Turtlerock Forum

I had a bit of a weird thing happen today.
After receiving my new matched pair of 4038s, I went to test them straight away.
Plugged into 3124 pre and all seemed good after some spoken word/ a few lines sang into one of the mics. Tried the other one..all good.
Got the acoustic gtr out to try a few lines on that and noticed a buzz/glitch at the end of lower notes. while they were fading out. So I pluck an open e string, let it ring and as the note fades out, there is a little glitch in my headphones. I repeat the same pluck a few times, and the glitch is always there, keeping the dynamic of coming in at the very end of the fading out note.
I think it might be the headphones, and quickly record a few notes to see if it's in the mic-pre-converter chain, and it does come up in the recording too.
I looked at my api pre and noticed that the glitch is synced with the fading out of the last segment of the led meter on the preamp. I think it's the preamp that I got just a couple of weeks ago, but never noticed anything like this.
I keep looking at the preamp's meters while plucking away on the gtr, and notice that sometimes the glitches are not in perfect sync with the meter fading off.
I then look at the unit below the preamp, which is the headphone amp i just installed yesterday, and...BINGO.
The glitches in the audio are in perfect sync with the led signal meter on the headphone amp coming on and off.
THe converters' outs were connected directly to the headphone amp for the tests.
I quickly switch to monitoring through the console and the confirmation of the BINGO..the glitch is gone!!!
The LED meter on my headphone amp was sending glitches through the whole chain.
I still don't understand how, as I'm not that tech savvy, but I know one thing... this hp amp is going back.

I ain't no tech but this might help to determine if it's just the hp amp or a mismatch of impedance between the amp and cans....

Did you try the test with different headphones?
In different ports on the hp amp?
With the headphones unplugged?

i recon rob will answer this
but to me... sounds like there is a bad something in the meter chain on the headphone amp, and its "leaking" some DC spike back to ground, and then something isnt grounded properly and is picking it up.
hows that for a non-tech explanation!

Drumstruck wrote:I ain't no tech but this might help to determine if it's just the hp amp or a mismatch of impedance between the amp and cans....

Did you try the test with different headphones?
In different ports on the hp amp?
With the headphones unplugged?

Very good points Ian, and yes, I tried all the 3 options. It's doing it on all the channels, on 3 different pairs of cans and with no cans plugged in.

gigpiglet wrote:i recon rob will answer this
but to me... sounds like there is a bad something in the meter chain on the headphone amp, and its "leaking" some DC spike back to ground, and then something isnt grounded properly and is picking it up.
hows that for a non-tech explanation!

Yep, definitely bad something
Actually, you reminded me there is a ground lift switch at the back of this HP amp, so might try that to see what happens.

whats the HP amp?

Gareth is probably on the right track. Turn lights / leds on and off causes a significant dump in current. If the power distribution is not good this can get imposed on the audio

Hi Rob,
THe HP amp is a Ta@#$% MH-8.
There's defin itely something wrong with the metering system of the unit, as I've afterwards found that not all meters are even working and some are showing weaker signal, even though the volume heard is the same as other channels.
I'm sending it back under warranty, as I've only had it for a couple of days, but the process is slow and annoying. Wait for RA# from supplier, send it back, they have to confirm the fault blah, blah, so i had to get a new one today.
Hope to get my cash back soon.
BTW, this Ta@#$% unit is built like Crap!!

P.S> I see even the "famous" TASsie CAM is censored here
Not without a reason, that's for sure.

Geez .... you should let me build you a real hp amp...

haha..I would let you, but my pocket probably wouldn't at the moment and I need one for this week coming up.
I got the ART 6 pro today, which feels a tad better.
But if you want rob, PM some options on a 6ch one and I might even be able to get one built down the track.
I was really happy with the Presonus HP60 a few years back, but noone had one in stock last few days.

rob wrote:Geez .... you should let me build you a real hp amp...

The second I'm back in Aus (early Sept).