SRS 1.2TL - Biamping tubes and solid state

hauxon

This has probably been discussed before but I could not find exactly what I was looking for by searching. About 2 years ago I did build new crossovers for my 1.2TL using the Gimpod boards and all new quality components. I posted about the building process and got good advice.

Recently I decided to attend to a class in designing and building tube amplifiers. I've finished the first part that was theory and the second part will take early next year where we will "design" and build a tube amp of our choice. So I started thinking I should make an amp to take care of the tweeter array while leaving the current solid state amp I have doing the low mids and bass. The Polk SDA speakers are essentially a 2-way speaker system where you have the 6.5" drivers for the lows and the tweeters doing the highs. A simplification but basically true. The crossover point is fairly high, about 2kHz if I remember from making the crossovers. Frequencies 2kHz and above should be rather easy to drive and according to my seminar teacher almost any amp would be able to drive those frequencies to loud distortion free levels. So I started thinking that maybe I should build a tube power amp and biamp. The tube purists (I've met a few) have wet dreams about class A Single-ended (SET) amps usually with 300B power tubes, usually only about 8 wpc. I know they sound sweet but I kind of wonder if 8 tube watts will do for the SRS 1.2TL tweeter array. The problem of different gain is easily solved since I will be building the amp myself.

Does anyone know what effects the new crossover might have on the 1.2TL specs? According to the original brochure sensitivity was fairly high at 91db and speaker impendace 6 ohms. Any reason to believe my crossover mod changed these specs dramatically?

So has any of you went this path? Would you rather build a push-pull amp for the job? A push-pull configuration will allow me to build an amp that would be close to 40 wpc but I'd not be going the purist route.

I'd also be interested to hear experiences of using modestly powered tube amps with you Polk SDA's in general. A lot of good tube amps have been coming out of China that have brought tube amplification in reach of mortal people. Among many the Willsenton R8 ($1000 pp EL34/KT88 up to 40wpc) and R800i ($2000 300B+845) come to mind. Steve Huff seems to loves his R8. There's also an option of building a kit. I've been looking at kits from Transcendent Sound, Elekit and more (budget $1000-$2000).

Thanks, Hrannar

engie490

Assuming that you didn’t change any of the values of the crossover parts, but only changed the quality, then I doubt you would change the impedance or sensitivity of the system.

When you choose an amp for a speaker, you should understand your own listening preferences. In other words, if you only listen to solo guitar at 75 dB, you’ll have different amplification needs than someone who wants to replicate a full orchestra at 110db. That info, combined with the speaker’s sensitivity and impedance gives you an idea of what you need your amp to do.

In the original Stereo Review review, the SDA SRS’s impedance measured as 4 ohms at 3khz and stayed at 5-6 ohms up to 20khz. I’m not sure how the 1.2TL’s differences (different tweeters and crossover) change that performance, but if you’re planning to pursue single-ended triode amps, you’ll care deeply about that. Since you want to use tube amps on the tweeters, the amp needs to be comfortable with a 4 ohm load.

You’re also talking about running the amps in a vertical biamp scheme, which means that each amp is still reproducing the full range signal and feeding that to the crossover. In this setup, you don’t realize any gains for the amps in dynamic range.

michaeljhsda2

I have a Yaqin 50 wpc integrated tube amp that I've been running on my 1.2 TL's for almost 10 years. Sounds great and plenty of power to rock the house.

F1nut

To the OP. A far more popular and I think far better way is to run a tube pre amp with a SS amp.

invalid

You really can't biamp without an active crossover or at least a gain control on one of the amps, unless you are using identical amps. As F1nut suggested using a solid state amp with a tube preamp would be a far better option.

hauxon

Well tubes suddenly do add coloration but I don't want to "add" tubes in the signal path. By nature tubes are simpler and work consciously from zero volts to distortion levels opposed to silicone being non working until 0.7V and hard clipping at distortion levels and un-linear depending on operating temperature. Solid state amps have all kinds of patches to remedy these shortcomings when (in theory) tubes don't need any. It's not so simple but the thought of a single-ended, one tube, no feedback amp with as simple as possible circuit is alluring, especially at the 2kHz and over frequencies where the human ear is most sensitive. These frequencies should not demand much power. Tubes are of course not perfect. From what I've learned from the tubeheads of the internet the 300B tube comes close.

The only thing I'm concerned about is the 1.2TL having four tweeters but then they don't all work at the same frequencies. To me it would be a total waste to bi-amp using the same amp, why use a 200-500 wpc amp to drive a tweeter? Why not use something more delicate an less crude for the highs? The problem of mismatched gain should be easily solved since I'll be building my own amp. It could also be implemented by a adjustable resistor in the signal path and then match using a microphone (and possibly DSP).

I'll be making a tube amp anyway for the seminar. I just need to decide if a make an 8wpc 300B SET or a 40wpc push-pull. If it doesn't add any magic to my setup I can use it for some of my other (smaller) speakers. I will let you guys know if the journey will fail or succeed.

invalid

You can definitely try it and if it doesn't sound great use it on a high sensitivity speaker later.

engie490

I don't know that anyone looks to add a coloration to the sound of their system, but that's just semantics.

I use a tube preamp, a SS phono preamp, SS DAC (actually an Oppo BDP-105), and a SS amp. My tube preamp happens to measure very well and still possesses some of the see through "tubes quality" in the midrange.

On the other hand, SET amps tend to measure very poorly. Here's a $13K single-ended, monoblock 300B amp that Stereophile measured several years ago:

https://www.stereophile.com/content/thöress-300b-monoblock-power-amplifier-measurements

It puts out a whopping 3.5W at 1% THD at 1Khz into 8 ohms. It will definitely sound different than any "properly engineered" amp and it's frequency response will tend to deviate with (or follow) the impedance curve of the speakers.

I'm not saying you can't use a SET amp and enjoy it as you discussed above, I'm just informing of you the "problems" you'll face from a technical perspective. Only your ears can tell you if what you describe above (or any other configuration) is what you're looking for.

I do have a Rogue 88 Magnum, which is a push-pull, 6550-based amp that puts out 60W (per the specs), I can pull it out of storage and attempt to do what you are describing, but I can't find any mention of gain into the 4 or 8 ohms taps. Which makes matching it with a SS amp problematic. I'll probably just see what it sounds like run full range.

tonyb

Though not the only solution, a tube pre amp and solid state amp as others suggested has been a tried and true preference over the years for many hard to drive speakers. Especially if you like to kick it up when the wife and kids are out of the house.

Everything matters in the chain too.

F1nut

Well tubes suddenly do add coloration but I don't want to "add" tubes in the signal path.

Say what!?!

hauxon

F1nut wrote: »

Well tubes suddenly do add coloration but I don't want to "add" tubes in the signal path.

Say what!?!

What I mean here is that different tubes seem to have different sounds and even different tubes of the same type sound differently, so one can assume alteration/coloration is happening to some extent.

hauxon

engie490 wrote: »

On the other hand, SET amps tend to measure very poorly. Here's a $13K single-ended, monoblock 300B amp that Stereophile measured several years ago:

https://www.stereophile.com/content/thöress-300b-monoblock-power-amplifier-measurements

It puts out a whopping 3.5W at 1% THD at 1Khz into 8 ohms. It will definitely sound different than any "properly engineered" amp and it's frequency response will tend to deviate with (or follow) the impedance curve of the speakers.

Well, 3% seems pretty high but like you said distortion values for tube amps are much higher than for a transistor amp. I read somwhere, probably in Bruce Rozenblic's Audio Reality that you can't hear distortion until it passes 1%, so less than 1% would be desirable but whether it's 1% or 0.0001% won't matter since you can hear neither one.

What I need to figure out is how much energy my tweeters need to keep up with the woofers on the solid state. Will i only need 3-8 watts while the woofers are pumping out 100 times the power? Would 25 watts do ..or 50? that's I'd like to know. The tweeters only do their thing above 2000 Hz, needing less power but how much less.

invalid

It puts out a whopping 3.5W at 1% THD at 1Khz into 8 ohms. It will definitely sound different than any "properly engineered" amp and it's frequency response will tend to deviate with (or follow) the impedance curve of the speakers.



Even order harmonics are audible at 1% where as odd oder harmonics are audible at .01%. solid state amps have higher order odd harmonic distortion which is audible at a lower percentage, which can make them sound harsh.

F1nut

hauxon wrote: »

F1nut wrote: »

Well tubes suddenly do add coloration but I don't want to "add" tubes in the signal path.

Say what!?!

What I mean here is that different tubes seem to have different sounds and even different tubes of the same type sound differently, so one can assume alteration/coloration is happening to some extent.

Oh boy.....

hauxon

F1nut wrote: »

Oh boy.....

No need to moan! The "get a tube preamp" suggestion might work for most but doesn't for me. My DAC has an excellent preamp section so I won't be adding another preamp into the mix.

I would value a reply to the original question. Why would you not use a tube power amp for the 1.2TL tweeters? Is it a bad idea, then why? Sonic imbalance? Technical issues? You generally don't like biamping? ..or you just need to moan.

TroyD

I don’t mean to be critical here but you are sorta all over the map on this.....you don’t want to add a tube preamp in the mix but you do want to add tubes via a tube amp on the tweeters.

Biggest problem that I see here is that the gain on the amps is likely to be different.....that’s a problem to solve. The easiest way to solve it, and achieve your goal of adding tube magic is via a preamp. The same number of devices in the chain (less actually because you’ll need more pieces to solve the gain mismatch) and the added bonus of it being overall less complicated and less expensive.

Now, you can say.....but I want to bi-amp....and I want to keep my Dac as a pre etc etc....cool, just do it then. If you just need validation, nobody is stopping you.....but when it sounds worse, don’t say the issues weren’t raised....

SeleniumFalcon

The important consideration is that both amplifiers (solid state, vacuum tube or hybrid) need to have the same input sensitivity. If not then one of them needs to have someway to adjust the output to match the other amplifier.

hauxon

TroyD wrote: »

I don’t mean to be critical here but you are sorta all over the map on this.....you don’t want to add a tube preamp in the mix but you do want to add tubes via a tube amp on the tweeters.

Not really. Tubes don't do magic, they are not a spice or flavor to the music, it's not what I'm after. Tubes have many problems that mostly have to do with them doing too much work, being overdriven. However their amplification is "purer", what comes in is what comes out but amplified. In theory a single-ended tube amp working within it's operating limits should provide amplification in closest relation to the signal put in. Solid state obviously works but is a mess in comparison to tubes.

I however don't believe one form of amplification is really superior, each has its strengths and weaknesses. Tubes seem like the right tool for the mids and highs to my eyes (ears). No hurt in trying, if it doesn't work it doesn't and if it does ...great!

TroyD

No, I get what you are after here.....but, the practical application is what I'm describing. (IMO)

Again, the issue you are going to have is gain.....

On the theoretical side of it, look, I LOVE tubes. LOVE....but they aren't the panacea that some folks think just as analog (LP) superior is to digital. On paper, sure, the analog waveform is perfect....but the devil is in the details. We don't listen to theory. We listen to the implementation.....and in both cases, the inherent pitfalls have been worked on and mitigated over the years.

I think it's awesome that you are getting into building your own gear.....again, I'm not a poo-poo guy....absolutely, try it and if it works great and if not, well, you tried......but, again, the biggest problem with what you are looking at is mismatched gain.

invalid

The OP said in a post above that he would introduce a gain control when building the amp. Sounds like he's going to build it no matter what is said here. I don't think any of the SDA's are really a candidate for biamping. I would think a hybrid amp would be a better option.

hauxon

invalid wrote: »

Sounds like he's going to build it no matter what is said here.

Correct and I wanted to hear from people who have actual experience of using a tube amp with the big Poks. Seems work fine for Michael using a more powerful push-pull amp with his 1.2TL. I just might find someone to lend me a tube amp to try out. I’ll let you guys know what happens.

TroyD

It's not about gain control or if tube amps work with SDA (I ran my 2.3tl's with a CJ MV-75 for a long time...SDA's aren't super power hungry regardless what people say). My point is.....and look, I think what you are doing is cool AF and I'm not trying to be Debbie Downer but bi amping with different amps is WAY more complicated than it would appear and I'm just not sold that the performance gains are going to be there.....

That said, keep on rocking in the free world

SeleniumFalcon

For whatever it's worth Matt Polk bi-amped his speakers with a solid state amp on the low end and tube amps, I refurbed, on the top. He seemed happy to me.

motorstereo

About once a year I'll use my Yaqin mc100 integrated on my 1.2tls just to change things up and add a little heat to the room during a cold snap.

Gardenstater

SeleniumFalcon wrote: »

For whatever it's worth Matt Polk bi-amped his speakers with a solid state amp on the low end and tube amps, I refurbed, on the top. He seemed happy to me.

Worth quite a lot I'd say! To the OP, looking forward to your experiences when you go forward with this. There must be people on the other forums, if not here, who have done what you are planning to do, although maybe not with these exact speakers.

invalid

Tube amps can work fine with SDA's just not biamping.

SeleniumFalcon wrote: »

For whatever it's worth Matt Polk bi-amped his speakers with a solid state amp on the low end and tube amps, I refurbed, on the top. He seemed happy to me.

With the 1.2tl's. I thought he was using the threshold monoblocks full range at that time?

hauxon

Well, I did build a SET 300B amp based on the Audio Note Kit 1. It is operational with few minor tweaks left for later (like the input selector switch). I connected it to my SRS 1.2TL and it sounds terrific, especially with vocals and acoustic instruments, guitar, piano, trumpets, saxophones etc. And the measly 8 watts to my surprise do easily drive the speakers at low to moderate levels. I would guess the 300B amp half way up is about the same gain as my Cambridge Audio 851W at -25db. I does give in when playing at very loud levels, for example listening to Pink Floyd's Mother at loud level it sounded great until the song goes powerful (guitar solo at 2:51) then it didn't deliver the punch I'm used to with my CA 851W. ...so next up is building an active crossover and a tube preamp. I can wire the 300B as a power amp. Until then I'll listen at moderate levels (99% of the time anyway) and enjoy it's quality, and my CA 851W will get a little rest.

Here are (phone) pictures of my tube amp.



Building it was great fun and really, really time consuming. The starting point was (good quality) PCB plates I got off ebay based on Audio Note Kit 1. The cost of the project also was a bit higher that I had planned. I thought I would be able to assemble it for maybe $1000 to $1500 but when everything is counted (not work hours) it ended up costing about $2500. The 300B heater and power supply are built with fairly cheap components but for the driver board and 300B hardwiring I decided to have premium parts, Takman and Mills resistors and good quality capacitors. The transformers were made to specs for me in Greece and tubes are NOS Tung-sol in the preamp section and new matched JJ 300B. There was also a lot of work doing the copper chassis top using a CAD program and back and forth visits to the metalworkers. Lots of drilling! Great fun and next up is probably an active crossover.

Next post probably around christmas!

Hrannar

VR3

Looks great!

hauxon

VR3 wrote: »

Looks great!

Thanks, I decided having a copper top plate after looking at the Japanese Audio Note (Kondo) amps. Still need to find copper nuts and bolts to match. The white on the transformers is how the come from the guy who makes the transformers (Thermionic Labs). I kind of like having em white, makes it a bit different.

I may upgrade some parts later but no hurry since there is nothing really wrong with it.

Building the amp was the most satisfying thing I’ve done in years.

nooshinjohn

hauxon wrote: »

VR3 wrote: »

Looks great!

Thanks, I decided having a copper top plate after looking at the Japanese Audio Note (Kondo) amps. Still need to find copper nuts and bolts to match. The white on the transformers is how the come from the guy who makes the transformers (Thermionic Labs). I kind of like having em white, makes it a bit different.

I may upgrade some parts later but no hurry since there is nothing really wrong with it.

Building the amp was the most satisfying thing I’ve done in years.

Rookie…

lightman1

nooshinjohn wrote: »

hauxon wrote: »

VR3 wrote: »

Looks great!

Thanks, I decided having a copper top plate after looking at the Japanese Audio Note (Kondo) amps. Still need to find copper nuts and bolts to match. The white on the transformers is how the come from the guy who makes the transformers (Thermionic Labs). I kind of like having em white, makes it a bit different.

I may upgrade some parts later but no hurry since there is nothing really wrong with it.

Building the amp was the most satisfying thing I’ve done in years.

Rookie…

Show off.... punk a**