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Deepdark

Re: LA-2A point to point build Sowter TXF
« Reply #60 on: October 25, 2014, 03:36:01 PM »
Tightly twist the filament and all your ac wire. How is your ground schem?
"I'm givin' you that money so I don't have to kill your ass."


Spencerleehorton

Re: LA-2A point to point build Sowter TXF
« Reply #61 on: October 25, 2014, 03:45:58 PM »
Hi,

AC wires all twisted nice and tight, grounding scheme may need looking at as have tried to copy the original with the the isolated pins to group up all connections close to the tubes.
From the IEC I feed a gnd to the xlr's and another feed to gnd B+ and H+, there is another point on pin6 on 6QA5 where the 510pf goes to a solder tag on the chassis close to the tube.
Is there a specific plan I should implement here, happy to do this as specific as possible.

Regards

Spence.

Spencerleehorton

Re: LA-2A point to point build Sowter TXF
« Reply #62 on: October 25, 2014, 05:03:41 PM »
Hi,

Have had another look at the gnd scheme, it seems the gnd scheme is split into 4 point sections, and I can see from the original that the power TXF are grounded to the IEC gnd along with the 47uf and 33uf, nothing else is grounded at this point.
These next ones need your solder tag idea I think? Rather than the isolated pins which then feed all the way back to the IEC with long wire.
The next is by the T4B which had the input TXF, 1k V2, 1.5k, 2.7k and 470k.
3rd section is gnd of input XLR pin 1, 47k/330pf, 510pf, 100uf/1meg.
4th is output TXF, 470pf/ Zener, 330k.

My gnd scheme is not like this so I'm going to change it and see if it improves.

What do you think?

Regards

Spence.

Spencerleehorton

Re: LA-2A point to point build Sowter TXF
« Reply #63 on: October 26, 2014, 06:23:15 AM »
hi,

have just redone the gnd scheme as ive detailed above and now the unit has no hum on output!! hooray!!
still got the acoustic noise from the case of the txf but this will be sorted once i install the toroidal hopefully.
very clean punchy sound, lacks a bit of bottom end but that is OEP txf, once i get the Sowters in there full bandwidth will commence but i am predominately using this for vocals so a natural roll off on the low end is good.
not a bad unit for £255!!! very happy me!!

regards

Spence.

Spencerleehorton

Re: LA-2A point to point build Sowter TXF
« Reply #64 on: October 31, 2014, 12:38:49 PM »
Hi,

Starting on 2nd unit now, have all bits together, will add in jack socket for stereo connection on both units.
Will put up pictures, hopefully this build will go better than how the first went!

Regards

Spence.

Spencerleehorton

Re: LA-2A point to point build Sowter TXF
« Reply #65 on: November 02, 2014, 02:41:39 PM »
Hi,

Here's how it's starting out.

Regards

Spence.

Spencerleehorton

Re: LA-2A point to point build Sowter TXF
« Reply #66 on: November 02, 2014, 02:43:11 PM »
Front panels a little different as I have a smaller case this time.
Just moved the in/GR/out  switch to the left of the gain control.

Regards

Spence.

Spencerleehorton

Re: LA-2A point to point build Sowter TXF
« Reply #67 on: November 04, 2014, 07:35:24 PM »
Hi,

Have just wired up the power toroidals and checked voltages, getting 250v and 2 x 10v AC.
Have then put the 250v to the bridge rectifier and when unit is not turned on at power switch on unit but IEC has power I get 5v at the bridge rectifier? Voltage is not 350v as it should be at bridge as well?
Only 275v at + at bridge?
Something is a miss, need to sort this.

Regards

Spence.

Spencerleehorton

Re: LA-2A point to point build Sowter TXF
« Reply #68 on: November 17, 2014, 05:39:11 PM »
Hi,

my second version is now sort of working, getting good voltages throughout and have signal to output, just dont have compression yet? i know the T4B works as i have tried the other one from my working unit. must be something simple hopefully.
Also the gain is very hot, with the gain hardly turned up there is loads of signal, goes into distortion very quickly?


regards

Spence.
« Last Edit: November 17, 2014, 05:59:27 PM by Spencerleehorton »

Spencerleehorton

Re: LA-2A point to point build Sowter TXF
« Reply #69 on: November 17, 2014, 06:17:20 PM »
hi,

gonna get all my valves tested and put in the best pair as the ones i got in there are defo shot to pieces! a/b with a stereo output from a dat machine going into the unit for the left and right hand channel into desk, setting levels and then switching between them reveals a top end loss.
also going to think about replacing the plate resistor of the first 12ax7 from 220k to 100k and replacing the valve for a 12at or 12au7.

regards

Spence.


Spencerleehorton

Re: LA-2A point to point build Sowter TXF
« Reply #70 on: November 19, 2014, 02:35:00 AM »
Hi,

Have  second unit all working now, although a cold solder joint was playing up.
Good compression and output just need to fine tune both units.
I have put in 12AT7 and they sound good, Going to test with 12AU7 as well and check biasing.

Regards

Spence.

Spencerleehorton

Re: LA-2A point to point build Sowter TXF
« Reply #71 on: November 20, 2014, 10:18:53 AM »
Hi,

Have put in 12AU7 into first unit and compared with second unit having 12AT7 both are mullards.
First unit to my ears sounds slightly better.
I have not changed the anode resistor yet as I want to have a bit more technical data for changing the 220k for 100k.
Could anyone explain what is happening with the change please.
Also do I change both 12AX7's or just V1
And do I change all anode 220k as there are 3 of them R9, R33 and R13.

Clarity on this would be excellent please, but laymens terms preferred.

Regards

Spence.

Spencerleehorton

Re: LA-2A point to point build Sowter TXF
« Reply #72 on: December 11, 2014, 01:14:26 PM »
Hi all,

Just thought I'd report on my findings now I've had a chance to put both units through their paces now.
Both units compress a lot and I can get a very high level of audio down when using them with Neve and SSL9k pre amps.
If anything I will investigate being able to bring the amount of compression down a little.
Also the amount of distortion is in question and would like to get both units a bit better in this department.
One it is actually a little better, so with some testing now I will find out why.
I'm sure the distortion will be reduced once I use the sowter TXF.
If anyone has any ideas on either of these fronts please chirp in.
Other than these points which to be honest with setting the gain and peak reduction very low I can get a very good sound out of these units.

Regards

Spence.


 

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