thomann t.racks DSP 4x4 Mini Review

[bennybbbx]

Good tip! I am considering to use the RCA output on my preamp. My poweramps are the Stageline STA2000 and that also accepts RCA inputs. I check that the RCA has 10 db less output than the XLRs. That could already be a a good option too.

No, dont use RCA if youn can. When you connect a RCA output to t.racks dsp you loose 20 db dynamic because the dsp have only a fixed gain that do ~+6 db as full sample (FS). RCA have only -10 db. and when you connect the mini DSP to RCA in poweramp make the signal 16 db louder and so noise can hear from dsp

did you currently hear noise even when you use studio levels ?. if so, your volume knob is too much right. when the knob is in such a position that the amp can play FS with 115 db then of course you hear noise of the dsp.

RCA use line Level. you can see on this diagram. to get best dynamic your input should produce ~+6 db. and your amp need produce with +6b the volume you want hear. if you are 1 meter away 115 db kill your ears but this 2400 watt amp can do it. and when you are more away then you hear less noise. maybe this diagram show more clear what i mean

Line level - Wikipedia

en.wikipedia.org

 

[BlackBushBaby]

My amps specs says.

Inputs

1 V/10 kΩ (XLR, bal.), 1 V/5 kΩ (RCA)

This is confusing. So does this mean this amp will be able to reach its full output from either RCA or XLR with only 1 V?

 

[BlackBushBaby]

No, dont use RCA if youn can. When you connect a RCA output to t.racks dsp you loose 20 db dynamic because the dsp have only a fixed gain that do ~+6 db as full sample (FS). RCA have only -10 db. and when you connect the mini DSP to RCA in poweramp make the signal 16 db louder and so noise can hear from dsp

did you currently hear noise even when you use studio levels ?. if so, your volume knob is too much right. when the knob is in such a position that the amp can play FS with 115 db then of course you hear noise of the dsp.

RCA use line Level. you can see on this diagram. to get best dynamic your input should produce ~+6 db. and your amp need produce with +6b the volume you want hear. if you are 1 meter away 115 db kill your ears but this 2400 watt amp can do it. and when you are more away then you hear less noise. maybe this diagram show more clear what i mean

Line level - Wikipedia

en.wikipedia.org

I think the noise is from the preamp and not the DSP.

 

[TimoJ]

I think the noise is from the preamp and not the DSP.

In my system it was the DSP. Does the noise disappear if you mute DSP channel inputs (or lower input levels) with the DSP editor program?

 

[BlackBushBaby]

In my system it was the DSP. Does the noise disappear if you mute DSP channel inputs (or lower input levels) with the DSP editor program?

I have not tested muting, but the noise does drop when I lower the input levels.

 

[bennybbbx]

My amps specs says.

Inputs

1 V/10 kΩ (XLR, bal.), 1 V/5 kΩ (RCA)

This is confusing. So does this mean this amp will be able to reach its full output from either RCA or XLR with only 1 V?

to reach full level with RCA is only 0.447 volts peak need. to reach full level with XLR need 1,7 Volt.
A RCA input in poweramp do more amplifikation and cause more noise and clipping on higher levels when you connect a XLR with 1,7 volts peek output to the RCA with 0.447 Volts peek input in power amp

when have a RCA output with 0.447 volt peak connect to 1,7 volt input cause no clipping but cause noise. the t.racks have no analog amplifiers or attenutor to match the gain. you loose with RCA digits in the AD/ DA converter which cause noise. this doesnt matter if you have AD/DA converter with over 106 db dynamic then you can get with RCA 90 db. but as you can see in the test the t.racks have no 106 db. so you hear noise when you use in in RCA equipment.

 

[bennybbbx]

In my system it was the DSP. Does the noise disappear if you mute DSP channel inputs (or lower input levels) with the DSP editor program?

what equipment you have before and after the DSP ? . you should set the level of the poweramp after the DSP so that you hear no noise from the DSP and if this when you play music is loud enough.

 

[TimoJ]

what equipment you have before and after the DSP ? . you should set the level of the poweramp after the DSP so that you hear no noise from the DSP and if this when you play music is loud enough.

I have Monoprice HTP-1 preamp and after DSP is 2 x Crown XLS-1502 bridged. I adjusted poweramp's level so that there was no noise, but then there was not enough output from the subwoofers. And if I raised subwoofer channel level from the preamp or DSP input level control, then the DSP was clipping when loud bass was playing.
So I could not resolve this issue. I also enabled power amp's lowpass filter to cut the hissing but that still left low level "rumbling" hiss (not ground loop noise!).

But as I mentioned, I returned the t.racks DSP and got MiniDSP 2x4HD instead and all is fine now.

 

[BlackBushBaby]

I have Monoprice HTP-1 preamp and after DSP is 2 x Crown XLS-1502 bridged. I adjusted poweramp's level so that there was no noise, but then there was not enough output from the subwoofers. And if I raised subwoofer channel level from the preamp or DSP input level control, then the DSP was clipping when loud bass was playing.
So I could not resolve this issue. I also enabled power amp's lowpass filter to cut the hissing but that still left low level "rumbling" hiss (not ground loop noise!).

But as I mentioned, I returned the t.racks DSP and got MiniDSP 2x4HD instead and all is fine now.

what equipment you have before and after the DSP ? . you should set the level of the poweramp after the DSP so that you hear no noise from the DSP and if this when you play music is loud enough.

The issue for me is the same as for TimoJ. I put the volume low enough on the amp gain to not hear the noise, then it will clip the output of the DSP( as the preamp is outputting a lot hotter signal). This is with my low shelf filter in place with a bassboost of +8db. In order to not clip the DSP I have to raise the volume on the amp, so that there is less signal level needed from the pre-amp. This prevents clipping at the outputs of the DSP with the shelf applied. Then it is very noisy. with some strange popping noises.

 

[bennybbbx]

clipping at the outputs of the DSP with the shelf applied. Then it is very noisy. with some strange popping noises.

is it possible that you have ground loop, or digital noise over USB port ?. when you remove the USB cable from the t.racks, maybe the noise reduce ? . but anyway you both have over 500 Watt amps and i know, such systems are for stages and they always give noise when play no music and when you are 2 meter near . if you have clean noise as analog then it is good. if the noise sound strange and have popping it not good.in general noise is less with the 2x4HD, because this is more expensive but have higher dynamic

 

[TimoJ]

but anyway you both have over 500 Watt amps and i know, such systems are for stages and they always give noise when play no music and when you are 2 meter near .

My Crown XLS1502 amps are very quiet. No idle noise from speakers when listened near speaker cone.
And also no fan noise, the fan spins only when needed and at that time you won't be able to hear it...

 

[bennybbbx]

My Crown XLS1502 amps are very quiet. No idle noise from speakers when listened near speaker cone.
And also no fan noise, the fan spins only when needed and at that time you won't be able to hear it...

power amps can reach more easy high dynamic, but what happen when you add an analog EQ instead of the t. racks and do the boosts you need.

I see in the crown specs.

Selectable input sensitivity; 1.4Vrms and .775Vrms options so that amp can be driven at full power.

Signal to Noise

>103dB (at .775Vrms, 6dB lower)

Crown XLS 1502

Meet the new XLS DriveCore™ 2 Series The next generation of XLS got a makeover with a sleek n...

www.crownaudio.com

this mean you need set the amp with the t.racks to 1.4 and with the mini dsp HD to 0.775 Vrms . if you have both DSP same setting then you loose 6 db dynamic of the t.racks . the t.racks does not reach the dynamic of the crown. it depend on you, if you really need this high dynamic. the speakers i have and not hear noise at 1 meter distance have only 30-60 watt amps. woth ful gain they are too loud. A 500 watt amp need much more amplifikation and so you hear this when you are near. question is if you need the 500 watt.

maybe you try a sound level meter and look what happen how loud you hear https://www.who.int/news-room/questions-and-answers/item/deafness-and-hearing-loss-safe-listening. the hours is the ttime per week. i guess they have test it on hearing cells or animals. but it seem be true . there are many musicans that hear not good

Sound intensity in decibels

Time for safe listening per week (7 days)

Example of type of sound at the specified intensity

80dB

40 hours

85dB	12h 30 mins	Heavy traffic (inside car)
90dB	4 hours	Shouted conversation
95dB	1h 15 mins	Motorcycle
100dB	20 mins	Hair dryer
105dB	8 mins	Car horn at 5 meters
110dB	2.5 mins	Shouting in the ear
120dB	12 sec	Standing near a siren
130dB	<1 sec	Jackhammer
140dB	0 sec	Airplane taking off
150dB	0 sec	Firecrackers

 

[TimoJ]

the speakers i have and not hear noise at 1 meter distance have only 30-60 watt amps. woth ful gain they are too loud.

But I'm using the amps for subwoofers. 500W is pretty low number for home theater subs.

 

[bennybbbx]

But I'm using the amps for subwoofers. 500W is pretty low number for home theater subs.

and which subwoofers you have ? . passive subwoofers in this 500 watt range they write in spec have high sensivity . for examples the passive subzero for ~200 $ have 96 db (per watt).

SubZero C15S Passiver PA-Subwoofer | Gear4music

SubZero C15S Passiver PA-Subwoofer | Gear4music

www.gear4music.de

but calc with 90 db sensivity. this is measure at 1 meter

96 db need 4 watt
102 db need 16 Watt
108 db need 64 watt
111 db need 128 watt

if think the subwoofers are with 4 watt not loud enough the most happen problem when have more subwoofers is that they wrong in phase. so they cancel each other the bass. .when this happen on hearing place then increase gain of both help not much, because they cancel each other. only you then hear lots noise because the noise is not cancel when high gain is used. you can test easy. if on hear place 1 subwoofer have not less bass as 2 subwoofer then there is phase problem. or the bass differ much depend on position in room

 

[TimoJ]

and which subwoofers you have ?

Dayton Audio Ultimax UM18-22 in 110 litres closed enclosures. There is no bass cancellation or phase issues. So are you saying that, for example, SVS who uses 1000-2000W amps in their subs is totally wrong and they should just switch to 50-100W amps...?

 

[bennybbbx]

So are you saying that, for example, SVS who uses 1000-2000W amps in their subs is totally wrong and they should just switch to 50-100W amps...?

this i want not say. it depend how far away sit from the speaker.
How far away you sit from speaker ?.

On stage people are 4-20 meter away from speaker. so it doesnt matter if can hear noise at 1 meter because listener position is more away. And of course you need enough power that people at larger distance hear enough. . when use 1 watt in the dayton it is ~85 db loud and at 4 meter distance 73 db loud. double distance is 6 db less. so 4 meter distance is 12 db less. but not exact, because room reflections and room modes can boost some frequency alot.

Dayton Audio Ultimax UM18-22 Tieftöner kaufen

Bestellen Sie den UM18-22 online bei SoundImports ✓ Versand am selben Tag ✓ Kostenloser Versand

www.soundimports.eu

the dayton is list with 88.6 (SPL 1m / 2,83V) . to get the watts need calc 2.83 volt/4 Ohms = 0.7075 ampere. now when calc 2.83 * 0.7075 you get the watts. i calc 1.981 watt. normaly they should give the SPL at 1 Watt. now the 88.6db they tell need do - 3 db. then its 85.6 db this is also ok.

EDIT: another thing i get in mind. If you have 1 sub at same distance as front speaker and have on other side of the wall near hearing pos another sub, as some suggest, you need phase correct and levelcorrect it. the rear sub is maybe 1 meter away to hear position, the front sub 4 meter. then the rear sub should play 12 db less than the front sub. then it also play less noise from the DSP also you need REW measure to correct the phase shifts

 

[BlackBushBaby]

I have now now done extensive testing and I will send the T.Racks back for checkup. The unit is dead quiet when using input 2or 3 but noisy on channel 1 and 4. This is with my class 2 AV preamp. Using a grounded preamp the noise is gone.

 

[bennybbbx]

I have now now done extensive testing and I will send the T.Racks back for checkup. The unit is dead quiet when using input 2or 3 but noisy on channel 1 and 4. This is with my class 2 AV preamp. Using a grounded preamp the noise is gone.

you can do screenshot of the t.racks editor all pages. maybe you have something in settings because input 2 and 3 is silent. the noise normaly gone when you use ungroundet equipment. does it not change anything with or without connected USB cable ?.

maybe i overread but i did not remember that you write which preamp you have. another thing is important how much away is the 110 or 230 volts connetor of the preamp poweramp to the t-racks. all cables should be near as possible. I have the expirience when they are more than 30 cm away it can cause noise too when no symetric connection is used. best use 1 multiple power outlet bar and connect all equipment you have into this.