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dbx DriveRack VENU360 Review (audio processor)

Amir,
It looks like there are some variance between VENU360 units base on their revision or production date.
As I wrote in my previous post I have two of them , older one that was measured correctly and actually very good performance from the start, and newer one that was measured bad as the unit you measured, that I succeed to fix with small mod on the DAC output.
In my previous post I posted the measurements for both of them, and comparing them to the DCX2496 and for reference the SMSL M500 to show the capabilities of the R&S UPL that I am using.
If the unit is a good one or fixed like the mod I apply they measure is excellent ,and they are really great versatile units.

Did you post the actual mod? Thanks
 
Amir,
It looks like there are some variance between VENU360 units base on their revision or production date.
As I wrote in my previous post I have two of them , older one that was measured correctly and actually very good performance from the start, and newer one that was measured bad as the unit you measured, that I succeed to fix with small mod on the DAC output.
In my previous post I posted the measurements for both of them, and comparing them to the DCX2496 and for reference the SMSL M500 to show the capabilities of the R&S UPL that I am using.
If the unit is a good one or fixed like the mod I apply they measure is excellent ,and they are really great versatile units.
I saw that and mentioned in that in my post. Until I can remeasure a device though, and there is a way for owners to tell which is which, there is nothing I can do about the data as presented.
 
This is the older unit that measured correctly as it is without any mod:
View attachment 124422

View attachment 124423



I will post later the newer model , but I think it is similar to this one :

DBX DriveRack Venu360 Internal Photos - diyAudio

Please pay attention to the shielded power supply in my older unit compare to the open power supply in the link above.


The fan appears to be disconnected from power in the picture above. Disconnecting the fan, or rerouting the fan wires away from the output of the SMPS seems an obvious, beneficial change. At least some units have the fan power wires and the SMPS output connected tightly with a cable tie.
 
Projecting Venu360 measured performance at a lower voltage output level

In the ASR review the Venu360 is run at a high output level: +22dBU as seen in the graph below.

The Venu360 has a voltage output AKM DAC with a nominal SE output of 2V after the filter circuit. The final analog stage of the Venu360 uses a dual opamp to provide a differential output with a nominal level of 4V. This output seems to correspond with the 14dBu (3.88V) output setting. This means that no additional gain is applied to the 14dBu output other than the SE to differential stage.

There are three additional higher output level settings:

17dBu

20dBu

22dBu

These higher levels appear to be obtained by using a 4-way solid state switch to change the resistors around an opamp voltage gain stage to provide the added gain required. The opamp used is the same opamp used in the remainder of the Venu360.

This sort of circuit is similar to the circuit used in the 8-channel NJR volume control in Denon AVR's. The NJR unit has many more resistor combinations and allows .5dB level changes.

In the NJR unit gain above 0dB gain is directly subtracted from the gain available for feedback around the opamp. That's just how the circuit works, it's a tradeoff. In the graph of X6700H performance shown in the 2nd graph below it can be seen that a 7.5dB increase (90db - 82.5dB) in gain (green line) from the volume control results in almost exactly a 7.5dB gain in distortion as would be expected from the reduction in the level of feedback available.

It seems likely that if the Venu360 is used at higher output levels than 14dBu that the gain required to achieve these higher output levels results in an increase in distortion. While this increase in distortion would need to be verified by measurement, the following calculations show the amounts that distortion might decrease, with an associated increase in SINAD, if the circuitry works in this manner.

17dBu - 14dBu = 3dB reduction in distortion (increase in SINAD)

20dBu - 14dBu = 6dB reduction in distortion

22dBu - 14dBu = 8dB reduction in distortion

It would be nice if someone who owns one of these units would measure the unit to determine if this theory holds in practice.


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It would be nice if someone who owns one of these units would measure the unit to determine if this theory holds in practice.

How?
 
In the ASR review the Venu360 is run at a high output level: +22dBU as seen in the graph below.
I actually measured the unit with two output levels. Lowering the setting gave the exact same result as higher one so I stayed with the latter.
 
Here are the pictures of my newest VENU360 with the mod change I did.
To improve the measurements performance I had to remove all the capacitors showing in the picture.
Two capacitors for each DAC output ( C117,C102,C119,C104,C121,C106,C123,C108,C125,C110,C127,C112 ).
These capacitors are part of the DAC output low pass circuit and theoretically will influence the total DAC low pass filtering section.
As I don't have the schematic, but from analyzing the DAC output stage it looks like there are additional filtering.
I didn't notice any issues removing them only great measurement improvement.
I find the issue using my UPL to track the distortion changes from the DAC output the same way you use a scope. This is one of the great features of the UPL that you can use it in this way.
I cannot explain yet why removing it help, the only explanation that maybe it is a wrong value.
This change work for my newest unit so for all looking to implement it I will suggest the following steps:
1. Check your unit current measurement performance , if you don't have access to Audio analyzer , a good 24 bit sound card with software like Arta I think will be sufficient.
2. If your unit is one with bad measurements, I will first try to remove two capacitors from one stage only to see if the measurements improved , with the assumption that if it doesn't work for you will be able to solder them back.
3. If you see the improvement without any issues go ahead and remove the rest.

You can see few changes between the units the older good unit has shielded power supply with PCB board no 5034682-E.
The newest unit with the issue has unshielded power supply with board no 5060604_B




1618848501088.jpeg

1618848558643.jpeg
 
Last edited:
Here are the pictures of my newest VENU360 with the mod change I did.
To improve the measurements performance I had to remove all the capacitors showing in the picture.
Two capacitors for each DAC output ( C117,C102,C119,C104,C121,C106,C123,C108,C125,C110,C127,C112 ).
These capacitors are part of the DAC output low pass circuit and theoretically will influence the total DAC low pass filtering section.
As I don't have the schematic, but from analyzing the DAC output stage it looks like there are additional filtering.
I didn't notice any issues removing them only great measurement improvement.
I find the issue using my UPL to track the distortion changes from the DAC output the same way you use a scope. This is one of the great features of the UPL that you can use it in this way.
I cannot explain yet why removing it help, the only explanation that maybe it is a wrong value.
This change work for my newest unit so for all looking to implement it I will suggest the following steps:
1. Check your unit current measurement performance , if you don't have access to Audio analyzer , a good 24 bit sound card with software like Arta I think will be sufficient.
2. If your unit is one with bad measurements, I will first try to remove two capacitors from one stage only to see if the measurements improved , with the assumption that if it doesn't work for you will be able to solder them back.
3. If you see the improvement without any issues go ahead and remove the rest.

You can see few changes between the units the older good unit has shielded power supply with PCB board no 5034682-E.
The newest unit with the issue has unshielded power supply with board no 5060604_B




View attachment 124993
View attachment 124994
Glad there is a soldering iron fix for the Venu, as it really is a feature rich piece if kit.. However, that sort of thing is way above what I would want to be doing myself.. Slightly odd that those caps had no other real function other than to degrade the signal. but if it works, without a downside than again a real boon for those who either already have a Venu, or those with electronics backgrounds to utilize this otherwise fine and feature rich device.
 
It's not perfect, but it's also a sub-$600 audio processor. I'd say it performs *very* well for what it is. The review is fair and I see no evidence that Amir's measurements are flawed.

It's not a good choice for an audiophile system, but it's also not designed for that. In all honesty, it would probably sound pretty good in a hifi system, but the only time that makes sense is if you're going to use it as an active crossover, and you might as well just build your own a-la BSS FDS360 style.

These days a lot of active crossovers in the pro world get done through Q-Sys or Soundweb.

It'd be interesting to get something from XTA on Amir's bench, but I doubt it would excite him very much- the pro world seems to have figured out the level at which things "don't realistically matter" and stuck with it, and honestly, maybe they're right. At least in a blind test, I can't hear the difference between 0.01% and 0.0001% THD.
 
I cannot explain yet why removing it help, the only explanation that maybe it is a wrong value.
Wrong dielectric is more likely. The Behringer 2496 series has always been like that, I am guessing X7R or X5R caps (right down to the hundreds of pF!). Generally smaller and cheaper than what you actually want in the signal path, NP0/C0G.

Similar issues can also be found in other, small and/or inexpensive audio gear, like handheld recorders and some USB audio interfaces (one made by Zoom comes to mind... UAC-2 I think it was - its RMAA results are nothing short of bizarre).
 
While it is apparent from many posts on another forum on a set of pre-pro's that Harman is non-responsive to issues, and I've found the Revel marketing managers to be aloof at best, it is unfortunate that someone with contacts at Harman hasn't pursued this performance issue. The work and measurements described in this thread demonstrate poor measurements likely due to screw-ups by Harman.

The ADC in the VENU360 appears quite good, the AKM DAC IC is older and OK, but has specs and measurements close to the AK4458 found in the Denon X4700H and X6700H. The NJR opamps used have similar rated performance to the NJR opamps used in all the upper level Denon gear. The overall appearance of the board appears good and the case is solid. There is no apparent reason why the performance shouldn't be better.

It would be nice to have the service manual or at least a schematic of the unit. The DBX website has a limited set of service manuals available, but not the service manual for the VENU360.

If someone here as an "in" with Harman/DBX, it would good to get Harman's input on this situation. The poor performance measured in ASR appears to be due to poor execution by Harman, not the basic design.
 
Ok I became curious about the unit I have in the attic, given that @ObjectAudio described such differences in performance between an older and a newer unit. According to him, one of the giveaways between the older and newer units is that the older (and better) ones have a shielded power supply. So I opened up my unit, and behold - a shielded power supply!

IMG_0791.jpg


That makes sense, given that I purchased it second-hand in 2017.

Does this unit measure as well as @ObjectAudio 's older unit, or like the one @amirm measured? I have no way of telling
 
Harman is non-responsive to issue

Not sure how true this is. Their customer service is pretty well regarded from what I've heard.

Your point about getting them to look at this is duly noted though. They have the best audio peope in the world (besides the ones apple stole from them)
 
Not sure how true this is. Their customer service is pretty well regarded from what I've heard.

Your point about getting them to look at this is duly noted though. They have the best audio peope in the world (besides the ones apple stole from them)


JBL, a Harman company.

The product discussed in this tread has been a mess:

(512) JBL Synthesis SDP-55 (16ch, 9.1.6 Atmos Surround Sound Processor) | AVS Forum

Even one of the managers identified with Revel made a few posts, but seems to avoid the heat now. Since Denon has achieved good measured performance, some of the posters have referred to Denon substituting capacitors in the X6700H. This thread should give them an example closer to home.

A new processor from ARCAM, a Harman company, has been just as bad.

Floyd Toole no longer works at Revel and hasn't for several years. Dr. Toole in now a consultant.

The Mark Levinson products now go in for "interesting" electronics, not electronics with the best performance. The worst is that the late Sidney Harman has been out of the picture for at least a decade.
 
oivavoi,

As I suggested If you have or can get a good 24Bit audio interface with analog audio in and digital out , you will be able to measure the performance by yourself. I think it worth it as if measured correctly the performance should be excellent and the unit capabilities with the excellent iPad app are great.
 
oivavoi,

As I suggested If you have or can get a good 24Bit audio interface with analog audio in and digital out , you will be able to measure the performance by yourself. I think it worth it as if measured correctly the performance should be excellent and the unit capabilities with the excellent iPad app are great.

I actually have an audio interface which could work. Ok, this will be a new thing for me, but I'll have a look at the process!
 
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