[f] AMB on Facebook

β22 Repair Help

beta22

β22 Repair Help

Postby crosensteel » May 29th, 2019, 7:26 pm

Hi all,

I bought a β22 off of eBay a while back and after a few months I started to notice a humming noise. Earlier today, I opened it up to see if there was anything obviously wrong. I don't know anything about electronics, but I tried to see if there were loose wires or something.

Big mistake... after a couple tries of opening the case up, checking that wires are firmly attached and that kind of thing, it stopped powering on.

So, I am obviously pretty incompetent, but I'd still like to have my amplifier. I'd also like to not die of electric shock if possible. I was wondering if anyone could guide me through even the initial process of diagnosing/safety for an absolute beginner, or failing that does anyone know if there are any people that repair these professionally?

Thanks very much for reading.

Best,
Cameron
crosensteel
 
Posts: 8
Likes: 0 post
Liked in: 0 post
Joined: May 29th, 2019, 7:12 pm
Location: Lancaster, PA
Country: United States (us)

Re: β22 Repair Help

Postby amb » May 30th, 2019, 1:32 am

First, did you check the fuse? I hope there is one. Do you know who built the amp?

Please post some photos of your amp, including some close-ups of the internals with the boards and wiring, so we could assess the basics.
User avatar
amb
Site Admin
 
Posts: 10381
Likes: 175 posts
Liked in: 482 posts
Joined: March 29th, 2010, 9:49 pm
Location: Sunnyvale, CA
Country: United States (us)

Re: β22 Repair Help

Postby crosensteel » May 31st, 2019, 8:14 pm

Thank you for the reply!

I created an album of pictures here:
https://photos.app.goo.gl/ShG9wgjd7X4fzdVh6

Please let me know if you need any other or more detailed pictures... I am not really sure what the most important parts are.

I hadn't checked the fuse before, but I just popped it out and it looks bad. There is a picture of it in the album.
Also, the IEC socket was loose and I attempted to glue it in place with E6000 glue.

According to the eBay listing, "The amp was professionally built by head-fi user ShinyFalcon."
crosensteel
 
Posts: 8
Likes: 0 post
Liked in: 0 post
Joined: May 29th, 2019, 7:12 pm
Location: Lancaster, PA
Country: United States (us)

Re: β22 Repair Help

Postby amb » June 1st, 2019, 2:12 pm

Did you replace the fuse to see if the amp would power up?

While the workmanship is a bit sloppy, I didn't see anything obviously wrong with the wiring. I can't tell for sure from the photos, but it appears that the input RCA jacks are isolated from the chassis with plastic washers. In a separate amp/PSU chassis configuration such as this, the RCA jacks should be connected to the chassis directly so that the chassis would serve as an RFI shield.

Do you have a multimeter with which to make voltage and resistance measurements?
User avatar
amb
Site Admin
 
Posts: 10381
Likes: 175 posts
Liked in: 482 posts
Joined: March 29th, 2010, 9:49 pm
Location: Sunnyvale, CA
Country: United States (us)

Re: β22 Repair Help

Postby crosensteel » June 2nd, 2019, 11:19 am

Yep! I just got new fuses and it powered up again. I am very happy we at least fixed that problem.

The buzzing/hum is still there however.

And I can confirm that the RCA jacks do appear to be separated with plastic washers. So, I can investigate further and see if there is a way to connect the RCA jacks to the chassis.

I will get a mutli-meter soon and take the measurements. Would you be able to suggest where to connect it or what parts to measure?
crosensteel
 
Posts: 8
Likes: 0 post
Liked in: 0 post
Joined: May 29th, 2019, 7:12 pm
Location: Lancaster, PA
Country: United States (us)

Re: β22 Repair Help

Postby amb » June 2nd, 2019, 11:57 am

Ok, aside from the hum, is the amp basically working and playing music without discernible distortion?

Is the hum something new, or was it there since you got this amp? Did anything else change, such as new headphones? What headphones are you using? What’s the voltage gain of your amp, if you have that information?

Just some basics before poking around in there with a multimeter, so that we can determine what to measure.
User avatar
amb
Site Admin
 
Posts: 10381
Likes: 175 posts
Liked in: 482 posts
Joined: March 29th, 2010, 9:49 pm
Location: Sunnyvale, CA
Country: United States (us)

Re: β22 Repair Help

Postby crosensteel » June 2nd, 2019, 3:22 pm

That is correct - it is basically playing music without discernible distortion.

The hum seems to be new, but I can't remember exactly when it happened. There may have been a slight hiss at certain volumes even from the beginning. For example the hiss might start at the 12 o clock position but be gone when the knob is at maximum.

About three weeks ago, I started using the DarkVoice 336SE as a pre-amp, which is a tube amp. I wasn't really paying attention to buzzing or distortion it added since I figured it was a tube amp and they are noisy anyway.

I really started to notice it last week when I moved my workstation to a new place. All the equipment is the same, except for the removal of the DarkVoice. Adding DarkVoice back in now does not help the hum, but it does add its own noises.

I've also been changing DACs from Schiit Modi to SMSL SU-8, but that doesn't seem to make a difference.

Even when there is no RCA cables connected the hum is present, and actually it gets quieter when I connect RCA cables.

My headphones are the same, and I've tested it with the Fostex TH900, and the MassDrop Plus IEM -- there is hum in both.

According to the eBay listing it is two-channel and 2X gain.

Thanks much for the detailed questions :)
I will let you know if I find out anything new from poking around.
crosensteel
 
Posts: 8
Likes: 0 post
Liked in: 0 post
Joined: May 29th, 2019, 7:12 pm
Location: Lancaster, PA
Country: United States (us)

Re: β22 Repair Help

Postby crosensteel » June 2nd, 2019, 3:51 pm

Sorry - small correction.

When I plug in RCA cables, the hiss from the volume knob is reduced so that it is from 12-2 o'clock instead of from 12-maximum volume.
It has no effect on the hum.
crosensteel
 
Posts: 8
Likes: 0 post
Liked in: 0 post
Joined: May 29th, 2019, 7:12 pm
Location: Lancaster, PA
Country: United States (us)

Re: β22 Repair Help

Postby crosensteel » June 2nd, 2019, 3:52 pm

I removed the plastic washers from the RCA jacks and the hum seems to be unchanged.
crosensteel
 
Posts: 8
Likes: 0 post
Liked in: 0 post
Joined: May 29th, 2019, 7:12 pm
Location: Lancaster, PA
Country: United States (us)

Re: β22 Repair Help

Postby amb » June 3rd, 2019, 12:35 am

It sounds to me that the basic power supply and amplifier circuitry is working properly in your amp. To verify, you can go over the "Initial setup" section at the β22 website and check the amp boards with a multimeter. Since you state that you're a novice at this, you should be very careful so you don't cause damage by a slipped test probe making an unintended short circuit, or something like that. Ask a friend with DIY electronics experience to help you if you can.

Running with no source connected to the input and turning up the volume will surely cause increased hum and noise, because an open input will act as an antenna and pick up noise. This is not a valid mode of operation anyway.

The volume pot is a variable resistor, and over certain positions where the equivalent resistance to ground is at maximum, you will hear more noise because resistors have inherent noise, and some of it varies by resistance (search the web for "Johnson noise", "Shot noise" if you're interested in more details). Since the volume pot is at the input of the amp, any resistor noise it generates is amplified by the gain of the amplifier. Normally this noise is below the threshold of audibility if the amp has the appropriate amount of gain for the headphones being used. You are using very sensitive headphones. The Fostex is 25Ω and rated at 100dB/mW. The Massdrop Plus IEM is even more sensitive at 109dB/mW. At this level of sensitivity, even a gain of 2x is probably too much. It's arguable that such headphones need any voltage gain at all, some may benefit from attenuation. Unfortunately the lowest gain for a β22 is 2x. After all, these amps were designed to drive inefficient power-hungry headphones, especially high impedance ones that could use the high output power the amp provides.

Do you have any other headphones, for example Sennheiser HD6x0, HD800 or Audeze planar-dynamics to try? See if you could still hear noise over these types of headphones.

As for the hum, it may be a symptom of ultrasonic instability. Some headphones present highly reactive loads to the amp and cause oscillations in ultrasonic frequencies. Those frequencies are outside the audio band, but could produce audible sub-harmonics. I noticed that your amp is not equipped with an output zobel network. Such a network may alleviate the audible hum. The zobel network is described at the β22 website.
User avatar
amb
Site Admin
 
Posts: 10381
Likes: 175 posts
Liked in: 482 posts
Joined: March 29th, 2010, 9:49 pm
Location: Sunnyvale, CA
Country: United States (us)

Next

Return to β22 amplifier

Who is online

Users browsing this forum: No registered users and 0 guests

Quick Links

AMB audio DIY resources
AMB audio shop