MONO Ver1 Mic pre kit BUILD THREAD

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MONO Ver1 Mic pre kit BUILD THREAD

Post by Joe Malone »

JLM MONO mic pre is a compact tough transformer balanced input mic pre with electronic balanced output which can run on 2 x 9v Normal Alkaline or Rechargable NiMH batteries and provide 18v phantom power which will run most modern condensor microphones or you can use our 48v 520mA SMPS which can charge NiMH batteries at the same time as running the mic pre with 48v phantom power and greater headroom. One 48v SMPS can run and charge 8 MONO Mic pres easy. As usual the same large variety of input transformers can be used as Baby Animal and Baby Animal Dual. The pre is made to run one Dual OPA2604AP opamp on 18v battery power up to 48v SMPS power but can have 2 x JLM99v and compatable footprint discrete opamps fitted with no component changes but the battery power option is then lost. Kit comes with a full laser cut diecast aluminium box and black epoxy baked screenprinted top.
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Internal single sided PCB fitted with components for electronic training version for JMC Academy and TAFE Colleges.
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Parts List MONO Training Version
MONO Schematic

MONO Upgrade options on JLM web shop
(Main upgrade the training version needs is the input transformer to get a real top end mic pre & 48v SMPS for true 48v phantom power and +28dBM huge output level)
JLM14 Input transformer (Great for drums, bass, samples and general very good all rounder)
OEP262A3C/VTX Input transformer (Great Vocals, Acoustic Instruments. Bit more coloured as used in our Dual99v mic pre)
JLM99v discrete opamp (Fatter low end and silky high end then OPA or Hybrid)
6 Sockets to plug in JLM99v etc
48v SMPS power supply (Can run & charge 8 x MONO mic pre at one time)
2 x 9v NiMH batteries

1. Install all resistors in there correct locations using chart to the left or better still by using a multimeter with no leads fitted and bending the legs of the resistor and putting them in the meter sockets to double check you have the right value before putting it into the PCB.

Red Transformer Training Version RPad = 120R, RGain = 22R Rload = Not Fitted, RZobel = LINK, Czobel = 390pF.
(If you are thinking of upgrading your college version later to one of the better transformer versions below it is fine to fit the below values now with the Red transformer. Rload will not affect the red transformer and the larger Rgain will just give less gain until the upgraded transformer is fitted.
JLM14 Transformer fitted fitted to Training Version MONO RPad = 120R, RGain = 68R Rload = 10k, RZobel = LINK, Czobel = 390pF.
JLM14 Transformer fitted fitted to Normal Version MONO RPad = 120R, RGain = 68R Rload = 2k2, RZobel = LINK, Czobel = 390pF. Impedance pot 50k log
NOTE OEP/VTX transformers need to have the shield pin folded over and a cut off component leg soldered to it so the transformer can go on turned 180 degrees.
Primary should be closest to the XLR's. Extended shield pin can be solder to any of the 3 large holes under the transformer
OEP 262A3C / VTX Transformer fitted to Training Version MONO RPad = 120R, RGain = 68R Rload = 27k, RZobel = LINK, Czobel = 390pF.
OEP 262A3C / VTX Transformer fitted to Normal Version MONO RPad = 120R, RGain = 68R Rload = 10k, RZobel = LINK, Czobel = 390pF. Impedance pot 100k log
(The MONO PCB has a impedance pot option which is not used in the Training kits so when fitting RLoad the small white line between 2 holes at one end of RLoad needs to be jumper over with a resistor leg cut off. See near bottom of this post)

Fit all resistors before soldering them as this can also help check that you haven't put a resistor in the wrong place.
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2. Install all diodes with there Grey/White/Black strip band lining up white white band on the PCB.
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3. Once all resistors and diodes are fitted solder them in with the PCB held upside down on a flat surface and then cut there legs just flush above the solder joint.
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4. Fit IC Socket with the U aligned with the overlay. Then fit the 100pF cap either way around.
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5. Place the 6 x 470uF caps on the PCB with there long leg fitted in the hole marked + which is a square pad under the PCB.
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6. Solder in all 6 caps which should all be facing the same direction when finished.
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7. Fit transformer to the PCB. No gap needs to be left for any of the transformers as the PCB is single sided. Red transformer shown below. JLM14 bolts to PCB and the four colours of its wires are marked on the top of the PCB. Black is not connected to anything. OEP transformer only fits one way on the PCB making it easy.
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8. Solder in the transformer wires and then fit the XLR's and solder them in.
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9. Push in all toggles with there U notch away from the XLR's. Make sure they are sitting flat and level to the PCB.
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10. With the XLR's fitted you can do a test fit into the case and check the 4 toggles switch up & down in there slots ok with only one centre pad soldered encase the toggle needs to be moved slightly before soldering all the switch legs.
(Yellow Circle - Watch out when cutting of soldered legs that they are actually soldered otherwise they can be hard to fault find later)
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11. Extend the DC connector legs with 3 cut off diode legs as shown. The diode legs are thicker and stronger than the resistor legs.
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12. The DC connector center leg actually bends across the middle so the connector goes into the PCB 180 degrees to what you might have first thought.
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13. The 3 LED's are placed into the positions long leg to A. Do not swap the LED colours around at all as this will affect the charge circuit.
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14. LED's in positon but will not be soldered until fitted to the case with the gain pot to get the right height.
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15. Use long nose pliers to bend the 3 pot legs 90 degrees.
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16. Cut off the locate tag on pot with sidecutters.
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17. Extend the legs by using the full leg length from the two spare zero ohm links in the kit.
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18. Pot sitting in PCB ready to be placed upside down on top of the case to get lengths right and then LED's, Gain pot, DC connector and LEDs can all be soldered.
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19.Cut the Battery leads to length. Note positive and negative are reversed on each side.
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20. Fitting the Battery leads.
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21. Leave these solder pads unsoldered for normal 9v batteries.
Only solder together when using rechargeable NiMH batteries.
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22. MONO training version fully built.
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23. Fit OPA2604AP IC into the DIP socket with its U aligned with the IC socket upwards as shown below.
Note extra 100pF cap between out and -in on the second opamp side that the OPA2604AP was found to need to work at its best. Fit as shown on all MONO kits using any opamp type.
Ready to test in the open with 2 x 9v batteries or 48v SMPS.
If testing without batteries fitted put some tape on the 9v clips to stop them shorting to anything.
Please make sure you have your monitors or headphones turned down when power on or off on the MONO mic pre to save your ears :-)
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24. Z pot wiring on MONO normal version.
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Shows Z pot wiring and MONO with 2 x 99v Fitted.
NOTE When fitting JLM99V to MONO do NOT fit C7 or 100pF across second 99v -in to out as we have found this makes the MONO pre more stable and less prone to oscillation when using the 99V
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25. Shows the stick on black rubber strip for holding in the 9v batteries firmly.
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26. Shows plastic protective sheet used to stop the 3 points in red circles from touching the lip of the diecast bottom panel.
Make sure all soldered pad joints especially the ones in the red circles are cut short and the plastic sheet need to be a tight fit in the back of the case.
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New Lexan stick on front panel info for 2010 training version
Black edge of slots and XLR holes with black permanent pen to remove shine from edges.
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The leds on the Lexan panel are covered so must stop flush with the top panel of the case.
Best to put a kink in the legs so the leds can be push down flush.
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Fit PCB to case and do a test fit of the lexan panel before removing the backing to check best alignment.
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Remove sticker backing
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Flex lexan panel so it can be aligned by the DC and Gain pot holes.
Sticker can be removed if not pressed hard down on.
(Sticker can be fitted with the case empty or with the PCB fitted so DC connector and Gain pot can help to align the sticker)
(Note sticker holes for DC connector and Gain pot are 0.5mm larger so the sticker can still be moved around slightly for better overall alignment)
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Once alignment is correct the sticker can be pressed down hard from the center out.
After about 24 to 48 hours the glue on the sticker will bond with the case making it very hard to remove.
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conleycd
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Re: MONO Mic pre kit BUILD THREAD

Post by conleycd »

Looks neat - handy - and the size of a DI box!

What do you think the cost will be on this one?

CC

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MONO Mic pre kit building errors we have seen.

Post by Joe Malone »

The Photo below shows in the red circles solder joints that didn't have enough heat to flow and join to the solder pads to the component legs and in the yellow circle a cold solder joint which always has a frosted look. Almost all solder joints in the photo have to much solder on them but some have so much they look like a round ball.
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The Photo below shows soldered pads that have been torn from the tracks usually by to much heat or the component not fully sitting down on the top of the PCB and being pushed on after soldering or during trying to reheat the joint.
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The photo below shows a 10k swapped with a 120R. 10k 1% resistors can look similar to 120R resistor color code read backwards. Make sure you do not start reading the color code from the wider spaced color band which is the tolerance band.
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The Photo below shows what can happen to the pot if you fail to cut off the locate tag and try to bolt the pot into the case.
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Joe :-)
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MONO Mic pre kit works but gain control does nothing

Post by Joe Malone »

MONO Mic pre kit works but gain control does nothing

If you have signal but the gain does nothing usually means you have not fitted the RGain resistor
or the Gain pot is faulty or not soldered to the PCB properly. To test the pot turn off the mic pre and with the back of the mic pre case removed place a ohmmeter across the 2 pot pads that are not connected by a track on the back of the PCB and check you get 0ohms with the pot turned to one end and 10k with the pot turned to the other end.
Joe :-)
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peat
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Re: MONO Mic pre kit BUILD THREAD

Post by peat »

Just finished putting one of these together with a vtx transformer and 2x 99v's

incredible, more gain than you could poke a stick at and quiet as hell, absolutely no hiss.

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so far have only tried it with
strat - DI - MONO - PT

and it sounded great, deep and clear, great low end and smooth transients
will post a clip soon!

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Re: MONO Mic pre kit BUILD THREAD

Post by Joe Malone »

conleycd wrote:Looks neat - handy - and the size of a DI box!

What do you think the cost will be on this one?

CC
Available on the JLM web shop here
Joe :-)
JLM Audio
Capturing Audio without Injury

weroflu
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Re: MONO Mic pre kit BUILD THREAD

Post by weroflu »

is this the same circuit as the baby animal?
i'm a little confused about how much gain the baby animals can put out. it says in one place that it is a 60db amplifier, but on the build page it says you can get 72 db with an oep input transformer.

so what is the maximum gain you can get with this?

also, would you sell the pcb and kit without the case?

chrisp
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Re: MONO Mic pre kit BUILD THREAD

Post by chrisp »

Joe can answer the rest of this, but I can help out with the gain question.

The gain of the circuit is the sum of the gains from the input transformer, the amp circuit and the output transformer. The first and last of these depend on the transformer windings: the JLM 1:4 has a gain of 12db, the OEP262A3 has a gain of roughly 17db in its low setting or 23db in its high setting, Lundhal 1538 has gains of 9db or 15db and the LL1578 gains of 15db or 21db. The JLM 1:1:1 has outputs of unity (no gain) or 6db (when wired as 1:2).

The JLM 99V is an opamp and obeys the general rule of non-inverting opamp gain: Vout/Vin = 1 + Rf/Rg (Rf is the feedback resister from the opamp output to the -ve input, while Rg is the gain resistor from the opamp -ve input to ground). In the BAs, Rf is 10K. Rg is a combination of a fixed resistor (RGain) and the Gain pot (up to 10K). From the gain equation, the smaller Rg is, the larger the gain, yes? So the BA's RGain resistor sets the maximum value for the gain (when the pot resistance is close to 0R).

So follow the maths: The standard Rgain for a normal BA is 68R, so the opamp gain (as a voltage ratio) is 1+ 10K/68, = 148. In db, this is 20*log(148), or about 43db. So total gain for a JLM1:4 (12db), a 99V opamp (43db) and a JLM1:1:1 wired as 1:2 (6db), is thus 12 + 43 + 6 = 61db. This is the "standard" BA build and hence the most quoted gain figure. If you use an OEP as above wired to high gain (23db), this becomes 23 + 43 + 6 = 72db gain - the additional gain all coming from the input transformer.

The maximum gain can you get from the amp circuit depends on the point at which your choice of opamp departs from its linear behaviour and start to distort or oscillate. A perfect (ie theorectical) opamp gain deliver gain up to the point when its output is the same voltage as the supply rails (by making Rg close to 0R), but no real world opamp would achieve this without distorting (and also, remember, amplifying noise as well as signal). This is where Joe's design expertise comes in - he knows the point at which his 99V should call it a day as far as gain is concerned. If you want more gain than this, you daisy chain the opamps, and that's what this board and the BAD can achieve. But again, you don't want too much gain or you simply head into noise/distortion territory, and that's why the BAD for example has a higher value for Rgain - the higher value reduces the maximum gain for each 99V opamp (in fact to a point where you often don't need to fit the Cload cap to avoid oscillation) while the daisy chaining still delivers insane amounts of gain for things like older style ribbon mics, or a passive EQ or compressor circuit.

A final word of caution. A great signal chain does not have all the gain at one point. The purpose of a preamp to is get the signal level from a mic, guitar or other source up to some nominal level (usually +4dbu). The idea is to "standardise" the signal levels from all sources, for mixing or subsequent processing. The fact that your digital converters can handle signals of up to +18 or +22dbu does not mean you have to, or even should, go there. There is a whole other debate about the proper nominal signal level for digital recording, but asking for a preamp to deliver an output signal with an RMS average over about +8dbu suggests to me that the rest of the signal path (whether digital or analog) is not being used appropriately.

Good luck with it all.
Chris P
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weroflu
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Re: MONO Mic pre kit BUILD THREAD

Post by weroflu »

thanks for the reply.

just a few more questions.

the opa2604 is a dual opamp, correct? so using this opamp you have two gain stages?

will you get comparable amount of gain using a single 2604 compared with 2 jlm99v opamps?

still unclear whether this amp is more like a baby animal dual, or a regular baby animal.

i am interested in running it with battery power alone, so trying to find out how much gain i can get with the opa2604 and the oep input transfomer

weroflu
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Re: MONO Mic pre kit BUILD THREAD

Post by weroflu »

forgot one thing. i just noticed that there are no options for an output transformer on the mono. so i think you would have to deduct 6db from your calculations.

chrisp
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Re: MONO Mic pre kit BUILD THREAD

Post by chrisp »

weroflu wrote:the opa2604 is a dual opamp, correct? so using this opamp you have two gain stages?
Yes, and maybe. The 2604 is certainly a dual opamp, but opamps have many uses apart from amplifiers. In the basic BA, for example, you can use a 2604 instead of a 99V - the circuit uses 1 of the opamps as the gain stage and the other as an inverting buffer (at unity gain) to run the -ve balanced output. In the JLM hybrid, the 2604 opamps are used as an input stage buffer and as a DC servo path, the actual gain coming from a pair of transistors. So we cannot assume that 2 opamps equals 2 gain stages.

Looking at Joe's schematic, this kit follows the BA scheme where the second opamp (whether 1/2 OPA2604 or separate 99V) is used to buffer the balanced -ve out, and is not involved as a gain stage. So its a BA, not a BAD.
will you get comparable amount of gain using a single 2604 compared with 2 jlm99v opamps?
In this kit? Yes, but there will be sonic differences - "clean" (OPA) vs "rock" (JLM) would be a simplified comparison. Err, and you cannot use battery power for 2x99Vs, so if you plan to use batteries, the OPA is your only option.
i just noticed that there are no options for an output transformer on the mono. so i think you would have to deduct 6db from your calculations.
Just 'cause the PCB doesn't have space for one doesn't mean it cannot be done!! But I agree, if there is no 1:2 output transformer then there is no 6db gain. My numbers were simply to show how the BA gets touted as a 60db preamp, rather than making any comment on the gain of this kit.

The schematic for the MONO kit shows Rf as 10K and Rgain somewhere from 22 to 68R. If you use 68R, the opamp gain is 43db as per my above post. If you use 22R, the gain is 20log(1+10K/22) which works out to about 53db. So choose your Rgain, add in your input tranny gain and there's your MONO gain value when the pot is turning full on. FWIW, a gain of about 50db or so is usually enough (like 99% of the time) to get a mic signal up to +4dbu. So a JLM1:4 at 12db and the 99V with Rgain at 68R (total of 55db) is still going to get you there. With the OEP wired for high gain and Rgain at 22R, you'd be looking at 76db or so on paper.
Chris P
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Re: MONO Mic pre kit BUILD THREAD

Post by Joe Malone »

weroflu wrote:is this the same circuit as the baby animal?
Similar but output is always electronically balanced. Second 99v opamp or Second half of OPA2604AP is used as the inverted -out adding 6dB gain like a 1:2 output transformer would normally do.
i'm a little confused about how much gain the baby animals can put out. it says in one place that it is a 60db amplifier, but on the build page it says you can get 72 db with an oep input transformer.

so what is the maximum gain you can get with this?
It depends on the transformer ratio/gain and opamp gain and stability. 99v can on do 42dB (48dB with inverting opamp) max so Rgain can only go to 68R. OPA2604AP can do 54dB (60dB with inverting opamp) so Rgain of 22R is possible. JLM14 adds 12dB, OEP/VTX adds 15dB.
also, would you sell the pcb and kit without the case?
Maybe but why.
weroflu wrote:forgot one thing. i just noticed that there are no options for an output transformer on the mono. so i think you would have to deduct 6db from your calculations.
The inverting second opamp stage adds the 6dB. So they are the same gain.

Otherwise Chris has covered it correctly :-)
Joe :-)
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weroflu
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Re: MONO Mic pre kit BUILD THREAD

Post by weroflu »

thanks for the detailed explanations.

so the mono is actually capable of 83db of gain with the opa2604 and the oep wired for 23db of gain. excellent. ( you might want to explicity state this somewhere so you don't miss out on sales)

would it be hard to modify a baby animal to use with two 9v batteries if you didn't need phantom power?

i am just looking for a preamp with no phase, phantom, di, or anything fancy, to use with a ribbon mic or two. i may already have a case, that's why i asked about the pcb sans case. plus the added weight in overseas shipping will probably add up cost wise.

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Re: MONO Mic pre kit BUILD THREAD

Post by Joe Malone »

weroflu wrote:thanks for the detailed explanations.

so the mono is actually capable of 83db of gain with the opa2604 and the oep wired for 23db of gain. excellent. ( you might want to explicity state this somewhere so you don't miss out on sales)
No the OEP on the mono is fixed at low ratio which is the only remommended ratio for the OEP/VTX so 15dB + 60dB = 75dB. But I would still only ever run it as the 60dB total gain for best performance and keep a better feel/range on the gain control.
would it be hard to modify a baby animal to use with two 9v batteries if you didn't need phantom power?
Just connect any voltage from 18v to 48v to the baby animal with a OPA2604A or NA5532A fitted and it will work fine. The phantom power will be what ever the voltage connected to the baby animal is. There are heaps of guys using BA this way for field recording. Same applies to the BAD.
i am just looking for a preamp with no phase, phantom, di, or anything fancy, to use with a ribbon mic or two. i may already have a case, that's why i asked about the pcb sans case. plus the added weight in overseas shipping will probably add up cost wise.
If you are using a ribbon mic and need heaps of gain use the BAD with JLM14 and 2 x OPA2604AP as you can get 80db of gain easy. The whole mono kit with case is very light to ship and has the battery rechage option built on the PCB so rechargable NiMH 9v can be used.
Joe :-)
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chrisp
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Re: MONO Mic pre kit BUILD THREAD

Post by chrisp »

Joe Malone wrote:Second half of OPA2604AP is used as the inverted -out adding 6dB gain like a 1:2 output transformer would normally do.
I'd like to make sure I understand this.

R11 and R12 are both 10K, so the opamp is simply unity inverting, yes? BUT, when you apply this inverted signal as the -ve in a balanced line transmitter, the differential between the +ve and -ve signals is effectively doubled, and hence the 6db gain. Think of it this way - if you have a +2V signal on the +ve line, invert it (to a -2V signal) and apply the inverted signal to the balanced -ve, the differential on the balanced line is now +2 to -2, ie +4 V. Magic!

I think I've seen this little trick before in schematics, and never had thought it through as being the opamp equivalent of a 1:2 output balancing transformer.
Chris P
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I do lots of things. I believe eclectic skills are best.

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