SSL2+ Low Volume Direct Monitoring Vocals

[mr_nervouswreck]

Hi there,

I have just purchased a SSL2+.

I am having a problem where I am not getting enough sound level through my microphone when Directly Monitoring through the SSL2+.

I have a Rhode NT1-A plugged into my SSL2+, with Phantom Power 48V switched on. I have the gain turned up to a good level without clipping. For testing purposes I have got the Monitor Mix turned all the way to the left to the on 'Input'. The volume of my input 'Microphone' is not loud enough, however the level readings are perfect.

I have also got my Phones level turned all the way up. I would have expected there to be plenty of head room for louder input volume when direct monitoring with the SSL2+. When recording to a track in Logic, of course I blend the monitor mix slightly to hear the track and microphone input together, however my vocal is completely washed out. Almost impossible to record with when you can't hear yourself.

If I turn the gain up I can most definitely hear enough of my vocal when direct monitoring, but that results with the audio clipping. This is not a solution. I should also point out that when listening back to music the volume is most definitely loud enough through the SSL2, only when I am direct monitoring my Microphone Input.

The vocal level is extremely quiet. I have also tried both Input sockets, with the same results. Is this normal behaviour of the SSL2+?

I have used many other interfaces in the past and have not come across this problem. Is my product faulty? This is really disappointing.

I need to find a resolution as soon as possible, any assistance would be great.

My setup is as follows:

Macbook Pro (Early 2011)

OS X El capitan 10.11.6

Logic Pro X 10.0.6

Rhode NTA-1 Microphone

DT770 Pro - 250 Ohm Headphones

Thanks in advance!

[Hugh Robjohns]

If you are getting a clean signal at a sensible level into the DAW, and DAW replay is loud enough in the phones, it certainly seems odd that you can't get enough direct monitoring level. So something probably isn't right.

Whether there's an 'operator error' with the interface configuration, or a technical fault in the unit I can't say. In situations like this is often a good idea to walk away, sit down with a cup of tea and the user manual, and read through the book again and how to set up the hardware and any software controls to adjust the monitoring.

In the absence of any other suggestions from those using the same unit your best bet is probably to contact your dealer or SSL directly to discuss the issue with them.

[Sam Inglis]

I wonder if the problem here is that the 2+ simply can't generate enough level into your headphones. Like most bus powered interfaces it has a relatively low-powered headphone amp: the specs give a maximum output level of +10dBu. With a pair of sensitive low-impedance headphones that's fine, but the 250Ω DT770s will put out a much lower volume and it may be that this simply isn't enough. It'd be worth trying a different pair of phones if you can.

[shufflebeat]

I'm using the SSL2+, usually with Shure srh840 or Senn hs25 h/p which are, I believe, 44 and 70 ohm respectively. I do find myself fiddling with the in/out mix more than I have done with previous interfaces because even at that low impedance I'm always at the limit of "leaving well enough alone and getting on with stuff".

I was initially recording quite hot into the system and have been trying to ease back into the green which hasn't helped.

I have a little c-moy battery headphone amp which I've considered using to bridge the gap. I don't think any lack of quality during tracking would jeopardise anything vital so long as I'm not actually going deaf, which had crossed my mind so kinda glad to read your post.

[James Perrett]

One thing that I'm trying to work out...

If you have a signal going in at -20dBFS and a signal coming out at -20dBFS are they at a different level in the headphones? Can you adjust the monitor mix control so that they are the same?

[shufflebeat]

My experience differs from the OP's in the sense that if I set a decent input level and mix to "input only" I have a good (as expected) level going to phones, it's only when I mix with playback that the in/out waltz is any kind of issue, even then it's a distraction rather than an obstruction.

If memory serves the SOS review which prompted my purchase did marvel at the feature list that had been achieved on a platform of USB bus power only. I have seen the perceived economy of SPL to be part of that balancing act.

[mr_nervouswreck]

I wonder if the problem here is that the 2+ simply can't generate enough level into your headphones. Like most bus powered interfaces it has a relatively low-powered headphone amp: the specs give a maximum output level of +10dBu. With a pair of sensitive low-impedance headphones that's fine, but the 250Ω DT770s will put out a much lower volume and it may be that this simply isn't enough. It'd be worth trying a different pair of phones if you can.

I'm beginning to feel that my headphones impedance is causing the issue.

I don't quite understand impedance in its entirety, my SSL2+ seems to power my DT-770 Pro 250ohms perfectly fine when listening back to the track. Setting the monitor mix all the way to USB gives my plenty of phone's level headroom to play with, as soon as I switch over to input monitoring, is simply not loud enough for tracking vocals.

Is it a hardware fault or simply a limitation with the SSL2+ headphone pre-amp?

This is really frustrating if that's the case, I was about to purchase the Ambient ID14 Mkii & it seems they have a more powerful headphones pre-amp. Bummer!

I find it hard to believe that many people haven't brought this up as an issue with the SSL2+? All I can seem to find is rave reviews from everyone.

[James Perrett]

It sounds to me like an internal gain issue inside the SSL2. Is there any kind of software control panel where you could change the internal levels used or is everything controlled from the front panel?

[mr_nervouswreck]

It sounds to me like an internal gain issue inside the SSL2. Is there any kind of software control panel where you could change the internal levels used or is everything controlled from the front panel?

James, all the controls are on the front panel. Do you think a lower impedance headphones would solve the problem. I was thinking of getting a cheap set of AKG K52's just for tracking vocals. They are 32 ohms.

[James Perrett]

James, all the controls are on the front panel. Do you think a lower impedance headphones would solve the problem.

It is hard to say because it sounds like there is plenty of power available but only when the monitor control is fully in the playback position. Unless I've missed something, it sounds like there is a problem with the internal levels in the 2+ with insufficient input level being sent to the monitor control. I'd suggest contacting SSL to see what they say.

[mr_nervouswreck]

James, all the controls are on the front panel. Do you think a lower impedance headphones would solve the problem.

It is hard to say because it sounds like there is plenty of power available but only when the monitor control is fully in the playback position. Unless I've missed something, it sounds like there is a problem with the internal levels in the 2+ with insufficient input level being sent to the monitor control. I'd suggest contacting SSL to see what they say.

This was SSLs initial response to the problem, not very helpful:

'One thing that you can do is to put a limiter on the track that you are overdubbing to and boost the track so that it is just under clipping - this way you can leave the monitor mix knob closer to input while you still hear your track.

The other thing to do is to work in a quieter environment or to get headphones that provide better isolation - an over-ear closed back design or even a headphone designed for maximum isolation.'

[James Perrett]

That's very disappointing advice - especially the part about increasing the recording level by using a limiter which is just plain bad advice.

It may be worth buying a pair of really cheap low impedance headphones from the local pound shop just to check whether it is a headphone drive problem but, to me, it sounds like a design fault with the unit which may (or may not) be fixed when they bring out the Mk2.

Edited to add: If you bought this online then you could always send it back under the Distance Selling Regulations if you have had it less than 14 days. If you bought it in person from a shop then it may be worth contacting the shop to see if they would swap it for something that works better for you.

[Wonks]

Sounds like SOS may need to revise the online review to add a word of caution when using high impedance headphones.

[ef37a]

I would be interested to know,...
When recording at say -20dBfs (and getting a low level in the direct sound in the phones) does the subsequent playback still run at -20?

If the two levels are comparable (should be identical really?) then IMHO this can only mean a difference in the level sent to the headphone amplifier, either by accident or design. I cannot however see any reason for the latter!

I would guess some half dozen interfaces have passed through my hands in the last ten years or so, such behaviour has never happened in my experience.

Dave.

[mr_nervouswreck]

That's very disappointing advice - especially the part about increasing the recording level by using a limiter which is just plain bad advice.

It may be worth buying a pair of really cheap low impedance headphones from the local pound shop just to check whether it is a headphone drive problem but, to me, it sounds like a design fault with the unit which may (or may not) be fixed when they bring out the Mk2.

Edited to add: If you bought this online then you could always send it back under the Distance Selling Regulations if you have had it less than 14 days. If you bought it in person from a shop then it may be worth contacting the shop to see if they would swap it for something that works better for you.

Any old pair of phones should do the trick? I've got my smartphone headphones I could use using the adaptor.

My biggest confusion here is:

Why do I have more than enough volume/power to my phones when turning the Monitor Mix knob to 'USB' for track playback, but when turning it to 'Input' to monitor my Microphone levels its extremely low, even when my phones are turned all the way up?

This is from SSLs website regarding Headphone Impedance on the SSL2, how do you interpret this, is 250 ohm sufficient?

The source impedance (headphone output impedance) of the SSL 2 series is 10 ohms.

SSL 2 series is designed with professional audio quality in mind, which means that there is ample power to drive any headphones from the SSL 2 series headphone output.

For optimum performance, a typical ratio of headphone impedance to source impedance should be 8:1 or better.

This leads to an optimum impedance of 80Ω or greater; this covers most professional headphones.

Concerning headphones with much higher impedance:

Typically headphones with very high impedance (250 Ω, for example) may suffer from a lack of power when used with a very low source impedance output.

[Sam Inglis]

Here's something to try.

Just temporarily, set things up so that you are monitoring through Logic. Record-enable a track with the fader at unity and don't mute it, then set the SSL's monitor knob all the way to USB. You should hear your input signal (perhaps with a short delay depending on the buffer size setting).

If you then mute the track in Logic and turn the monitor knob all the way to Input, does your signal seem to get louder, or quieter, or stay the same?

It should stay roughly the same. If it does then the problem is that the SSL can't drive your headphones as loud as you want, as previously discussed. If it gets significantly quieter there may be a fault with your unit.

I would still bet that the problem is down to impedance. Your backing track is likely to be quite a full-sounding source which peaks close to 0dBFS, which is why that comes through clearly. A live vocal recorded with a decent amount of headroom is much much quieter.

[James Perrett]

It may be worth buying a pair of really cheap low impedance headphones from the local pound shop just to check whether it is a headphone drive problem but, to me, it sounds like a design fault with the unit which may (or may not) be fixed when they bring out the Mk2.

Any old pair of phones should do the trick? I've got my smartphone headphones I could use using the adaptor.

I find smartphone earbuds a little annoying but they'd be worth a try. Proper 'over the ear' headphones might give a clearer picture.

[Bob Bickerton]

So I've just managed to find time to set up my SSL2 (which I assume has the same headphone amp as the SSL2+).

Using a set of DT880 250 Ohm headphones I'd struggle to get sufficient levels for self-monitoring assuming sensible gain settings.

Things certainly improve with a set of 80 Ohm DT770s and get even better with 70 Ohm HD25s. Whether that improvement is sufficient for you I can't say.

Remember it's not a balance issue between monitoring your input versus the DAW output as you can tweak the 'Monitor Mix' to suit.

So you could either try low-impedance headphones or hook in a headphone amp.

Bob

[mr_nervouswreck]

So I've just managed to find time to set up my SSL2 (which I assume has the same headphone amp as the SSL2+).

Using a set of DT880 250 Ohm headphones I'd struggle to get sufficient levels for self-monitoring assuming sensible gain settings.

Things certainly improve with a set of 80 Ohm DT770s and get even better with 70 Ohm HD25s. Whether that improvement is sufficient for you I can't say.

Remember it's not a balance issue between monitoring your input versus the DAW output as you can tweak the 'Monitor Mix' to suit.

So you could either try low-impedance headphones or hook in a headphone amp.

Bob

Hi Bob, thank you so much for your input and feedback.

A few questions, I hope you don't mind.

I'm certainly not the most technical minded genius when it comes to these sort of things. Would your analysis conclude that in fact there is no hardware fault with my SSL2?

Is there any reasoning behind why the SSL2 can power music playback just fine with plenty of headroom in the cans, but for self-monitoring the difference is incomparable. Just not enough volume with my DT-770 Pro 250omh.

I don't have another pair of professional grade headphones to test with, so instead I plugged in a normal pair of headphones, similar to iPhone ears buds.

AiAiAi Pipe Earphones @ 16 ohms. I would say the self-monitoring increase was about 15% louder, with the phones turned all the way up on the SSL2 Input mode. It still wasn't loud enough, and before any suggests 'yes my hearing is fine'.

I'm not sure if using these type of phones is a worthy comparison, I also had to plug them in using a jack adaptor as they are normal consumer headphones.
https://aiaiai.audio/headphones/pipe/black

Bob I was thinking of purchasing a pair of AKG K52s 32 ohms. Do you think these headphones should perform better with more self monitoring volume?

[Wonks]

The 8:1 rule for headphone impedance compared to the headphone amp output impedance is all about keeping the frequency response of the headphones uncoloured by the headphone amp being unable to supply enough current across the frequency range.

Here’s a good explanation of the rule with some examples.

https://youtu.be/SpTsWVLI-ig

So 80 ohms is about the minimum impedance for the SSL2 headphone amp not to colour the sound.

Headphone level is not just about impedance, it’s also about the headphone efficiency. A headphone with a 96dB SPL for a 1mW input will be considerably quieter than headphones with a 104dB SPL for a 1mW input. But as there is no standardised test for headphone SPL measurement, it’s hard to accurately compare on maker’s headphones against another maker’s phones as they could be several dB different due to the test set-up.

But even so, if you compare efficiency figures as a rough guide, they will help you see which headphones make the most of the power available, with higher impedance phones reducing the available power.

But you’d provably chose headphones based on sound quality and comfort. It’s not easy!

[Arpangel]

Maybe it’s just the time of year, but I seem to be hearing a lot about interface outputs being either too low or too high, I’ve fallen victim to this myself.

[ef37a]

Just watched the YT vid. Unscientific, poorly presented tosh IMHO.

The preamble about impedance and current delivery completely ignores the fact that a HP amp with a 100R OPZ could easily deliver the same current as one of 10R if there was enough voltage to drive it.

The 'frequency response' at 044/9.18 is alarmist rubbish. Worst case is a 1.3dB blip at ~100Hz and another of only +0.6dB at ~2.4kHz and I don't think anyone will be bothered by a lift of just 0.4dB at 20kHz?
BUT! that is NOT a frequency response of the headphones. If you took a plot of the current drawn by any passive speaker you would get much the same, probably worse!

What is also always left out of this 'zero amp Z' debate is the fact that headphone amps have always historically had an OPZ of 20 to 100 Ohms or so, therefore SURELY the manufacturers take this into consideration when designing the cans? If therefore you have some headphones designed to be driven from say 33Ohms* they will surely wave the 'wrong' response when connected to a sub one Ohm amp?

*And strictly speaking it is not an 'impedance' but a pure, physical resistor in most cases.

Dave.

[Bob Bickerton]

So I've just managed to find time to set up my SSL2 (which I assume has the same headphone amp as the SSL2+).

Using a set of DT880 250 Ohm headphones I'd struggle to get sufficient levels for self-monitoring assuming sensible gain settings.

Things certainly improve with a set of 80 Ohm DT770s and get even better with 70 Ohm HD25s. Whether that improvement is sufficient for you I can't say.

Remember it's not a balance issue between monitoring your input versus the DAW output as you can tweak the 'Monitor Mix' to suit.

So you could either try low-impedance headphones or hook in a headphone amp.

Bob

Hi Bob, thank you so much for your input and feedback.

A few questions, I hope you don't mind.

I'm certainly not the most technical minded genius when it comes to these sort of things. Would your analysis conclude that in fact there is no hardware fault with my SSL2?

Is there any reasoning behind why the SSL2 can power music playback just fine with plenty of headroom in the cans, but for self-monitoring the difference is incomparable. Just not enough volume with my DT-770 Pro 250omh.

I don't have another pair of professional grade headphones to test with, so instead I plugged in a normal pair of headphones, similar to iPhone ears buds.

AiAiAi Pipe Earphones @ 16 ohms. I would say the self-monitoring increase was about 15% louder, with the phones turned all the way up on the SSL2 Input mode. It still wasn't loud enough, and before any suggests 'yes my hearing is fine'.

I'm not sure if using these type of phones is a worthy comparison, I also had to plug them in using a jack adaptor as they are normal consumer headphones.
https://aiaiai.audio/headphones/pipe/black

Bob I was thinking of purchasing a pair of AKG K52s 32 ohms. Do you think these headphones should perform better with more self monitoring volume?

I’m afraid I’m no technical minded genius either. Your posts have described what I have found - so from that point of view I don’t think it’s a fault, just a headphone amp design issue.

I wouldn’t like to hazard a guess on whether your suggested headphones would be suitable, sorry.

Bob

[James Perrett]

The 8:1 rule for headphone impedance compared to the headphone amp output impedance is all about keeping the frequency response of the headphones uncoloured by the headphone amp being unable to supply enough current across the frequency range.

The thing is, headphone amps have traditionally had a high output impedance which is mainly resistive in order to prevent large volume variations between high impedance headphones and low impedance headphones.

A good headphone amp should perform equally well into 8 ohm or 600 ohm headphones - both of which could be encountered in traditional studios.

[mr_nervouswreck]

The 8:1 rule for headphone impedance compared to the headphone amp output impedance is all about keeping the frequency response of the headphones uncoloured by the headphone amp being unable to supply enough current across the frequency range.

The thing is, headphone amps have traditionally had a high output impedance which is mainly resistive in order to prevent large volume variations between high impedance headphones and low impedance headphones.

A good headphone amp should perform equally well into 8 ohm or 600 ohm headphones - both of which could be encountered in traditional studios.

Thank James for your help, looking for some steering as to what half decent headphones would work well with the SSL2+

I was considering the AKG K52 (32 OHM), simply because of it's price point and decent reviews for vocal tracking. The question is will they be loud enough for self-monitoring on the SSL2?

Frequency range: 18 Hz to 20 kHz
Sensitivity: 110 dB spl/V
Max. input power: 200 mW
Input impedance: 32 ohms