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High Voltage ADL 600 Mic Pre. Too sensitive to Touch?
Old 26th July 2013
  #1
High Voltage ADL 600 Mic Pre. Too sensitive to Touch?

I recently bought a used ADL600 high voltage mic pre. Tubes have been replaced twice with known good tubes during my initial run-through. I am experiencing severe 'sympathetic' output from the pre if it is 'tapped' with my fingers for instance. This is tube noise. Not microphonics, but 'thump'.

In other words, with the gain up 25% or more, and no mics or instruments connected, I can tap on the top or front of the ADL 600 and it is 'alive' with sensitive output.

Is this normal for high voltage tube gear? The only other tube gear I own is LA610 and several tube amps. I cannot duplicate this with those. It is so sensitive that if the desk is bumped when recording, it would potentially pick it up.

Any insight would be really appreciated. Thank you!
Old 26th July 2013
  #2
When building my first LA-2A, I had this issue. Tapping it would make an audible noise. I realized I had wired the whole thing with 300v wire and should have used 600v. I rewired the whole thing with 1000v wire and the thing is perfect.

Maybe a similar issue?
Old 26th July 2013
  #3
Quote:
Originally Posted by analogexplosions View Post
When building my first LA-2A, I had this issue. Tapping it would make an audible noise. I realized I had wired the whole thing with 300v wire and should have used 600v. I rewired the whole thing with 1000v wire and the thing is perfect.

Maybe a similar issue?
Thank you. I don't expect Anthony DeMaria would have made this error with the ADL 600 design. It is a very well designed and well built tube pre. Clocks in at nearly 30 lbs. I wonder do any other ADL owners experience this?

ADL 600 Stereo High Voltage Tube Microphone Preamp Specifications:
Input impedence:
Microphone: Selectable, 150/300/900/1500 ohm
Balanced line: 2k ohm
Instrument: 100k ohm
Maximum input level:
Microphone (1500 ohm, +20dB pad out): +5dBu
Microphone (1500 ohm, +20dB pad in): +25dBu
Balanced line: +30dBu
Instrument: +30dBu
Gain range:
Microphone (1500 ohm, +20dB pad out): +5dBu
Balanced line: -12dB to 40dB
Instrument: -5dB to 42dB
Noise floor (all inputs, minimum gain): -95dBu (A-weighted)
Microphone equivalent input noise (EIN): -125dBu (A-weighted)
Frequency response: 10Hz to 45kHz Β±1dB
Maximum output level: +23dBu @ 0.5% THD+N
Output impedance: 600 ohm
Tube complement (per channel): 1 - 12AT7A, 2 - 6922
General:
Power (factory-configured): 115 or 230V AC/100 watts
Dimensions: 19"W x 3-1/2"H x 17"D
Weight: 28 lbs.
Old 26th July 2013
  #4
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shatz's Avatar
I haven't had this particular issue. Mine would get "jumpy" like that when using the gain pot on one channel, but replacing it fixed it. But haven't had any problems when tapping at it. FWIW mine is one of the very 1st production runs and later revisions had fixed the problem I was experiencing.
Old 26th July 2013
  #5
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jmp72's Avatar
Not this problems but a lot of other problems, stucked vu and meter... Good design but poor construction, but it sound really good!
Old 26th July 2013
  #6
Quote:
Originally Posted by shatz View Post
I haven't had this particular issue. Mine would get "jumpy" like that when using the gain pot on one channel, but replacing it fixed it. But haven't had any problems when tapping at it. FWIW mine is one of the very 1st production runs and later revisions had fixed the problem I was experiencing.
Thank you. I am pretty certain this is a first production run unit as well. Based on photos of the inside of new units. Layout is the same, but new units have tube clip retainers, different I/O transformers, different I/O XLR jacks. I will try to get Presonus or ADL on the phone. Appreciate the reply!

Quote:
Originally Posted by jmp72 View Post
Not this problems but a lot of other problems, stucked vu and meter... Good design but poor construction, but it sound really good!
Right, I understand. Though it seems to be on par with every piece of gear out there in its class. The ADL 600 has never had consistent QC issues, just those things that showed up in the field of use (where testing really happens) for a new piece and they seem to have managed it every step of the way. It really is a robust design and big big smooth sound. Headroom is really deep. Cheers and thanks!
Old 26th July 2013
  #7
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shatz's Avatar
When I talked to presonus about mine (waaaay out of warranty). They were very nice and helpful. They even sent me the parts free of charge to do it myself.
Old 26th July 2013
  #8
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tha]-[acksaw's Avatar
 

I have the exact same problem. I really pissed me off for a unit.of this price. But I have found units that don't so it. My is not only affected by tapping, but if I record percussion or bass guitar in the same room as as the preamp, I can't use my monitors. I have to track on headphones.
Old 26th July 2013
  #9
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by tha]-[acksaw View Post
I have the exact same problem. I really pissed me off for a unit.of this price. But I have found units that don't so it. My is not only affected by tapping, but if I record percussion or bass guitar in the same room as as the preamp, I can't use my monitors. I have to track on headphones.
Wow, something very wrong..Get it checked out..NO Tube pre should do this...
Old 26th July 2013
  #10
Quote:
Originally Posted by nosebleedaudio View Post
Wow, something very wrong..Get it checked out..NO Tube pre should do this...
I don't know enough about tube gain structure. Though, can you tell me how this is avoidable at really high stages of gain? I wonder would something to use as a support for the tubes on the PCB itself would help. Kinda of like the foam used on newer fender amps preamp tubes?

The 6 tubes are sitting in porcelain tube sockets connected to a PCB which is centimeters from the chassis bottom. Even good tubes rattle, tubes are 'lively' or microphonic and to what degree will be seen when they are cranked like that. If the 'box' the tubes are in is receiving sympathetic vibration, why is it wrong that we would hear the microphonics? Or in other words, the box would act as a microphone. Just seems like the tubes in the ADL are very 'alive' with OUTPUT when touched or moved.
Old 26th July 2013
  #11
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tha]-[acksaw's Avatar
 

Quote:
Originally Posted by nosebleedaudio View Post
Wow, something very wrong..Get it checked out..NO Tube pre should do this...
I wrote PreSonus when I first bought it, and they offered to take it back for a replacement, but I was right in the middle of a project and I needed it. As an alternative they sent me a whole set of brand new factory tubes which did not correct the issue. When changing the tubes, I do remember there being a metal cap with a spring, that goes over the tube, holds it down, and locks it in place. I've always thought the issue might go away if I took those off. Although my MPA Gold has them too, and it doesn't make any kind of noise. At the end of the day, I really only use the ADL for tracking ac gtr, and vocals. Even in the control room, it doesn't give me issues.

At the end of the day, I'm not in the slightest bit happy about it. But I'm not sure I wanna spend the time or money getting it fixed based on how much of an issue it is.
Old 27th July 2013
  #12
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Janesaid2me's Avatar
Now i want to go tap mine and see if it has this issue....ive never noticed it with mine but ive only had it a few months...bought used though....
Old 1st April 2014
  #13
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Basslik's Avatar
 

I just got pretty darn lucky yesterday on a mint ADL600, couldn't tell if it's an original?, but from the bumping and tapping I did on the unit I didn't hear any anomalies whatsoever, or micro-phonics. I'm now sketchy (really), seems to good to be true since I paid $600 for it from a local chaplain in a retirement community just down the road, and he said he got from a client who closed down his studio. But it's flawless, and never been racked.

I'll just run it through it's paces for a period of time and see if something rears it's ugly head?, but talking with the chaplain he told me the best he could about the unit, but knows nothing about recording.
Old 1st April 2014
  #14
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Janesaid2me's Avatar
WOW thats a steal!
Old 2nd April 2014
  #15
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Basslik's Avatar
 

Quote:
Originally Posted by Janesaid2me View Post
WOW thats a steal!
I reckon so, I put through it paces and it seems to be rocking big time. although the manual doesn't tell how to push the pre to saturate?

My TL-Audio PA-1 has a output knob i can set after the gain stage to drive the pre, but this one doesn't have one?
Old 2nd April 2014
  #16
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Quote:
Originally Posted by Basslik View Post
....although the manual doesn't tell how to push the pre to saturate?
Engage the 20db pad and then just push the gain hard.
Old 2nd April 2014
  #17
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Basslik's Avatar
 

Quote:
Originally Posted by stevelindsay View Post
Engage the 20db pad and then just push the gain hard.
Thanks SteveLindsay, will give that a whirl after work today, I'll have to check the serial number also to see if mine is one of the units that has the impedance issue.
Old 2nd April 2014
  #18
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Janesaid2me's Avatar
Yep gotta use the pad to push it for the more creamy tube sound - the ADL can be very clean for a tube pre - but can also be pushed
Old 2nd April 2014
  #19
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I used to have one of those and that is not normal behavior for it. If the tubes are known good then it could be a loose tube, tube socket, or connection. Could even be a solder joint cracked from replacing the tubes. Do both channels do it?
Old 3rd April 2014
  #20
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Basslik's Avatar
 

Quote:
Originally Posted by Janesaid2me View Post
Yep gotta use the pad to push it for the more creamy tube sound - the ADL can be very clean for a tube pre - but can also be pushed
janesaid2me thanks for the info. I'm now interested to see if my unit has the impedance issue. Although is sounds great other than trying what you great folks suggested. Will be back
Old 3rd April 2014
  #21
Gear Maniac
I bought mine from Sweetwater when they first came out. It did have the impedence issue that the first run had. Presonus fixed it for free. I have had zero problems with this unit and consider it a truly great piece of gear.
Old 3rd April 2014
  #22
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shatz's Avatar
What is the impedance issue? I've never had a problem with mine.
Old 3rd April 2014
  #23
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Janesaid2me's Avatar
Consider a tube change too - only the one tube (of the 3 on each channel) really needs to be changed - talk to Bowie about it....he hooked me up with a low noise NOS mullard
Old 4th April 2014
  #24
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Basslik's Avatar
 

Quote:
Originally Posted by Janesaid2me View Post
Consider a tube change too - only the one tube (of the 3 on each channel) really needs to be changed - talk to Bowie about it....he hooked me up with a low noise NOS mullard
Will definitely contact bowie, thank you.

OK, I know one thing for sure is that I'm not as experienced as all you cats in the world of mojo / but man I recorded snips on the drums at all the different impedance settings and and I can't hear any differences, -20 pad in?

Room is treated well, (AURALEX) designed the acoustical layout, monitoring through my event 20/20s

Chain is Shure KSM32->ADL600->DIGIMAX FS. (maybe get better convertors?)

Although it sounds fantastic other than that, and I'm blown away how even each piece on the drums sounds through this beast.

Maybe it works through a dynamic mic
Old 4th April 2014
  #25
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shatz's Avatar
I use KSM 32's thru ADL 600 for overheads everyday. It's subtle but noticeable. Listen for the low and low mids to drop off as you turn the impedance down. Sometimes there can be a bit too much 200-400 hz that can be knocked out by using a lower impedance. I think the lows on the higher impedance is what makes this thing sound so huge when you need it to.
Old 4th April 2014
  #26
Gear Maniac
Quote:
Originally Posted by shatz View Post
What is the impedance issue? I've never had a problem with mine.
The first production run had a incorrectly set of jumpers and possibly something else. Basically, the listed impedance settings were incorrect and no one noticed. Craig Anderton did a glowing review of the unit but did note this issue. Truthfully, I used the unit for over three years before I sent it back to have this corrected. It still sounded wonderful.

The folks at Presonus were extremely helpful and responsive. I did not actually "have" to send it back. They were happy to send me schematics and directions on how to do the fix. However, I am visually impaired and working on anything like that is challenging to say the least. I sent the unit to them and had it back in under two weeks.

I am still using the original tubes it shipped with and am quite happy with it. The only thing better I can imagine would be a 8 channel unit built to the same specs.
Old 4th April 2014
  #27
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Yea a truly underrated preamp....because it caries the presonus name.....changing the preamp tube to something low noise really helps it shine even more....
Love it on overheads too!
Old 5th April 2014
  #28
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Basslik's Avatar
 

Quote:
Originally Posted by shatz View Post
I use KSM 32's thru ADL 600 for overheads everyday. It's subtle but noticeable. Listen for the low and low mids to drop off as you turn the impedance down. Sometimes there can be a bit too much 200-400 hz that can be knocked out by using a lower impedance. I think the lows on the higher impedance is what makes this thing sound so huge when you need it to.
Fantastic, thanks shatz, training my ears now (LOL)
Quote:
Originally Posted by SteveE9C6 View Post
The first production run had a incorrectly set of jumpers and possibly something else. Basically, the listed impedance settings were incorrect and no one noticed. Craig Anderton did a glowing review of the unit but did note this issue. Truthfully, I used the unit for over three years before I sent it back to have this corrected. It still sounded wonderful.

The folks at Presonus were extremely helpful and responsive. I did not actually "have" to send it back. They were happy to send me schematics and directions on how to do the fix. However, I am visually impaired and working on anything like that is challenging to say the least. I sent the unit to them and had it back in under two weeks.

I am still using the original tubes it shipped with and am quite happy with it. The only thing better I can imagine would be a 8 channel unit built to the same specs.
SteveE9C6, is there a way to tell if I have the impedance issue by my serial number alone? serial number 900-ADL - AL1005b21

Peeking inside I do see spring clips over the tubes, if that helps, will also try contacting Presonus.

BIG THANKS FOLKS
Old 6th April 2014
  #29
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its called tube microphonics. the gutz of the tube are like a microphone. its pretty normal for tubes that are set up with high gain.

its a design thing. they should have split the gain between two tube stages with lower gain.
Old 6th April 2014
  #30
Gear Maniac
Quote:
Originally Posted by drtechno View Post
its called tube microphonics. the gutz of the tube are like a microphone. its pretty normal for tubes that are set up with high gain.

its a design thing. they should have split the gain between two tube stages with lower gain.
Woo hoo! Finally! My MsEE from MIT is coming in handy ( a joke... my degrees are from Baylor and the US Army Academy of Health Sciences medical school) Hey! I did recently finish some course work at Berklee

The ADL600 is a class A high voltage +/-300Volt power rails using custom wound cinemag transformers. Each channel uses one 12AT7A and two 6922 tubes. Looking at my block diagram, it looks to me like that is exactly what Anthony De Maria did with these.

I'm not a genius.... but Anthony De Maria used a brilliant design on this hand built preamp. Let follow the signal path of a mic input. (Not every tiny detail though) The signal comes in and is met with switchable impedance 1500,900,300, and 150 ohm. It then is routed to the choice of no pad or -20dB. We then travel to the seriously high end cinemag input transformers. You want iron? Now it's off to the first preamp tube. This has 35 dB of stepped gain. The first gain stage is the higher gain 12AT7A. That gain stage is at unity gain when the control labeled gain that has 35 dB of stepped gain is turned all the way to the left. (0 dB of additional gain.) This is fed into the second tube, a lower gain 6922. The signal is then sent to the high pass filter (40/80/120 Hz) or bypasses the filter. Our very happy signal now goes to the final preamp tube/output stage.... another 6922. The trim control of +/- 10 dB is active on this final gain stage. Our output signal is now sent to the cinemag output transformers as well as the meters. (The meters are your output signal...not your input)

Take the cover off and look inside this unit. I don't agree with any comments here that disparage the build quality of this unit. The only reason this is not $4k or higher is because it has a Presonus tag. I bought mine in June of 2006 and have thousands of trouble free hours using it. I will buy every single one of these that I can find at the forementioned $700 price tag. Mine was considerably more

My typical signal path will be one of several different Neumans's/AT4050/Tube clones into it. Most of the time I use the 1500 ohm setting with the -20db pad inserted and the high pass filter set on at 120 in the vocal booth. Gain switch will be set usually for 40-50 dB on vocals and lower on instrument mics. The signal is sent into my HILO. Since I have primarily a songwriters studio, I am using a HILO for just about everything. If I need more input channels than two, I just use my Sonar/VS700. I prefer the ADL600 pre's over all of my other pre's including Avalon, Langevin, Meek, Avid, Onyx 400F, and my old large format Soundcraft board... most of these now gone after I downsized from a much larger facility.

I don't work for Presonus and have no relationship with them other than as a customer of the ADL600. There are just simply some things I have found in the last 40+ years of recording and making music that are true keepers. This is one of them. It is a incredibly versatile preamp that is a stunning bargain even at MAP or whatever discount you can wrangle.
Attached Files
File Type: pdf ADL600_OwnersManual_EN2.pdf (1.58 MB, 178 views)
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