Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #140 on: April 21, 2020, 07:49:04 AM »
seems the schematic that ive posted is wrong? Ive disconnected signal from 283 at U input and im still getting output on pin 2?

anyone explain this?
website: www.mohawkstudios.co.uk
email: [email protected]

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


Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #141 on: April 21, 2020, 11:47:25 PM »
found my errors, didnt use screened leads for 2nd txf, all hum and noise really quiet now, stereo 2254 sounds amazing now!!

Been a long hard slog but im there now!! Just need to put in a few resistors for some different attack times!
website: www.mohawkstudios.co.uk
email: [email protected]

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

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #142 on: April 22, 2020, 03:50:06 PM »
When doing this build it is essential to use screened leads on 2nd input txf and for 2nd input txf to be mumetal shielded and case shield put to case gnd.
Gnd connections on Neve builds is very important I have learnt!!!
Using screen leads on input and output sockets and having pin 1 connected to case gnd or star gnd but do not connect the screen of the lead when connecting lead to Pcb audio gnd, just leave unconnected.
I’ve gone over all my Neve builds now and improved the S/N a lot by using this method of mumetal shielding and GND connections.
website: www.mohawkstudios.co.uk
email: [email protected]

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

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #143 on: May 21, 2020, 11:23:12 PM »
still having some noise issues with this build!!, now im monitoring on headphones and ive gone through nearly all my Neve preamps with a fine tooth comb and fixed the 48v hum, it seems i still have a little hum on both channels.
no hum when in bypass as the 4pdt switch just puts the signal straight through.
The hum sounds like a gnd loop, 100hz area rather than 50/60hz.
the only thing i can think of is none of my transformers are grounded, which leads me to my question.
Ive made all my transformers, 4 x 10468 ive put a internal screen inside and attached to core but this is not down to audio gnd or chassis ground, the 1166 output txf ive built also doesnt have a connection to gnd?
will i get hum without these connections?
website: www.mohawkstudios.co.uk
email: [email protected]

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

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #144 on: May 24, 2020, 06:16:17 AM »
Well it seems my gnd scheme is wrong and I may have an issue with the ba185 pcb?
I now hopefully understand the gnd scheme correctly.
Will change and document if it works.
website: www.mohawkstudios.co.uk
email: [email protected]

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

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #145 on: May 25, 2020, 03:04:31 AM »
Just been trying to fault find this problem with the BA185 so ive download the ba185 schematic from the technical docs section, and the ba185 schematic is wrong!!!

compared it to the original schematic and from F it goes to R17 which is R19 on original neve schematic it says it connects to T6 Collector C8 +, T5 Collector and T4 collector, the T4 collector is wrong as F connects direct to it.
website: www.mohawkstudios.co.uk
email: [email protected]

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

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #146 on: May 26, 2020, 01:44:55 AM »
Well it seems my next step is to move the psu completely out of the box again as it still might be this issue!
I did do this before and no change.
I routed the signal just into first txf then into 283 and no buzz, signal into 2nd txf and into 283, no buzz, signal into 185 then into 283 with 191 disconnected and I get buzz!!
So it seems it's either 185 which has a problem or possibly 191?
I've gone over and over the two pcbs and cant see or find any issues?
There is obviously a mistake somewhere but without good working voltages I'm just not going to find this problem!!

Any ideas how to tackle this anyone?
website: www.mohawkstudios.co.uk
email: [email protected]

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

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #147 on: May 26, 2020, 10:22:36 AM »
well i seem to have found my problem but i also have another problem!!!

ive taken the PSU outside the case and now installed into another case which can now live about 6 foot away.
last time i checked the psu outside the case i didnt take the psu and toroidal away enough to make any differnce.
It has to be at least 1-2 feet away to make any difference.

noise is now taken care of but there now seem to be another gnd issue.

when i plug a bass into a DI and then preamp it, ive checked without the 2254 first and signal and sound has no issues.
but when put through the 2254 if i dont touch the strings there is hum!!
so this seems to be a gnd issue?

this is with the volume down on the bass btw
website: www.mohawkstudios.co.uk
email: [email protected]

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

Rob Flinn

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #148 on: May 26, 2020, 11:03:41 AM »
well i seem to have found my problem but i also have another problem!!!

ive taken the PSU outside the case and now installed into another case which can now live about 6 foot away.
last time i checked the psu outside the case i didnt take the psu and toroidal away enough to make any differnce.
It has to be at least 1-2 feet away to make any difference.

noise is now taken care of but there now seem to be another gnd issue.

when i plug a bass into a DI and then preamp it, ive checked without the 2254 first and signal and sound has no issues.
but when put through the 2254 if i dont touch the strings there is hum!!
so this seems to be a gnd issue?

this is with the volume down on the bass btw

Still sounds like you have a grounding issue with the 2254.    Pulling the power supply out of the box may just be a red herring for a grounding issue.
regards Rob

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #149 on: May 26, 2020, 11:26:41 AM »
A little more success, if you build a case for the toroidal out of mumetal and put it to chassis GND it gets rid of the hum completely and I can have the toroidal very close now with no hum. (its actually ontop of the enclosure now)
I still have this stray GND thing when I don’t touch the guitar? Also when recording through the computer I can now hear some computer noise?

Will investigate further!!

Yes Rob your right, the GND still isnt right, but im the closest ive ever been to getting this working right!!!
« Last Edit: May 26, 2020, 11:40:46 AM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

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


Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #150 on: May 26, 2020, 02:23:49 PM »
Well I'm going to detail how I've done the gnd.
Chassis gnd is too IEC.
The only connection from chassis star gnd to 0v (AUDIO GND) is through 10R 1watt resistor which has cap in parallel with it.
Xlr input socket pin 1 is shield of cable which goes to 4pdt switch and connects to other screen on the switch which goes to pin 1 of output xlr socket.
Input txf cores are down to audio gnd.
There are no other connections to chassis gnd, all other gnd are to 0v.
I've used screened leads from the 4pdt to the input txf and the same for the output txf the screens are not connected at the 4pdt side.

Hope this is ok to follow?

Is my gnd scheme correct?
« Last Edit: May 26, 2020, 03:28:10 PM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

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

djn111

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #151 on: May 26, 2020, 04:16:10 PM »
Hi,

You are a bit on you own, but I like it !! :-) keep it up , you might get me in to building a pair.


Rob Flinn

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #152 on: May 26, 2020, 04:35:25 PM »
Question.

When you plug into DI are you just connecting the input jack straight into the transformer & nothing else i.e the input is completely floating ?   If you are plugging an electric guitar in, you may need to connect the screen of the incoming cable to ground.  In other words for DI input one side of the input transformer would be grounded.  Otherwise you will have no screen on the guitar and you would expect it to buzz when you are not touching the strings.
regards Rob

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #153 on: May 27, 2020, 03:34:53 AM »
Well I've connected pin 1 on input socket to 0v and no change, still getting hum when not touching strings?

I've continuity tested from iec gnd to pin 1 input and it is connected?
website: www.mohawkstudios.co.uk
email: [email protected]

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

Rob Flinn

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #154 on: May 27, 2020, 06:18:48 AM »
Well I've connected pin 1 on input socket to 0v and no change, still getting hum when not touching strings?

I've continuity tested from iec gnd to pin 1 input and it is connected?

Have you continuity tested from iec ground to the sleeve of you mono jack plug that you are plugging into your instrument ?
regards Rob

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #155 on: May 27, 2020, 06:33:30 AM »
I'll do that when I get in tonight!!

Thanks dude
website: www.mohawkstudios.co.uk
email: [email protected]

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

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #156 on: May 27, 2020, 03:12:02 PM »
ok, well im very nearly in business!!

The hum when i dont touch the guitar is only on my cheap squire bass, doesnt happen when i plug in my musicman, so its the bass which has a problem!!
The hF which i can hear computer noise coming must be HF interference, need to get rid of this as the only sound which doesnt sound quite right now is the 2254 is quite hissy, i can deal with a bit of hiss just not computer beeps and stuff as well!!

Anyone got any bright ideas on how to tackle get rid of the computer HF noise?
website: www.mohawkstudios.co.uk
email: [email protected]

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

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #157 on: May 28, 2020, 12:53:50 AM »
Also I've spotted a few caps I could change to polystyrene ones, as these are better for noise, also I haven't put on the 1.5k and the 0.01uf cap on output txf.
Also the centre tap of the output txf is put to the output socket pin 1.
Will do this then see what its like.
website: www.mohawkstudios.co.uk
email: [email protected]

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

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #158 on: May 28, 2020, 03:16:31 PM »
I hate to say it as well, but the ba185 schematic in the tech docs section is wrong, its left out a polystyrene cap!!?
I'm gonna find the original schematic and find out what one it is.
I have a original picture of a ba185 pcb and it's on there

I checked the schematics and it's very different, I've just binned that copy and sticking with the original neve version!!
« Last Edit: May 29, 2020, 10:15:37 AM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

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

Spencerleehorton

Re: Neve 2254 build with ba185, ba191, ba192, ba283
« Reply #159 on: May 29, 2020, 10:21:55 AM »
Ive changed  the 330pf caps on the 185 and slightly less his now!!
There are still a few ceramic caps which I need to replace then I'm going to test again for noise.
Also put in the 1.5k and 0.01uf on the output txf, no really noticable change with this.
Both channels are powered up and sounding and responding well.
I think the hiss maybe to do with the 283 pcb as I have at least 4 caps that need to be changed for polystyrene caps here!!

Still no clue to this HF issue, it may even be my mixer which is playing up?
website: www.mohawkstudios.co.uk
email: [email protected]

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


 

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