New Budgie

a 3W single ended EL84 amp for home, work & school

New Budgie

Postby opa1 » Sat Jan 16, 2016 9:37 pm

I'm just about finished with the Budgie. I didn't use the headphone resistors and jack. I also didn't use the 1uf dc blocking caps on the input. Just a direct wire. I use a passive pre so the volume pot is not needed either. I did leave room for the volume and HP jack if I wanted it later. Vitamin Q's for coupling caps. The rest is stock from BOM Mouser list. GXSE 10/8/5K OPT's.
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Last edited by opa1 on Fri Feb 19, 2016 12:52 am, edited 1 time in total.
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Re: New Budgie

Postby opa1 » Thu Jan 21, 2016 1:27 pm

It's finished. It has a low level hum through my 604 Altecs. :( Not sure where to look to fix.
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Re: New Budgie

Postby WA4SWJ » Thu Jan 21, 2016 4:44 pm

Very, very nice!! Congrats!
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Re: New Budgie

Postby opa1 » Thu Jan 21, 2016 7:02 pm

Thanks! The hum was a ground issue. It still has a very slight hum with your ear up to the 604's. I'm going to let it burn in for a few days. Then I'll rearrange some things.
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Re: New Budgie

Postby opa1 » Sun Jan 24, 2016 1:54 pm

Here's a pic of the bottom. I tried fixing the hum. I put two 270k resistors on the input rca's. Also ran a ground from the output neg. to the ground on the feedback at j8. The hum is constant and doesn't change with volume. All voltages are correct. Any ideas???????? I didn't install the r 22,23,24,25 for the headphone input.
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Re: New Budgie

Postby battradio » Sun Jan 24, 2016 10:05 pm

Isolate one of the chassis grounds of the RCA connectors with a 10 ohm resistor
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Re: New Budgie

Postby opa1 » Sun Jan 24, 2016 10:38 pm

I don't quite follow what your saying. Are you saying to put a 10ohm resistor on the black wire to ground or the shielded cable to the jack grounds.? Should I take off the two 270K ohm resistors too? I have the shielded cable grounded to the jacks but not the board, the two resistors and a ground to the board from the jacks. Without the black wire to board ground the hum get really bad. Also the jacks have the insulating washers on them too. So they are not grounded to the chassis plate.
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Re: New Budgie

Postby battradio » Sun Jan 24, 2016 11:58 pm

Separate the two ground lugs on the RCA connectors , and put all the grounding wires on one ground lug , solder a 10 ohm between the two ground lugs on the RCA connectors , this will raise the ground of one rca connector by 10 ohms above ground preventing a ground loop between the the signal source and the amp .

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Re: New Budgie

Postby opa1 » Mon Jan 25, 2016 12:00 am

Thanks Mark!!! I'll give that a try in the AM. I'll report back. (y)
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Re: New Budgie

Postby opa1 » Tue Jan 26, 2016 10:56 am

battradio wrote:Separate the two ground lugs on the RCA connectors , and put all the grounding wires on one ground lug , solder a 10 ohm between the two ground lugs on the RCA connectors , this will raise the ground of one rca connector by 10 ohms above ground preventing a ground loop between the the signal source and the amp .

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This is the way I have the amp now. So far it's working best. I still have a very low level hum that is constant and doesn't change with volume. Set up this way the hum is louder on one speaker than the other. I tried the board to ground with the inputs insulated from the chassis. This doesn't work, hum gets worse. I'm going to lift the input shielded cable ground from the input ground tab and see what happens.(shielded cable is only grounded at the input tab, not the board)

I have taken the amp apart and checked all solder joints. Checked hookups/different tubes more than a few times. :)
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Re: New Budgie

Postby Shannon Parks » Wed Jan 27, 2016 7:17 pm

Hard for me to tell from the pic (which is before latest updates) but:

1) Looks like the wire from the PCB GND goes to the input ground? This should go to chassis only. As connected this is a ground loop AND the chassis is not referenced to the PCB at any point.

2) I'd add a safety earth ground to the same chassis point.

3) The input wiring looks confusing to me. I see the shield connected as ground at the connectors but then floating at the input 3P connector. This needs a board connection.

Good luck!

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Re: New Budgie

Postby opa1 » Fri Jan 29, 2016 9:34 am

Update! The low level hum is gone!!!!!!!!! I set it up like You said and the amp is quiet. :) Excellent! (banana)
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