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Topping Pre90 Review (preamplifier)

TjindarSingh

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Yes, Denafrips Ares II has rather high output impedance for a DAC and Pre90 has rather low input impedance for a preamp. End result will be higher distortion from the Denafrips and level attenuation. To me a preamp should allow you drive more difficult loads (like say a Purifi amp with no input buffer) but the Pre90 doesn't really do that because it is a somewhat difficult load itself.

Michael
I have a audiophonics purifi amp, is that s bad combination?
 

mdsimon2

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I have a audiophonics purifi amp, is that s bad combination?

The Pre90 will drive the Purifi fine (with or without the input buffer) but the Denafrips will not drive the Pre90 well and will have the issues discussed early in this thread (higher distortion, attenuated output, frequency response deviation). If you are using the Denafrips with the Purifi with no preamp in between that will also be fine but you must avoid the "bypass" gain setting but this is fine because you will want to use at least the 20 dB gain setting to drive the amp to full power.

I assume your main motivation for using a preamp is to add volume control as the Denafrips does not have it?

Michael
 

TjindarSingh

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The Pre90 will drive the Purifi fine (with or without the input buffer) but the Denafrips will not drive the Pre90 well and will have the issues discussed early in this thread (higher distortion, attenuated output, frequency response deviation). If you are using the Denafrips with the Purifi with no preamp in between that will also be fine but you must avoid the "bypass" gain setting but this is fine because you will want to use at least the 20 dB gain setting to drive the amp to full power.

I assume your main motivation for using a preamp is to add volume control as the Denafrips does not have it?

Michael
Yes that's correct. Need to adjust the volume. Will look for another DAC then if they're not a good match.
 

mdsimon2

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Yes that's correct. Need to adjust the volume. Will look for another DAC then if they're not a good match.

IMO I would get a low noise DAC with 4 V output and digital volume control. The 20 dB gain setting on the Purifi will give you excellent system noise performance because the Purifi itself is very low noise and 20 dB gain will not excessively amplify noise from the DAC. The 20 dB gain setting is using an input buffer which will make it easy for pretty much any DAC to drive.

Michael
 

bsas

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Hi, I have the same setup: Denafrips Ares II, VTV Purifi with the EVAL1 input buffer and the Topping Pre90 and I would like to know the best way to connect them. If I use the RCA outs on the DAC instead of the XLR does it fix the impedance issue? If not, what should I do? Thanks!!!
 

Final

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The Pre90 is said to have peak performance between 4 and 8 volts of output. I wonder what this translates to in volume. I use XLR out only and can go up to +16 on the volume knob.My DAC outputs approx 4 volts. On normal listening I usually see -20 in the display. How much voltage output might that be?
 
Last edited:

nagster

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THD, THD+N and Noise were measured at each volume position of Pre90.
I referred to this post. Check the details. I have no English ability.
Thank you @MC_RME

pre90_thd_thdn_vsML_03_s.png
 

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nagster

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Pre90 input impedance and output impedance.
pre90_inputimp_rca_02.png
 

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nagster

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How do you measure that ?
The input impedance graph used AP2700, jig and AP macro. (I want you to provide the APx500 version as well.)
Inside the jig is a 16kohm resistor for RCA and a 2x 3.3kohm resistor for XLR. When I was using the AP2700, I remodeled the box I had at hand.
The jig has one input and three outputs.
The input connects to the output A of the AP.
Output 1 connects to input A of the AP. Output 1 is internally shorted to the input.
Output 2 connects to input B of the AP. Output 2 is internally connected to the input via a resistor.
Output 3 connects to the input of Pre90. Output 3 is internally shorted to output 2.

The capacitance value is a screenshot of the LCR meter.

The output impedance graph used APx500 and AP utility.
Any external resistor can be used, but I used the 600 ohm built into the AP.
ap2700_inimpjig_bnc_01.jpg
 

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bsas

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OK, I think my Pre90 has a major issue… the left side is 5db louder than the right side.

I was doing some speaker measurements and I noticed the discrepancy. So, I tried to change L and R on the DAC, on the speakers, on the amp. I tried all combinations and definitely the one to blame is the Pre90.

I got my A90 and used as a pre just to test. Channel imbalances gone… Very sad with this and honestly disappointed. I blindly trusted Topping so it didn’t cross my mind to test it.

I hope Apos audio help me out doing an refund or an RMA on this :(
 

RETSELDRIB

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Just bought the Pre90 and the D90LE DAC.

In the hidden menu I have left the default setting for setting volume output whereby the Pre90 remembers the volume output of each input - namely the XLR for the D90 and the RCA for my phonostage. What I do not seem to understand is what setting the volume input option will do? Can anybody tell me please and what function advantage this might provide? Thankyou.

On a separate note, the Pre90/ D90LE combo is replacing my Benchmark DAC2 HGC. I know that the Benchmark is really built to last - you can leave it on permanently and it will go on for years and years even though it runs very warm when idle.
Q. Do we have any idea on the longevity of the Topping Pre90/ D90LE? They do run very warm when on similar to the Benchmark. I know that they have an auto off function when the units are idle.
 

Kal Rubinson

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Do we have any idea on the longevity of the Topping Pre90/ D90LE? They do run very warm when on similar to the Benchmark. I know that they have an auto off function when the units are idle.
Here's an anecdote: I have three of them and they run 24/5 (off on weekends). After 7+ months, no problems.
 

Kal Rubinson

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Thanks for this - can you advise on the volume input function as opposed to the volume output?
No, I cannot. In fact, they say this:
1655840066783.png

Note the last sentence. Seems to imply that reading the first
paragraph with output and input swapped describes what "Vol
memory: IN" does. Obviously, one can choose one function or
the other but not both.
 

bsas

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OK, here is my story. My Pre90 was obviously 5db louder in the left side.

I isolated all components and it was clearly the Pre90. When I measured with my multimeter it was clearly 30-40% more voltage on the L side (both on the RCA outs and the XLR outs). Then I plugged on my oscilloscope, lined up both channels and clearly the difference was very visible there too on any volume setting.

I contacted Topping, explained the problem, and they told me it really looks like a defective unit and asked me to contact Apos. I contacted Apos audio and I am waiting for their response, but because of timezone they will probably just answer tomorrow.

But...

While I was waiting for Apos to answer I got curious. I dig in the secret menu to see if there was a "balance L/R" option that was somehow misconfigured but no, there is no such an option on the Pre90 (as I remembered). Then, I tried to click "7. Factory reset" and BAM! It just fixed it. Both channels are in perfect balance again.

Then here is the question: why the hell that happened??? There is no option to change that anywhere in the Pre90 that I know. Also, if the software is capable of doing L/R balance, why there is no option in the menu for it? It would be great if Topping added the +-10dB L/R balance to the Pre90 like they did on the D90SE firmware update (but the Pre90 doesn't have an obvious FW upgrade port unfortunately).

Now I am really confused. Should I still send it to Apos? I have no idea what happened to make it unbalanced in the first place... :p

@JohnYang1997 , please help me :(...
 

RETSELDRIB

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While it doesn’t appear in the instructions, when I accessed the so called secret menu to set up the unit i came across an option that had C on it which I presumed meant centre - it had some other stuff with it which I thought might have a left/ right balance. Sorry to be so vague - only did it once on set up.
 

bsas

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While it doesn’t appear in the instructions, when I accessed the so called secret menu to set up the unit i came across an option that had C on it which I presumed meant centre - it had some other stuff with it which I thought might have a left/ right balance. Sorry to be so vague - only did it once on set up.

Where? Mine has just the following options:
"1. Display | M (A, L, M, H)"
"2. Remote | ON (ON, OFF)"
"3. Vol Memory | IN (IN, OUT)"
"4. Safe Vol Mode | OFF (ON, OFF)"
"5. Safe Vol | -20dB"
"6. Save and exit"
"7. Factory reset"

Are you not getting confused with the D90?
 

RETSELDRIB

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I’m not by the Pre90 at the moment but I do remember it being an option not listed in the instructions; that said its possible that I am confusing it with the D90 but, again, my recollection is it being an option not listed in the instruction.

I will look on the weekend and report back.
 

essence

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OK, here is my story. My Pre90 was obviously 5db louder in the left side.

This sounds like the individual channel was set to XLR + RCA which shouldn't be possible. I've measured the channel balance across my two units and its picture perfect.
 
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