Power amp under development

[quasi]

Hello Jmateus

You're starting to build quite a collection of amps there. I agree with you, "Brother of Quasi" the bi-polar version is going to be hard to beat in terms of sonics. This is especially true with your choice of Sanken output transistors. The mosfet versions offer more robustness especially the Nmos350 / 500.

Mostly the 3 variations of this design allows contructors to use parts they might already have or parts that can be sourced easily and with lower cost.

Congrats on a another succesful build.

Cheer

 

[marus]

Why Nmos200 don't have L1 like Nmos350 ?

 

[keypunch]

Hi Keypunch,

Yes, the actual core ring fix the VA. I'm not sure what formula is used on toroids ( i think it's the same) but at classical E+I cores it is : VA= core area^2. You can make any combination of current and voltage but the power is given by The Core

For isolation I use a thick paper hold it with electrical tape.

I just finished my 430W transformer for one Nmos350 amp 😀

An externally hosted image should be here but it was not working when we last tested it.

Hello Marus,

Thanks for confirming VA is fixed by the core dimensioning. I am not too worried what the related formulas are that fix VA to the core unless I could find some bare toroid cores to start winding on from scratch.

I understand rewinding a EI is quite the challenge and skill. From your pic of one EI you have modified you have done an excellent job. Keep up the good work.


Regards,

John L. Males
Willowdale, Ontario
Canada
22 September 2007 14:02
Official Quasi Thread Researcher

 

[keypunch]

Hi John,

Hi Ashok,

Thanks so much for your very informative and concise replies. My comments, questions and answers are below:

I used to have a transformer winding guide from long ago on cyclostyled sheets ( remember cyclostying ?) As they are falling apart I decided to put them on Word . This will take a few days . If you want I could email you a copy.

I am not familar with cyclosting. That said I do date back to knowing of and using 78rpm LPs. I am in no hurry for the document. If you are putting it into Word for your needs and when you have it completed and proofed I would be interested in a copy. Just let me know first so I can advise you where to eMail it to.

The core material ( determines max operating flux ) and cross
sectional area determines the max VA that the core can be used for. The basic operation is to take electrical energy , convert it to magnetic energy using the primary coils and then convert it back to electrical energy using the secondary coils. Hope the concept is clear. Larger core ... more VA can be passed through.

I am familar with the concept of a transformer, I was just not aware until now VA was fixed by the core dimensioning.

You can have any reasonable voltage and current combination as long as Volts x Amps does not exceed the VA rating of the core . There are losses etc but then we are simplifying the current situation. So 30 v x 2 is fine and you can have higher current flow than a 38.5 x2 coil. About 30% higher . This is if you wind a new secondary coil.

Question, if the toroid has a CT secondary is that one set of windings about the core once with a CT or two times about the core with the CT? If I wind the 30-0V additional secondaries onto of the existing secondaries I will be able to acheive the 650VA per the additional two newly wound secondaries without sigificant additional losses?

I mentioned 'options' because I do not know how your transformer is currently wound. Most have their secondary wound on top of the primary . You can see this if the wire is fairly thick. Primary wire will be much thinner.

It appears the secondary is wound atop the primary. The wire is fairly thick, my guess is about 16AWG. It appears there is one layer of the secondary wound about the core.

Since you need a 110 volt primary and the transformer already has this , you can unwind just the seconday coils . How is that wound ? Bifilar or a series connected coil ? Often it is just a series connected coil. 39.8 volts followed by another 39.8 volt coil and the center is brought out ( 0 Volt ). You could count the number of turns you are unwinding .When you reach the 0 Volt tap , you have the number of turns that they have used , say N turns. Your new coil will need N*30/38.5 turns per coil . That is for each 0 to 30 volts coil.

I would say the transformer is not Bifilar wound. Would the two 39.8 secondaries be wound about one at time about core so the lead out connecting leads can be at the same basic location of the toroid?

Your math makes perfect sense if I unwound the existing secondary. Personally I would count the turns as unwound to confirm my test winding calculations. I would want to use new wire when wrapping a new secondary.

The metal core will usually have a moulded plastic former on top of it . Better to be careful and not damage it if you intend unwinding all coils for some reason. You have a ready made primary coil and so there is no need to unwind that . Unless the primary voltage has to be different.

Agreed, I would keep the primary winding. I had mentioned unwinding the primary and secondary on the assumption I had of changing the VA rating. As you have noted the VA rating is fixed by the core dimensioning there would be no need for me to unwind the primary winding.

To check the wire guage , just wind 10 or 20 turns of a straightened section of wire on a pencil and measure the length of the winding. Divide by 10 or 20 and you will get the dia of the wire.

I did a quick test with a 20-0-20 toroid I have here. I decided to wrap more than 10 turns simply to reduce the calculation error for V/turn determination for the core. I also made sure the ends were twisted together to make it exactly complete turns and not missing part turns for the lead out. The result was for 14 turns the voltage was 4.44VAC. So the math is:

1) 4.44/14=0.3171428571428571429V/turn

2) Primary of transformer rated at 110VAC with the input AC measured as 122.6VAC

3) 110/122.6=0.8972267536704730832

4) 0.3171428571429*0.8972267536704730832=0.2845490561640643207V/turn

Therefore for 30VAC I need 105.5 turns for a 30V secondary.

The other options I mentioned have to do with adding windings to bring down the secondary voltage though the windings will not be "optimal" for that core.
You can add an 'extra' ( single ) primary winding to reduce volts per turn of the primary coil and that will reduce the secondary voltage. Current rating of the coil will be determined by the original seconday coils but might not matter for most audio use.

So that means you will have 'another' primary coil wound on top of the existing coils and add a layer of insulation and then wind your 75VA coils again on top of this one.

The new 'primary coil' will be connected in series with the original primary coil . The secondary coils will remain the same ( now 30 - 0 - 30 volts ) and you have a new set of 75VA coils . These are less optimum windings but should be able to do what you want without major surgery or loosing too much power .

I follow what you are suggesting as one of the many different options.

Addng coils without dismantling the transformer must be an easy way out ?

Personally; avoiding, removing or changing any of the existing windings is a definite preference for many reasons.

To avoid the addition the winding of a 'primary' coil again , you can wind less number of turns for the seconday and connect this out of phase with the secondary to reduce the votage. This means less number of turns to wind. Wind two independent sets of 9.8 volt coils and connect each with one section of 39.8 volt coil ( in series) and it will drop the output voltage to 30 volts.

Interesting idea and approach.

You need to use insulating mylar or leatheroid sheets between winding . You can use tape also but it should be able to withstand high temperatures. Normal PVC tapes are not recommended as they will soften ( and also get gooey ) very easily at say less than 100 deg C if there is a short circuit etc. I'm sure some good electrical tape will be available at a hardware store.

Thanks for this aspect of insulating. I will try to find insulating mylar. Plitron is about 20 minutes from me. Maybe I can buy some insulating mylar from Plitron.

The 39.8 volt coils are meant for high current use and it would be meaningless if you use it for low current use. Their coils take up a large amount of space . You probably will not be able to wind another set of high current 30 - 0 - 30 volt coils over that due to space constraints.........maybe. I don't know how big your torroid is.
Better to wind two 9.8 volt coils and connect out of phase to get 30 volts. Then wind the low current 30 odd volt set of coils which will have enough space.

Actually I do believe I have space to wind two 30-0VAC additional secondaries on the toroid without having to remove any existing insluating mylar or toroid windings. I think I would rather take that approach than remove the existing secondaries. I am not hard and fast about this, but I would think this makes the most sense for a number of reasons. My second option would be to remove the existing secondaries and then add the two 30-0V 650VA secondaries and the two 40-0V 75VA secondaries.

This might be getting a bit confusing .Want diagrams ?

I think I am ok with what you have written Ashok. I am sure I can figure out which way to connect the small out of phase secondaries if I need to use that approach. Personally I do not think in this case I will, but it is useful to know about the out of phase small winding option to reduce the secondary voltage.

Cheers,
Ashok.

To Anyone,

One more question if I may. I have some toroids that have some sort of epoxy filling the centre hole of the toroid. Could this centre epoxy be removed easily so I could add some windings to these toroids? This of course assumes it makes sense for other reasons to consider removing this centre hole expoxy.


Regards,

John L. Males
Willowdale, Ontario
Canada
22 September 2007 (16:45 -) 17:58
Official Quasi Thread Researcher

 

[keypunch]

Splitting Supply Rails of Output Stage from Input/Driver Stage

Quasi,

What I need to know is what the current or VA requirement for a single NMOS350/500 input/driver stage will be so I can properly dimension the added secondary windings I wish to add or will use in lieu of the added 30-0VAC secondary windings I am adding to some toroids of interest? This way if the toroid modification idea I am trying works out, I will also add secondaries that will supply the input/driver stage. In this case I will need to know the VA dimensioning requirement for one NMOS350/500 module so I can properly dimension the new secondaries I add to the existing toroids I have.

I believe I have a reasonable option in terms of space and cost to be able to run seperate supplies to the modules. It was my orignial intent to do so, but from the same transformer feeding different PSU circuits. I also had been thinking of regulating the rail supply to the input/driver stages. This was was more about keeping the supply sagging for the output stage isolated from the rest of the module. It was not really about trying to drive the output stage closer to the rail voltage.

I really do not think I need more than 100WRMS per module and the availability of electrolytic capacitors above 63V locally is also a challenge or very costly for the number and manner I wish to configure the output stage PSU for the modules I want to build. Also there is a MOSFET I really like that only has a Vdss of 100V which also limits my output supply rails to abou 33VAC at best. So I am considering buying some 650VA 39.8-0-39.8VAC toroids which I will add two 30-0VAC secondaries to use to supply the output stage of the module and use the existing 39.8 secondaries to supply the input/driver stages. I know I will not be able to have the output stage swing fully rail to rail. I will have these higher voltage secondaries to enable me to feed them to a regulation circuit and with the higher voltage after the regulation help me reduce some of the output stage related losses that a single supply configuration has.


Regards,

John L. Males
Willowdale, Ontario
Canada
22 September 2007 (18:20 -) 18:56
Official Quasi Thread Researcher

 

[keypunch]

Hello Quasi
and guys at large

After a few months of doing the BJT brother of Quasi I finally finished
the Nmos 200 that I had thought to assemble just for comparison.
Unbelievable the way your designs are, they function at the first attempt there are no flaws or mishaps whatsoever, the results are
right there and sonically evident.

Great to add to the list of reasons why the Quasi designs are so excellent.

I built a few amplifiers in the past few years and for one reason or another I always had little problems to contend with, especially
dealing with complementary designs. Some were thrown out the
window either because they didn't work or the results were less
than optimal.

I agree. I did not built a few other popular designs partly due to fake parts issues generally related to the output drivers, but also some quasi-complementary (no pun intended quasi) designs that had obvious to my very simple amp design knowledge or stability problems many builders had. Some of the builders were very seasoned.

Not with your designs Quasi, they work at first attempt with the quality that surpasses by large all the others.

Again so wonderful for you to articulate your experience with the quasi designs.

And even though I'm not a big fan of Mosfets I did this one just
for the sake of comparison. I used IRF 450, they were what I
had at hand, the quality is excellent, however there is no love like the first one and I really prefer the BJT version.

I read so much about BJT vs MOSFET it is so hard for me to compare. I suspect I will built a BJT pair to let me compare the MOSFET vs BJT preference camps.

What I like about the quasi designs all of them, MSOFET, BJT and Class A are basically the same except for the output stage and/or slightly different driver stage to that is part and parcel of the output stage. Still despite these small differences the designs are for all intents the same making the quasi designs truely the only designs that can enable a person to compare MOSFET vs BJT vs Class A as comparing Red Delicious Apples to Five Pointer Apples to Macintosh apples.

Happy to have embarqued in these projects and thanks for your
interest in the DIY community providing it with these true quality
designs.

jmateus, thanks so much for you sharing your experiences with your quasi experiences. Much appreciated.

Hi Andrew T

This is a very interesting question....
And to be very honest with you I almost don't remember how the
Cyrus sound like because it has been almost a year that I don't
turn it on.

From what I remember it seems that the Cyrus is a very sweet amplifier being only comparable with the tube sound, whereas
the Quasi BJT has a little more impact as far as crescendos are
concerned. Both amplifiers pleased me a lot but that question
(thanks for it) gave me the urge of installing the Cyrus again in
my system. I'll do it soon and perhaps I'll get back to you.

If you have the time and can acticulate the comparison with the Cyrus I am sure many here would appreciate your always balanced evaluations.


Regards,

John L. Males
Willowdale, Ontario
Canada
22 September 2007 (19:00-) 19:17
22 September 2007 19:29 Typo correction. jlm
Official Quasi Thread Researcher

 

[quasi]

Hi John,

In theory the size of a power transformer in VA should be about 1.5 times the total power output of the connected amp modules. I.e. if the combined power capability is 500 watts then the transformer should be rated at 750VA. But music is nothing like this and unless all amp modules were to be under test conditions at the same time for extended periods then a small transformer can be selected.

In my build I used a 500VA transformer to power 2 x Nmos350 modules. These deliver around 210 watts into 8 ohms and so I should really be using a 600VA transformer. I have also run this amp into 4 ohms and the transformer barely gets warm. This is because the duty cycle of music is quite low.

So I would just match the VA rating of the transformer with the combined power output capability of your amplifier modules. Under music conditions this transformer will still be cruising. Make sure though that your DC filtering section is large.

Cheers
Q

 

[keypunch]

Hi Quasi,

Thanks for your reply. I guess I was not clear on what I seeking a VA rating for. I wanted to know what the VA rating for only the input/driver stage when one uses two supplies to supply one module? One supply for the output stage, and one supply for the input/driver stage. Is it a simple matter of adding up the current flows of 1.3mA + 1.3mA + 12.6mA + 18.1mA = 31.3mA. So would 50ma be sufficient for the input/driver stage?

I will run the supply for the input/driver stage at a higher voltage to reduce some of the losses when running a single supply configuration and to enable regulation of the supply for the input/driver stage. I know and do not intend to try to run a higher supply voltage for the input/driver stage to reach full rail to rail swing of the output stage as I know this design will not be able to do so.


Regards,

John L. Males
Willowdale, Ontario
Canada
23 September 2007 07:32
Official Quasi Thread Researcher

 

[jmateus]

Hi John
I had to do it!
Today I installed my Cyrus clones (2 monoblocks) back in my system.

I can't describe what I felt when I started listening to the music through these amps. I mentioned before the tube sound like I heard
when I first turned on these amplifiers right after being built. However these impressions didn't last long cause my urge was to build the next amplifier that was on the conveyor belt, so to speak.
(These urges lasted for some time, I was looking for the best amplifier I could build).
And...I really forgot to listen to its quality first and analyzing the music after.
So being I only had a chance to evaluate the Cyrus clone today,.
I was simply amazed with its quality, besides the kind of tube like
sound I experienced before, which I confirm, there is a sense of depth
difficult to describe, a magnificent soundstage (perhaps due to the
2 monoblocks) and a degree of detail only paired by the Quasi BJT.

Comparing the two amps? I don't know if I can but I'll try.
There subtle differences, yes, there are.
Detail and transparency are common to both.
Soundstage, Cyrus is the winner.
Bass, I prefere the Quasi BJT.
Dynamics are a little better on the Quasi, but not much
Sweetness, Cyrus wins
Attack on crecendos, Quasi wins.

But by no means, they are both winners and I wonder why did I wasted before money and time assembling other amplifiers when I had two jewels around which at the time I didn't pay too much attention?

This only proves my point, the quasi complementary topologies sound much much better to me.

I used only 3 CD'c in this critical listening:
Diana Krell, love songs
Joe Califano, instrumental flamengo like rumba with lots of acoustic guitars.
Jose Salinas, an argentinian jazz acoustic guitar player.

Unbelivable!

 

[keypunch]

Re: Post #2369

Hello jmateus,

Thanks for your comments re Post #2369.

Do you know if the Cyrus clones have a seperate regulated supply for the input/driver stage? One builder has commented on the NMOS350 that providing a seperate supply, which was unregulated "... I find that isolating the Front End almost always cleans up the Bass and Mid/Bass resulting in a more resolving Mid band; it was the same case with this amp." I know I have read others commenting on the rational for using a seperate front end/driver supply was also increased soundstage, but in those cases they used a regulated input/driver supply instead.

I assume you used one Bridge/Filter/PSU for both BJT modules?. I think you might find a noticable improvement using two dedicated Bridge/Filter/PSU circuits so each amp module had a dedicated Bridge/Filter/PSU even though they shared a common transformer? If you did, I am not sure having seperate transformers for each quasi amp module would make as big a difference as using a regulated supply for the input/driver stage and a dedicated Bridge/Filter/PSU for each module. I believe most builders of the quasi NMOS designs have used a dedicated Bridge/Filter/PSU circuit for each amp module.

You are using a toroid for your transformer for the "Brother of Quasi". For space reasons and because you are using a toroid you may want to add an additional CT secondary or two secondaries to your toroid and then a simple unregegulated Bridge/Filter/PSU circuit for each and split the PSU traces between the BJT output devices and input/driver stage and connect the dedicated unregulated PSU to the input/driver side of the split PSU rail traces. If you like the sonic improvement of a seperate PSU for the input/driver stage maybe later you can decide if you like to use a regulated PSU circuit instead for the input/driver stage. Samuel described in "4)" his simple unregulated PSU he used for the NMOS350 that I think would be a good starting point for your "Brother of Quasi" version as well as you adding in a second Bridge/Filter/PSU so you have one Bridge/Filter/PSU per amp module.

Again thanks for takeing the time to compare the NMOS design, "Brother of Quasi" and Cyrus amplifiers you have. Of as FYI, you might find if you built the NMOS350 instead of the NMOS200 there might be less differences to the "Brother of Quasi" version. The NMOS200 does not have as much rail filtering and you may have used different transistors for the LTP than are in your "Brother of Quasi" version, if that is case might also account for some of the sonic differences. Just a thought, I cannot say for sure. I just know the more variables the more possibilities.

I am sure you will be enjoy listening to your music.


Regards,

John L. Males
Willowdale, Ontario
Canada
23 September 2007 (12:10 -) 13:19
23 September 2007 13:39 Typo correction. jlm
Official Quasi Thread Researcher

 

[jmateus]

Hi John

I've used separate supplies as the Cyrus amps are monoblocks,
obviously. They are Bridge/Filter only and I couldn't use regulated ones
as didn't have space in the boxes for that. It's possible that these regulators would improve the sonics... BTW both have toroids, 35 + 35 V AC.

The Brother of Quasi has a regular EI transformer, a monster of iron
let me tell you. I had a chance to post some pictures before.

Yes, John, I'm enjoying my music, that's for sure.

However if I have the patience I'll be considering to improve both supplies, I've regulated my big JLH and the results are clear, so I
understand the benefits of a regulation. But lately I'm a little tired of building amplifiers, as Quasi said in his post I have quite a collection of completed projects and I really don't know what to do with them,
once in a while I swap amplifiers in my system and that's what I can do.
They take a lot of space by now! Besides I have a feeling that I have attained the end of my endeavors as far as sound reproduction is concerned.

To summarize I have very good sound...and I am a little tired,
moneywise too! Eh,eh,eh.

 

[anatech]

Hi jmateus,
Well, if you like those Cyrus amps ....

The new X series are much better amplifiers. That's progress for you. It's neat that you built the older design as mono blocks. They probably perform better than the originals could.

Hi keypunch,
The Cyrus amplifiers normally run everything from one supply. Running the voltage amp stage from regulated supplies make a huge improvement. Cyrus also offered the PSX series outboard supplies. They were regulated and did improve sound quality as a result. Given they were higher voltage increased the power output also. Toroid transformers are the only thing that will fit in the case that Cyrus likes to use. I prefer EI cores.

-Chris

 

[keypunch]

Re: Post #2371

Hi jmateus,

Regarding your Post #2371.

Your "Brother of Quasi" amplifier I thought you used a toroid based on your Post #1645. Based on your comment in Post #2371 the toroid I saw was just to test/check out your completed "Brother of Quasi" amplifier. Sorry for my assumption.

What is most important is you are enjoying the music. In the end this is what it all about.

It seems from all the reading I have done, with few exceptions, agree regulating the input/driver amplifier stage improves things over one common supply for the input/driver and output stage. All the more motivation for me when I build my quasi amplifiers to use a regulated supply for the input/driver stage. Add one more modification on my To Do list of the PCB. Also I need to sort out the best voltage to choose for the regulation as the NMOS design had some challenging issues when used with seperate rails 10V above the output device rails.

I assume you have built more than the JLH, Cyrus, "Brother of Quasi" and the NMOS200? I have not had the chance to build any quasi's partly as I have been on a learning curve, the manual edits I have been making to the PCBs, other addons I want to do at same time like Balanced, VU Meter, enhance the DC and Slow Start circuits that add research and discussion time. I have also struggled with getting certain transistors, which is basically done with now. The remaining parts challenges have been PSU electrolytic capacitors of at least 80V, case, sorting out how to implement the regulated element both in terms of where the supply will be from and the actual circuit to use. Added to this I have had some major personal matters taking me from many interests for extended periods of time. I have to assume you had some of these and/or the time it takes to find all the parts required, the time and care it takes to build including you taking time to design your own PCBs. If you have built more than 4 stereo amplifiers I can well imagine how much time this has required of you. If yoiu have built mroe than 4 power amplifiers I guess you have been doing so for a few years?

At least now you have the time to relax and enjoy the music. I would think you may want to do so before you embark on making the PSU modifications you are interested in. I also think by taking a building time out and settling on your amplifiers you will better understand the sonic changes of the PSU enhancements you wish to do that you feel have been work the effort in past and in general opinion.


Regards.

John L. Males
Willowdale, Ontario
Canada
25 September 2007 (17:35 -) 18:12
Official Quasi Thread Researcher

 

[keypunch]

Hi keypunch,
The Cyrus amplifiers normally run everything from one supply. Running the voltage amp stage from regulated supplies make a huge improvement. Cyrus also offered the PSX series outboard supplies. They were regulated and did improve sound quality as a result. Given they were higher voltage increased the power output also. Toroid transformers are the only thing that will fit in the case that Cyrus likes to use. I prefer EI cores.

-Chris

I seems jmateus was wise to make his Cyrus's mono blocks.

It seems from all the reading I have done, with few exceptions, agree regulating the voltage amplifier stage improves things over one common supply for the voltage amplifier stage and output stage. All the more motivation for me when I build my quasi amplifiers to use a regulated supply for the input/driver (voltage) stage. Add one more modification on my To Do list of the PCB. Also I need to sort out the best voltage to choose for the regulation as the NMOS design had some challenging issues when used with seperate rails 10V above the output device rails. The only reason I like to use higher voltage amplifier rails is with the 20-0-20 and 25-0-25 toroids I have that I like to build some NMOS amplifiers for. Maybe I will end up building the "Brother of Quasi" instead due to the lower losses with BJT designs.

I have read the odd time some builders have a preference for EI rather than Toriods? Can you advise me what your reasons are to prefer the EI over the toriod?


Regards,

John L. Males
Willowdale, Ontario
Canada
25 September 2007 (18:14 -) 18:24
Official Quasi Thread Researcher

 

[anatech]

Hi John,

Add one more modification on my To Do list of the PCB.

Nope. Just break the circuit at the filtering stage (if there is one). Or you can simply break the copper trace and build another PCB for your voltage stage supply.
That way you can adapt it to other amps.


I find EI cores to be less susceptible to a whole host of line borne noise. You can also cool the core against the chassis. Effective DC offset in the line has less effect on noise also.

Toroid type transformers do have a different form factor (lower height on average), but they suffer from a large inrush current it seems. They also tend to cost more. No thanks! This when they don't buy me anything but problems compared to an EI core.

I never did understand the rush to promote toroid transformers. It was mostly a marketing thing.

-Chris

 

[keypunch]

Hi Chris,

Making a break in the PCB is easy to add a regulated voltage stage supply and easy to do in the PCB image as an edit. What takes a bit of time and effort is adding in the additional space for PCB electrolytic rail bypass capacitor. The rest of the voltage regulator would of course be on its own seperate PCB, therefore would no emcumber any amplifier module.

I was unaware EI transformers were "less susceptible to a whole host of line borne noise" compared to toroids. I suspect EI cores can have high inrush currents when their cores are much bigger. As I recall for the same VA rating the EI core is usually larger than for the toroid version, but I am not so sure this is all that big a difference.

Cost wise for me I have found toroids in the order of 1000VA for $20.00 so it made sense from cost perspective to buy the toroid. 500VA and 650VA toroids have shown up for about same price or bit more as well. I have not see a EI yet with the same VA capacity in surplus so far.

I will say the toroids generally lend themselves to making it much easier to add or remove winding if the rare need arises. In my case than goodness for the toroid. The 1000VA toroids I have have some sort of expoxy in the centre. My guess is to enable the toroid mounting to be physically better given the large size and weight of a 1000VA. I wish I knew if there is an easy way to remove this expoy centre as I there would be excellent to rewind their secondaries down to in the 30-35V secondary range plus add anotehr secondary for the regulated voltage stage. These toroids are currently 44-0-44. This would result in amplifiers of about 150WRMS, which is a bit more than I need for mid and high frequency amplifers in an active system. Ideally amplifiers of about 100WRMS would be fine for my needs. The biggest reason is it is far easier and less expensive to find electrolytic capacitors for the PSU if I can use 63V rated electrolytics.

I need to build at least 21 amplifiers, likely 27 to meet the active crossover configuration for a 7.1 system that also has a Yamaha DSP-1 and DSP-3000. For a 5.1 based HT system this of course means 15 amplifiers and with the DSPs means 21 amplifiers. This as you can appreciate greatly amplifies the cost due to the number of electrolytics for the PSUs.

The Yamaha DSPs have normal front and effects front which adds an additional stereo pair to the standard HT 7.1. There is a setting on the DSPs to merge front stereo and front effects L and R respectively, but even with active crossover based fronts ther eis some clarity issues as summing front effects and stereo is sort of like an IM signal to the amplifier and speaker.

As always Chris you have excellent insight and experience to share. Thanks for your comments on your preference for EIs.


Regards,

John L. Males
Willowdale, Ontario
Canada
25 September 2007 21:21
Official Quasi Thread Researcher

 

[quasi]

Why Nmos200 don't have L1 like Nmos350 ?

Hi Marus,

The output coil has two functions.

1. It presents a high impedance to any RF that may appear on speaker lines.

2. It can offer some compensation to highly capacitive loads.

It has been left off the Nmos200 mainly because of a lack of room and in my experience can be left off for the application the amp is intended for. A coil can be inserted if desired in the wiring to the speaker terminal where it may help with very long speaker leads or difficult speaker loads.

CHeers
Q

 

[anatech]

Hi John,
Toroid transformers have a higher frequency cutoff than EI types. This works against you when designing a supply to keep the hash out. Due to the fact that there are no air gaps in a toroid (that naturally exist in an EI), they saturate more easily as well.

Normally when I am shopping for transformers, the toroids are more expensive. Your $20 price sounds pretty good to me.

-Chris

 

[AKSA]

Chris,

I agree 100%. Engineering says EIs, market says toroids.

One disadvantage I've found with EIs is that they have substantial external magnetic field at low power. This can interact with the case, causing vibration. Toroids do not do this, but man, that inrush is difficult to accomodate, and DC on the mains is not tolerated at all. And occasionally you get one which rattles, and only replacement will silence it.

Hugh

 

[AndrewT]

.......I find EI cores to be less susceptible to a whole host of line borne noise. You can also cool the core against the chassis. Effective DC offset in the line has less effect on noise also.

Toroid type transformers do have a different form factor (lower height on average), but they suffer from a large inrush current it seems. They also tend to cost more. No thanks! This when they don't buy me anything but problems compared to an EI core.....

Hi,
a soft start using a relay bypassed resistor on the primary supply removes the inrush difficulty and also allows a close rated mains fuse to be fitted. This ends up better than an EI without a soft start.

A DC blocking cap in the primary feed completely cures the susceptibility of the toroid to saturation in normal operation. Again this solution results in better performance than an EI without DC blocking.

Both these solutions cost only a small sum in comparison to the transformer cost. If both "improvements" were fitted to a big EI, then it costs nothing extra financially nor in board space for either type of transformer.

What are the other insurmountable problems that make an EI better than a toroid?