Spencerleehorton

1176 Rev J Mod to Rev D
« on: June 07, 2018, 12:35:55 PM »
Hi All,

I thought i'd give my mod a go, Mnats pcb Rev J and mod it to Rev D.
Have sorted the Line Amp, just need to sort the Preamp, will let you know what i've done once its all working.
Have wound my own output transformer and using OEP on input 2:1.
Using 2n3391 and 2N5088 transistors, bypassing 5532 input section, G.R driver amp leaving as is,  G.R control amp i think is the same but will check.
Love my other Rev D so i thought i could do with a couple more in a 2U enclosure.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!


Spencerleehorton

Re: 1176 Rev J Mod to Rev D
« Reply #1 on: June 08, 2018, 09:34:02 AM »
put a bit more work into it today, have an output of sorts, not nice looking!!!!
need to replace the BC109 transistors along with a few tants and caps, but getting there now.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!

Spencerleehorton

Re: 1176 Rev J Mod to Rev D
« Reply #2 on: June 13, 2018, 03:04:28 PM »
Getting weird oscillation so will check voltages and find out where it’s coming from.
Have changed all transistors, tants and caps so hopefully I’ve done it correctly but will fix any mistakes tomorrow.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!

Zebra_PD

Re: 1176 Rev J Mod to Rev D
« Reply #3 on: June 15, 2018, 05:36:09 AM »
Interesting to follow your progress here. Can you perhaps list all the changes you made?

Did u you find the oscillation problem?
___________________________________________________
Semiprofessionell producer but newbie DIYer.
----------------------------------------------------------
www.zebrastudios.se

Spencerleehorton

Re: 1176 Rev J Mod to Rev D
« Reply #4 on: June 15, 2018, 06:50:38 AM »
Not yet but checking all voltages later so will report back.
So far i have changed all the transistors Q2, Q3, Q4 for 2n3391.
Q1 is BF245
Q5 from RevJ is now Q4 2N3391
removed Q6 on Rev J
Q7 on Rev J is Q5 2N5088
Q8 removed
Q9 rev J is Q6 2N3053.

thats the transistors

R4(270R) to gnd
C9 to 1uf
C10 changed to 0.15uf poly
removed C11
R31 / Q5 collector to R29 connected 2.7M resistor
removed R28
R30 to 2.7M
remove R29 and put in link
R32 to 1.5k
R33 to 10k
C13 to 270pf add in R32 39R
remove R34
C12 to 1uf (C10)
R37 to 150k (R30)
R38 to 1N914 diode
remove R39 put in link
remove CR1 & CR2
remove C29
R36 remove and put in link
Q9 cut track at base
Q8 remove
R41 to 560R
remove C14 / C15
R40 to 4.7nf (Grey link to Q4 emitter with 27K)
R35 is 1.2M (R29) and C11 10pf in parallel
disconnect +30v and put in 8.2k will explain where i did this
remove C29

thats so far
« Last Edit: June 16, 2018, 05:07:40 PM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!

Spencerleehorton

Re: 1176 Rev J Mod to Rev D
« Reply #5 on: June 15, 2018, 01:30:57 PM »
i'm getting voltage oscillation in the preamp, cant seem to find where its coming from!!!

Was Q1, had mistakenly put in 2N3819 rather than BF245!

Voltage check has revealed preamp is low on voltage at Q2 so will check connections and wiring.
« Last Edit: June 16, 2018, 02:00:54 AM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!

Spencerleehorton

Re: 1176 Rev J Mod to Rev D
« Reply #6 on: June 18, 2018, 04:13:25 PM »
have sorted out the preamp now and all voltages in the preamp are good,
getting signal throughout but it doesn't look very clever yet!!

Now the line amp is a bit off, going to check it through and find the error.
Problem is at Q4 after the output pot, will trace connections and make sure i don't have a rogue connection.
Then i will check the GR control amp and meter driver.
Once i've got it all working i'll put up in detail what i've done.
« Last Edit: June 19, 2018, 03:04:24 AM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!

Spencerleehorton

Re: 1176 Rev J Mod to Rev D
« Reply #7 on: June 21, 2018, 06:32:20 AM »
All working now, good clean signal, checked all connections and voltages and all within limits.
Just need to tweak the GR meter driver so i have a bit more adjustability with the VU meters i'm using,
so will change R53 from 15k to 25k trimmer and R56 to 10k trimmer., so i can set the GR to zero and its a bit off at the moment.
now i've figured it out its actually a fairly easy mod!!!

Correction, i have changed R59 for 10k trimmer and get a bit more adjustability on GR but tracking is out now so will play with R58 100k
R51 for 10k trimmer adjusts VU point set.

« Last Edit: June 21, 2018, 08:52:36 AM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!

Spencerleehorton

Re: 1176 Rev J Mod to Rev D
« Reply #8 on: June 21, 2018, 02:16:34 PM »
Could anyone explain what to change to adjust the GR meter, I still need adjustability to get the GR to zero.
VU setting is fine.
If not I’ll just redo it as per Rev D but would like to see if it works with TL071 rather than transistor.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!

Spencerleehorton

Re: 1176 Rev J Mod to Rev D
« Reply #9 on: June 22, 2018, 10:37:01 AM »
Changed R58 for 100k trimmer and twiddled and set meter to zero.
All seems to setup apart from one thing, I have hum!!! Only a little but enough to be annoying.
Gonna enjoy some sun and have a look next week.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!


Spencerleehorton

Re: 1176 Rev J Mod to Rev D
« Reply #10 on: June 27, 2018, 02:58:19 AM »
Changed gnd config as per rev d, input pin 1 to chassis, output pin 1 to chassis and neg rail on Psu to chassis.
All sounds good now.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!

Zebra_PD

Re: 1176 Rev J Mod to Rev D
« Reply #11 on: July 01, 2018, 02:12:32 PM »
Amazing job!! Have a rev j I'm starting to populate and might do this mod too. Are you using a pot or attenator for the input gain?
___________________________________________________
Semiprofessionell producer but newbie DIYer.
----------------------------------------------------------
www.zebrastudios.se

Spencerleehorton

Re: 1176 Rev J Mod to Rev D
« Reply #12 on: July 02, 2018, 02:13:17 AM »
I’m using the T-pad pot
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!

Spencerleehorton

Re: 1176 Rev J Mod to Rev D New
« Reply #13 on: July 02, 2018, 02:38:36 PM »
the key to removing noise is on the input txf, you will need to disconnect the gnd/screen connection on the input txf and run that to chassis.
as my unit was a stereo mnats 1176 rev J, im going to mod the other channel now!
need to wind a couple more output transformers!!
« Last Edit: September 19, 2018, 01:23:31 AM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!


 

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