Topping Pre90 Review (preamplifier)

[Atanasi]

All devices which use a transformer in the output. Very rare today, I think.

RME UCX II, for example, has servo-balanced outputs. Those require shorting the negative pole to ground when connecting unbalanced:

The short circuit protected, low impedance line outputs of channels 1 to 6 are available as 1/4" TRS jacks on the back of the unit. The electronic output stage is built in a servo balanced design which handles unbalanced (mono jacks) and balanced (stereo jacks) correctly.

The servo balanced input and output circuitry allows to use monaural TS jacks (unbalanced) with no loss in level. This is the same as when using a TRS-jack with ring connected to ground.

Servo-balanced outputs are more common with professional devices.

 

[LTig]

RME UCX II, for example, has servo-balanced outputs. Those require shorting the negative pole to ground when connecting unbalanced:

AFAIK they can handle a short, and may deliver more voltage when shorted, but I'm not sure that the short is required.

 

[DHT 845]

I want to connect Pre90 with 2 subs, each sub has either L, R line inputs (target connectors) and sub input (no low pass filters so no use with Pre90).

1. Could such 2 cables be used (1 for each sub, XLR to double RCA's)? I suspect that not since L and R will be opposite phase.

2. If I use two XLR to single RCA cables the subs will play (-3dB) i.e. twice as quiet, right? But it should be no problem since there is volume control anyway.

I would like to ask you guys to verify my assumptions.

 

[LTig]

I want to connect Pre90 with 2 subs, each sub has either L, R line inputs (target connectors) and sub input (no low pass filters so no use with Pre90).

View attachment 331908
1. Could such 2 cables be used (1 for each sub, XLR to double RCA's)? I suspect that not since L and R will be opposite phase.
View attachment 331909View attachment 331910

You can use this cable if the second sub has a 180 degree phase switch. Just engage it to get the correct phase.

 

[DHT 845]

You can use this cable if the second sub has a 180 degree phase switch. Just engage it to get the correct phase.

Yes it has phase switch as on photo above (2 identical subs).
But I want to use these subs in stereo (1 playing L channel and other playing R channel).
So it is impossible to connect Left XLR to Left sub and Right XLR to Right sub because 2 halfs of the sine wave (of one channel) are opposite in phase.
Am I right?

 

[DHT 845]

Since I will be ordering cables, I wonder if it is better to order two XLR to single RCA cables...

 

[LTig]

Yes it has phase switch as on photo above (2 identical subs).
But I want to use these subs in stereo (1 playing L channel and other playing R channel).
So it is impossible to connect Left XLR to Left sub and Right XLR to Right sub because 2 halfs of the sine wave (of one channel) are opposite in phase.
Am I right?

They are opposite in phase. Engage the phase switch on one sub and they are no longer opposite in phase.
However, they do both get a mono signal (L or R) so not playing in stereo as you wish. A balanced output using XLR does not carry L+R (as seen in your posting) but zero phase of one channel at pin 2 and its opposite phase on pin 3.

 

[LTig]

Since I will be ordering cables, I wonder if it is better to order two XLR to single RCA cables...

Yes.

 

[DHT 845]

Yes.

And additionally to use RCA Splitter (1 Female to 2 Male) to utilize both L and R sub's inputs?

 

[LTig]

And additionally to use RCA Splitter (1 Female to 2 Male) to utilize both L and R sub's inputs?

No, this does not work. Use just one of the inputs, this is fine.

 

[Atanasi]

AFAIK they can handle a short, and may deliver more voltage when shorted, but I'm not sure that the short is required.

The output maintains the signal voltage between the positive and the negative pole. If the negative pole is floating, its potential receives noise relative to ground. This noise will be added to the resulting unbalanced signal.

 

[nagster]

It's not only correct, it is required.

Sorry if I'm wrong. I'm not good at English so it's Google Translate.

 

[nagster]

AP dashboard and 32 tone of the Pre90 XLR output connected to the SE input.

 

[Sokel]

AP dashboard and 32 tone of the Pre90 XLR output connected to the SE input.

Balanced to SE connections with pin 3 (cold) either open or connected to ground (pin 1) is a horror show,probably that's what Topping has seen and (rightfully) suggests not to do it.
Nice demonstration!

 

[CleanSound]

Because they couldn't fit everything into one chassis, they have to have a extension chassis. God, I hate desktop form factors, it's like a little child's toy.

 

[nagster]

It looks a little better compared to D10 Balanced. Of course, neither result is recommended.
However, in the case of Pre90, the offset does not seem to worsen, so pin 3 open may be used only in emergencies.

Topping D10 Balanced Review (USB DAC)

It looks (in my case) ,that the onboard switching power supply + 5.65V / -5.6V, which supplies the output analog circuits (3 OA) behind the DAC, fails / does not start ..). That PSU is powered from 5V inputs. The all other onboard sources (3.3V, 1.2V, 1V) start up normally, they are linear (not...

www.audiosciencereview.com

 

[maudio]

I have a problem with Topping RCA in / XLR Out -> Amp XLR in. As opposed to pure RCA signal path, this sound is somehow weak, dynamically constricted, sounds like a a bad copy on cassette from 80s.

Does Pre90 convert the RCA in into a full blown XLR signal, or just pass it somehow trough?
My amp has also RCA in and this way the sound is great, but wanted to get those 3dB better signal and what i got is i dunno 20 dB worse

So it can be 2 things: my Amp XLR in is screwed OR
Pre90 does not really convert RCA in into full scale XLR out.

If the latter case, was i too naive expecting it would do it? I had 2 preamps that did this and it was no problem, RCA in XLR out. They costed also more.

 

[ZestClub]

I have a problem with Topping RCA in / XLR Out -> Amp XLR in. As opposed to pure RCA signal path, this sound is somehow weak, dynamically constricted, sounds like a a bad copy on cassette from 80s.

Does Pre90 convert the RCA in into a full blown XLR signal, or just pass it somehow trough?
My amp has also RCA in and this way the sound is great, but wanted to get those 3dB better signal and what i got is i dunno 20 dB worse

So it can be 2 things: my Amp XLR in is screwed OR
Pre90 does not really convert RCA in into full scale XLR out.

If the latter case, was i too naive expecting it would do it? I had 2 preamps that did this and it was no problem, RCA in XLR out. They costed also more.

It can't convert RCA to balanced that's not how it works.
You need balance all the way down the chain from the source player/ streamer to the Pre amp and then onto the main amps.
A player may have a balanced 4.4mm jack or XLR's - but if its just phono then you need to stay with that all the way down the chain.
Only option is to upgrade the source latter.

 

[Jimbob54]

It can't convert RCA to balanced that's not how it works.
You need balance all the way down the chain from the source player/ streamer to the Pre amp and then onto the main amps.
A player may have a balanced 4.4mm jack or XLR's - but if its just phono then you need to stay with that all the way down the chain.
Only option is to upgrade the source latter.

Forget the word balanced and focus on just input and outputs. You absolutely can input an RCA source into the Pre90 and it can be output via the XLR outputs. Other than output level (I assume XLR out should always be 6dB more than RCA out) they should sound the same. That isnt what @maudio is reporting.

I assume @maudio has selected the right input and output options via the dials/ remote. Something is definitely wrong if the output level out of the XLRs is noticeably less than the RCA out. Checked all your connections? If you have both RCA and XLR out connected to the same amp is there a noticeable drop in level at the same volume level on the Pre 90 when you switch from RCA out to XLR out (and obviously select the relevant input on the power amp? I would test this at quite low levels in case you get a big jump from one to the other. What level on the Pre90 do you need to use for RCA out and XLR out to get the same perceived volume out of the speakers .I would have thought like you that the XLR output should be higher so you would turn that down compared to RCA output.

What is the poweramp by the way?

 

[mocenigo]

It can't convert RCA to balanced that's not how it works.

Oh yes it does.