Valve recommendations for tighter bass in PrimaLuna PL2

Hi,
Been living with a PrimaLuna PL2 for some months now. I really love the overall sound and performance of the amp but have decided it could do with slightly tighter base if possible - outlined below. It’s still with stock 4x KT88, 2x 12AX7, 2x 12AU7; and driving ProAc Studio 140 mkII speakers.
What I’d want
- Tighter bass. Primary requirement. The bass is wonderfully fulsome and deep, but can sound slightly loose on some tracks. The speakers were previously driven by a Cambridge 840a and the bass was notably tighter, if less (wonderfully) deep and organic. I’ve read about people addressing the particular thing on the PL2, mainly through the AX7s (and with one guy recommending the Sovtek 12AX7LPS in particular)
- Enhanced texture and resolution. I don’t say this as a weakness of the amp as it doesn’t feel lacking, but any tubes that would also bring more of it across the board would be no bad thing
- To retain the overall tone of the amp – wouldn’t want it any warmer or cooler really; nor no denser or sparser
- To retain the balance across the frequencies – really not after mid-band emphasis at the expense of extremes
Any experiences/ recommendations around this would be much appreciated. I’ve never tried any other tubes so have no direct frame of reference for others.
If I could achieve the above by just changing the input valves for now that would be ace; especially financially. I’ve read (and kind of feel) that the stock KT88s in the amp are meant to be ok and most seem to focus on changing the Au7s and AX7s – though I’m open to suggestions.
I’ve no prefenrence re NOS vs. re-issues as such – whatever works. But I’ll happily pay extra for something that will last.
Please bear in mind I’m in the UK regarding availability and any recommendations for where to buy any suggested valves etc.
Thanks in advance,
Rob

 

I would call Kevin Deal at Upscale Audio or a European dealer, and see if you can use KT120's in the PL2. The 120's would firm up the bass for you. I use the KT150's in my Dialogue Premium, and love the sound across the frequency spectrum.

 

Kevin (mentioned above) would give you a well informed opinion. I have a 40 watt tube amp that is native KT88. My sense of the KT120s is that they do deliver more power. With a 91 db efficient speaker, this may or may not be what you want/need. My speakers are 92 db, but not floor standers.

If your speakers are rear ported, you might position them further into the room to soften the corner reinforcement of the bass.

It could be that the KT120s would take you in the wrong direction. If you don’t want more power, I might be inclined to try the Golden Lion KT77s. They are very neutral and linear, as they say, and from my experience have the lush mids of the EL34 with very well controlled extension top and bottom.

http://www.upscaleaudio.com/gold-lion-kt77/

Kevin stocks all these tubes and sells the PrimaLuna line.

 

I had a Prologue 2 and my favourite tube set was Sovtek 12AX7LPS, 1960s RCA black-plate 5814A tubes in the 12AU7 positions and personally I preferred EL34s to KT88s, but if you are struggling to control the bass probably best to stick to 88s as they are a more powerful tube. I just prefer the EL34 mid, my best results being with some NOS 70s brown-base Teslas, but Svetlana Winged-Cs are pretty good too. With this tube set the Prologue 2 was a superb amp IMO. I arrived at the small tubes after trying many, many alternates, e.g. I prefered the 12AX7LPS in this particularcontext to yellow print early '60s Mullards that would be >£100 a tube these days. The RCAs
I mention really are stunning too.

 

Thanks for the replies.

The amp certainly doesn't seem to lack power in its current guise - serious volumes and dynamics without being pushed. The speakers are bottom-ported and a reasonable distance from the walls. I've brought them futher in to the room to listen and the slightly loose bass (with the PL2) is still there - ie appears to be a sound characteristic rather than a reflected emphasis. Again it's not the depth or volume of the bass that I'd like to tackle, it could just do with being a bit tighter.

There are a couple of decent valve stores in the UK that I've had it in mind to contact - including this one which actually has created an upgrade kit for the PL2, actually including Gold Lion KT88s: https://www.watfordvalves.com/product_detail.asp?id=2196

Tony - thanks for the specific suggestion (your reply came in as I wrote the above). Good to know. How would you describe the changes in sound moving from the stock to those tubes please? And where did you get them from?

I've been reading around the different power valves the PL2 can take - KT77s, 66s, 88s, 120s, EL34, 6550s, maybe others - and must say it's a touch perplexing, especially as some describe the same sound improvements coming from the input valves that others aim for via output ones. But the EL34 and KT77 mid-band emphasis does get mentioned. I don't think I'd like to lose any power/frequency balance in favour of a mid emphasis, as outlined, especially if it didn't simultaniously address the bass-tightening issue. Would be interesting to hear though.

 

In my experience, KT77s are very flat/neutral, and might supply a bit less power overall than the KT88s. You might also stuff the bottom ports with a bit of polly fill (equal amounts in each) and see what that does. Would not cost much.

Other opinions.

http://forums.stevehoffman.tv/threads/anyone-try-the-genalex-gold-lion-kt77-tubes.188183/

 

Good suggestions - cheers

 

I didn't like the Prima Luna stock small tubes much at all. Ive no real opinion on the '88s as I swapped to EL34s fairly quickly, I never tried any other '88s in it. I've heard a few people suggest that whilst it can take all the tubes it claims it can it was actually voiced with EL34s as IIRC the output transformers are just the same as the ones in the Prologue One. To my ears it sounded more open, three-dimensional and natural with EL34s, albeit with a slight reduction of bass grip, which may be an issue for you given your initial post. They did a decent job with my Tannoys.

If anything the small signal tubes make more of a difference than switching output tubes. I didn't get on with the stock chinese AX and AU7s, just flat, grainy, small and flubby compared to better tubes. Definitely view as a 'starter set'. I found the Sovtek LPS brought much tighter, deeper and more extended bass and sounded really even throughout the range, a seriously good tube for peanuts in this amp. I'd go there first as you are not out much even if for some reason you hate them. I went through a fair few NOS AX7s and never managed to beat them in that amp as even if I could better the top end (Mullards are lovely in this regard) nothing had the same bass weight and grip. Silver-plate EIs are a pretty good tube here too, very nice mid and top, but you lose a bit if grip and extension. I never got to try proper Telefunkens upon which they are based. For the 12AU7s I tried Mullard, Brimar, RCA clear-tops, RCA grey plates, Svetlana, and various others and by far the best were a set of black plate RCA 5814A. Just much bigger and more powerful sounding somehow, a wide open sound with great control. Next best were the RCA grey plates, which are a lovely tube.

 

Cheers Tony - some great specifics in there.

I really think I'll address the small tubes first. The effect you found in the Sovteks and RCAs is encouraging.

I explained what I was after over the phone to a guy at Watford Valves this morning - he recommended the Harma ECC83-STR and Philips Jan Military Specification ECC82; so others to consider. (He also explained how highly he rates Primalunas among all the valve amps he's worked with - which was cool)

 

From a lot of reading around and, not least, direct recommendation above, I got some Sovtek LPS 12AX7s and RCA black plate 12AU7s.

I’d have loved to be able to play around with different valve makes and types and combinations but unfortunately not an option. Still, these provide essentially the effect I was after and it seems a fantastic upgrade.

Notably a more controlled, tight bass response but still with a solid, deep extension where it matters. The bass actually receded back physically in to the soundstage slightly too. Together with a new-found crispness and texture in the mids, the overall presentation is more buoyant and effervescent, but in nice natural, balanced way.

Some high frequencies (high hats, cymbal decay etc) appeared a touch dry at first and caused a slight concern but that seems to have improved –guessing from the valves breaking in. Est 80-90 hrs on them now.

Really no plans to switch the KT88s at present but hey we’ll see...

Thanks again for the advice.
Rob

 

I used Winged C KT88s Tele 83 and Mullard 82s in my P2 with Rogers LS5/9 speakers.
I use the 4 ohm output and the bass is just about perfect, weight, presence, and quite fruity but never
smudging the mid range.

I'd start with changing ohm output used, and in my experience the amp has very little influence in
the quality of the bass, the room is the biggest factor, then the speaker placement/isolation
then the source isolation.

I bet putting your amp on a Mana table would get you nearer than changing the valves.

 

I've used the 4 ohm output from the beginning, thanks - much fuller, more coherent sound than the 8.

The system is in a decent-sized living room and indeed experimenting with speaker/furniture position maked a huge difference - I tried all sorts within reason. But still the slight flabbiness in the bass output fundamentally remained whatever configuration. The new valves really have helped with that, as described.

Did you swap to your described valves in the P2 from the original stock ones? And if so really didn't notice much difference in the bass delivery/quality?