BUF634 vs HA5002 buffers in headphone amp ?

[gurevise]

Guys,
What are your thoughts on these two buffers ?
I see that HA5002 is used a lot in headphone amps.
What about BUF634 ? It has a nice specs, at least on paper.
Is HA5002 really much better sounding IC then BUF634 ?
Let me know what you think. Thanks

BUF634 is easity available from digikey.com
HA5002 is harder to source.

Thanks
Sergey

 

[mlloyd1]

I just ordered some from Arrow Electronics

mlloyd1

 

[john curl]

If you really want quality, just make a discrete push-pull class A buffer from Fets or bipolar devices. The only other alternative is tubes. Trust me. ;-)

 

[PMA]

If you really want quality, just make a discrete push-pull class A buffer from Fets or bipolar devices. The only other alternative is tubes. Trust me. ;-)

There might be more kinds of "trust" 😉 .
I have the best experience with BUF634T, both parameters and sonic quality (you can visit my www to see an example of a circuit design). I am very sure that it is practically impossible to reach the same parameters by several discrete transistors, monolithic technology is superb for this purpose. The speed, thermal junction between components, repeatability ... And with BUF634 inside feedback loop you are able to reach THD of 0.0001% with OPA627, for example. You'll hear the result when listening to great philharmonic orchestra, violin, organ, trumpets ...

 

[jean-paul]

Don't trust your website, the link on your www site to the audio-buffer is broken.

At the moment it is:

file:///C:/Dokumenty/HIGHEND/MAC_hifi_publish/pokusny/buffer_en.html

This one works:

http://www.pha.inecnet.cz/macura/buffer_en.html

I would take advice of John Curl serious. He has some experience with preamps to say the least.

 

[analog_sa]

have the best experience with BUF634T, both parameters and sonic quality (you can visit my www to see an example of a circuit design). I am very sure that it is practically impossible to reach the same parameters by several discrete transistors, monolithic technology is superb for this purpose. The speed, thermal junction between components, repeatability ... And with BUF634 inside feedback loop you are able to reach THD of 0.0001% with OPA627, for example. You'll hear the result when listening to great philharmonic orchestra, violin, organ, trumpets ...

I have only used the dip BUF634 and have been consistently underwhelmed. As i don't care one bit about thd, the zeroes fail to impress me. Outside fb loop i find the sound pathetic; inside it's much better but you can always hear the presense of the BUF and not necessarily in a pleasant way. I haven't touched opamps for more than 10 years and only recently spent some time investigating how far have the little chips progressed. Well, in some respects the best are now truly better than the 5534 - a good design conveys a degree of a sense of space, delicacy and PRAT, but in respect of genuine, lifelike, startling dynamics they still have a long, long way to match the sonics of discretes, be that valves or SS. For the record my experiments have included a phono in which a opa637 is followed by a buf634 driving a fb type riaa network and a opa627 with a buf634 as a line stage.

cheers
peter

 

[PMA]

Don't trust your website, the link on your www site to the audio-buffer is broken.

You are right, thank you very much. I have just repaired it.

Pavel

 

[PMA]

As i don't care one bit about thd, the zeroes fail to impress me. Outside fb loop i find the sound pathetic; inside it's much better but you can always hear the presense of the BUF and not necessarily in a pleasant way.

Hi Peter,

yes, low thd is not the only sufficient parameter 😉 , but necessary (in case that the whole audio chain is perfect 😉 , otherwise it may emphasize another flaws). From my experience - low THD, IMD and perfectly stable design (to any load - this must be measured) are absolutely necessary in case that I want to listen to all the details of symphonic orchestra. Valves are fine for a jazz quartet or single saxophone, but I do not prefer to hear new colorations. Valve itself is further musical instrument in the audio chain 😉

Pavel

 

[analog_sa]

Valves are fine for a jazz quartet or single saxophone, but I do not prefer to hear new colorations. Valve itself is further musical instrument in the audio chain

Valves require an incredible amount of care to sound good with complex music. In my experience each amplification stage has to have its own independent power supply, or at least dedicated regulator. The results can be truly rewarding but there is a price to be paid in size and weight. Of course microphony is another curse... To my ears, though, valves ultimately win as far as dynamic expression is concerned.
Have you compared the sonics of the dip BUF634 to BUF634T? Is there a substantial difference (assuming both are driving easy loads, far from max current)?

cheers
peter

 

[PMA]

Have you compared the sonics of the dip BUF634 to BUF634T? Is there a substantial difference (assuming both are driving easy loads, far from max current)?

cheers
peter

Nice post, peter. Regarding BUF634 in DIP-8 and BUF634T in TO220-5, I did not have chance to compare them. My choice was the BUF634T from the simple reason - in my buffer application I use the coax. cable terminated at both ends by 50 Ohms, i.e. 100 Ohms load for the buffer. This, especially terminating resistor (R12 in the Audio Buffer schematics) has brought dramatical improvement of the whole soundstage. Any hint of grain or harsh is over.

Pavel

 

[peranders]

I should choose the TO220-5 or SMD type if I could choose. If you use high speed mode, the DIP verison gets really hot and that is not a good thing. My headphone amp with SMD BUF634 and pcb with groundplane is a good combination. The cooling properties is rather good.

 

[PMA]

HA5002

Back to the roots. HA5002 should be the same as LH0002. This is one of the first buffers from National Semiconductor, constituted by 4 transistors (2 CFP pairs). This product is dicontinued and its parameters, not bad some 15 years ago, are not sufficient now, especially when compared to BUF634.

 

[ppl]

BUF634 vs HA5002 abstract

I have used both the BUF634 and the HA-5002 in headphone amps and overall the 5002 is better if accuracy in the midrange and High end is importent. the downfall of the HA5002 is its low bass, The 5002 seams to provide a over dampened quality to the low bass this can result in the Bass sounding thin, however fast sounding.

The BUF634 presents a fat slightly underdampened Bass giving a sence of weight and heft, however IMHO Bloated somwhat, also the Midrange is slightly washed out. the BUF634 also has to be operated at more than its minimum bias current to sound good at least 5 mA and up to the full 15 mA is better.

Regarding the comparrison of the HA-5002 to the LH-0002 the only thing these two have in common is pinout. if you look at the schematics in the data sheet you can see the added Biasing and slew inhancement used in the HA-5002. I have also compaired these two buffers and the HA-5002 is the winner by a large amount in all sonic qualities. The HA-5002 also is rated at twice the output current of the LH-5002.

The BUF-634 has output current limit protection as well as thermal shut down. The HA-5002 dose not. another Buffer you might consider is the HA-5033 this has half the output current of the HA-5002 offers a 250 MHz. bandwidth vs the 110 MHz. of the HA-5002. The HA-5033 will be pin compatible with the HA-5002. The OPA-633 is Burr Brown's equliv. to the HA-5033 however more costly and is claimed to be an improved replacement.

PMA> You might consider adding a small 50-100 ohm resistor between the Buffer input and the op amp output so as to isolate the op amp from the input capacitence of the Buffer input as well as any PC board capacitence. This isolating resistor also allows the op amp to see a real resistence when the Buffer's input impedance turns negitive. this Resistor should also allow you to get clean transients with out the need for the Phase lead cap around the op amp.

 

[PMA]

Good job. I completely agree that it is important to operate BUF634T at the highest possible quiescent current (pins 1 and 3 shorted). The small resistor between OA output and BUF input works, with small capacitance between pins 2 and 6 of the OA added. Also agree with a bit darker midrange of BUF634T. But I want to add that these phenomena can be strongly affected by input signal filtration and PCB and shielding design, as with most solid-state global NFB designs.

 

[audiodesign]

Look this my solution.

This is a very incredible no feedback design directly connected to the DAC chip.

http://www.audiodesignguide.com/DAC_final/DacFinal.html

 

[vacuphile]

Look this my solution.

This is a very incredible no feedback design directly connected to the DAC chip.

DAC Final

Based on the measurements I have been doing for a DC application of the 634, there might be good reasons to put it in a feedback loop with a good opamp. The first reason is that gain of an 634 on its own is quite dependant on load. Since all audio transducers have non-flat impedance curves, this might not be a good thing. The other is that I found an unbuffered 634 to be quite sensitive to parasitics. The mere touch by hand of an output will produce small oscillations (I measured in the 10 uV region). Not that much, but who knows how it will behave in different settings. Since I found these oscillations to happen, I put an opamp in the loop at a small noise cost, but the 634 became rock stable.

vac