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post #8956 of 9592
post #8957 of 9592
Quote:
Originally Posted by b1o2r3i4s5 View Post

Even though the beta22 itself IS a discrete op-amp? rolleyes.gif

 

Overkill is my middle name wink.gif

Nah, a truly good amplifier should be able to drive anything from sensitive IEMs all the way to Speakers right?

 

Nobody gets my subtleties, congrats. 

 

I lean towards the school of thought that headphone amps should be "high power pre amps" not "low-power speaker amps."

 

There is something to say for both design methods, but I prefer an elegant solution to brute force. 

 

Quote:
Originally Posted by samsquanch View Post

I'm a fan of Jensen Transformers, but that might just be because I've worked with them more than any other company, it's funny how we form favoritism like that...

 

http://www.jensen-transformers.com/ln_in.html

 

 

Cinemag also makes well regarded 10K:600 transformers, for a bit less money. 

 

Edcor is another option, but the more expensive options are probably worth it... 

 

Quote:
Originally Posted by b1o2r3i4s5 View Post

 

And TBH, toroidal transformers provide some degree of self-shielding in the first place, the electromagnetic radiation coming from the transformer is probably very small compared to other current-carrying wires in the system.

 

With that said, I cannot empirically prove that what I just said is correct because I don't have the necessary equipment to do so. If you just happen to have a EM radiation meter laying around then by all means, take some measurements of toroidal transformers when they're operating and see if they will cause EMI in amplifiers. wink.gif

 

Toroidal transformers do leak EMF - just not as much as EI transformers.

When the transformers saturate due to DC on the mains or operation at or above rated power all bets are off. 

When EI transformers leak EMF they do so quite predictably even when they saturate. It is easy enough to spin a toroid to quiet hum in normal operation but when toriods saturate they spew EMF everywhere. 

 

The 2-box B22 was a very popular solution to transformers leaking EMF into what should have been a quiet amps. The issue with the 2-box B22 (or even one-box if you're not careful) is that DCR and inductance between the power supply and amp boards has been linked to a few B22 failures. 

post #8958 of 9592
Quote:
Originally Posted by nikongod View Post

 

I lean towards the school of thought that headphone amps should be "high power pre amps" not "low-power speaker amps."

 

There is something to say for both design methods, but I prefer an elegant solution to brute force. 

What's the difference? confused.gif

post #8959 of 9592

Here's a little something silly I built, it's simply two pairs of rca's with a resistor placed across each channels signal and ground.  I'll be using this to lower the input resistance of a phono preamp.  My pre has an input resistance of 47k ohms, I'll be using this to drop it down to ~8k ohms by using 9.6k ohm resistors.  This puts them in parallel with the 47k input resistor in the preamp, using the formula for resistors in parallel:  1/((1/R1)+(1/R2))=Rt

 

R1 = 47k ohms

R2 = 9.6k ohms

Rt = 7971 ohms

 

The resistors are in sockets, so if I want to lower or raise the value I can just swap them out for other resistors.  I can also just remove them and have 47k again.

 

 

 

 

 

I made it out of some scrap oak and lexan...

post #8960 of 9592

samsquanch, that is awesome...killer idea. Some of my best cases have come literally from the scrap bin.


Edited by vixr - 2/6/13 at 6:11pm
post #8961 of 9592
Quote:
Originally Posted by nikongod View Post

Nobody gets my subtleties, congrats. 

I lean towards the school of thought that headphone amps should be "high power pre amps" not "low-power speaker amps."

There is something to say for both design methods, but I prefer an elegant solution to brute force. 

</snip>

 

Quote:
Originally Posted by b1o2r3i4s5 View Post

What's the difference? confused.gif

One is brute force and the other is elegant?

post #8962 of 9592

*edited* See below
 


Edited by elliottstudio - 2/7/13 at 5:53pm
post #8963 of 9592
Quote:
Originally Posted by b1o2r3i4s5 View Post

Looks great!

How did you make that silver PCB?


I had it made for me! It's a double sided PCB with tinned plating, I usually don't opt for the green enamel coating as it costs more and is just another dielectric. PCB Express has CAD software (their own) that's pretty good. You design it w/ their software and they send the finished product 2 days later.
 

post #8964 of 9592
Quote:
Originally Posted by nikongod View Post. The issue with the 2-box B22 (or even one-box if you're not careful) is that DCR and inductance between the power supply and amp boards has been linked to a few B22 failures. 

 

Hey NG, I'm not aware of the failure case(s) you mention there.... Having built a few Beta22s, all of which were 2-box builds, and having seen most all Beta22-related posts since I've joined, the failure cases I've seen have to do with shorting of one type or another.   I'm curious about what you noted - could you maybe point me to problem posts/threads about it that I could read up on?  Merci beaucoup...

post #8965 of 9592
Quote:
Originally Posted by b1o2r3i4s5 View Post

Learn the maths!

Bigger transformer ≠ more magnetic field.

 

There is another good reason to use an appropriate transformer for the job. An underloaded tranny will typically put out a higher voltage than spec, giving your regulators a harder time (=more heat and other problems down the line).

 

I can't think of any advantages to using an oversized transformer at all.

 

 

Quote:
Originally Posted by nikongod View Post


I lean towards the school of thought that headphone amps should be "high power pre amps" not "low-power speaker amps."

 

There is something to say for both design methods, but I prefer an elegant solution to brute force. 

 

The 2-box B22 was a very popular solution to transformers leaking EMF into what should have been a quiet amps. The issue with the 2-box B22 (or even one-box if you're not careful) is that DCR and inductance between the power supply and amp boards has been linked to a few B22 failures. 

 

See this thread for another good reasons to use a robust headphone amp as a preamp, namely a very low output impedance is very beneficial for both (damping for the former, ability to drive very long cables for the latter).

 

I also doubt your claims in the second point. The website suggests to keep the umbilical to less than 3 feet to keep inductance to a tolerable level when the power supply is in the second box (which is fine as the sigma22 is a beast). Alternatively (as I'm doing) you can keep the power supply and amp boards in the same box and run some long AC lines from the transformer in the umbilical. Problem solved.

post #8966 of 9592
Quote:
Originally Posted by joeyjojo View Post

 

There is another good reason to use an appropriate transformer for the job. An underloaded tranny will typically put out a higher voltage than spec, giving your regulators a harder time (=more heat and other problems down the line).

 

I can't think of any advantages to using an oversized transformer at all.

The rated output voltage is usually given as the unloaded one.

 

Just to be clear, the only reason I'm a 300VA transformer is because I ripped it out of one of my older builds so I don't have to buy a new one.

 

I will never do stupid things for the hell of it.

 

Likewise, the only reason why a person like me who thinks headphones amps should be nothing more then a few op-amps is even making a 4-channel beta22 is because I got most of the stuff for free.

 

To be completely honest, I think the beta22 is an absolutely stupid design.


Edited by b1o2r3i4s5 - 2/9/13 at 8:40am
post #8967 of 9592
Quote:
Originally Posted by b1o2r3i4s5 View Post

The rated output voltage is usually given as the unloaded one.

 

Just to be clear, the only reason I'm a 300VA transformer is because I ripped it out of one of my older builds so I don't have to buy a new one.

 

I will never do stupid things for the hell of it.

 

Likewise, the only reason why a person like me who thinks headphones amps should be nothing more then a few op-amps is even making a 4-channel beta22 is because I got most of the stuff for free.

 

To be completely honest, I think the beta22 is an absolutely stupid design.

 

You do get the point that a beta22 is just an over blown discrete opamp, right?  So, if you think a headphone amp should be nothing more than a few op-amps, then why would you be opposed to one that is just a large op-amp?

post #8968 of 9592
Quote:
Originally Posted by samsquanch View Post

 

You do get the point that a beta22 is just an over blown discrete opamp, right?  So, if you think a headphone amp should be nothing more than a few op-amps, then why would you be opposed to one that is just a large op-amp?

Well, it's not the opamp architecture but rather how the design wastes so many components for the sake of being overkill an no real advantage in boosting the performance at all.....

post #8969 of 9592
Quote:
Originally Posted by b1o2r3i4s5 View Post

Well, it's not the opamp architecture but rather how the design wastes so many components for the sake of being overkill an no real advantage in boosting the performance at all.....

 

That depends on what you mean by performance. The amp was designed to excel in performance metrics (measurements), and therefore (according to the theory) also sound great. You can see this from the "specifications" pages on the website - I haven't yet seen better specs in ANY amp. The B22 beats everything by large factors, often by orders of magnitude. It's a shame it hasn't been retested with some serious test kit yet, but I believe this on the "to do" list, as it far exceeds the audio interface it was tested with.

 

Whether this approach automatically leads to something that sounds good isn't known. But by putting together a discrete amp you definitely have more control over its performance. More than anything it's a great example of simulation-driven circuit design.

post #8970 of 9592
Quote:
Originally Posted by joeyjojo View Post

 

That depends on what you mean by performance. The amp was designed to excel in performance metrics (measurements), and therefore (according to the theory) also sound great. You can see this from the "specifications" pages on the website - I haven't yet seen better specs in ANY amp. The B22 beats everything by large factors, often by orders of magnitude. It's a shame it hasn't been retested with some serious test kit yet, but I believe this on the "to do" list, as it far exceeds the audio interface it was tested with.

 

Whether this approach automatically leads to something that sounds good isn't known. But by putting together a discrete amp you definitely have more control over its performance. More than anything it's a great example of simulation-driven circuit design.


No, I mean performance as in measurements.

 

I can name a few power amps that out performs the beta22, take Doug self's "blameless" amp for example or Bob cordell's MOSFET amp.

They ALL use less components then then beta22, are cheaper the build, delivers more power AND has higher performance.

 

Even integrated op-amp based power amps can achieve similar performance to the beta22 if implemented properly.

Take a look at amps based on National semiconductor's Texas Instruments' LME49810 / LME49811 / LME49830 chips.

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