[Graham Maynard]

Hi painkiller,

Parallelling drivers with low resistance wound components and a decent amplifier will gain almost 6dB at LF.  If you need maximum LF then try removing any R in series with the choke and use a low resistance component.  The circuit itself cannot help more than 6dB around 30Hz where the output of a higher Qes higher Fs driver is already falling even more sharply (approx 15dB/oct), so if you were already using EQ at or below this frequency, then it can be reduced but not removed.  This circuit induced 6dB boost does still help though, because with lesser EQ boost then being necessary the phase shift at LF with respect to mids is also reduced and thus the overall reproduction is improved.

Increasing the C value and reducing the R in series with it will further cut the midbass.  These values must be related to driver Fs, Qes and mounting, so maybe going up to 1,000+470=1,470uF, or 3x470=1,410uF would help.  Also try reducing the R in series with the capacitor to 0.47 ohms as well.

The T-bass circuit is only to help with LF roll-off losses, and cannot be thought of as if it is the crossover.  Also some crossover adjustments might be necessary if there is a 'thickening' of upper bass reproduction where two drivers are operating within the same frequency range.

These aspects are not something I can work out remotely, so maybe you could try another series choke between the T-bass circuit and the Alpha(s) as well as crossover arrangements on the mid/wide driver.  Try a 10 ohm damping resistor in parallel with the mid driver;  yes this is inefficient, but it can have considerable good effect in damping mid/upper bass crossover circuit to driver interactions, also damp output in the breakup region.

Cheers ..... Graham.

[painkiller]

Thanks for the tips. I'll try some different capacitor values and a parallell damping resistor for the midrange.

I just found out that my inductor has a DC resistance of 2 ohms. Maybe I'll get one of those lower resistance ones, even if they're a bit expensive.

[Graham Maynard]

Hi painkiller.

That choke sounds like one to keep for a small LS enclosure where choke R can increase bass output by effectively increasing driver Qes. 
In the T-bass it will just not provide enough solid depth to the LF because it will be acting like a 'damped electrical spring'.

You could try this. 

Take the transformer out of one channel and use a single 15V winding as the choke in the other (or even parallel the 15V windings).  This is bound to give you low enough winding R and the inductance will not be so far out that it won't work.

Cheers ......... Graham.

[painkiller]

That sounds advanced.  aa I think I'd rather pick up a couple of reasonably priced P-core inductors on my way home from "work" (). Those have pretty low DC-resistance in the range of 0,3 ohms.

Parts Express has some awesome looking Jantzen C-core inductors with close to 0 ohm resistance at $35 a piece.

I have a couple of good 1500uF caps I could try. They only have a 20V rating though. Do you have any favourite caps for this application?

[Graham Maynard]

Hi painkiller,

It might be that you do not have to increase the C if you go for a lower resistance choke.  Wait until you have tried that first.

(Wish there was a counter here where I could go and buy chokes.)

Cheers ...... Graham.

[painkiller]

Wish there was a counter here where I could go and buy chokes.

It's really convenient. I work 5 minutes away from www.dynabel.no, which sell drivers, crossover components, diy kits and so on. And there's only a 10 minute drive to ELFA, which is the largest electronics supplier in Scandinavia. 

[painkiller]

Well, the low dcr chokes gained me somewhere between 3 and 5dB extra bass, so that was quite a significant upgrade. I still think I'll need an extra pair of drivers though, and also additional low pass filtering. But I think I'm really close to my goal of making a passive 100dB/w OB speaker. I can actually listen without any EQ now, which is quite nice. Still a bit lean, but not that bad.

[Graham Maynard]

Hi painkiller,

Good to hear you are still making progress.

You could overlap the baffles and parallel the Alphas to see what 2x 15" will sound like.  I find that 2x 15" seems more than twice as loud, and that should complete the balance for you.

I've just ordered 2x Eminence DeltaPro-18A to parallel with my Beymas.  Higher inductance, slightly lower Fs and expected to make a good share by boosting LF whilst the Beymas do better dynamics.
Different Fs frequencies to further lower bass Q.

Cheers ....... Graham.

[painkiller]

After switching caps and resistors a bit I ended up with 0,5 ohm resistor in series with 690uF caps. This gave me good extension, and pretty tight bass. The bass is actually so good at this point that I'll rather spend money and time on ribbon tweeters and trying to optimize their integration. So the extra bass drivers won't be first priority.

Thanks for all the help with the T-bass. It's been a wonderful experience.   

[Graham Maynard]

Hi painkiller,

The value of T-bass capacitor which provides the best sounding reproduction is inter-dependent with the series resistance of the choke.  You had a higher series R choke and therefore the larger value of C sounded better because some of the low LF boost had been missing.

You say the HF is next - something I too am thinking about here.
Given that an OB mounted main driver already runs with good efficiency and has additional LF augmentation (as opposed to crossover levelled output) this raises the overall sensitivity which must be matched.  Thus I am concious that many 'normal tweeters' are just not sensitive enough, and as I have parallel LF drivers, the sensitive B200 and a wish to go beyond 20kHz at outset, presently I have my eyes on -
http://www.visaton.com/en/chassis_zubehoer/ht_horn/tl16h_8.html

which is not cheap and would still require a second rear firing tweeter to maintain characteristic dipole 'airiness'.

I wish you luck in integrating your chosen device, and do please share your choice/results in case these can be help me.

Cheers ........ Graham.

[jkelly]

Anyone have a parts list for parts express to build this circuit? (single Alpha 15)

Jeff

[scorpion]

The Behringer DCX2496 costs 270 US$ at Parts Express. By European standards that is extremly cheap. It is very good from the beginning and there are some cheap tweaks to even get it perform at higer level digital-analog.  It is a 6-channel digital device with extremly versatile possibilities to change loudspeaker performance. For any loudspeaker set up. So just consider costs over benefits in making judgements. The Behringer is also a super crossover unit 6-channel.

/Erling

[ttan98]

The Behringer DCX2496 costs 270 US$ at Parts Express. By European standards that is extremly cheap. It is very good from the beginning and there are some cheap tweaks to even get it perform at higer level digital-analog.  It is a 6-channel digital device with extremly versatile possibilities to change loudspeaker performance. For any loudspeaker set up. So just consider costs over benefits in making judgements. The Behringer is also a super crossover unit 6-channel.

/Erling

I agree with you and go further to say if the speaker buider is happy with the sound his speakers and if desired can build a passive x-over to compared it against the DCX. If it is superior to DCX then selling the DCX is very easy and not losing too much money.

[painkiller]

Thus I am concious that many 'normal tweeters' are just not sensitive enough, and as I have parallel LF drivers, the sensitive B200 and a wish to go beyond 20kHz at outset, presently I have my eyes on -
http://www.visaton.com/en/chassis_zubehoer/ht_horn/tl16h_8.html

which is not cheap and would still require a second rear firing tweeter to maintain characteristic dipole 'airiness'.

I wish you luck in integrating your chosen device, and do please share your choice/results in case these can be help me.

I've chosen the Fountek NeoCD2.0. http://www.madisound.com/catalog/product_info.php?products_id=1556 It's said to be really great, and it has a convenient 100dB SPL above 7kHz. It's not dirt cheap, but it's the best alternative I've found. Can't wait to try it. I'll share my experiences later.

"Normal" tweeters just don't work. Even the most efficient dome tweeters are too weak, and their sound signature is too soft to be able to keep up with a big midrange.

Sorry. Off topic.

[Graham Maynard]

Hi Jeff,

I've looked at the Parts Express website, but I can't find SS amplifier PSU transformers for sale there;  only tube types.

Hi Erling and ttan98,

Whilst I cannot disagree that the Behringer would have its uses, unless a pair of separate LF amplifiers are also introduced neither it nor EQ can provide a necessary *increase* in LF SPL, whereas the T-bass can!

Signal level response shaping arrangements only cut 'unwanted' output (say above LF driver Fs), whereupon DSP and EQ introduce significant phase distortion at bass frequencies with respect to unmodified mid and treble frequencies.  The greater the levels of compensation introduced for OB response flattening - the worse the reproduction of dynamic wavefronts becomes.

The comparatively less expensive transformer based circuit introduces much less deleterious transient (first cycle) response distortion, this leaving much less need for any EQ or DSP where a flat SPL characteristic is still deemed necessary.  Once the T-bass output has been optimised there can then be a desire to preserve the improved waveform coherence in time it provides, by not using DSP or EQ.

Hi painkiller,

Thanks for the link.  I look forwards to hearing of your findings.

Cheers ......... Graham.

[fergs1]

Greetings Fellas, firstly Painkiller what midrange are you using and do you have photos of your setup? I would love to see where you are coming from.Graham I have printed out the whole thread and trying my hardest to sus it out as unfortunately when i did physics at school I was down the back playing with myself.
   I have a friend who makes his own valve amps including winding all power, choke and opt trannies. he can wind anything.With this in mind he wouldn't need to wind a power trffo? as he would just need to wind a high quality stepup with the extra tap?Is this right as the primaries on the  power traf in you circuit aren't being used. With the fact that he can wind very high quality coils and trafs would I be better trying the circuit in post 90# with my 1- alpha 15  and 1- b200 per baffle setup. Also since the alphas will only handle about 40 watts in ob could I use a gainclone which has about 60 watts.I know all ss amps have nfb but I'm not sure of the gainclone topology but my interest in them is that you can build very small amps which in my hifi stand is already dominated by a 300b set ajnd seperate valve preamp and pultec eq section. Sorry for all the questions but I am just keeping my head above all the ocean of theory. This is a great thread and I thankyou graham for taking the time to share all your findings with the parish
                               peace and goodwill       fergs

[painkiller]

Baffles are straight, even though they look a little strange on the pics.    The tweeter in the photos is a Peerless textile dome.  Midrange is a crossoverless Tone Tubby 15" bass driver. Alpha 15A on the bottom. The two speakers are made as a mirrored pair. Side "wings" are asymmetrical. Baffle width around 42cm.

[fergs1]

Thats fantastic! Its funny the alpha looks a bit pissy next to the tt, how does the tt sound.I thought you had b200 and if you did how do they compare?
                                    cheers  fergs

[fergs1]

by the way where is the tweeter brought in at and what is the tt good up too?

[Graham Maynard]

Hi Jeff,

This choke would probably be fine, and you could try these capacitors, say 2 of the 100uF and 220uF to give you a wide range of series/parallel value combinations.

http://www.partsexpress.com/pe/showdetl.cfm?Partnumber=266-574
http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=027-378
http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=027-360
http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=027-368

Ordinary 7 to 10W wirewound resistors will be fine;  non-inductive types not necessary at LF.

Regarding transformer;  a 225VA component as used by painkiller will be fine for an Alpha-15A or even two in parallel.  Two 20V windings would probably be best for saturation protection without going too high in winding resistance.  

Hi fergs,

Your 300B amp is a good choice for the B200, where a simple series input capacitor for LF roll-off at amplifier input will protect the B200 against over-excursion.  This is better than a capacitor in series between amplifier output and the B200 which fails to counter a phase shifted Fs resonance which still eats up driver linearity/X.max.

As you say OB mounting reduces driver power handling capability, so I cannot see any reason why a 60W gainclone will not be useful for driving a single Alpha-15A.  SS amps cannot drive as loud as equal power tube amps but a low impedance drive is necessary here, and tube amps tend not to have very low output impedance at LF.

I too have wound my own transformers, but for the T-bass I would suggest purchasing toroidal types which are generally bifilar wound.  E/I and T/U cores lead to a higher winding resistance, though if the primary was omitted then say four equivalent of 24V windings quadrifilar wound, and used in parallelled pairs would work very well.

Cheers ........ Graham.