Bob Pease on the New LM4562

[hags]

The offset from the first stage is being aggravated by the second stage, which I also increased the gain on to better suit my cartridge. I would assume this is the reason a servo was added in the application note. I don't like the sound of servos, though.

Mike.

Do you have a schematic?

 

[MikeBettinger]

Do you have a schematic?

http://www.national.com/an/AN/AN-1651.pdf. This the link to the application note. I was looking to build a sort of baseline design to use as a reference for a discrete FET based MC amp. This seemed to fit the need. I did not use the power supplies or the servo, just the main MC circuit. I designed the PCB for OPA27's but decided to try the single chip versions of the National chip after reading good things about them.

Mike.

 

[AndrewT]

Hi Mikeb,
you forgot to remove the full stop that the Forum adds to the end of the address.
http://www.national.com/an/AN/AN-1651.pdf

 

[Anzgar]

http://www.national.com/an/AN/AN-1651.pdf. This the link to the application note. I was looking to build a sort of baseline design to use as a reference for a discrete FET based MC amp. This seemed to fit the need. I did not use the power supplies or the servo, just the main MC circuit. I designed the PCB for OPA27's but decided to try the single chip versions of the National chip after reading good things about them.

Mike.

I think the output offset will be far too high without the DC servo.
A high grade capacitor at the output won't degrade the sound any more than a DC servo...I beleive.That circuit will take some time to design the pcb

 

[MikeBettinger]

I think the output offset will be far too high without the DC servo.
A high grade capacitor at the output won't degrade the sound any more than a DC servo...I believe. That circuit will take some time to design the pcb

I haven't found a 100mv of offset to cause a problem, maybe a small tick switching to the phono. Sonically no.

I already have designed the PCB. See attached.

Regards, Mike.

 

[Anzgar]

if there's .1 v at the output of the preamp and you have 30X amplification in the power amp it would mean 3V over the loudspeakers, but of course there's the attenuator beetween.
Very nice board,what pcb software do you use?

 

[Nordic]

I think those of you with amps without input caps know about it... because you took em out on purpose..... but for the rest 99% of amp have a cap right at the input anyway......

100mV on a buffer which may only be passing 1V... is quite a margin though... and I would suspect it needs some adjustment somewhere...way off from datasheet that....

 

[MikeBettinger]

if there's .1 v at the output of the preamp and you have 30X amplification in the power amp it would mean 3V over the loudspeakers, but of course there's the attenuator between.
Very nice board,what pcb software do you use?

I have a wet slug tantalum bypassed by a paper dialectric film cap on the preamp input so it's not an issue. Best sounding combination I've come up with over the years.

The board program is supplied free by ExpressPCB. Four boards cost less than $100. without silkscreen and soldermask. Great if you just want to bang something out and try it.

The second set will get the OPA627s and I'll recycle the power supply portion of the layout and insert a discrete design for my next attempt. Sort of an apples to apples comparison that way and easy to back up. I'm able to unplug the existing PCBs and plug in the next contender.

Regards, Mike.

 

[hags]

I have a wet slug tantalum bypassed by a paper dialectric film cap on the preamp input so it's not an issue. Best sounding combination I've come up with over the years.

The board program is supplied free by ExpressPCB. Four boards cost less than $100. without silkscreen and soldermask. Great if you just want to bang something out and try it.

The second set will get the OPA627s and I'll recycle the power supply portion of the layout and insert a discrete design for my next attempt. Sort of an apples to apples comparison that way and easy to back up. I'm able to unplug the existing PCBs and plug in the next contender.

Regards, Mike.

What type of discrete? Are you talking about a discrete buffer in combination with an op amp?

 

[MikeBettinger]

What type of discrete? Are you talking about a discrete buffer in combination with an op amp?

No, just a discrete JFET input, bipolar output/VA. It will replace my tired bipolar input design that I've used for a number of years.

Regards, Mike,

 

[hags]

No, just a discrete JFET input, bipolar output/VA. It will replace my tired bipolar input design that I've used for a number of years.

Regards, Mike,

So no op amps at all in what you're talking about?
Have you ever used an IC op amp for a gain stage and then a discrete buffer output?

 

[Daveis]

Have you ever used an IC op amp for a gain stage and then a discrete buffer output?

Yes, M3 headphone amp is such a beast. OPA627 and MOSFET.
Wondering if anyone has put a LM4562 into one.

 

[MikeBettinger]

So no op amps at all in what you're talking about?
Have you ever used an IC op amp for a gain stage and then a discrete buffer output?

No, actually. I've used op-amps in power supplies and as servos and quite often as part of my real work, but for audio I've always stuck with discrete transistor designs. I think the problem with an MC design is at the quiet end of the spectrum, I debated placing a FET buffer before the National chip to bring up the quieter end of the spectrum so that the chip would have an easier time of it. Out of my comfort zone right now.

This MC amp was actually a departure for me. Before designing a MC stage I wanted a reference that was relatively current and accurate. The applications note referenced earlier had High-end pretentions and the National chips came highly regarded. Thought I'd take a walk on the wild side. Actually the design as built is very impressive. My one lingering thought is that it doesn't scale well as far as handling the very low level detail from my cartridge. I keep trying to turn it up to get it to produce subtle details that I know are in my recordings.

This is a very slight effect, but there. My past MC amp would resolve this but had many other issues that were hard to ignore. I ordered the OPA627s from parts Connexion today, Maybe the Difets will clear things up...

Regards, mike.

 

[hags]

Yes, M3 headphone amp is such a beast. OPA627 and MOSFET.
Wondering if anyone has put a LM4562 into one.

I'm using a line amp with an LME49710 with a BUF634 in the feedback loop. I have a line amp that I use OPA627Ps in with no buffer.
I've started another thread about IC op amps for a gain stage and a discrete buffer output. I was curious to see if this is practical and a high quality approach. There seems to be alot of negative views on IC op amp line stages.

 

[MikeBettinger]

I'm using a line amp with an LME49710 with a BUF634 in the feedback loop. I have a line amp that I use OPA627Ps in with no buffer.
I've started another thread about IC op amps for a gain stage and a discrete buffer output. I was curious to see if this is practical and a high quality approach. There seems to be alot of negative views on IC op amp line stages.

IC's used in audio signal paths have always had a negative reputation, which doesn't mean that can't change, though. I thought I'd give the National chip a try since I had a reason. Now I'll try the Burr Brown.

What is the name of your other thread?

Regards, Mike.

 

[AndrewT]

http://www.diyaudio.com/forums/showthread.php?postid=1302238#post1302238
"Op amp based preamp with discrete output"

 

[MikeBettinger]

http://www.diyaudio.com/forums/showthread.php?postid=1302238#post1302238
"Op amp based preamp with discrete output"

Thanks

 

[Tolu]

I've heard the thin sound complaint from alot of users.
Even with copious amounts of decoupling and storage caps the sound has a thin, lightweight quality to it.
Not that it's a deal breaker, it is noticable but it's a sin of omisson. For me the OPA627P is less objectionable.

First when I built my new preamp with the 49710 I thought the sound was extremely thin but then I remarked that I forgot the grounding of pin 2.

After correcting that the sound was great. Rich, full, extremely detailed and perfect. Bass is very sufficient. (look at Post #327 ff.)

I am very content with it! Perhaps you have to vary the circuit!

Regards

Thomas

 

[hags]

First when I built my new preamp with the 49710 I thought the sound was extremely thin but then I remarked that I forgot the grounding of pin 2.

After correcting that the sound was great. Rich, full, extremely detailed and perfect. Bass is very sufficient. (look at Post #327 ff.)

I am very content with it! Perhaps you have to vary the circuit!

Regards

Thomas

Pin 2 doesn't get grounded, but I see the problem with yours. I would imagine that it would sound alot better after you made the correction.
That's not the problem with mine, maybe it just needs some time to "break in" .
The verdict is still out in my case.

 

[hags]

First when I built my new preamp with the 49710 I thought the sound was extremely thin but then I remarked that I forgot the grounding of pin 2.

After correcting that the sound was great. Rich, full, extremely detailed and perfect. Bass is very sufficient. (look at Post #327 ff.)

I am very content with it! Perhaps you have to vary the circuit!

Regards

Thomas

I'm wondering if I'm hearing the sound/effect of the BUF634, and maybe taking that to be the sound of the LME49710. I am now using the LME49710 without a buffer and I'm, at least initially, impressed with it.
I will have to do further comparisons.