Tom I finally want to try connecting summed SE signal by LL1684 audio transformer to Modulus 86. However I have THAT1200 soldered directly on the board.
Is it ok to:
- leave that1200 as is
- disconnect XLR
- connect SE signal to pin 6 and GND
or
I have to desolder THAT1200 to connected SE signal to Modulus-86?
Thanks,
If you build the Parallel-86 boards with the default 20 dB gain and connect them in a bridge configuration, the total amp gain will be 26 dB. Think about it... Apply 1.0 V in to both amp halves. One produces +10 V, the other -10 V. +10-(-10) = +20. Gain = Vout/Vin <-> Gain = 20/1 = 20. Gain(dB) = 20*log(Gain(lin)) <-> Gain(dB) = 26 dB.
Tom
No. You cannot leave the inputs to the THAT1200 floating and overdrive its output. You'll have to remove the THAT1200. If you then install a wire jumper from pin 3 to pin 6 of the (now) empty THAT1200 footprint you can connect the signal input to the normal input connector and still have some RF filtering.
An easy way to de-solder a DIP IC is to cut the leads with a pair of flush head end cutters, remove the IC package, and de-solder the leads one by one.
Alternatively, you can follow the instructions in the design doc for how to make a pseudo-differential cable. That will allow you to connect your single-ended source to the differential input of the MOD86.
Tom
Excellent, I've already done it 😀
Thanks Tom I'll work my way through those calcs and grow a couple of new synaptic connections
Tom I just tried the solution you suggested. THAT1200 is desoldered. pin 3 and 6 are shorted. I use GND and In+ as inputs from RCA. However I got ~-36VDC on speakers output ... should I do/short anything else?
The RCA should connect from Pin 1 (shield/shell) to Pin 2 (centre conductor) on the input connector. If you get significant DC offset on the output with the RCA shorted, you have a wiring mistake or build mistake (solder bridge from the THAT1200 removal?).
If you leave the RCA floating you're nearly guaranteed to get DC on the output of the amp as the LME49710's input stage doesn't have a DC path to ground in that case. I'd probably solder a 47 kΩ resistor from pin 1 to pin 2 on the input connector (should fit nicely under the board) to make sure the input never floats.
Do beware that you're colouring outside the lines here. Just saying...
Tom
If you leave the RCA floating you're nearly guaranteed to get DC on the output of the amp as the LME49710's input stage doesn't have a DC path to ground in that case. I'd probably solder a 47 kΩ resistor from pin 1 to pin 2 on the input connector (should fit nicely under the board) to make sure the input never floats.
Do beware that you're colouring outside the lines here. Just saying...
Tom
Last edited:
The RCA should connect from Pin 1 (shield/shell) to Pin 2 (centre conductor) on the input connector. If you get significant DC offset on the output with the RCA shorted, you have a wiring mistake or build mistake (solder bridge from the THAT1200 removal?).
If you leave the RCA floating you're nearly guaranteed to get DC on the output of the amp as the LME49710's input stage doesn't have a DC path to ground in that case. I'd probably solder a 47 kΩ resistor from pin 1 to pin 2 on the input connector (should fit nicely under the board) to make sure the input never floats.
Do beware that you're colouring outside the lines here. Just saying...
Tom
Tom, it is exacatelly like you wrote. With pin 1 and 2 floating there is ~36VDC measured. With 47k resistor soldered between pin 1 and 2 everything backs to normal.
I was curious and wanted to find out whether is better to sum signals by THAT1200 on the input of modulus-86 or on the output of the DAC (LL1684 transformers).
Thanks!
Newbie questions here, trying to take in all the information.
1. Would the lightspeed attenuator work (in some form) between a DAC differential output and the modulus-86?
I prefer manual / analog volume control, not trusting a software control too much (sooner or late the software will decide on a random setting.)
2. The SMPS300RE has a 12 V aux output voltage. Is that something I can to power it?
1. Would the lightspeed attenuator work (in some form) between a DAC differential output and the modulus-86?
I prefer manual / analog volume control, not trusting a software control too much (sooner or late the software will decide on a random setting.)
2. The SMPS300RE has a 12 V aux output voltage. Is that something I can to power it?
Though the rage, especially in DIY circles, I'm not so sure the LDR-based attenuators are good ideas. They have nonlinearities (read: induce distortion) and significant aging issues. Much better to use a high-quality potentiometer, stepped attenuator, ladder-of-relays attenuator, or even an IC volume control.
+100.
I had my LDR based attenuator ( designed by a rather infamous company that has won TAS “sound of the year” awards) measured professionally on an APx-525. The results in my opinion were incredibly eye opening and very disappointing (read:distortion!!!). It was sold rather promptly. Better to stick with stepped attenuators, even my TAPX measures great. But if you want to have a tricked out line stage, take a serious look at Christiansen’s Diff Pre.
But don’t believe the hoopla about LDR attenuators..
Best,
Anand.
I agree. The LDRs tend to have pretty steep voltage coefficients, it appears. I've measured THD in the 1-10 % (yes; one to ten percent) range at line levels on one of these highly acclaimed LDR volume controls.
I don't see the attraction.
The ±12 V aux power output of the SMPS300RE can be used to power the power-on indicator... I suppose you could power some line level circuits with it, though I don't know how clean it is. I suspect, "not very". At least I don't recall seeing a post-regulator on the board.
Tom
I don't see the attraction.
The ±12 V aux power output of the SMPS300RE can be used to power the power-on indicator...
I suppose you could power some line level circuits with it, though I don't know how clean it is. I suspect, "not very". At least I don't recall seeing a post-regulator on the board.Tom
Last edited:
The aux output is not regulated, but they do say it's within 10% .
Okay no dice with the LDR. Thanks for the advice! I'll have a look at some of Brian's alternative suggestions. Too bad, the lightspeed design sounds really cool.
... And I guess I'll need a secondary power supply if I want to do anything at all in addition to the amp itself.
.Okay no dice with the LDR. Thanks for the advice! I'll have a look at some of Brian's alternative suggestions. Too bad, the lightspeed design sounds really cool.
... And I guess I'll need a secondary power supply if I want to do anything at all in addition to the amp itself.
Well. Yes and no. Depending on your needs, you may be able to tap into the onboard regulators of the MOD86.
Alternatively, a pair of LM317/LM337 can quickly be fitted to provide whatever voltage you need. They can be bolted to the same heat sink as the LM3886, so suddenly you'll have plenty of current for whatever circuits you need to add.
In one amp I built, I rigged an LM317 as a constant current source to power the power-on LED. Overkill for the application? Sure! But it was easier to manage the power dissipation in a TO-220 package than in a power resistor and the couple of external components needed for the CCS were soldered directly to the LM317. All exposed components were covered in heat shrink.
Tom
Alternatively, a pair of LM317/LM337 can quickly be fitted to provide whatever voltage you need. They can be bolted to the same heat sink as the LM3886, so suddenly you'll have plenty of current for whatever circuits you need to add.
In one amp I built, I rigged an LM317 as a constant current source to power the power-on LED. Overkill for the application? Sure! But it was easier to manage the power dissipation in a TO-220 package than in a power resistor and the couple of external components needed for the CCS were soldered directly to the LM317. All exposed components were covered in heat shrink.
Tom
Absolutely not overkill
There is nothing worse than power lights and meter backlights doing a 'sound to light' display in time to the music. If you add a suitable zener to the LED then you can make sure the LED goes out very quickly after the power goes off.
The aux output is not regulated, but they do say it's within 10%
For audio circuitry, I'd be more concerned with the noise on that supply. I don't know how noisy it is and would rather not make assumptions.
Depends. There's nothing wrong with the AUX supply. You just have to be aware of its limitations. Should it not work for you, a pair of LM317/LM337 can easily be rigged to turn the VCC/VEE rails into something more opamp friendly.
Tom