Rt1000i and SMSL AD18 amp

mlbetter

I’ve been using my rt1000i’s for years without problem on my Denon AVR amp. However when switching to the smsl ad18 I am having a lot of issues.

when running the high and low posts bridged I get no sound whatsoever. If I unplug the power to the speaker and restart the amp then it works fine, but the sub obviously doesn’t work while unplugged. If I have the speaker power plugged in and un-bridge the posts I get sound when connected to the high frequency posts, but nothing when connecting to the low frequency posts. It seems like it trips a safety limit on the amp because whenever I connect it to the low frequency posts, that channel of the amplifier becomes disabled until I switch the amp off and on again.

Is there something unusual about the inbuilt amplifiers in the rt1000’s which might be causing trouble with my new amp?

I have tried using the line-in connection for the sub but that also seems to be having an issue with this amp. I think sub output signal from the amp is the culprit there. But I don’t know why I wouldn’t be able to use the high-level inputs for this setup.


Thanks!

SeleniumFalcon

Hello! Welcome to Polk's forum.
From reading your description of what's happening it is possible the bass amplifier, of the speaker, has a small amount of DC present on its input connections. This could be tripping the protection circuit of the SMSL amplifier. Do you have a DC voltmeter available?

mlbetter

Hi @SeleniumFalcon, yes that sounds logical. I do have a multimeter. Where do you think I should test for dc voltage? Between the two bass input posts?

SeleniumFalcon

I would try connecting the meter to the positive/negative speaker connections on the Polk bass amplifier while it's powered on.

mlbetter

@SeleniumFalcon, measuring between the +/- sub speaker inputs (high level inputs) when powered on and un-bridged reads 0v. There are a few mV momentarily when I plug and unplug the speaker amp power cord, but 0v when running. Any other measurements I should try?

SeleniumFalcon

Let me find out a little more information on your amplifier, hopefully a schematic.

SeleniumFalcon

Does your meter have an ohms function? If so measure the resistance between the SMSL's speaker's negative terminal and any grounding point on the amp, such as the outer area of any RCA connector. Then do the same with the speaker positive terminal and the ground of any RCA connector.

mlbetter

Yep, I’ll do that in a minute. Should I have the smsl amp powered off or on?

mlbetter

@SeleniumFalcon the impedance I measure seems to be above 20MOhm which is the limit of my multimeter. When I unplug the dc power from the smsl amp I continue to get an open connection reading on my multimeter for about 30 seconds, then I get a 19.9Mohm reading which continues to steadily drop. A few minutes after disconnecting them power it’s reading approx 8Mohm and still dropping. This is true for all the + and - speaker outputs, the values differ slightly, but are practically the same.

SeleniumFalcon

It would seem that the SMSL isn't happy being connected, using speaker connections, to a grounded load such as the Polk bass amplifier. I looked at the SMSL owner's manual and the sub-out uses a 3.5mm connector, but I don't completely understand the labeling and connection instructions. It looks like when you insert a 3.5mm connector the right channel RCA connector becomes the sub connection and the left channel RCA is another input choice. Try just connecting the right channel RCA to a sub input on the Polk and leave the left unconnected.

mlbetter

@SeleniumFalcon. Damn I was hoping there might be a solution to the high-level sub inputs. I have tried connecting the SW output from the smsl to the line input on the polks but that’s not working either. I think the sw output might be incompatible or faulty. I’ve been in contact with Smsl but so far haven’t come to a solution on that problem.
Interestingly I was able to get the subs working when I connected the headphone output to the line input on the sub, but that doesn’t help because you can’t use the headphone output and the speaker output at the same time.

mlbetter

@SeleniumFalcon Because the smsl amp is powered by a 24v DC power supply is it possible that it is a floating voltage and the negative is not tied to ground? And would it be possible to manually connect negative to ground to give the smsl and the Polk amp a common reference? Or possibly finding another 24v power supply brick which does have the negative tied to ground?
I haven’t checked to see if it is floating or not, but seems like it could be a possibility.

SeleniumFalcon

I don't believe the type of power supply has any effect, rather it is the output circuit topography. If you look at the schematic drawing for the TAS5342A integrated circuit (which I believe your amplifier uses) you can see the speaker outputs are not tied to ground.



The sub-out should work, be sure to remove both speaker's binding post jumper plates before connecting the sub-out. Try setting your volt/ohm meter to AC voltage and hold the probes on the right channel RCA cable that is connected to the SMSL and see if there is any signal present while you play the system. There might be some menu choice needed to activate the sub-out.