BrianGT, first timer w/ radio (accidentally)

[edjosh23]

This afternoon I completed my Gainclone, this was a first for me doing anything diy besides installing car audio. So far the SQ is "ok" its worse than my Denon but I still have many more hours until I can accutately compare SQ. There is quite a bit of interference, but there wont be as much when the box is complete. One problem I have and I saw someone else had this problem was I can hear the radio when volume is low.

I'm very proud of my amp just waiting for better SQ.

I was told a good way to speed up burn in was turn up the volume, I did so with a dummy 8 ohm load for about 10 min and then stopped because I wanted to hear some music.

Any other suggestions for speeding up burn in?

Right now i have the dummy load on with volume up all the way, and somehow the music from the cd player connected to the amp is playing through the terminals?? What? How is this possible?

I'm going to add pics.

An externally hosted image should be here but it was not working when we last tested it.

Thanks,

Josh

 

[karma]

not sure burning it in will get rid of the radio waves. make sure your input wires are properly grounded. and you are using a good
set of rcas for starts.

add pics?

 

[edjosh23]

The RCAs are dayton's from PE. My hum is louder with the input disconnected. I decreased some hum just by pulling the rectifier back, this definately is not my final chasis and the rectifier and toroid will have a seperate compartment.

I'm gonna shorten the signal path to my pot also.

Here is a pic of the back with RCA wires connected.

And I just wired my led in my on/off rocker

An externally hosted image should be here but it was not working when we last tested it.

Here is a link to the RCA, JoshHere
I would think they would be good enough? What else can cause radio interference?

Thanks,

 

[karma]

weird pics still not showing up just a white box with a red x

 

[edjosh23]

An externally hosted image should be here but it was not working when we last tested it.

White box with a red x?

 

[edjosh23]

Also I wanted to know of my current ground scheme is ok. I have 8 awg ground wire with a male disconnect, and the 2 channel ground from the PCBs are combined into a female disconnect. Is that ok? When I disconnect my grounds I seemed to have a hum still, that was just as loud.

Please post some suggestions for everything that you think would help.

Thanks,

Josh

 

[chipco3434]

Today I fixed a noisy BrainGT gainclone. It's all in the grounding.

Following Nuuk's site, run a 100R/.22uF between chassis star ground and the mains ground wire. Additonally, place a 220pF across the input signal and ground. Right across the tabs. Separate the power and chasis ground stuff from the input grounds, then bind them with a very small wire.

My results were PERFECT! I had the volume pot cranked all the way and not a sound.

Nuuk's Decibel Dungeon

 

[Greg Erskine]

Hi chipco3434 and edjosh23,

I recommend following Brian's instructions on earthing and not use a star earth. This PCB effectively has the a star earth on each PCB.

I initially had my BrianGT GC wired with a star earth and it hummed, when I rewired it as per instructions it was dead quite. BTW: I didn't connect CHG.

 

[edjosh23]

I disconnected my CHG, I still have a hum, could it be RFI? I have a wooden case, The finished case will be lined with copper and grounded and should be able to decrease RFI, but can RFI cause static or hum, or the radio interference?

My ground is 8 awg from AC outlet to a disconnect, and then the other disconnect connected 2 it is both CHG which are 16 awg each.

here is a pic of the connection

An externally hosted image should be here but it was not working when we last tested it.

 

[BlackDog]

I disconnected my CHG, I still have a hum, could it be RFI? I have a wooden case, The finished case will be lined with copper and grounded and should be able to decrease RFI, but can RFI cause static or hum, or the radio interference?

Hum and RFI are two differents problems:

Hum is normally solved by changing the earthing / star ground arrangements.

Your unintentional radio receiver can be solved quite easily. I tend to get a similar problem where I live, as I'm right next to the regional radio transmitter. Try soldering a 220pF ceramic capacitor across the chips inputs pins, as close to the chip as possible - on my BrianGT clones, I soldered them to the underside of the PCB. This should get rid of that radio!

Steve

 

[edjosh23]

Thanks, I'm about to go hunt down a 220pF ceramic cap, is there anything else than can help improve SQ/ get rid of static or hum?

How can I speed up the burn in process, its been about 15hrs burn in and it doesn't sound better than my dad's 7 year old Sony reciever or my Denon.

 

[edjosh23]

Well I talked to Brian and he gave me some more good advise, then I had a friend over to do some history work with. He turned down the volume when his phone was ringing, and had the phone in the same hand that he turned the volume down with and I heard mayjor interference! I took off my B&W speakers from the amp and connected raw drivers that I first tested the amp with, and moved the pol downwards and towards the toroid and rectifier, to see what it would be like if my volume knob was not floating, and hisssss in the left speaker, sizzle, and pop! left speaker blown, guessing DC power was going to it, then 1 minute later the same happened to the right speaker, then I was about to test DC voltage from the speaker terminals when POP went a cap when my face was less than a foot away.

I'm working on a project right now so I cant inspect the problem yet but it looks like I just ruined the panasonic cap and nothing else.

Unfortunately the smell of 2 burnt voice coils and the smell of a blown cap do not smell good at all and I have to use the computer to do the project for history.

Was I getting DC voltages going to the speakers?
Why would moving the pot make the speakers have DC?
Do you think everything on that board is ruined or just the cap?

Thanks,

please help,

Josh

 

[edjosh23]

Can someone give me some advise please?

 

[kneadle]

Bump.

I'm following. Have no advice. Here's hoping you get an answer.

Dave

 

[Nuuk]

I'm not sure that I can follow what you are saying.

When you say 'moved the pot', do you mean physically moved it or adjusted the volume?

What do you mean by 'floating pot'?

My advice is to start from scratch. Take everything out of the case and assemble it on a piece of wood. Start by measuring the AC voltages from the transformer., then connect the bridge and measure the DC rails.

If they are correct, replace the blown cap and connect power to the amp. Measure the DC offset and report back here.

BTW - you had a cheap lesson with that cap! A pair of safety glasses may be a very cheap investment!

 

[kneadle]

BTW - you had a cheap lesson with that cap! A pair of safety glasses may be a very cheap investment!

Some prominent contributors here (Peter Daniel?) have some horror stories to tell and old war wounds to show, like permanently damaged eyes.

Dave

 

[edjosh23]

I physically pushed the pot itself down into my case, as you can see in my pictures it was either on a peice of wood or it was held up by the wires about 3 inches above voltage lines.

I had my amp working properly for more than 24 hours, I checked Dc and Ac voltages (It was like 26.9 and 38).

I live in Atlanta and BrianGT offered to rebuild it with me. I have come to the conclusion that maybe when forcing the pot down, wires touched or something or maybe an arc. This was a test box to make sure everything was working alright but Brian helped me come to the conclusion that my design was pretty good but could be better.

Nuuk I've read your site many times and it has been very helpful, are there any suggestions you have that can help me for the next build and the next design?

I'm very open to anny suggestions and especially ones to help increase SQ with Brian's basic kit.


About the safty glasses, I use them when working on my table saw, but at the time that this happened I was doing homework I just pushed the pot down thinking about what it might sound like if it were in it's "to be" location but I am very glad I had the amps facing eachother because I'm sure that burns really bad!

Thanks,

Josh

 

[kneadle]

Another place to check for DC voltage is at the speaker outputs. If you have an excess of DC offset (more than 100mv), there may be something wrong somewhere else.

It's a bit of fortune that you live next door to the designer of the product, isnt' it?

Dave

 

[edjosh23]

I was going down to check the DC voltage of the speaker outs when it blew, (I keep my multimeter handy )

About an hour away but yea I would say its pretty nice, and he has been more than helpful. He probably gets a little annoyed but I'm able to call him and ask him questions (ones that I might be ashamed to ask on here) But he hasn't seemed to mind too much so far.

Unfortunately I dont know anyone else that knows enough about electronics to even think about being able to answer my questions. And I havent't taken Physics yet, thats next year.

 

[Nuuk]

Josh, I haven't actually completed a Brian GT kit yet but I would guess the usual advice holds true for any GC.

Check that you have made the best possible solder joints.
Keep all wiring as short as possible.
Pay attention to your grounding arrangement.

It seems that you didn't do a bad job of building your GC and that your problems were mainly due to moving that pot. So I hope you will remember to power down before making any such 'adjustments' in the future!