My two Drip V2 LA2A's are working fine now. Solved.

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wmb

Well-known member
Joined
Feb 15, 2007
Messages
62
Location
Pasadena, Ca. USA
THis was a cabling issue that is outlined by me in the second post on page two.

Tonight I crossed the finish line on my 2nd of 2 dripelectronics v2 LA2A's. I finished the first one over the weekend. It seems like there is some kind of roll off on the low end. It's kind of like an impedance mismatch or something.

Both units exhibit the same behavior. I ran some prerecorded material through one of the units and it seemed to reduced the bass greatly. While the prerecorded material was playing though one of the units I adjusted the limiter response and stereo adjust controls and the change in sound did not effect the bass response in a meaningful way.

I have the pcb mount sowters and I'm sure that the units have the input transformer installed with the index marker aligned with the mark on the pcb. I'm wondering if it's possible that both transformers could be mismarked.

Other than the bass issue the units seem to operate correctly (and in some ways they sound very good). Maybe a lack of bass is a part of the LA2A sound that I've never noticed. The record I'm working on has scratch vocals recorded though a reissue model and it sounds like it has an even response.

Maybe someone who has some experience with this circuit could offer some insight.

Thanks, William
 
Hi William,

I'm no expert but my first question would be to ask what were you feeding the LA-2A with? It may not have the output drive capability to drive the LA-2A correctly, for example a consumer cd player or even the insert point on some consoles would struggle.

Another possible thing is the termination of the input transformer, the schemo I have in front of me has a 68K resistor to ground from the secondary of the input tranny though it may differ on the Drip layout.

As I say just some ideas, others will be along soon to help I'm sure. Congrats on the new Drips, I hope to build one some day,

cheers,
Ruairi
 
If your feeding an unbalanced source into the unit, you'll need to run the cold signal to ground in the XLR, at the moment it sounds like the La2a is not debalancing correctly at the input trafo, hence lack of bass.
 
I really noticed the lack of bass when I tried to record an acoustic gtr. The preamp driving the la2a was a portico. When I just played some music though it I sent the signal from an aux-> Brent Averill 1272 DI#1 -> la2a -> BA 1272 DI#2. Removing the la2 from the loop brought back the full range sound.

It's like everything is rolling off at about .5 db per octave across the spectrum. I don't think this is the sound that was intended from the unit.

When I get to the studio a little later I will take a look at the pcb and check some values with my meter.
 
My Bloo La2a, with Sowter's is very heavy in terms of Bass, instant dubby tones from a clean DI bass source.
 
im pretty sure this has to do with the limiter response or stereo adjust
pots.

try counter rotating these ,

one left / one right , etc.

depending on how you wired them (the pots that is)

the frequency response (c4) seems to only effect the
hi end cut off.
so it wouldent do this .

this problem points to either the stereo adjust or the limiter response

pot.

g.
 
I think something is not right. I ran pink noise through one of the units and adjusted the two pots Greg mentioned. I could hear a slight change but nothing restored the frequency range. I recorded the output and then used the spectrum meter in wavelab to capture some images.

Good ol' pink noise...
pink_noise.JPG


Good ol' pink noise after my la2a
pink_la2a.JPG


I normalized the post la2a signal just to get a better image. The peaks you see in the second image are from the pure pink noise.

This seems like more then just a potentiomer adjustment. I think I need to start checking values. I though I was pretty careful but I guess I did something wrong... twice.

Just to be certain it's not an external problem I connected the units with the same cabling that I use to patch my UA La3a. It sounds fine.

Cheers, William
 
Yeah something is wrong for sure. It should be pretty flat. I have a nice smooth downward slope with pink noise. And I have my adjustments set as I stated earlier for the trims. I used the exact BOM and wiring diagram from the Drip document. Not sure what it could be but I hope ya get them going soon!
Looks like ya got a highpass filter on...
I'll pipe something thru it right now with alot of lows and a control channel to double check my measurements. I've only recorded vocals so far...
John
 
[quote author="Stagefright13"]I used the exact BOM and wiring diagram from the Drip document. [/quote]

Same here. The only things I changed were the xlr and power connector.

Does your meter switch work the right way? I swear I have looked at that thing a million times and that I wired it according to the diagram but it works backwards (the switch positions). This is not really a big deal. I can just turn the switch over. If everything seemed okay I would do that but for now I am feeling very suspicious about my work. I'm wishing I had a photo of the bottom so I could see the traces.

[quote author="Stagefright13"] Looks like ya got a highpass filter on...
I'll pipe something thru it right now with alot of lows and a control channel to double check my measurements. I've only recorded vocals so far...

John[/quote]

Yeah, it looks like it goes up to about 5k. I must admit I'm curious how it should sound.

Cheers, William
 
So I figure I'm the guy who's done something wrong and I just can't see it because I'm the one who misunderstood it from the beginning.

Here are some photos of all the components that I had to connect to the PCB and the points where they connect. With your help I might be able to locate the problem.

A couple of things that will need explanation:

In some places where you shoud see a bare shield wire you will see an insulated white wire. This is because I used four conductor cable with a braided shield. At the end of the cable where the shield does not attach to anything I connected the 4th wire to the shield. At the end of the cable where the shield connects to the pcb I used the much easier to work with insulated 4th conductor.

The 4 conductor cable was ironically white, white, blue, blue. In some cases I used yellow or green heat shrink to differentiate when I was using two blues.

I will try to order the photos together as much as I can.

Here is the area beneath the meter where so much happens...
normal_red_gain_sw.jpg


The gain and zero adj pot.
Gain_zero_adj_pot.jpg

THe reduction pot.
normal_Red_pot.jpg


These controls behave okay. I can control the volume and gain reduction. I think they are fine.

Below is the point where the meter switch connects to the pcb. I feel like the source of my problem could be in this area. My meter switch is operating in reverse despite the fact that I believe I followed the diagram in the manual.

For clarification the wire colors and the layout on the switch looking at it from the rear are:
Top L to R: Grey, white black.
Bottom L to R: Grey, white, blue.

sw_pcb.jpg


Here are the pots on the rear followed by their connection point on the pcb. This was a tight job (pcb connection) and not the best. The other unit was exectued a little better.
Stereo Adjust (blue, white, yellow)
st_adj_pot.jpg

limit response
lim_resp_pot.jpg

PCB
st_lim_pcb.jpg


Note the white "shield" wire and the yellow heat shrink.

Both units I constructed have the same issue. I feel it is likely something I hooked up incorrectly rather than a misplaced component but anything is possible. I guess it's possible that a cap is the wrong value but I wasn't short or having any left over.

The fact that my output/gain reduction switch is backwards and no one else has this problem makes me feel like I am missing something very obvious (and not that I just need to flip it over) about the way I understood the directions.

Finally, thanks for taking the time to look at all of this. I hope that as a new guy here I am not crossing any lines of decorum by posting all of these photos and asking for help.

Cheers, William
 
William,

No rules broken on the photos--quite the contrary. They help us to see what's going on in your build. I haven't built one of drip's pcbs, just the Bloo kit which is turret board and p2p (I used Sowter transformers as well).

Here are some basic things to consider. The audio chain in the LA-2a includes V1 and V2 and their associated circuitry. V3 and V4 are part of the sidechain and should not be able to affect your freq response. Carefully recheck C1, C2, C3, and C5. Are you certain you have the correct values here?

When you did your freq response tests did you:

-Switch the meter to GR
-pull the T4b
-Turn "Peak Reduction" all the way down

This should eliminate almost all of the sidechain leaving you with a transformer coupled tube line amp in effect.

As far as your "backwards" switch goes--remember that mechanically a toggle switch is backwards. If you push the toggle up, the poles are connected to the bottom terminals. If you push the toggle down, the poles are connected to the top terminals. Inside the switch is a slide mechanism and the pivot point of the toggle is above the sliding contact "sled" so you should be able to visualize why it is backwards. I'm still drinking my first cup of coffee, so maybe that wasn't the best explanation... :roll:

Good luck,

A P
 
[quote author="AnalogPackrat"]William,

Here are some basic things to consider. The audio chain in the LA-2a includes V1 and V2 and their associated circuitry. V3 and V4 are part of the sidechain and should not be able to affect your freq response. Carefully recheck C1, C2, C3, and C5. Are you certain you have the correct values here?[/quote]

This is something that I really need to look into more thoroughly. My DVM can do caps but I have to bend the leads all around to get them into the test holes. I did rely on the packaging for my values when stuffing the caps into the board. Probably a little lazy on my part.


[quote author="AnalogPackrat"]
When you did your freq response tests did you:

-Switch the meter to GR
-pull the T4b
-Turn "Peak Reduction" all the way down[/quote]

-At the time of the test that the image is demonstrating the meter switch was set to monitor output. During the "listening" phase of the test I was adjusting the controls and flipping switches to hear a difference. In no position did I hear or see the bass restored or meaningfully increased. I have a feeling that when this problem is resolved it will be like having a light restored or obstruction cleared.

-At the time of the test it was installed but once again, during other testing it has been in and out with similar results.

-Peak reduction was all the way down. By increasing the peak reduction I am able to hear a change in the character of the tone by adjusting the stereo adjust and limiter response controls but still no change in the HPF effect.

[quote author="AnalogPackrat"]
As far as your "backwards" switch goes--remember that mechanically a toggle switch is backwards.[/quote]

The switch issue is a combination of a hangup for me and also potentially a sign that I've done something wrong somewhere else. Perhaps a mistake I made someplace else is causing signal to flow in reverse. My concept of "correct" function for the switch is based on three unrelated sets of circumstances.

1. The drip manual extensively details the hookup of the switch.
2. Purusha's front panel screening.
3. Others who have recently completed the same project with the same case not commenting on the switch operating in reverse. Once I resolve the bass problem I will flip the switch or whatever I need to do. I only bring it up in the interest of full disclosure.

When I get to the studio later today I will pull the t4b and check the caps mentioned above. Thanks for the outline of which components to check.

Cheers, Wm.
 
How are you listening?
Headphones?
Monitor speaks?
Mono or Stereo?
Source Material?

Could be your signal is out of phase. You would notice a cancellation during stereo operation.

If this is not it, feed a signal into the input iron.
Put your scope or whatever on the input side and calibrate.
Next, move the scope towards the output trans, one step at a time.
This is called logical troubleshooting.
Learn it, and you can fix anything.

Don't just open up the schematic and start poking around.
You need a plan of attack in order to start reaching
for the cyanide capsule.

Another thing to remember, and schematic, no matter how large,
can be broken down into function blocks.

You see this a lot in TV sets.

Little dotted boxes on the Sams Photofacts that show

Color Killer
IF Amp
Sync Seperator
Horizontal Osc
Vertical Osc
Vert Deflection Amp
Tuner
Hi Voltage Supply
Flyback Transformer
RF Amp
Yoke Coil
CRT
Pwr Supply

So even a huge schematic like a TV, well, if you don't know logical troubleshooting, you will fish all day, and no fish.
But, if you know where to look, you can isolate that section, then break it down into sub sections, and finally components.
Then, you just check the components, see if there connected right, and there you are, sitting on the boat dock, with a dry martini, and the sounds of Duke Ellington (read:Billy Eckstein) thru your new LA2.


:grin:
 
I haven't built one yet, so I don't claim to be an expert, but I have read the Drip manual. Forgive me if I'm asking about something obvious (or something you've already checked), but are you absolutely sure that C3 is .1uF, not .01uF? Greg makes a note about this in the manual (stating that the value on the PCB is wrong).

Good luck!
 
Ugh, They are fine. Always have been except that I need to turn over the GR switch.

It was a cabling/input issue. I haven't yet patched the new comps into the rack and had a temporary setup going. I have been linking them with XLR to TRS cables. For example Bass DI->1272->patchbay->LA2A->312 line input. Thinking about it, I've never brought a balanced cable into the DI's on my Brent Averill pre's.

In an effort to do a more imperical test I decided to connect the LA2A directly to the AD. This would remove as many elements to the circuit as possible. The moment I passed signal though it I knew it was working fine.

I thought at first that I had somehow screwed up the cables. I rigged up a combo of cables to use as a return and went back into the DI's on the BA pre's. Same problem as before; no bass. I started to unplug the cable while the signal was still playing and as I removed the cable it returned to full range for an instant before leaving the connector. Inserting the cable again but only halfway yeilded full range sound.

Well, I learned some stuff. Without actually having these things working right I got some interesting things out of them. Mainly bass gtr actually sounds good with a very gentle HPF going way up to like 2.5k. There's enough fundemental to get the note and plenty of highs for definition. Slap a little RBass on there and get the subs back! Totally working for this project I'm doing scratch bass for... Oh yeah, cabling and impedance are very, very importatnt.

Thanks to everyone who spent so much time offering insights to help solve the problem. I'm looking forward to putting these things through their paces.

Cheers, William
 
That's great to hear! Congrats!

I think I may have had to flip my switch too now that I'm really thinking about it. But not positive. So I wouldn't worry about that. I also had to flip my limit compress after hearing it.

Have fun and happy smooshing!!


John
 

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