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Modulus-86  build thread
Modulus-86  build thread
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Old 7th November 2017, 09:28 AM   #3641
sq225917 is offline sq225917  United Kingdom
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Ian, the gain options on the 86p are 20db, 17db and 14db.

To flip them you need to replace D3and D8 with a wire link and swap the THAT 1206 with a THAT1200. I have a couple of 1200's if you want them.
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Old 7th November 2017, 12:47 PM   #3642
TioFrancotirador is offline TioFrancotirador  Poland
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Originally Posted by tomchr View Post
Pluck the THAT1200 from its socket and connect the single-ended output from the LL1684s between pin 6 of the THAT1200 socket and ground (R11).

Tom
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,
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Old 7th November 2017, 05:34 PM   #3643
tomchr is offline tomchr  Canada
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Originally Posted by Studley View Post
My Parallel 86 amps are bridged. Please advise of the component changes I'd need to make to convert them to 26db gain. 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
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Old 7th November 2017, 05:38 PM   #3644
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by TioFrancotirador View Post
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
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
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Old 7th November 2017, 10:38 PM   #3645
Studley is offline Studley  United Kingdom
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Quote:
Originally Posted by tomchr View Post
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
Excellent, I've already done it 😀
Thanks Tom I'll work my way through those calcs and grow a couple of new synaptic connections
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Old 8th November 2017, 04:05 AM   #3646
tomchr is offline tomchr  Canada
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Originally Posted by Studley View Post
I'll work my way through those calcs and grow a couple of new synaptic connections
Careful with that!

Tom
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Old 9th November 2017, 02:33 PM   #3647
TioFrancotirador is offline TioFrancotirador  Poland
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Quote:
Originally Posted by tomchr View Post
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
Thanks Tom!
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Old 11th November 2017, 05:54 PM   #3648
TioFrancotirador is offline TioFrancotirador  Poland
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Quote:
Originally Posted by tomchr View Post
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
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?
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Old 11th November 2017, 07:59 PM   #3649
tomchr is offline tomchr  Canada
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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
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Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
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Last edited by tomchr; 11th November 2017 at 08:02 PM.
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Old 12th November 2017, 01:16 PM   #3650
TioFrancotirador is offline TioFrancotirador  Poland
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Quote:
Originally Posted by tomchr View Post
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!
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