Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #40 on: October 16, 2016, 07:46:18 AM »
well going by what ive put i end up with the following:

0.774-0.776v AC pin 2 output from sinewave gen into transformer PRI one side then off PRI other side into DMM + and - attached back to pin 1 on sinewave generator, DMM now says 0.019 - 0.023v AC

does this help in now doing the calculations?

regards

Spence.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!


Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #41 on: October 16, 2016, 01:52:38 PM »
another couple of questions to do with in my mind adding to this preamps, could i use the attached pic in front of the input txf as per the way API-312 do it?
would i have to change the 2 x 470R and 120R resistors on the pad for something else?

also adding a VU meter, where would be the best connection to implement this?

regards

Spence.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

CJ

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #42 on: October 16, 2016, 04:37:43 PM »
like this>
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #43 on: October 16, 2016, 04:38:55 PM »
i was going to say i work better with pictures!!!
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #44 on: October 16, 2016, 05:23:19 PM »
im not being funny but i dont seem to be getting very accurate results?
my DMM is a fairly good one and i set it to AC volts it jumps around a bit but steadily it does seem to climb in volts?
i try and set as close as i can to 0.775v but one time it was 0.742-0.744v and then when i put it as per your picture it was 0.782-0.785v.
but i notice if it takes me 30 seconds to rig back up from testing the signal gen voltage to wiring up as per picture the voltage has gone up from what i first tested!!! i know its only a few volts but thats what im saying here, this doesnt seem very scientific?
could you be really clear with this please, and what is the calculation?

regards

Spence.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

CJ

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #45 on: October 16, 2016, 06:23:34 PM »
we want current, not volts,
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #46 on: October 16, 2016, 06:39:43 PM »
i thought that but wasnt sure as when i switched it to mA nothing showed up?
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

CJ

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #47 on: October 16, 2016, 06:54:05 PM »
AC ma?  is it an autoscale meter or does it have ranges?

if it has ranges, switch to the low range,

maybe there is so much permeabillity that the current is in the micro-amps and your meter is not sensitive enuff,

If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #48 on: October 16, 2016, 07:02:29 PM »
right i needed to remove the red lead in the DMM and plug it into another port!!!! doh!!

0.48mA is the answer!!!

can we do the calculation now?
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

CJ

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #49 on: October 16, 2016, 08:22:00 PM »
.75 vac / .00048 = 1562 ohms reactance

1562/2 pi f = 1562/(6.28*20)=1562/125.6= 12.4 H at 20 Hz.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html


Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #50 on: October 17, 2016, 02:48:52 AM »
So is that good? Or bad?

I've got a bit of practice now as I can do this calculation to all my transformers!
« Last Edit: October 17, 2016, 02:57:32 AM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #51 on: October 17, 2016, 05:24:44 PM »
some pics of my build so far

got a little hum on right channel, will need to investigate gnd and where screened cables are needed.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #52 on: October 17, 2016, 05:36:39 PM »
another
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #53 on: October 17, 2016, 05:57:20 PM »
could anyone help with a way of relay switching the input transformers so i could use them back to front as Line and Mic?
I think i may need 3 relays but im not exactly sure of how to wire this up?
anyone have a schematic?

regards

Spence.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #54 on: October 17, 2016, 06:29:59 PM »
the only way i can think of off hand is using 4 relays to reverse the transformer? is there a easier way?

regards

Spence.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

PRR

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #55 on: October 17, 2016, 09:36:40 PM »
4P2T

Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #56 on: October 18, 2016, 03:07:44 AM »
Thanks PRR! Brill

Do you happen to know where I should be using screened leads on the schematic, as I'm finding it a little confusing the way it's written on the original.
My left channel seems fine but there is definitely a bit of hum on my right channel, probably gnd loop. Just need to make sure I do the gnd and screening correctly.

Regards

Spence.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #57 on: October 18, 2016, 01:57:04 PM »
Have had a fiddle and now the left channel has slight hum at high levels?
Right channel is now him free, don't know what I've done but I've managed to move the hum from right to left!?
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

CJ

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #58 on: October 18, 2016, 03:26:02 PM »
12 Henries is about right for a mic input, figure a 150 ohm mic, you want ten times the input  from the transformer at the lowest freq, 12 H at 20 Hz is 1500 ohms so there you go.

can't vouch for the hum problems,  not there,
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Spencerleehorton

Re: Making Neve Style Input Transformer for 1073/1290 preamp
« Reply #59 on: October 18, 2016, 04:55:39 PM »
Great CJ, I'm happy with hopefully being within range!
I'm sure hum wise I'll be able to illuminate it with swapping a few god connections about.

Regards

Spence.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!