Active crossover for three way actively amplified speaker

[Tube Radio]

I've got Carver TFM-15, TFM-25 and TFM-35 amps that I use for a three way actively amplified speaker consisting of:

Altec 811B horns
Eminence Delta pro12A for midbass
Dayton Audio 12" subs

I currently use a DBX 234XS crossover which works fine except there is solid state hiss heard in the horns due to the TFM-15 not having any markings on the front panel for the input level controls nor does it have pots with detents. So there's no easy way to ensure the controls are set the same way every time the system gets used to DJ with.

I would prefer an analog crossover, but if there's a DSP crossover that is good enough for actual HI-FI use I'd be interested in that as well. The crossover also needs to be low noise as well given the Altec horns are quite efficient.

 

[AllenB]

Have you considered setting the level control to full and padding down the horn with an L-pad?

 

[Tube Radio]

The issue is the solid state hiss that comes from the crossover so padding the horn with an l-pad won't eliminate that issue.

I can either:

1. Get a quieter crossover.
2. Build a quieter crossover.
3. Pad down the input with a 75k resistor in series with the 50k level pot.
4. Find some small stepped attenuators that will fit the stock level control locations
5. Replace the pots with a fixed voltage divider.

I could go with a Behringer ultradrive

https://www.behringer.com/product.html?modelCode=0825-AAA

Or

DBX DriveRack

https://dbxpro.com/en-US/products/driverack-venu360

https://dbxpro.com/en-US/products/driverack-260

https://dbxpro.com/en-US/products/driverack-pa2

But I don't know how good they are for HI-FI.

Dayton Audio also makes a DSP.

https://www.amazon.com/Dayton-Audio-DSP-408-Digital-Processor/dp/B07D3H5X5V

 

[Tube Radio]

I do have a JBL MS-8 DSP that I used in a 2005 CRV for several years and it sounded great.

I could repurpose that, however it also has built in amplifiers so I'd need a several amp 12 volt supply to power it with.

It also has an auto setup feature using a headset with two mics in it so I'm not sure how well that will work with the stereo speakers given it's meant for car audio.

 

[eriksquires]

Minidsp

 

[Tube Radio]

The sensitivity of the TFM-35 is 1.5V for rated power output.
The sensitivity of the TFM-25 is 1.5V for rated power output.
Doesn't say what the sensitivity of the TFM-15 is, but it's likely 1.5V.

So that would definitely work provided there's no solid state hiss coming from the Minidsp.

That said how good does the Minidsp sound?

 

[ctrlx]

increase the signal level to the xover either externally or internally, then reduce the outputs of the xover.

 

[Tube Radio]

The problem is there's some solid state hiss coming from after the high frequency level control so it's likely coming from a stage there. I would have to figure out which stage is noisy and drop the level after that stage.

That said I could see what OP-AMPs are used and look for a suitable low noise OP-AMP to replace them with.

However I do like the Minidsp provided it doesn't put out any solid state hiss and has a good DAC and ADC.

 

[Tube Radio]

I can either get this minidsp

https://www.minidsp.com/products/ht-series/flex-htx

Or this one.

https://www.minidsp.com/products/minidsp-in-a-box/minidsp-flex-eight

 And an ADC.

https://www.minidsp.com/products/usb-audio-interface/adept.

If I like it good enough I could get a second one for my other system I'm working on which is a pair of Advent Maestro speakers I intend to tri-amp (original crossover was all wrong and made the speakers sound bad) with some Adcom GFA amps and the 8 channels will allow me to add a sub to make it a four way design.

 

[ctrlx]

I currently use a DBX 234XS crossover

have you setup your DBX unit for minimum noise ?

 

[Robh3606]

The issue is the solid state hiss that comes from the crossover so padding the horn with an l-pad won't eliminate that issue.

No but it can drop it by 10dB using a fixed pad voltage divider and still be able to keep up with the rest of the system. If you are using it as a portable DJ system that should be enough. How are you tailoring the frequency response on the 811 or just not using the raw driver/horn response?

Rob 🙂

 

[Tube Radio]

have you setup your DBX unit for minimum noise ?

Not sure how to do that unless I use a pad before the TFM-15 amp.

No but it can drop it by 10dB using a fixed pad voltage divider and still be able to keep up with the rest of the system. If you are using it as a portable DJ system that should be enough. How are you tailoring the frequency response on the 811 or just not using the raw driver/horn response?



Rob 🙂

I use the high pass out of the DBX set to around 2.8kHz

 

[ctrlx]

with the xover input at 0dB and the outputs at 0dB, there will be a certain level of noise.

if the input is now set to +10dB and the outputs -10dB there will be 10dB less noise.

 

[conanski]

I currently use a DBX 234XS crossover which works fine except there is solid state hiss heard in the horns due to the TFM-15 not having any markings on the front panel for the input level controls nor does it have pots with detents. So there's no easy way to ensure the controls are set the same way every time the system gets used to DJ with.

Can you describe where you have the gains set on the crossover and amplifiers?

The accepted best practice way of doing this is to put all amp gains at max and use the crossover output level controls to balance the sound, but that usually results in quite a lot of hiss from the CDs. Another way to do it that produces less hiss is to put all the crossover outputs at unity(0dB) and only turn up the HF amp gains as much as necessary. I get that that is hard to repeat but you could just put a couple sticky arrows on the amp. In all cases you should use the unity control position as the baseline on the crossover.. not the max gain available.

 

[Tube Radio]

I currently use a resistor divider in the TFM-15 to knock the signal down some.

The resistor divider is 75k in series with the 50k level pot for each channel.

That would take a 1 volt signal and drop it to 400mV.

The idea of using an l-pad on the horn is something I hadn't thought of and would likely better protect the driver should I forget and plug in or unplug the RCA cables with the amp on and connected to the horns.

That said to implement an l-pad I'd need a small project box to put the resistors in.

The DBX is pro audio where a little solid state hiss is acceptable that would be unacceptable in a stereo setup.

Plus the horns are efficient.

I use the same crossover on a system with speakers that have a 4" horn and the solid state hiss isn't noticeable.

Here's how the crossover is set.

To show how efficient the 811B is, without the l-pad on the input of the TFM-15 the high out level control has to be set to 9 o'clock if not slightly less to be balanced with the rest of the drivers and at near full output of the 35 driving the subs the 15 is averaging maybe 1 watt output based on the meters.