If you have a dual channel oscilloscope with math function, use one channel for positive speaker output, and the other channel for negative speaker output, then use the math function to take one from the other A-B
Thanks.... Yes I do have a dual channel one with the respective math functions. Do I connect the probe ground to the amp safety ground or to each other and leave the probe ground floating? Also not sure if I can run the A-B signal then also through the FFT function. I need to read the manual on this tonight.
Also I have an old / tiny battery driven osci. which hardly earns its name, so that would be another option I guess, but very very inaccurate one.
Meanwhile I also found this:
http://www.techni-tool.com/site/ARTICLE_LIBRARY/Tektronix%20-%20IsolatedInputOscopes.pdf
which in my simple eyes discusses the pros/cons quite nicely. However I am unsure what would be the best approach to the Mod686 floating voltages also with regard to safety and accuracy? Would it be still dangerous to float the osci. by temporarily disconnect the safety ground?
Also I have an old / tiny battery driven osci. which hardly earns its name, so that would be another option I guess, but very very inaccurate one.
Meanwhile I also found this:
http://www.techni-tool.com/site/ARTICLE_LIBRARY/Tektronix%20-%20IsolatedInputOscopes.pdf
which in my simple eyes discusses the pros/cons quite nicely. However I am unsure what would be the best approach to the Mod686 floating voltages also with regard to safety and accuracy? Would it be still dangerous to float the osci. by temporarily disconnect the safety ground?
I can wait - will give me time to clean up my work bench at home, and start selling off redundant gear/ collecting empties to finance the project.
Tom wrote in his Modulus 686 manual the following about the Single Ended to (Pseudo-) differential cable:
"If a custom interconnect cable is not desired, the single-ended to pseudo-differential connection can be moved inside the amplifier chassis and made at the input RCA connector."
Now I'm wondering if I can permanently wire my RCA connectors to my XLR connectors inside my chassis. As this implicitly connects pin 1 to pin 3, would the balanced XLR connector still work?
I'd like to offer both RCA and XLR inputs and allow both to work, (but obviously not at the same time)..
"If a custom interconnect cable is not desired, the single-ended to pseudo-differential connection can be moved inside the amplifier chassis and made at the input RCA connector."
Now I'm wondering if I can permanently wire my RCA connectors to my XLR connectors inside my chassis. As this implicitly connects pin 1 to pin 3, would the balanced XLR connector still work?
I'd like to offer both RCA and XLR inputs and allow both to work, (but obviously not at the same time)..
You could use combo XLR/TRS input connectors (which assures only one connector at a time is connected). Otherwise a switch between the RCA and XLR is warranted. I personally dislike the RCA connector and would like to see it gone.
You never use a scope with its ground floating. The probe ground goes to the ground on the board. I normally use the middle pin of the power connector. Just be careful not to short out the supply when you do that.
I'd think that'd be possible. It won't show you anything useful, though. You'll just see the THD of your scope as the THD of the amp will be much lower.
No. That'd short out the negative phase of the differential signal.
If you want to support both RCA and XLR, I suggest using a switch to switch between the two.
Tom
Tom,
For my M2X which has an unbalanced SE input I was going to put in a THAT Reciever. I was planning to use a switched combo XLR/TRS input connector. So as far as wiring, wire the 3 XLR connections to the THAT Receiver, the 2 unbalanced connectors from the THAT Receiver to the Normalled connections on the TRS connector, and the 2 unbalanced connectors to the amp input. I am using panel mount connectors instead of the board mounted ones you call out. I should be able to use the XLR connector or a TS plug with a single plug and no exterior switch.
For my M2X which has an unbalanced SE input I was going to put in a THAT Reciever. I was planning to use a switched combo XLR/TRS input connector. So as far as wiring, wire the 3 XLR connections to the THAT Receiver, the 2 unbalanced connectors from the THAT Receiver to the Normalled connections on the TRS connector, and the 2 unbalanced connectors to the amp input. I am using panel mount connectors instead of the board mounted ones you call out. I should be able to use the XLR connector or a TS plug with a single plug and no exterior switch.
M2x's power supply voltages might be too high for a THAT Corp differential receiver. The 1240 and 1250 specify (|Vcc| + |Vee|) <= 40 volts, but the M2x amplifier runs from (|Vcc| + |Vee|) of 46 to 50 volts depending on which diodes you use and which transformer you use. You may have to duplicate the voltage dropper circuitry from a power amp design which uses THAT chips with higher voltage supplies. Modulus-86 is one example.
Tom's THAT receiver board accepts +/- 18V to +/- 40V. It regulates the voltage to a level that the THAT 1200 IC can use. With a 2x18VAC transformer, the voltage will be in the range of +/- 23 to 25VDC. This should fall within the range of useable voltage with the board. Some of the same circuitry is used in the board as in the Modulus-86 (only way I know is that when I put all the components together for my Mouser order I ended up with some high part counts).
I find it pretty funny that when you search for the LM3886, Mouser's "suggested parts" show a good chunk of the BOM for the Modulus-86. 🙂
Tom
If the combo jack has a built-in switch on the TRS jack, what you describe should work. That's a pretty neat setup, actually.
Tom
And what about using a transformer such as the cinemag cmli-15/15b to transform the input signal from single ended to differential?
In theory it could also give galvanic isolation for the xlr connector itself if i am correct, but not sure if that is desirable.
... that’s exactly what I am hoping to see .... nothing;-) as it will be some indication that I didn’t screw up on my built.
Thanks for the hints.
You can do that ... if you like 0.02% THD @ 20 Hz, +4 dBu.
Transformers are great for galvanic isolation. However, the common input transformers distort 100-1000x more than the MOD686, which makes them rather unattractive in my opinion.
I've tested the Modulus-686 in at least five different systems now. Three used single-ended connections (with pseudo-differential cables) to the MOD686; two used differential connections. All setups worked flawlessly.
Tom
I could be interested in this amp, but I would like to read few comparisons with other amps... I've owned (and still own) quite a few amps, for example: NCore, 1200AS2, JOB225, Inline Maraschino, Holton NXL500R4, FO 1.2, 1.3 and 1.4, etc.
I still didn't find what I really like... However the 1200AS2 comes close. I am searching for an amp which is really true to the source. If the recording sounds warm, the amp should reproduce this. It should reproduce natural tone, very transparent and should be able to show a big soundstage when it's in the recording, with loads of depth. Furthermore it should be able to show emotion in voices, etc...
Perhaps I am looking for the impossible.... ��
Does this amp module have balanced inputs?
I still didn't find what I really like... However the 1200AS2 comes close. I am searching for an amp which is really true to the source. If the recording sounds warm, the amp should reproduce this. It should reproduce natural tone, very transparent and should be able to show a big soundstage when it's in the recording, with loads of depth. Furthermore it should be able to show emotion in voices, etc...
Perhaps I am looking for the impossible.... ��
Does this amp module have balanced inputs?
I found the NC400 to sound better than the 1200AS2. The NC400 offered very tight grip on the bass but did suffer from some harshness in the highs, which I did not care for.
To my ears, the Modulus-686 sounds better as it maintains the tight control of the bass while offering open and natural highs.
I don't think it's impossible to find such an amp, but it certainly takes some looking. I think my Modulus-686 is an example of such an amp and my measurements support me in this conclusion. 🙂
Yes.
Tom
I own Ncore 400 amps. I used to think they were the most neutral and transparent amps I'd ever heard. Then I made the Parallel 86 amps and they redefined those terms for me. What's more I know 2 other people who have had exactly the same experience. All 3 of us are Yorkshiremen, but I don't think that is the significant common factor . . . ��
Thanks for this clarity, for now i’ll be skipping the SE inputs. Looking to finish my build on thursday when i have the availability of a symmetric lab psu and an oscilloscope..
Exciting, really looking forward to testing the amp in my setup.
Should you need a single-ended input in the future, just use an RCA-XLR adapter or a pseudo-differential cable.
Tom
Tom