Break up with PrimaLuna Evo 300

subsonic1050 · « **on:** 19 Jul 2021, 08:00 pm »

Hi all, I am a relatively inexperience tube owner. I previously owned a Rogue Cronus Magnum II - but only for a short while. I just purchased a PrimaLuna Evo 300 integrated amp from a guy on USaudiomart. It appears to have arrived in good condition. It powers on, and it works. I purchased it for a future build of some GR Research NX-Treme's which are almost 95dB efficient. However, until those are done I decided to hook it up to my current speakers - Magnepan 1.7i's. I know they are extremely power hungry, but to my astonishment, it is able to drive them to very reasonable SPL at modest volume (50%) on the Primaluna dial.

However, it does not sound good, and in some cases I am getting some nasty break up. I then pulled out some B&W 602's (the only other speakers I have on hand) which are 90dB efficient. It seemed better, but I still can hear some of that breakup. Then I realized that my RME ADI-2 DAC was adding gain to the signal. When I reduced the volume on the RME and increased it on the PrimaLuna to reach similar SPL the break up had improved, but not been eliminated.

Does anyone have any insight into what is going on here? Can an amp be overwhelmed even at 50% volume? The thing I'm wondering about is if something is wrong with the amp.

richidoo · « **Reply #1 on:** 19 Jul 2021, 08:55 pm »

Yes, an amp can distort even at 50% of its rated input voltage if the load is very low impedance, which demands current above what the amp can source. But the B&W 602 is rated 8 ohms with minimum impedance 5 ohms, so that's not the problem. If you know your source and cables and everything are OK then it's the amp.

From your description it sounds like worn out power tubes. If they say Prima Luna on them then they are the likely culprit, imo. I would replace with Gold Lion 12AU7s and KT88s = $510 from Jim McShane.
It's wise to assume a used tube amp will probably need a set of new tubes and be pleasantly surprised if it doesn't. The seller might give you an idea of the hours on the tubes. This amp runs them gently, so you could expect to get 2000 hours for the output tubes which is only about 1-3 years if it's well loved.

Due to the good build quality of that brand it's less likely, but it could also be a fault in the amp. Resistors sometimes fail in tube amps, and can make horrible sounds. High voltage power supply caps could be faulty, bad solder connection, etc. I assume its coming from both channels, so it's probably worn tubes, or a power supply issue. A dirty volume control or source switch would make "static" noise, that doesn't sound like what you're describing.

Tom Bombadil · « **Reply #2 on:** 19 Jul 2021, 09:57 pm »

Some comments:

1) The volume dial does not tell you how much power you are using. If you are using a high output source then even with the volume set at 50%, you could be clipping the amp. This isn't common but it is possible. Normally a downstream source will feed a 2.0V signal into your amp. I have a couple of pieces which output 2.6 to 2.75V. When I use those I have to lower the volume setting on my preamp. Your DAC is a fully-functioning preamp, with pretty high maximum output. If set anywhere near its 13db maximum gain setting, it could overdrive the inputs in your integrated amp.

2) Are you operating the amp in triode or ultralinear mode? In triode operation the maximum power is halved. For that amp I believe that would mean 21-24 wpc. Now 21-24 wpc should drive the B&W 602 to a fairly high volume, but not to concert volume levels, or near them. I could easily see the Magnaplaner 1.7 struggling with this amp, if in a large'ish room and driven to higher volume levels. I haven't seen any lab measurements of the 1.7 but the 1.6 measured at 83.7db.

3) New tubes may well be needed. I have found that my power tubes wear out much quicker than my preamp stage tubes. Perhaps you do not need to replace the six 12AU7 tubes.

subsonic1050 · « **Reply #3 on:** 19 Jul 2021, 11:03 pm »

Thank you to both of you for the excellent insights. Yes, I did discover that my RME ADI-2 FS DAC was indeed at maximum volume, and was inserting quite a bit of extra voltage into the inputs. I'm not familiar with "overdriving" the inputs, but it certainly seems that was happening. By decreasing the output from the DAC and increasing the volume on the Primaluna to roughly the same SPL the result was much less breakup. I do not have the same issue with my Lyngdorf TDAI-2170 integrated amp, but I have only used the DAC with it in testing, as the Lyngdorf outputs a digital signal so using a DAC is just converting the signal twice for no reason (I use a digital input from a Bluesound Node 2i for streaming).

I only hooked up the B&W speakers to see if the same break up/clipping phenomenon happened with those, and it did. However, when I hooked them up I used the 8 ohm taps on the PL, and I used the 4 ohm taps when hooking up the Magnepan's. Given that the B&W drops to 5 ohms at some points, should I be using the 4 ohm taps?

Before I purchased the amp the gentlemen I purchased it from (who has excellent feedback on USaudiomart) told me the tubes have around 100 hours on them. I have already purchased some new Mullard 12AU7 tubes for the preamp stage (before I even received the amp). Maybe I should get new power tubes as well. I don't plan on really using this amp with either of the sets of speakers I have tried - I'm just trying to determine if the used amp I purchased is functioning as it should or whether I need to talk to the seller about a refund.

SlushPuppy · « **Reply #4 on:** 19 Jul 2021, 11:27 pm »

I had a Mytek Brooklyn DAC a few years ago that caused the same issue you described. It made a terribly distorted sound through my amplifier. I did a quick Google search and found that I could lower the output voltage by using computer jumpers on the DAC motherboard. It immediately fixed the problem. I hope you get this resolved soon.

Cheers!

Slush

Tom Bombadil · « **Reply #5 on:** 19 Jul 2021, 11:41 pm »

Typically an active preamp stage wants to see an input voltage of around 1V with a maximum of 2V. With your DAC output gain set to 0db, that should produce an output of 1V. Your DAC is spec'ed for a max gain of +13db, which would produce about 4.5V. Well higher than what your integrated amp's input stage is designed to handle.

I don't know where on your DAC's volume control, given your digital source, it would produce a 1V to 2V output. Maybe at half volume? I would try using it set at 4 or 5 (on a scale of 10) to see how that works. If set too low, then your amp's preamp section might produce too much noise. If set too high, it could push your preamp stage into clipping at well below your amp's maximum power.

Normally one would not run one preamp section into another preamp, which is essentially what you are doing. Sometimes DACs and other gear which have a high output preamp stage will also have a fixed line-level voltage output option, which is designed to run into a preamp. You might want to read your DAC's manual to see if it offers this option.

subsonic1050 · « **Reply #6 on:** 20 Jul 2021, 03:07 am »

Slush Puppy - that is very interesting. I'll have to do some more research on my DAC. I really haven't used it until now as there was no need with the Lyngdorf amp.

Tom - I did look through the RME manual last night. I have another DAC (not at my house right now or I'd try it) a Doge 10 which has a mode where you can select between Preamp mode or DAC only mode. I don't see that option on the RME but honestly the manual is a tome. I'll do some more investigating.

JakeJ · « **Reply #7 on:** 20 Jul 2021, 03:30 am »

I think Mr Bombadil is spot on here. It sounds like you are overdriving the preamp section of the Prima Luna. Another factor to consider is input and output impedances between the DAC and the preamp section. Sorry, I'm just responding with "off-the-top-of-the-head" ideas. I didn't do any research.

tull skull · « **Reply #8 on:** 20 Jul 2021, 05:31 am »

Another vote for Mr. Bombadil!

I am also wondering if you might be able to defeat the volume of the dac? Maybe it allows rerouting around the volume which hopefully would enable you to turn up the volume on the Prima Luna. That would be ideal.

richidoo · « **Reply #9 on:** 22 Jul 2021, 02:56 pm »

Sorry I didn't notice this for my first post above, but I just saw that the input sensitivity for the amp is only 270mV, so you're probably over driving it. This is likely the reason he sold it, has similar problem as you.

The amp's volume control should be able to attenuate the input signal to stop the distortion. You may be thinking it will play louder than it can and you are turning it up into the distortion range. Full volume setting has not attenuation and will allow a 270mV signal to drive the amp to full power. So when a hot 2V+ signal is being attenuated down to <270mV then the VC is limited to very small range of adjustment at the bottom of its range.

If you can turn down the output voltage of the DAC enough that will restore some of the volume control range on the amp.

A better solution is to add a voltage attenuating resistor network before the volume control (or external before the input jack) to bring down the voltage of all input signals to restore the full range of the amp's volume control. You want to reduce a 2V+ volt signal down to 270mV so roughly 10x attenuation, which equals 20dB. You need 20dB attenuation resistor pad. You can buy that as an inline adapter with RCA male and female, or DIY it very cheap. But attennuating the input signal will make the amp's internal noise more noticeable as mentioned above.

You might call Upscale Audio (the US importer) and talk to someone there about why the input sensitivity is so low, what their thinking was on that. As I understand, they have a big hand in the design. Maybe they can offer some advice.

If the amp has only 100 hours then you don't need new tubes. The preamp tubes should last 4000-5000 hours and the output tubes should last 1000-2000 hours, ymmv.

subsonic1050 · « **Reply #10 on:** 22 Jul 2021, 05:49 pm »

VERY interesting richidoo. So, the input voltage needs to be only 270mV? That seems crazy. Where did you happen to see that information? As I reduced the volume on the DAC it definitely helped with the breakup, but didn't fully eliminate it. However, I don't believe I ever reduced the volume enough to achieve 270mV - maybe 1V at best. Can I actually just hook a multimeter up to my cables and see what my voltage is? I've never had to worry about this kind of thing with any other piece of gear before.

richidoo · « **Reply #11 on:** 22 Jul 2021, 09:21 pm »

Quote from: subsonic1050 on 22 Jul 2021, 05:49 pm

VERY interesting richidoo. So, the input voltage needs to be only 270mV? That seems crazy. Where did you happen to see that information? As I reduced the volume on the DAC it definitely helped with the breakup, but didn't fully eliminate it. However, I don't believe I ever reduced the volume enough to achieve 270mV - maybe 1V at best. Can I actually just hook a multimeter up to my cables and see what my voltage is? I've never had to worry about this kind of thing with any other piece of gear before.

"input sensitivity" iis linked to the primaluna specs page in my last post. The amp will provide enough gain.
There was a time before time when sources didnt have 2v as common today with opamps, but that was LONG before this amp was designed.

To measure the output voltage of your DAC, play this test track on your DAC then measure the voltage across positive and ground on the output jack with multimeter set to AC volts. This track is recorded at "full scale" meaning its level is as loud as your dac can play anything. Full digital volume. Adjust your dac volume control to make 270mV while playing this and see what happens.

Your dac may sound better/quieter when its turned up higher than .27v max. With all those small tubes on the amp you probably have an active input buffer before the volume control, so may or may not be able to increase
the volume of the DAC a little higher (.5v maybe) to get better sound from while still avoiding the distortion and retaining decent range on the amp volume control. In any case, you want the Dac output volume to be as high as possible before the amp distorts. That depends which amplifier stage is distorting. Experiment!
Rich

rotarius · « **Reply #12 on:** 22 Jul 2021, 11:17 pm »

Nasty break up and distortion? I imagine a volume control would solve the input voltage issue. There must be something else going on with the amp.

JakeJ · « **Reply #13 on:** 23 Jul 2021, 03:58 am »

I think Richidoo is on track here. And don't fall for line level attenuators, IME they just introduce noise.

Kw6 · « **Reply #14 on:** 23 Jul 2021, 03:24 pm »

Quote from: richidoo on 19 Jul 2021, 08:55 pm

Yes, an amp can distort even at 50% of its rated input voltage if the load is very low impedance, which demands current above what the amp can source. But the B&W 602 is rated 8 ohms with minimum impedance 5 ohms, so that's not the problem. If you know your source and cables and everything are OK then it's the amp.

From your description it sounds like worn out power tubes. If they say Prima Luna on them then they are the likely culprit, imo. I would replace with Gold Lion 12AU7s and KT88s = $510 from Jim McShane.
It's wise to assume a used tube amp will probably need a set of new tubes and be pleasantly surprised if it doesn't. The seller might give you an idea of the hours on the tubes. This amp runs them gently, so you could expect to get 2000 hours for the output tubes which is only about 1-3 years if it's well loved.

Due to the good build quality of that brand it's less likely, but it could also be a fault in the amp. Resistors sometimes fail in tube amps, and can make horrible sounds. High voltage power supply caps could be faulty, bad solder connection, etc. I assume its coming from both channels, so it's probably worn tubes, or a power supply issue. A dirty volume control or source switch would make "static" noise, that doesn't sound like what you're describing.

Btw I have PL Evo 300 arriving soon. Are Gold Lion best new production 12AU7? What about RFT. My best 12AU7 I have is my only pr of Mullard NOS CV4003! Also are JJ or GL KT88 better all around than KT77 Gold Lion?

richidoo · « **Reply #15 on:** 23 Jul 2021, 07:33 pm »

Quote from: Kw6 on 23 Jul 2021, 03:24 pm

Btw I have PL Evo 300 arriving soon. Are Gold Lion best new production 12AU7? What about RFT. My best 12AU7 I have is my only pr of Mullard NOS CV4003! Also are JJ or GL KT88 better all around than KT77 Gold Lion?

I like Gold Lions because they are reliable, sound really great to me, consistently good reviews of all their tubes, and they are made by an American-owned company in Russia.

I have used and loved GL KT-88 but I've not tried the Gold Lion 12AU7 as it was not available the last time I ran a 12AU7 preamp. My tube seller raves about GL quality and he says that his customers like most of the GL types.

I never tried RFT.

Maybe you can use your Mullards as two of the 6 preamp tubes if you learn the tube layout, that is, which tubes make what amplifier stages. Some of the six will have more effect on SQ than the others, usually the voltage gain tubes.

I never used GL KT77, but I did use JJ KT77 way back and it was utter shit.
I loved my GL KT88s in ARC VT100, very nice!

JackD · « **Reply #16 on:** 23 Jul 2021, 09:05 pm »

The output level on the RME is switchable from 19db to 1db on the XLR outputs and from 13db to -5db on the RCA outputs so go in the setup and turn it down before investing in new tubes. All should be in the manual. I suspect that the default setting from the factory is probably full output.

Kw6 · « **Reply #17 on:** 24 Jul 2021, 06:03 am »

Quote from: richidoo on 23 Jul 2021, 07:33 pm

I like Gold Lions because they are reliable, sound really great to me, consistently good reviews of all their tubes, and they are made by an American-owned company in Russia.

I have used and loved GL KT-88 but I've not tried the Gold Lion 12AU7 as it was not available the last time I ran a 12AU7 preamp. My tube seller raves about GL quality and he says that his customers like most of the GL types.

I never tried RFT.

Maybe you can use your Mullards as two of the 6 preamp tubes if you learn the tube layout, that is, which tubes make what amplifier stages. Some of the six will have more effect on SQ than the others, usually the voltage gain tubes.

I never used GL KT77, but I did use JJ KT77 way back and it was utter shit.
I loved my GL KT88s in ARC VT100, very nice!

Thanks Richidoo! Appreciate you sharing your experience with tubes!😃

Kw6 · « **Reply #18 on:** 24 Jul 2021, 06:05 am »

Btw I read online free that RFT are cool side of neutral! So not for me!

subsonic1050 · « **Reply #19 on:** 24 Jul 2021, 07:18 am »

Well I'm *fairly* certain that the issues I was having were mostly related to the RME input voltage and not the amp. I was going to try the test file that richidoo shared, but I use a bluesound node 2i for streaming and don't have a computer hooked up to my DAC to try it. Since I really just needed to play with it anyway I decided to see if I could find some starting values online. I ended up needing to turn the RME down to around -20 on the volume dial (I don't understand the way the volume on the RME works - there seems to be 2 different volume numbers), but in any case all the distortion and break up went away. Of course it wasn't playing anywhere near as loud any longer, but that was expected with power hungry speakers like Maggie's. There were a few tracks that seemed to have more gain and played louder, and in a few cases there was still a tiny amount of break up. I think this may have been the amp clipping as I had the volume turned up almost all the way (on the primaluna). I mainly wanted to make sure the amp was OK, and I believe it is. I'll have to wait until I get some efficient speakers in here to really test it out, but I think I'm safe!