ron_swanson

Re: D-LA2A Support Thread
« Reply #1920 on: March 11, 2019, 11:36:29 AM »
My build gets a high frequency oscillation at max gain (~18kHz)  -  I've been wanting to sort it out.  I'll look at your build pics and try to find how mine is different.  Yours is dead quiet even at high gain?

It's my understanding that LA2A's run very hot gain-wise by nature and running them with the gain above 7-ish or so can / will result in artifacts.  Mind you, I don't have past hands-on experience here as this is my first hardware LA2A.  I have read within this forum and on the Interwebs suggesting that this is 'normal' behaviour, so at this point I haven't worried about any of that.    If I remember correctly, some of the 'fix' included swapping the 12AX7 out for lower gain tubes.  Honestly, at a gain setting of 7 the signal is WAY too hot for anything I'd ever use or want.  The signal is very distorted at those levels and not in a pleasant way IMHO.

If others here have contrary information to add here, a little help / input would be appreciated.

Be that as it may be, I'm interested in actually testing here.  So I undertand.... when you turn the gain up above 7 or so, you get an oscillation at 18KHz with no audio signal being input?   If so, I'll give this a test when I get a few minutes and report back. 


Rlucas41

Re: D-LA2A Support Thread
« Reply #1921 on: March 11, 2019, 01:21:40 PM »
I don't think I understand this correctly. We start with the audio part and let compression circuits be compression circuits.
Put the T4Bs out.

Both channels pass unity gain signal without power?
Now power with power on, left channel only on, does it pass signal (dependent on your gain potentiometer?)
Next, right channel only, does it pass signal (dependent on your gain potentiometer?)
Cool.
Now both channels together. Do they pass signal dependent on the gain potentiometers?

Volker thanks for the quick reply! I have definitely missed or messed up somewhere... so powered off,  passes signal in both channels. Powered on, passes signal in both channels but the gain potentiometer has no affect/not working.

[silent:arts]

Re: D-LA2A Support Thread
« Reply #1922 on: March 11, 2019, 01:28:45 PM »
Sounds like it is still in bypass.
The relays must be "on" (5V) to pass signal thru the circuit.

Rlucas41

Re: D-LA2A Support Thread
« Reply #1923 on: March 11, 2019, 01:40:30 PM »
Sounds like it is still in bypass.
The relays must be "on" (5V) to pass signal thru the circuit.

LOL
I have the relays on or at least I can hear them switch audibly... the gain still has no affect... this is with the T4B's out or in. How do I bypass the relays?
Thanks for your help and patience... I've built several projects but this one has stumped me  :o

Hopefully its something simple I have missed.
« Last Edit: March 11, 2019, 01:50:36 PM by Rlucas41 »

Rlucas41

Re: D-LA2A Support Thread
« Reply #1924 on: March 13, 2019, 09:45:46 AM »
Making progress, ordered new voltage regulator for 5v, installed and now unit it switching the circuit in... ;D

excited!!!

Rlucas41

Re: D-LA2A Support Thread
« Reply #1925 on: March 13, 2019, 03:47:19 PM »
Progress...
getting signal through one circuit now, but one is not passing signal ...in the channel passing signal both the Gain control and Peak reduction increase gain in the channel with no compression taking place. I will keep muddling through but obviously need some help :)
« Last Edit: March 13, 2019, 04:08:12 PM by Rlucas41 »

[silent:arts]

Re: D-LA2A Support Thread
« Reply #1926 on: March 13, 2019, 04:30:33 PM »
You are puzzling me. How do you recognise increased gain in a channel not passing signal?


 

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