Follow Up: Lounge Audio LCR Mk III measurements

[SIY]

Thanks to you both. Have had three phono preamps that used it, or a pair of the (single) 5534. Was not familiar with the (10-pin) OP1622. Looking at the LM4562 / LME49710 . Reasons why not?

Again, thanks!

Voltage noise is good, current noise isn't much of an improvement and may even be a bit worse. FET input is your friend for MM preamps.

As a practical matter, layout is very critical for the LM4562, otherwise oscillation is an issue.

 

[jan.didden]

Thanks to you both. Have had three phono preamps that used it, or a pair of the (single) 5534. Was not familiar with the (10-pin) OP1622. Looking at the LM4562 / LME49710 . Reasons why not?

Again, thanks!

These are all quite useable and will work fine. But I make a habit of not paying $ 5 for an opamp where a $ 0.50 one would do exactly the same or better. ;-)

 

[restorer-john]

FET input is your friend for MM preamps

What's not to like here, plenty of paralleled 2SK-369s, a uA741 based DC servo (ideal for this job) and +/-32V rails and DC coupled all the way through. RIAA 20-100KHz +/-0.2dB. 320mV@1Khz overload, 90dB (A) re 0.25mV etc.

Out of all my preamps, I like this one the most (for MM). @SIY, what do you think?

 

[SIY]

There's some very nice design features in that circuit. The input stage is cascoded with bootstrapping, which is intended to minimize the Miller input capacitance- but I would still want to measure it. Even with the bootstrapping, four FETs per side on the differential amp could make the input C excessive for some cartridges (like the A-T). Certainly the 220 pF input cap would have to go, but if the circuit is depending on that for RF immunity...

 

[Ecaroh]

These are all quite useable and will work fine. But I make a habit of not paying $ 5 for an opamp where a $ 0.50 one would do exactly the same or better. ;-)

Very sensible, sir. OTOH, I have the LME49710 already - samples. And it's only a question of a mod to one unit. Is it certain the 5534 does "exactly the same"? Output current, not a factor at all? There is such a thing as a phono preamp that lacks clout ("punch," dynamics), no? Thanks. (Any/all replies welcome.)

 

[SIY]

VThere is such a thing as a phono preamp that lacks clout ("punch," dynamics), no?

Only if it's broken, really badly designed, and/or the EQ is way off. This could be the case if there's an IEC rolloff, which depresses low bass.

Output current is not a major factor in a competent design. Where that goes wrong is if the designer uses a really small terminating resistor for the feedback network in an attempt to minimize noise. For passive systems, this can be seen if the passive EQ network has too low of an impedance- I haven't dug into the Lounge, but that could well be a major reason why harmonic distortion is so high and so predominantly odd order.

 

[jan.didden]

LME49710 is a good match, sure. Not sure what the concern is with output current? What is the load presented by your pre/power amp? 10k? Output voltage max before the phono output slams into the rails, 10V? So that's 1mA output current peak. With a capability of several 10's of mA (to lazy to look it up) I think you have enough belts and suspenders for safety ;-)


BTW The 'does exactly the same' does not mean that an NE5534 and an LME49710 are exactly the same beasts; they are not. What I mean is that either one, in this application, fulfills all sensible performance requirements on linearity, noise, output capability and such. You probably can measure differences between the two, but I would bet they sound the same. In a properly controlled test series, of course..

Jan

 

[SIY]

LME49710 is a good match, sure. Not sure what the concern is with output current?

See the bit I added onto my last post while you were typing in yours. The current issue may relate to driving the EQ, not the line amp or power amp.

 

[jan.didden]

Yes that could be the case, although with sensible design easily avoided.

BTW2 'do the same thing' does not mean you can just indiscriminately roll opamps in this app (or any app). Sometimes circuitry is designed with a specific opamp in mind. For instance, the NE5534 is often used with a small comp cap of say 22pF on two pins that are present for the purpose, to assure stability. If you have a circuit with say an LME49710 and plug an NE5534 in that spot that lacks the comp cap, you may cause instability. Or not; it all depends on the specific circuit..

 

[SIY]

Which reminds me... @Lounge Audio could you please PM me a shipping address to send @dinglehoser 's preamp for the upgrade? Thanks.

 

[LTig]

Thanks to you both. Have had three phono preamps that used it, or a pair of the (single) 5534. Was not familiar with the (10-pin) OP1622. Looking at the LM4562 / LME49710 . Reasons why not?

No, these are fine as well [1]. Actually I used an LT1028 in the first stage of my DIY MC phono preamp and an OPA134 in the second stage. Was fine so far, noise was so low that when I increased the volume so much that I could hear the noise lowering the needle into an empty groove resulted in much louder noise. I concluded that I don't need a phono stage with less noise, not with my pickup (VdH MC-1 special, 0.65 mV rms at 200 Ohm load).

Nevertheless, after reading Douglas Self's book Small Signal Audio Design I replaced the LT1028 by an AD797 and the OPA134 by an LM49710 (could not use the LM4562 as it is a dual amp). Can't really say if the sound got better, but the noise may have been gone down a tiny bit. When I have built a properly designed attenuator I shall measure the phono preamp to see how good it really is ...

[1] problem with the LM49710 is that is is no longer available . It was on the market for just 10 years, compare this with the still available NE5534A ...

 

[Ecaroh]

LME49710 is a good match, sure. Not sure what the concern is with output current? What is the load presented by your pre/power amp? 10k? Output voltage max before the phono output slams into the rails, 10V? So that's 1mA output current peak. With a capability of several 10's of mA (to lazy to look it up) I think you have enough belts and suspenders for safety ;-)


BTW The 'does exactly the same' does not mean that an NE5534 and an LME49710 are exactly the same beasts; they are not. What I mean is that either one, in this application, fulfills all sensible performance requirements on linearity, noise, output capability and such. You probably can measure differences between the two, but I would bet they sound the same. In a properly controlled test series, of course..

Many thanks to you and SIY, also LTig, for multiple answers here. I must say you guys are very accommodating, not to mention fun to talk with.

The case as to meagerness of required amperage is persuasive (I doubt that the design issues SIY cites are likely in this case, but don't have a schematic unfortunately). Yes, 10K ohms is the load posed (by an integrated amp). Lazy or industrious ;-) I'm not sure you can find a spec on the output current of 5532/5534. I haven't. So don't know that assurance is absolute; despite the tiny requirement.

What I'm speaking of here is my McCormack Micro Phono Drive, btw. Goes back to mid-to-late 1990s.

 

[SIY]

Yeah, if you're talking 10k as a load, the current requirements are eentsy (that's a technical term). That's an incredibly light load for a 5534.

Putting a number to it, if max swing is 1V, I = 1V/10,000 ohm = 100 microamp.

 

[LTig]

Many thanks to you and SIY, also LTig, for multiple answers here. I must say you guys are very accommodating, not to mention fun to talk with.

You're very welcome.

The case as to meagerness of required amperage is persuasive (I doubt that the design issues SIY cites are likely in this case, but don't have a schematic unfortunately). Yes, 10K ohms is the load posed (by an integrated amp). Lazy or industrious ;-) I'm not sure you can find a spec on the output current of 5532/5534. I haven't. [..].

Well, of course, see the datasheet on page 5:

• Maximum output-swing bandwidth 70 kHz with VCC±18 V and RL= 600Ω - this is a hint that 600 Ω is allowed.
• output short-circuit current 38 mA (unlimited duration, see page 4)

 

[Ecaroh]

Following the suit of Restorer-John. Anyone care to comment on this circuit? Used by Arcam for a good many years as phono board in integrated amps. Said to be in the Delta 290, Alpha 9 and 10, FMJ A22. I have it and might restore it to use. Felt that I had something of greater clarity, detail, and impact in a Graham Slee phono preamp and others that followed, but unheard in many years.

 

[SIY]

Looks like a very straightforward circuit. I don't know what the rbb of those input transistors might be, but if you experience any noise on the MC input, that might be a fertile place to look at upgrades.

 

[restorer-john]

JFETs galore, MC gain. NP's beast with a thousand JFETs used these classic Toshiba parts.

Sansui AU-D11:

 

[jan.didden]

You're very welcome.

Well, of course, see the datasheet on page 5:

• Maximum output-swing bandwidth 70 kHz with VCC±18 V and RL= 600Ω - this is a hint that 600 Ω is allowed.
• output short-circuit current 38 mA (unlimited duration, see page 4)

Yes but this is an internal current limit spec and the opamp will be very non-linear way before that. Doug Self has some measurements on it in SSAD, page 146 (my 2nd Ed.). 10mA peak should be about the max in linear operation, but that still is huge compared to the usual output current requirements.

 

[jan.didden]

No, these are fine as well [1]. Actually I used an LT1028 in the first stage of my DIY MC phono preamp and an OPA134 in the second stage. Was fine so far, noise was so low that when I increased the volume so much that I could hear the noise lowering the needle into an empty groove resulted in much louder noise. I concluded that I don't need a phono stage with less noise, not with my pickup (VdH MC-1 special, 0.65 mV rms at 200 Ohm load).

Nevertheless, after reading Douglas Self's book Small Signal Audio Design I replaced the LT1028 by an AD797 and the OPA134 by an LM49710 (could not use the LM4562 as it is a dual amp). Can't really say if the sound got better, but the noise may have been gone down a tiny bit. When I have built a properly designed attenuator I shall measure the phono preamp to see how good it really is ...

[1] problem with the LM49710 is that is is no longer available. It was on the market for just 10 years, compare this with the still available NE5534A ...

LT1028 is good, AD797 even better, especially if you use the distortion cancellation feature (although many designers don't even bother, the distortion is already far below the other non-linearities in a phono chain).

The LME49710 (and others) fell victim to product portfolio rationalization when TI took over National. They recommend the OPA1611 as replacement for the LME49710, but I never tried that. Still have a batch of the '710 in my stash ;-)
The other thing is that newer products tend not to be available in DIP08, so I had to learn SMD soldering. It's not that bad, really, except that you can't quickly swap opamps when fault-finding.

 

[Ecaroh]

Looks like a very straightforward circuit. I don't know what the rbb of those input transistors might be, but if you experience any noise on the MC input, that might be a fertile place to look at upgrades.

Thanks for this, SIY. I wouldn't be using the MC input, so nothing to address there...