Finished BA6A Limiter

[Bryson]

... the absolute best AGtr / Bass Gtr compressor ever!

Jimmy Page would agree with you (AGtr).

 

[penquista]

a pic of the messy wiring of my ba6a

 

[schlamn]

Hi Christian,
I really like the case you got there. Wish I could catch bargains like that on evilbay ! I was worried about heat build up with all inside my box, but it hasnt been a problem yet. If I remember correct I left a thermometer inside for an hour and the temp got to ~40C - not too bad I think ?
I have just completed the second, so now there are 2 ! They seem to get along in stereo happily with no dramatic stereo shifting (I was expecting some !)
I used the diode and 1Meg (fairchild) to connect CVs together rather than change cap/resistor values (as per manual)and that worked. 
Now I just need to find some time to get some use with them ! Things are busy at the mo. I will post a clip soon or maybe you have summit ?
That output transformer is huge in your pic ! If bigger is better thats got to sound good as it looks twice the size of the Sowter output.?
The Sowter sounds pretty good to me. Big bottom and pleasing overall to the ears.. However I am likely a poor judge as this is the first (stereo) limiter I have owned.
Good thing I like about turret boards is you can hide all the wires underneath ! Its like putting everything under the bed as a kid !

 

[penquista]

yeah i was so lucky to find that case
what pot did you use for the attack?

for the threshhold pot, are you sure that it should be 250k? in my schematic the place you put that pot is a 33k resistor.
also in your drawings i couldn't find the side chain hipass you mentioned.

 

[schlamn]

For the threshold 50K pot  gets you 17V -> 85V (Threshold sits at 66V with the 33K) A 250K pot gets you a range of 8V -> 118V... Cant argue with that ! Of course the elevated filament ac is now at only 8V but it remains completely quiet, so no worries.
I left the SC out because I thought my way maybe a poor way to do it, but it works (as High pass )and I cant hear anything else changing for the worse..
I serialled the 2 x .2uF coupling caps to 6H6 with 2 x .01uF and controlled them with a dual 1M pot. I used the pot as a tryout instead of using a switch, but it seemed to work fine so I kept it. If there is something obviously wrong with the method I would like to be told tho!
Sorry for poor drawing - I have only drawn 1 side..

For Attk I stuck in a 1M and release 500K. This is probably overkill and I will probably take them out for a smaller values in time.

 

[gary o]

Hi ....nice build  what are the Sowter audio transformer model numbers ? I recognise the output tran.


Thanx

 

[lassoharp]

Super Fine build there!  Congrats on your . . . twins.  Only bad thing about building a BA-6A is after you build one - you just gotta build another.  True labor of love.

I agree, the Sowter iron I've used does have good bottom end.

Cheers

 

[schlamn]

Hi ....nice build   what are the Sowter audio transformer model numbers ? I recognise the output tran.
Thanx

Hi Gary,
Cheers...Transformers are -
Sowter 9835 : Input
          9830 : Interstage

Congrats on your . . . twins.  

Thanks ... Yes Im lovin this pair very much  ;D

 

[EvLoutonian]

Hi guys,
I know this is an old thread, but it seems like the most appropriate bunch of chaps to ask, so here goes:

Do you reckon this old (out-of-action) RCA 69-C (Noise and Distortion Meter) would be an appropriate basis for building a BA6A?
It has a bit of corrosion on the left hand side of the front panel, but I should be able to clean that up somehow..

If anyone has schematics or knowledge of the 69-C's (and its transformers), can you tell me, are any of them appropriate to use somewhere in the BA6A circuit?

Thanks in advance!
Evan.

 

[EvLoutonian]

The 69-C transformers are marked as:

(signal)
900781-501
900782-501
900783-501

and

(power)
900784-501 (mains power)
XT-2016 chokes (x2)


* DC multimeter measurements on the signal transformers suggest that these must be something like:
900781-501    20k : 20k ohms              (1.5k ohms DC each side)
900782-501    ??                                  (~60k ohms DC per side)
900783-501    150 ohms : 10k ohms    (13 ohms & 850 ohms DC)


--
Here's a bigger pic of the front panel:

 

[emrr]

The catalog says 20k input Z and 50-15k response, also mentions using it as an amplifier. 

 

[EvLoutonian]

The catalog says 20k input Z and 50-15k response, also mentions using it as an amplifier.

Thanks Doug, that certainly sounds promising (transformer-wise).  Decent frequency response for regular audio use, and I imagine 20k could be used (perhaps with some tweaks) where a 10k transformer is normally used?

 

[emrr]

20K is the input transformer, likely SE rather than PP.  10K isn't the original Z, more like 50K.  I don't find it promising without further testing.  The Sowter Z's and windings and structures and materials are completely wrong, apples to apples.  They may work, but that's a different question, and a different end result.  No one winds an equivalent modern transformer, to that end it may be 'promising'.