AML 52F50

Help Support GroupDIY:

Bonsaimaster

Well-known member
Joined
Apr 17, 2013
Messages
189
I got the compressor from AML and it built up nicely. Anyone doe the calibration on this unit. It has two cards and although I got the calibration process Collin did not include schematic or pinout of the cards.

Thanks in advance
Bonsaimaster
 

CalGTR

Member
Joined
Mar 22, 2013
Messages
9
OK, hoping someone can point me in a helpful direction. I've put together two of these kits. First one calibrated perfectly and appears to be in great working order. However, for the second unit, it calibrates just fine all the way up until the meter switch is placed in gain reduction mode and the compressor engaged. The meter falls to the bottom, as expected, but then never moves from that spot. Adjustments to the threshold trimmer do not appear to move the meter. When applying the +12dBu signal, the meter stays at the bottom. The output changes with a change in compression ratio, so it appears that the unit is working fine with the lone exception of the meter not working in gain reduction mode. Meter works fine in input and output modes.

A visual inspection has not turned up any errors in the build yet, but obviously something's not right. I've checked a few components that touch the gain reduction metering line, but the few things I looked at appear to be fine.

Anybody have any likely areas to look at? 
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,886
Location
Nashville, TN
OK, hoping someone can point me in a helpful direction. I've put together two of these kits. First one calibrated perfectly and appears to be in great working order. However, for the second unit, it calibrates just fine all the way up until the meter switch is placed in gain reduction mode and the compressor engaged. The meter falls to the bottom, as expected, but then never moves from that spot. Adjustments to the threshold trimmer do not appear to move the meter. When applying the +12dBu signal, the meter stays at the bottom. The output changes with a change in compression ratio, so it appears that the unit is working fine with the lone exception of the meter not working in gain reduction mode. Meter works fine in input and output modes.

A visual inspection has not turned up any errors in the build yet, but obviously something's not right. I've checked a few components that touch the gain reduction metering line, but the few things I looked at appear to be fine.

Anybody have any likely areas to look at?
Is it powering up correctly? Does it have the correct voltages on each one of gold fingers of the edge card connector? The reason I'm asking is that I had vaguely a similar issue with one of mine. It turned out that the input transformer was bad. Pin 9 and Pin 11 (earth) were shorted together, which was shorting V- and the chassis ground. Also, I would double check the clearances around the skinny PCB that has the subminiature switches. I had to reverse the orientation of the screws and nuts that held it to the bottom PCB to get it fit better when mounting the boards to the front panel.

Thanks!

Paul
 

CalGTR

Member
Joined
Mar 22, 2013
Messages
9
Is it powering up correctly? Does it have the correct voltages on each one of gold fingers of the edge card connector? The reason I'm asking is that I had vaguely a similar issue with one of mine. It turned out that the input transformer was bad. Pin 9 and Pin 11 (earth) were shorted together, which was shorting V- and the chassis ground. Also, I would double check the clearances around the skinny PCB that has the subminiature switches. I had to reverse the orientation of the screws and nuts that held it to the bottom PCB to get it fit better when mounting the boards to the front panel.

Thanks!

Paul
Thanks for your reply. Sorry I didn't see it until today.

The unit does power up just fine. In fact, the unit appears to be working just fine with the sole exception of the metering in gain reduction mode. The meter works just fine in input and output modes, but never moves off of the bottom in gain reduction mode (even though there is gain reduction happening). Seems like it should be a fairly easy thing to track down, but I haven't managed to figure it out yet. I'll check the clearances again more carefully, but I didn't see anything amiss in that area upon first inspection.
 

tyskstil

Member
Joined
Sep 9, 2020
Messages
9
I have built and calibrated a 52f50 and it functions overall, but it seems that I have a pretty loud noise floor, louder than I would expect, which is audible when I engage the unit via the switch. Would anyone have any obvious troubleshooting tips for what could case a louder-than-usual noise floor? Its running off a 51X 11-space rack with the external PSU, so I don't suspect the issue is from the PSU.
 

beatnik

Well-known member
Joined
Oct 18, 2009
Messages
907
Location
Dorset, UK
Have you tried the PSU and rack system with other modules ?

What kind of noise ? hum , hiss , etc.

To troubleshoot the module you will need either an extender card or a test jig so that you can power it up outside the rack system.

If you have an oscilloscope you can follow the schematic and find if the noise is generated in a specific section of the circuit.
 

tyskstil

Member
Joined
Sep 9, 2020
Messages
9
Hiss, lake tape hiss, classical noise floor type hiss. I don't have this problem with other modules, but the comp shows the same issue in my Midas L6 PSU. I just talked to AML who said the noise spec of the Neve comp is -60dB, and the 52F50 should be similar +/- a dB or two.

So Ill try to measure mine but I expect its much higher. And then, signal tracing is probably whats next.
 

JMan

Well-known member
Joined
Oct 26, 2019
Messages
328
Location
Chicago
Question for those of you who have built this:

I finished my build, went through all of the calibration steps without issue, and now have a great sounding compressor that works as it should. HOWEVER, I was not able to adjust the meter in the first step, and the reason is confusing me a little. I don't think my meter has the screw that is supposed to be used to make this adjustment. I have looked and looked and for the life of me I can't figure out what I'm missing! The meter sits close enough to the -20 mark (left/white side) that it is perfectly usable as is, but it's blowing my mind that I can't find the screw to make this adjustment. Am I just reading the guide wrong??? Attaching a picture of the access port where the screw should be for reference...anyone want to tell me what super obvious thing I'm overlooking? I feel like an idiot.

IMG_2135.JPG
 

Rob Flinn

Well-known member
Joined
Jun 3, 2004
Messages
4,557
Location
Sussex, UK
Question for those of you who have built this:

I finished my build, went through all of the calibration steps without issue, and now have a great sounding compressor that works as it should. HOWEVER, I was not able to adjust the meter in the first step, and the reason is confusing me a little. I don't think my meter has the screw that is supposed to be used to make this adjustment. I have looked and looked and for the life of me I can't figure out what I'm missing! The meter sits close enough to the -20 mark (left/white side) that it is perfectly usable as is, but it's blowing my mind that I can't find the screw to make this adjustment. Am I just reading the guide wrong??? Attaching a picture of the access port where the screw should be for reference...anyone want to tell me what super obvious thing I'm overlooking? I feel like an idiot.

View attachment 84730
I could be worng but that looks like the screw hole to mechanically zero the meter. You use this so the meter sits at zero on it's scale when the box is turned off & it really has not a lot to do with calibrating the meter. From experience repairing real 2254's, I think what you need is to look for trim pots on the pcb's.
 

JMan

Well-known member
Joined
Oct 26, 2019
Messages
328
Location
Chicago
I could be worng but that looks like the screw hole to mechanically zero the meter. You use this so the meter sits at zero on it's scale when the box is turned off & it really has not a lot to do with calibrating the meter. From experience repairing real 2254's, I think what you need is to look for trim pots on the pcb's.
Hey Rob! Sorry, I don’t think I was clear with my wording in my previous post. I am in fact trying to mechanically zero the meter. The rest of the calibration procedure went great (trim pots and all that), but I couldn’t seem to figure out the mechanical zeroing.

Both Colin’s build guide and you have said that this is a screw hole (and I agree) — is there a screw there, though? I know my picture might not make it easy to see, but I can’t find one in there at all…
 

Rob Flinn

Well-known member
Joined
Jun 3, 2004
Messages
4,557
Location
Sussex, UK
Hey Rob! Sorry, I don’t think I was clear with my wording in my previous post. I am in fact trying to mechanically zero the meter. The rest of the calibration procedure went great (trim pots and all that), but I couldn’t seem to figure out the mechanical zeroing.

Both Colin’s build guide and you have said that this is a screw hole (and I agree) — is there a screw there, though? I know my picture might not make it easy to see, but I can’t find one in there at all…
Right. The hole looks like the right one. The brass (?) oval loop is the bit that adjusts the meter but normally there is a plastic bit in front with a screwdriver slot on the front & a spigot on the back that sits inside the brass loop. When you turn the plastic bit the brass loop moves which gives you a little bit of adjustment for the mechanical meter zero. you might be able to see what I am talkinv about in the attached pic..... but maybe not
 

Attachments

  • 20210918_212720.jpg
    20210918_212720.jpg
    52.3 KB · Views: 10
Last edited:

Matt Syson

Well-known member
Joined
Dec 17, 2005
Messages
156
Location
France
As an observation, the noise floor (for 'white noise hiss) is likely worse than is expected nowadays because the diode bridge used for the gain control has to work at a low audio level for distortion to be vaguely acceptable, thus more gain is needed after that stage, thus giving more hiss.
Similar arguments apply to FET compressors for the same reason although some distortion cancellation allows slightly 'hotter' levels for the FET attenuator part. There should be no excuse for hums, buzzes or squeaks these days however as it is pretty simple to make a low noise power supply.
Matt S
 

JMan

Well-known member
Joined
Oct 26, 2019
Messages
328
Location
Chicago
@Rob Flinn Thanks for lending your expertise! My meter is definitely missing this screw. Oh well, I'm not going to harass Colin for this -- the compressor (and meter) work great, and as long as it is sitting below eye level in the rack, it looks close enough to zero.
 

axcell

New member
Joined
Jul 23, 2020
Messages
1
Hi everyone!
I built a pair of 52F50 around March/April this year, tried to calibrate them, ended up with shorts due to really tight design (the whole "measuring current with the 1 ohm resistor thing), replace the non-working resistors but I'm stuck with a specific issue.
One of my units is now shorting my entire case when plugged. I can't seem to be able to trace back the issue to a specific component, but somebody that usually make repairs on various electronic gear mentioned I should look into the TIP3055 being defective/fried. Although, except for the fact that it's hooked on a big heat sink, I'm not sure why this specific part would be the cause for the entire unit.

I was wondering if anybody else had this issue, if the 3055 was the answer to fixing it, or if anybody had an idea of what to check for this specific issue?
Thanks!
 

Rob Flinn

Well-known member
Joined
Jun 3, 2004
Messages
4,557
Location
Sussex, UK
Hi everyone!
I built a pair of 52F50 around March/April this year, tried to calibrate them, ended up with shorts due to really tight design (the whole "measuring current with the 1 ohm resistor thing), replace the non-working resistors but I'm stuck with a specific issue.
One of my units is now shorting my entire case when plugged. I can't seem to be able to trace back the issue to a specific component, but somebody that usually make repairs on various electronic gear mentioned I should look into the TIP3055 being defective/fried. Although, except for the fact that it's hooked on a big heat sink, I'm not sure why this specific part would be the cause for the entire unit.

I was wondering if anybody else had this issue, if the 3055 was the answer to fixing it, or if anybody had an idea of what to check for this specific issue?
Thanks!
You probably have a short on one of the boards
 

Latest posts

Top