Moreplay gain questions / Education

[Finkle]

Howdy,

First post here and completely new to tube gear. The overall system is sounding great but I'm running into a volume bottleneck that I believe is because of the output voltage on the Moreplay. Truly loving all the components in the system and wondering if others feel this assumption is correct and what easy fixes there are without changing out gear but more mods or cable attenuator type ideas. Honestly I'm a bit lost in the gain or impedance conversation as it seems needs to be a bigger forethought than anticipated with tube gear. The overall volume is close to what I'm looking to achieve but it's not quite there.

I'm running a Seas driver kit that says 89d sensitivity, those are powered by a Buckeye SS class D amp containing 2 Hypex NCx500 amp boards. Feeding those is the newly built Moreplay, feeding that is a Topping d70 Sabre DAC set at DAC only and output thru XLR to RCA at 5v, also feeding the Moreplay is a Parks Audio Waxwing running thru coax to the DAC but also RCA cables directly to a second input on the Moreplay. To my surprise the turntable thru the waxwing is what I can make the loudest by increasing gain in the DSP of the waxwing but then it says there's clipping and again I'm not sure if that's a bad thing to be sending thru the tube set up. The 5v gain out of the DAC is the max it will go. The Buckeye amp I had chose the buckeye gain stages and those are at high right now, spec states 24.2db gain and 3.4Vrms. I can bypass the gain switches and it will increase to the stock Hypex gain stage of 26.8db and 2.5Vrms. this is where I'm planning to start but before I did so I wanted to see what the forum said.

My hopes are there's a simple fix without completely changing gear. Also to pick up some education into any rule of thumbs into this avenue of thought. For those looking at pictures, I will be adding the spalted maple veneer to the face of the Moreplay and painting the rest of it's enclosure black but leaving chassis stock finish. Honestly pumped how it's coming together and to also be getting my feet wet into tubes.

 

[Paul Birkeland]

I would suggest playing a 60Hz tone through your DAC and using your meter to measure the AC voltage present at the ends of the RCA cables feeding into your Moreplay.  You have way, way, way more than enough gain in your system to play those drivers into distortion.  I ran into this very recently with a Topping DX3 in someone's system, and after two years of asking him to actually measure the output voltage from the DAC, it was about 20dB less than it should have been. 

Beyond that, we can run some simple checks on your Moreplay to be sure it is working correctly.  24.2dB of gain with a 400W amp means you need about 3.5V to go to full power (which you probably wouldn't want to do anyway) and the Moreplay will put out substantially more than that with a typical 2V DAC.

 

[Finkle]

Paul, fastest response this side of the mississip! 60 hertz test tone running, measuring .123 V AC at each RCA connecter. Measured by positive probe to center pin and neg probe to metal surround of cable side plug all disconnected from preamp. Is this the test you're recommending?

Below is Amazon description for the XLR to RCA cable running between DAC and Moreplay pre. It won't let me post a link for the cable.

Disino Dual Female XLR to Dual RCA Cable, Heavy Duty 2-XLR Female to 2 RCA/Phone Plug

 

[Paul Birkeland]

Yeah that will kind of screw everything up.  Your 2V DAC is 24dB below where it's supposed to be. 

In the previous situation I encountered, I suspected there was some volume slider somewhere not set to maximum, so we ended up pivoting to a Bluesound Node to simplify things a little bit. 

 

[Finkle]

After thinking, the volume from the test tone source was low. Cranked to 100%, same probe locations, now measured .720 V AC at both connecter ends.

 

[Paul Birkeland]

That's better, but still about 9dB off.  I'd dig through all the settings you can find and put everything to maximum so you can squeeze that 2V out.  It's probably also worth using just a regular RCA cable just to be certain the adapter isn't having any unwanted consequences.

 

[Finkle]

Using a different test tone I'm now measuring 1.6 V AC at both plugs with the 5 V output selected. Closer to 1.3 V with 4 V output selected. Pixel 9 phone wired USB to DAC, volume on phone max, DAC set to pre with volume 100% or DAC only both had exact same measurements. Not finding any additional info with quick web searches of what other settings, phone or DAC, could be impeding the output voltage. Shouldn't the 4V and 5V put the same 2 V out we're looking for or shouldn't they be up at the 4 and 5 V? The only settings in the DAC are PCM filter, 4/5V output, bandwidth. All of which were changed and tested without getting to 2V. Any way it is cable related? DAC power supply? Or pretty sure it's the DAC? Anything top of mind I could check in the DAC settings? Is it the phone? All tests have been through pixel android USB to USB DAC.

I am finding a post about Android USB output and an app to bypass that and allow the DAC to figure it all out, it's called UAPP pro. Maybe the phone is the culprit? Almost putting a limiter on the USB media transfer?

 

[Paul Birkeland]

It's certainly worth trying that bypass, but also double checking that the 5V isn't peak-to-peak rather than RMS.

 

[Paul Joppa]

I googled "pixel usb dac" and found that Pixel phones 6 and higher have unresolved issues with many audio DACs. Some even produce only noise, so you're luckier than many others! I followed a few of the links but did not find any comments from Google itself, or any solutions.

 

[Finkle]

Now I'm getting 1.89 V AC at both plugs, only thing I could find that would change the measurements toward the positive was the app UAPP for Android phone. Immediately felt like a cap came off everything, highs really came to life. Just got my new diy speakers in place yesterday so really glad this change happened now. Really can't believe the difference. When testing the RCA's with a song file instead of a test tone, was getting around .200-.500V, after the change it's more consistently .600-.900V ish.

But, still not getting 2 ohm and thinking the system isn't as loud as it could be. Not just that volume is what we're going for but it's when you know something isn't right. It's bothering me, much less now that there's some clarification and the speed of some what/mostly solving it was more than great so thank you guys. If there's any additional input on things to look into I'm all ears. Ty!

 

[Paul Birkeland]

Are you listening with the Moreplay turned up all the way now?

 

[Finkle]

Yes. Why do you ask?

 

[Paul Birkeland]

I'd measure the AC voltage coming out of the Moreplay, then also the output voltage coming out of the speaker jacks (you'll have to put one probe on each binding post on that amp I suspect).  Something still isn't adding up with the maths...

 

[Finkle]

60Hz test track with all volumes maxed including Moreplay. Measuring positive submerged into center of RCA's and negative on the outside, left channels are both showing 3.5V and rights both 9.5V. measuring the speaker connectors after the buckeye amp speaker wires disconnected from speakers, using test tone, all volumes maxed, positive on red speaker input and neg on black speaker input. Getting 5.51V left channel and 6.47V right channel. When not using the test tone and the loudest sounding track I could find disconnected all speakers again and left side never got higher than 3.8V and right 4.6V. Not sure if I did the speaker test right, what does this all mean or should I test anything differently?

 

[timindq]

Do you have a standard source? Something like a simple cd player with a non-variable output? I ask because with a standard source, I can't turn my Moreplay up past 12 o'clock without blowing myself out of the room.

 

[Finkle]

I'd have to ask around for one. There's a PC I could try and have been using the record player. The record player is approximately the volume of most music coming thru wired from the phone. I did increase the gain thru the waxwing to 46db to get it increased.

 

[Paul Birkeland]

60Hz test track with all volumes maxed including Moreplay. Measuring positive submerged into center of RCA's and negative on the outside, left channels are both showing 3.5V and rights both 9.5V.

This would be bothersome, is the balance pot centered? That's about a 9dB difference.  Are the 10K and 100K potentiometers in the correct holes?  Accidentally swapping these parts can quite the negative impact on how the Moreplay works.

 

[Finkle]

The pot is not centered, I manipulated it until the soundstage seemed/felt center. Maybe room gain, as the one side is close-ish to a wall and the other isn't? I'm thinking you're onto something with the pots. Thinking back at the build and not seeing a difference in build I'm feeling like I thought they were the same and I could've swapped them. Looking under the hood at the moment, both pots are stamped with "3ch" and that's it, they look identical. How do I test for which one is which? As I don't think pictures would clear it up, there's no other labels, stamps, manufacture type marks, body are both the same too.

 

[Paul Birkeland]

Set your meter to read resistance and measure the resistance between the inner and outer lugs on the top level of the volume pot.

 

[Doc B]

The markings are on the phenolic part of the pots and are facing the chassis plate. PB's suggestion to use a meter is the easiest way to check which is which or you can undo the mounting nut and pull the pot away from the chassis to read the print on the top of the phenolic. Page 20 in the manual explains which is which.