In simple English, why do we need a custom buffer for Hypex/Purifi eval kits?

[alanhuth]

Greetings, All,

I’m obviously not electronically inclined, but I’ve recently discovered the pretty simple-to-assemble evaluation kits for Hypex NC400 and Purifi 1ET400A. I think I would like to build a couple. I’ve also seen quite a bit of activity on the need (advisability) of a custom buffer for these amps. And it looks like prominent member @tomchr (Neurochrome) has already built said buffer and is offering it for sale.

Reading through the discussions, for the life of me, I cannot figure out whether this buffer is necessary or optional and, as an end user, what benefits I can expect.

Can someone explain the necessity and/or user benefits of this buffer in simple English? Also, if highly advised, can it easily be added to the EVAL1 or GhentAudio or DiyClassD kits? Are there instructions somewhere?

Thanks

 

[russc]

Study the Hypex data sheet.
You will be using a pre-amp or a source that can control the volume.
Provided the source has an output impedance less than 1Kohm (and why wouldn't it) you can expect no improvement.

 

[alanhuth]

So why bother? A lot of people are very excited about this fancy buffer.

 

[Zentronics]

Many standard preamplifer's can and will drive these amplifier units yet some may not.
The Hypex NC400 has an 1800 ohm input impedance and the Purifi 1ET400A has a 2200 ohm input impedance. Like russc said, look at the data sheets. Do you have a preamplifier/linestage/buffer that can drive such a load? If not, then you are a candidate to buy one that can or you have the option to join the bandwagon with Neurochrome. You have many options and the decision is yours.

 

[russc]

From Hypex data sheet I read 104kohm diff in & 1.5Mohm SE in.

 

[Zentronics]

From Hypex data sheet I read 104kohm diff in & 1.5Mohm SE in.

Correct, I was looking at the NC500 at the same time!

 

[alanhuth]

From Hypex data sheet I read 104kohm diff in & 1.5Mohm SE in.

This is quite a far distance from simple english. Looking at spec sheets is not simple English. For all you electronic wizards out there, simple English looks sort of like this:

“In order for one of these amplifiers to operate properly, they need [words here]. Most pre-amps typically have [words here]. But some pre-amps only have [words here]. This is not an ideal situation because [words here]. To remedy this situation, [words here] is needed. Luckily, our friend @tomchr has the talent, time, and resources to create [words here]. This “buffer amp” is really good because, not only does it solve the [words here] problem by [words here], but it also has additional benefits to the user, most notably [words here]. If you buy @tomchr’s buffer boards, your audio listening life will be improved because you will be able to [words here] and you will not have to be burdened by [words here]. And, @tomchr did such a great job with this buffer that you can [easily/not so easily] install it in the kits you identified by generally doing the following:

1. [words here]
2. [words here]
3. [words here]
.......

The first person who takes the time to fill in all those words, will earn my lifelong love and gratitude. Furthermore, I will pay money. Send me a Paypal request.

 

[russc]

Post 2 is simple English.

Most sources can drive an input of say 600ohms and up.
The NC400 has a much higher input impedance and is therefore easy to drive.
The buffer is essentially already built in to the module.
Hypex do not suggest in the product manual that a buffer is required.

If I was to buy an NC400, I would not buy an additional buffer. I would be delighted with the buffer already installed in the module.

Advice freely given.

 

[rayma]

It appears that the amplifier has a balanced input, and the buffer can function (if desired)
as a single-ended to balanced converter.

 

[e_fortier]

By knowing your music source we could provide the right answer.

So, what will you be connecting to the inputs of the NC400 ?

What’s your music source ? Do you have a Preamp or simply a DAC ?

Thanks
Eric

 

[russc]

It appears that the amplifier has a balanced input, and the buffer can function (if desired)
as a single-ended to balanced converter.

By knowing your music source we could provide the right answer.

Really? Unless he is driving really long cables then the buffer will offer no advantage.
If he is driving several metre long cables then the buffer would be used as an output buffer (driver) not an input buffer.

I'm out of here. Everything's been said.

 

[alanhuth]

Russc, thanks for your advice. I apologize for characterizing your answer as not simple English. As post 7 lays out in some detail, you guys use a shorthand that goes over the head of a complete noob, in my case at least. I still don’t have any understanding of several of the [words here] topics in that post. But I plan to follow your advice, so thanks again.

As far as how I plan to feed this beast, I don’t know for sure. I have a few options in-house, or I could get another one if necessary. Right now I have digital streaming through a Cambridge Audio DacMagic Plus. I also have a BluDento HD Bluetooth DAC, and the line out of a Denon AVR3310ci receiver. I assume the Cambridge Audio is the best of the three, but I have no idea whether it is worthy of, or compatible with, one of these high-end class D amps.

 

[russc]

You have the option with the DacMagic of unbalanced (RCA) or balanced (XLR).
Spec sheet states - OUTPUT IMPEDANCE <50 Ohms; this is way lower than the 1kOhms maximum specified by Hypex, therefore no problems.

I don't know how you are housing the Hypex modules and power supplies.
Personally (and this is how my non-Hypex units are constructed), I would build each Hypex amp and powersupply as a monoblock (one amp, one power supply in a single case). Position one amp close to each speaker. Short speaker cables, long signal interconnects. 'Professional' interconnects -
XLR Mic Lead. Van Damme Cable. Black / Low Vis Connectors. All Lengths / Colours | eBay
If you think these can't be any good because they're not audiophile priced, just imagine how many metres of similar cable your signal has passed through in the studio before reaching your speakers.

 

[Mark Tillotson]

So why bother? A lot of people are very excited about this fancy buffer.

A lot of people have irrational emotional responses to audio technology, its not just this buffer! A buffer is needed when its needed.

 

[Douglas Blake]

Can someone explain the necessity and/or user benefits of this buffer in simple English? Also, if highly advised, can it easily be added to the EVAL1 or GhentAudio or DiyClassD kits? Are there instructions somewhere?

In general, buffer stages are used in amplifiers to either

a) Manage input levels. This works two ways, it can be used to boost the input to fully drive a power amplifier or it can cut the input to prevent overloading the power amplifier.

b) Noise reduction. A good buffer stage, properly built, can often reduce the noise and hiss from a power amplifier significantly.

c) Interference reduction. All electronics is susceptible to interference from other electronics, the question is how badly? In many cases a buffer stage is used to block interference on the incoming interconnects.

d) Balancing. Some amplifiers have balanced inputs and do not like the single ended kind from RCA cables. A buffer stage can make this conversion.

e) Marketing. Somebody designed a buffer stage and is now trying to sell it.

Hope that answers your question.

I would suggest building your project... then if you need this extra bobble, you can add it later.

 

[MorbidFractal]

Don't forget that Purifi operates at 500KHz and therefore toilets all over the AM band.

 

[tomchr]

I’m obviously not electronically inclined, but I’ve recently discovered the pretty simple-to-assemble evaluation kits for Hypex NC400 and Purifi 1ET400A. I think I would like to build a couple. I’ve also seen quite a bit of activity on the need (advisability) of a custom buffer for these amps. And it looks like prominent member @tomchr (Neurochrome) has already built said buffer and is offering it for sale.

Reading through the discussions, for the life of me, I cannot figure out whether this buffer is necessary or optional and, as an end user, what benefits I can expect.

The input impedance of the Hypex NC500 is 3.6 kΩ differential (1.8 kΩ from each signal pin to ground). The input impedance of the Purifi 1ET400A is 4.4 kΩ (2.2 kΩ from each signal pin to ground). That is a very heavy (low impedance) load to drive for most preamps. It's not until within the past decade or so that we've had opamps available that could drive (i.e. source enough current) 2 kΩ cleanly (i.e. with low distortion). Many audio opamps of years past were specified to 10 kΩ load. The same goes for many preamps.
So job #1 of the buffer is to source enough current to produce a clean signal at the input of the amplifier module.

Job #2 of the buffer or input stage is to provide gain. The Purifi/Hypex modules have 12-13 dB gain, so you need another 13-14 dB of gain "somewhere" to get to the THX standard 26 dB.
Now, 26 dB is a bit of an arbitrary number. Many - me included - argue that any gain in the signal path should be as early (closer to the source) as possible as this gives better signal-to-noise ratio. "Gain structure" is a good search term if you'd like to read up on it. Also, some of us use pro sources with 4-8 V differential outputs, thus, really do not need any additional gain. That's why you can set my buffer to unity gain by moving a jumper.

Regarding the EVAL1 vs other buffers, including mine: I think the EVAL1 is a great starting point. If you're building a stereo amp and are content with Purifi's choices of connectors and such, you'll likely be quite content with the EVAL1. However, those who would like more flexibility or who are building amplifiers with an odd number channels will probably find the EVAL1 to be a bit inconvenient.

My Purifi/Hypex Buffer offers the options of using an external voltage regulator for the opamps, which many fancy. Furthermore, it offers access to more advanced options, such as direct access to the input of the Purifi/Hypex module and support for remote sensing on the speaker connections. It also brings out the connections to the status LED(s), which is convenient.

Finally, my Purifi/Hypex Buffer has a true differential output. This allows you to drive the Purifi/Hypex module to clipping, even with a single-ended source (RCA connection), which is something the EVAL1 cannot do.

Another reason people use a different buffer than the EVAL1 (or equivalent Hypex evaluation board) is to get a specific "house sound". For example, you could build a vacuum tube based buffer and get some second order harmonic distortion. Some may enjoy that. I prefer a clean sound, which is why I designed the Purifi/Hypex Buffer to add as little as possible to the sound, as evidenced by the ultra-low distortion, including multi-tone intermodulation distortion.

Tom

 

[alanhuth]

Thanks, Guys. That helped me understand a lot.

 

[Running4shape]

Greetings, I am a pretty technical guy, but not in this space. I like the Purifi 1ET400A and think I can create a great amp. I want to create an amp around the Purifi and it seems that using tomchr buffer could be very helpful. I do not fully understand where it would go in the food chain in a solution available from Ghent Audio. They do say they will add mods to their case if needed.

ghentaudio --- Purifi EVAL1 Stereo case-kit

In addition, I would like to add Dirac Live 3.x support using the miniDSP.
Audio plug-ins : 2x4HD to DDRC-24 upgrade

Is there an opinion about the quality of this room correction implementation with the above AMP? Is it good or lacking?

Regards,

 

[egellings]

I have the UcD-100 Hypex modules with differential inputs and 1.8K input resistance for each input (W.R.T. ground). They need a diff. amp buffer in order to be used with ordinary preamps with single ended outputs that must have no less than 10K loading.