It is going, but I had some technology problems the last couple days that did not allow me to spend any time continuing the thread reasearch. Just be aware this request requires me to quickly read each posting to see if proper reading is required to determine if there is related information. I am almost at Post 400 now. I take a summary of the information and put it in a text file I can later quickly edit and convert text to links for people to look back. I convert the text file as the last step once the research is complete.
Regards,
John L. Males
Willowdale, Ontario
Canada
08 February 2007 19:35
anatech said:
Chris,
Thanks. I am not sure what the "Yeah, I know" is about, but if is anything about Electrosonic I have always found Electrosonic to be a great place. Let's just say I date back to Electrosonic was on Yonge St just south of Wellsely St on same east side as the days of Dominion Radio. Have I dated myself yet?
Regards,
John L. Males
Willowdale, Ontario
Canada
08 February 2007 21:09
Hi Chris,
Yes they were the fun days. Yes, Dominion Radio was a few doors south. Frankly speaking Dominion Radio was a much more interesting store and the one I spent most of the time in when in the area. I still have a clear memory of the store layout and the upstairs office area that looked over the main level. Electrosonic was and still is more like a catalogue store. Why I guess I like places like Active Surplus, A-1 Electronics, Sayal, et al.
I have lived in Toronto all my life. I still have the metal small mini meter I bought there and still have it in its box with the original test leads. Granted the box has some wear to it, but that is ok.
Have a good evening Chris.
Regards,
John L. Males
Willowdale, Ontario
Canada
08 February 2007 22:59
Yes they were the fun days. Yes, Dominion Radio was a few doors south. Frankly speaking Dominion Radio was a much more interesting store and the one I spent most of the time in when in the area. I still have a clear memory of the store layout and the upstairs office area that looked over the main level. Electrosonic was and still is more like a catalogue store. Why I guess I like places like Active Surplus, A-1 Electronics, Sayal, et al.
I have lived in Toronto all my life. I still have the metal small mini meter I bought there and still have it in its box with the original test leads. Granted the box has some wear to it, but that is ok.
Have a good evening Chris.
Regards,
John L. Males
Willowdale, Ontario
Canada
08 February 2007 22:59
Using ohms law and factoring in a duty cycle of 50% the average dissipation of source resistors can be calulated.
Example: For an A/B amplifier with;
- sustained rails of 70v
- driving into a speaker with an Re=3 ohms
- with 0.47 ohm source resistors.
The effective dissipation with a sine wave at full power (not clipping) is about 5.5 watts. So in every application other than bench testing the effective dissipation will be way below this.
In terms of surge capability, resitors in my experience do really well. As an example the 5 watt resistors in my slow turn on cct dissipate many times their rated capability for a brief period and are saved only by the closing contacts of a relay a second or two later. The resistors in my first application of this are still alive some 15 years later.
Even small resistors do really well, able to dissipate way beyond their rating for brief periods.
Cheers
Q
Example: For an A/B amplifier with;
- sustained rails of 70v
- driving into a speaker with an Re=3 ohms
- with 0.47 ohm source resistors.
The effective dissipation with a sine wave at full power (not clipping) is about 5.5 watts. So in every application other than bench testing the effective dissipation will be way below this.
In terms of surge capability, resitors in my experience do really well. As an example the 5 watt resistors in my slow turn on cct dissipate many times their rated capability for a brief period and are saved only by the closing contacts of a relay a second or two later. The resistors in my first application of this are still alive some 15 years later.
Even small resistors do really well, able to dissipate way beyond their rating for brief periods.
Cheers
Q
Hi marus,
-Chris
These days, it would depend on the resistor (actual construction). I would back away from this blanket statement and read the data sheet. I also like to design away from overloading any parts except in the case of inruch current limiting and possibly emitter resistors. Hmmm, maybe not with emitter resistors.
-Chris
Just finished my NMOS 10 FET version. So im planning now to buy a good toroidal transformer. Can anyone please specify me the specification on what rail this amp will give best performance.
The output devices i used are IRFP450’s. Can't find PF ceramic cap rating 100v, available in 25v, Possible to replace with some other type?
Also im much interested in Quasi Con, PA amp project “Another quasi-complimentry design”
Twice i send email on his account. But unfortunately haven’t responded to me.
Bushulo
The output devices i used are IRFP450’s. Can't find PF ceramic cap rating 100v, available in 25v, Possible to replace with some other type?
Also im much interested in Quasi Con, PA amp project “Another quasi-complimentry design”
Twice i send email on his account. But unfortunately haven’t responded to me.
Bushulo
Hi,
50Vac to 60Vac depending on what impedance you want to drive.
55Vac is the voltage that those isolating portable site transformers run at. Secondhand, they are pretty cheap even in 3kVA size.
Ceramic 100V are available, I wanted 150V and had to jump all the way to 1000V since my peak voltage was just above 100V.
50Vac to 60Vac depending on what impedance you want to drive.
55Vac is the voltage that those isolating portable site transformers run at. Secondhand, they are pretty cheap even in 3kVA size.
Ceramic 100V are available, I wanted 150V and had to jump all the way to 1000V since my peak voltage was just above 100V.
marus said:If I have protection to PSU should i also do DC-protection to Nmos200 amp ?
I think my PSU will have Softstart too ....
Quasi's 2 rules to DC protection;
Rule 1. Always have it.
Rule 2. Refer to rule 1.
You will burn your speaker voice coil if you get a fault and the amp latches to rail. It will burn quicker than you can turn your amp off after you've realised what was going on. So refer to rule 1.
You should build soft start in as well. Especially if your using a toroidal transformer.
Seeya
Quasi
Hello,
Today I finished my Soft-Start and DC-Protection boards. Therefore I crammed out my 500VA Trorroid (bought for another project about 3 years ago, it was never used).
When I connected the primary winding to the mains, I was again remembered of the enomous current surge of torroids. After that I noticed that my torrodial was humming a bit.
I never had a machanical hum with trorroids, is that normal?
Greetings,
Black
PS: Right now I am going to assamble my two NMOS200 boards...
Today I finished my Soft-Start and DC-Protection boards. Therefore I crammed out my 500VA Trorroid (bought for another project about 3 years ago, it was never used).
When I connected the primary winding to the mains, I was again remembered of the enomous current surge of torroids. After that I noticed that my torrodial was humming a bit.
I never had a machanical hum with trorroids, is that normal?
Greetings,
Black
PS: Right now I am going to assamble my two NMOS200 boards...
In these days, there are as many P device as N device, well I should say they are easily available too. As anybody ever thought of making use of these P devices that may be lying around somewhere in the dark corners of your drawers? Since we had brother of Quasi, may we start making a sister too? Or are these P devices natural-born=retards that could have no seats in this arena?