audio-talk

I've got the kit we need, maybe we can arrange something if I'm heading down that way. I would like to hear these too, ears are the final arbiter !

Ray, I have a couple of miniDSP in storage. Getting them is not so easy as its only open during the week. See what I can do.

IslandPink wrote: ↑Thu Dec 19, 2019 9:55 am I've got the kit we need, maybe we can arrange something if I'm heading down that way. I would like to hear these too, ears are the final arbiter !

Let's sort something out in the new year Mark - as Judy, my partner, isn't in the best of health it might be easier to come up to you - I'll be interested in your experiments anyway.

Ali Tait wrote: ↑Thu Dec 19, 2019 12:52 pm Ray, I have a couple of miniDSP in storage. Getting them is not so easy as its only open during the week. See what I can do.

That's really kind of you Ali - don't put yourself to any trouble though as there's plenty of time before I'll need to experiment.

As and when...

I think this is closely related to Ray’s SLOB project. Following this thread raised the question about the best x-over again.

Some years ago I tried an OB with the PM6A in combination with my La Scala bass horns but always felt that the speed was lacking behind the bass. So I tried a midBLH with the PM6A and the speed problem was no longer there.
I wanted the full sound character of the OTLs but neither a simple 6dB passive x-over with high quality parts nor the Behringer Ultradrive could deliver it in comparison to single driver BLHs. I am still wondering if a tube based x-over would do a better job regarding the "sound character".

Does anybody know the P. Millett tube based x-over? There are still some PCBs available on ebay.
http://www.pmillett.com/tube_active_crossover.htm

Just seen these on the HFC web site, a new product to them.

https://www.hificollective.co.uk/drive- ... 0-neo.html

pre65 wrote: ↑Fri Dec 20, 2019 3:35 pm Just seen these on the HFC web site, a new product to them.

https://www.hificollective.co.uk/drive- ... 0-neo.html

Have you seen the asking price for a pair of these drivers? £4300 a pair excluding VAT + p&p
So Phil, you gonna be the first to take the plunge and give us a review how they sound on your own OB speakers?

WOW !!!!

I only had a quick look and I thought it was £430.00.

I was wondering earlier why you had posted that link Phil!

Still cheaper than a pair of AER's, hard to believe !

Wolfgang wrote: ↑Fri Dec 20, 2019 3:11 pm I think this is closely related to Ray’s SLOB project. Following this thread raised the question about the best x-over again.

Some years ago I tried an OB with the PM6A in combination with my La Scala bass horns but always felt that the speed was lacking behind the bass. So I tried a midBLH with the PM6A and the speed problem was no longer there.
I wanted the full sound character of the OTLs but neither a simple 6dB passive x-over with high quality parts nor the Behringer Ultradrive could deliver it in comparison to single driver BLHs. I am still wondering if a tube based x-over would do a better job regarding the "sound character".

Does anybody know the P. Millett tube based x-over? There are still some PCBs available on ebay.
http://www.pmillett.com/tube_active_crossover.htm

Hi Wolfgang. My plan is to not hamper the full range drive unit with any passive crossover components and aim for an active crossover. That should mean the OTL amp connects directly to the full range unit and should even have an easier time because it's relieved of low-end bass duty.

There seem to be many ways to approach the crossover requirement but I'm gradually narrowing it dowwn as I read around the subject. One approach I'm contemplating is that as an HQPlayer I have the opton of using its convolution option to apply any room correction I may want, meaning I can keep the crossover to simply defining the roll-off slopes.

I think you might be wise to experiment with a high-pass for the Lii driver on OB, even if it's only at 100 or 120Hz. As you can see from the plot I showed on the first page, it will go down below 60Hz , where the excursion could get quite significant. Their recommended enclosure would limit the bass excursion somewhat, unlike OB. You can easily try this with a smaller coupling cap in the OTL amp.

IslandPink wrote: ↑Fri Dec 20, 2019 10:14 pm I think you might be wise to experiment with a high-pass for the Lii driver on OB, even if it's only at 100 or 120Hz. As you can see from the plot I showed on the first page, it will go down below 60Hz , where the excursion could get quite significant. Their recommended enclosure would limit the bass excursion somewhat, unlike OB. You can easily try this with a smaller coupling cap in the OTL amp.

That is what I plan to do Mark but have assumed the active crossover would take care of it and hadn't considered that the amp's output cap already offers the option of a high-pass filter, however that gives a very slow roll-off and I'm not sure it would be sufficient? For example, assuming the drive unit is an 8ohm load, a 1000uF output cap gives an optimal LF response of about 200Hz but it's only 3dB down at 20Hz?

It would be a shame to use an active crossover into a super-transparent OTL amp and a FR driver - you're limiting your sound quality from the start.

Ray P wrote: ↑Sat Dec 21, 2019 4:24 am ....a 1000uF output cap gives an optimal LF response of about 200Hz but it's only 3dB down at 20Hz?

I don't understand what you mean by optimal response about 200Hz, when it's 3dB down at 20Hz. I'm suggest you try sizing the cap (smaller ) eg. for 3dB down at 100Hz in which case it's about 9dB down at 50Hz. Is the output cap the only coupling cap ? - Is there not one between driver and output valves, that would be a smaller thing and easier to swap ?

IslandPink wrote: ↑Sat Dec 21, 2019 12:27 pm It would be a shame to use an active crossover into a super-transparent OTL amp and a FR driver - you're limiting your sound quality from the start.

Ray P wrote: ↑Sat Dec 21, 2019 4:24 am ....a 1000uF output cap gives an optimal LF response of about 200Hz but it's only 3dB down at 20Hz?

I don't understand what you mean by optimal response about 200Hz, when it's 3dB down at 20Hz. I'm suggest you try sizing the cap (smaller ) eg. for 3dB down at 100Hz in which case it's about 9dB down at 50Hz. Is the output cap the only coupling cap ? - Is there not one between driver and output valves, that would be a smaller thing and easier to swap ?

Sorry Mark, didn't sleep well last night and it was probably not a good idea to be posting at half past four in the morning as my thinking and communication were clearly pretty confused! I'll try again.

Ideally I would like to do as you suggest and run the full-range driver straight of the OTL amp outputs but my thinking until now had been along the lines of needing to roll-off the unit at the bottom end and I hadn't thought beyond the active crossover approach but your suggestion has nudged the thinking along several notches.

The bit where I really was sleep-walking was the cap calculations. I used this cap calculator but I have no real idea why I put those values in to it;

https://www.v-cap.com/coupling-capacitor-calculator.php

The calculator notes talk about phase anomalies around the corner frequency and recommends a rule of thumb of using a corner frequency a tenth of your target frequency to avoid the anomalies and I think that's what adled my brain. Anyway. a -3dB frequency at 100Hz requires an output cap of around 200uF (which puts it into plastic film cap territory). So bandwidth limiting the OTL woud just leave the problem of balancing the bass unit to fill in at the bottom end.

Cheers Mark and thanks for being patient.