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?

Holger

Re: D-LA2A Support Thread
« Reply #1927 on: April 06, 2019, 01:45:06 PM »
Another one: built around an old Weston 862 meter. Currently I'm using Kenetek's here. I/O TX are Carnhill 9k6:600.The meter has a sticker marked 1966 on it. The 5V PSU went crazy when connecting the meter bulbs so I used a little 5V MeanWell SMPS for relays and meter illumination. Knobs are 40mm dia. Fat looking guy...





[silent:arts]

Re: D-LA2A Support Thread
« Reply #1928 on: April 07, 2019, 02:52:36 AM »
Nice as always - only one but big meter as always - a true CLAßEN.

This will be used in the Röhren(Rein)Raum at the Krässemaschinenwerke Hamburg?

Holger

Re: D-LA2A Support Thread
« Reply #1929 on: April 08, 2019, 02:42:53 PM »
Nice as always - only one but big meter as always - a true CLAßEN.

This will be used in the Röhren(Rein)Raum at the Krässemaschinenwerke Hamburg?

;-) yes...


dmp

Re: D-LA2A Support Thread
« Reply #1930 on: April 08, 2019, 02:51:39 PM »
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.

I have to go back and look into it again, but my recollection is that with peak reduction way up and the gain way up, we got this ~18kHz noise. We were running a track into it at the time .
I made mine with Jensen 1:1 line in transformers which works really well (unless you want to run mic signals into it).  The gain is needed in this configuration when compressing heavily.

Eliani

Re: D-LA2A Support Thread
« Reply #1931 on: May 03, 2019, 04:09:32 PM »
I haven't gon through the whole thread yet...  ::)
But the BOM to dropbox link is broken on the first post...
Is anyone willing to share his.. mutch appreciated
"Iron Projects" at Eli-Audio.com

QNote

Re: D-LA2A Support Thread
« Reply #1932 on: May 09, 2019, 07:29:41 PM »
I haven't gon through the whole thread yet...  ::)
But the BOM to dropbox link is broken on the first post...
Is anyone willing to share his.. mutch appreciated

See Page 89 in this thread.  I have an updated link there, along with other resources.  New theory and troubleshooting videos in just a few weeks (I shot one of them yesterday).

BOM Link:  https://www.dropbox.com/s/2xky62b30ccsvfw/D-LA2A_BOM_QNS.xlsx?dl=0
« Last Edit: May 09, 2019, 07:54:40 PM by QNote »

weiss

Re: D-LA2A Support Thread
« Reply #1933 on: May 09, 2019, 09:01:51 PM »
Another one: built around an old Weston 862 meter. Currently I'm using Kenetek's here. I/O TX are Carnhill 9k6:600.The meter has a sticker marked 1966 on it. The 5V PSU went crazy when connecting the meter bulbs so I used a little 5V MeanWell SMPS for relays and meter illumination. Knobs are 40mm dia. Fat looking guy...

where do you always find them?
i only come across these way overpriced meters for several hundred bucks..  :o

https://reverb.com/item/11073137-1950-s-weston-electric-model-862-vu-meters-vintage-bakelite-with-black-panel-free-shipping
« Last Edit: May 09, 2019, 09:04:56 PM by weiss »

Holger



 

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