Guess I will use what I have on hand for testing, then order the ones from the bom to swap out when they get here. I plan to shoot pix of the process, and post them on audiokarma.org. This was a request from a member there. Pete, you are welcome to use any of it for a manual if it helps. I will update with a link when I post it.
Again many thanks to your contributions to the Diy community,
Al Purcell
Again many thanks to your contributions to the Diy community,
Al Purcell
How big of an improvement the $12 Radiodaze choke (or any similar Hammond or Triad choke) can make in this particular amp compared to the resistor? I have collected all the parts same as on the BOM. Yes, I understand a choke will sound better any how, but will this particular amp benefit greatly or just marginally from a choke?
Now the question about chassis..
Are the headphone jacks and potentiometer grounded on PCB? I'm thinking about using aluminum top plate bolted on a frame of wood, drilling the holes for headphone jacks and potentiometer on the front piece of wood. Speaker posts, RCA and IEC all will be mounted on the top aluminum plate. So, is it safe to use wooden front panel or the headphone jacks and pot must be grounded on a metal chassis like Hammond?
Now the question about chassis..
Are the headphone jacks and potentiometer grounded on PCB? I'm thinking about using aluminum top plate bolted on a frame of wood, drilling the holes for headphone jacks and potentiometer on the front piece of wood. Speaker posts, RCA and IEC all will be mounted on the top aluminum plate. So, is it safe to use wooden front panel or the headphone jacks and pot must be grounded on a metal chassis like Hammond?
The jacks are grounded on the PCB, and are actually insulated from the panel. So no problems there. The pot mechanicals (shaft, front) are not grounded to the PCB. You may or may not need to somehow ground this. Sometimes if you leave it ungrounded, especially with a metal knob, you will hear hum/noise when you bring your hand near the volume knob.
Pete
Just a way to defeat the ground loop breaker and connect signal ground directly to AC ground. You probably will not need it.
Pete
I completed the amp this afternoon. It sounds nice, except for the hum. I thought that this thing would be dead quiet with the added choke. I haven't taken any voltage readings yet, nor have I lifted the ground to see if that quieted things down. You can't hear it when the music is playing, only in quiet passages, but I am sure it will sound even better when the hum is gone.
Al
Al
Is the hum still there when the pot is all the way down? If so, how far are the OPTs away from the power transformer and choke(s)?
Hi Pete..
I have a question for you, on you website it says that a 5K primary could be used. This would increase the gain. About how much? and could you change the value of the volume pot to get more range out of the knob?
The reason why I ask is because I have a pair of electra prints that are 5K Primary @ 65ma 3W Secondaries are 32, 120, 300, 400 for headphones
I was going to sell these since I decided not to finish the project I had them wound for. But it looks like they might work for this amp.
What do you think?
I have a question for you, on you website it says that a 5K primary could be used. This would increase the gain. About how much? and could you change the value of the volume pot to get more range out of the knob?
The reason why I ask is because I have a pair of electra prints that are 5K Primary @ 65ma 3W Secondaries are 32, 120, 300, 400 for headphones
I was going to sell these since I decided not to finish the project I had them wound for. But it looks like they might work for this amp.
What do you think?
Ok
I disconnected the choke and installed a resistor. Still hummed, so reconnected the choke. Hum does not change with volume pot.
If anyone else decides to use a Hammond chassis, get sockets without a shoulder. Install the board then the sockets. Otherwise you will have to drill holes large to get the board to go in. It doesn't look too bad, but I will be getting a new chassis and doing it this way.
Al
I disconnected the choke and installed a resistor. Still hummed, so reconnected the choke. Hum does not change with volume pot.
An externally hosted image should be here but it was not working when we last tested it.
If anyone else decides to use a Hammond chassis, get sockets without a shoulder. Install the board then the sockets. Otherwise you will have to drill holes large to get the board to go in. It doesn't look too bad, but I will be getting a new chassis and doing it this way.
Al
Hi Apurcell, late to reply I know, but I'm finishing up mine and I found that I needed to put a jumper across JP1 to connect signal ground to AC ground to eliminate noise. I initially thought the problem had to do with the pot not being properly grounded as the noise is mostly present at 50% on the pot, so I ran a wire from the chassis ground to one of the rear screws on the Alps, but that didn't offer any decrease in noise.
Sorry I didn't see these posts - you should have sent me email!
If the hum is still there with the volume all the way down and with no source connected, I suspect you are hearing magnetic coupling from the power transformer to the OPTs. This will be worse if your line voltage is high, and/or 50Hz, and/or if you are using very high efficiency headphones or IEMs. I can just barely hear it on my amp with IEMs, maybe or maybe not with Grados. Not at all with AKG K701 or Senn HD600's.
The only way to tell for sure would be to try moving the transformers apart. Maybe unbolt one and tilt/rotate it as much as you can without extending the wires, and see if the hum changes in that channel.
If that is the problem, I'm afraid the only solution is to move them further apart.
On the ground jumper: if your source uses a 2-wire AC cord and there is no other "real" ground connection in the system, things do work better with that jumper in place. This is caused by the EMI filter in the source, which sends a bunch of AC line current into the signal "ground".
Pete
If the hum is still there with the volume all the way down and with no source connected, I suspect you are hearing magnetic coupling from the power transformer to the OPTs. This will be worse if your line voltage is high, and/or 50Hz, and/or if you are using very high efficiency headphones or IEMs. I can just barely hear it on my amp with IEMs, maybe or maybe not with Grados. Not at all with AKG K701 or Senn HD600's.
The only way to tell for sure would be to try moving the transformers apart. Maybe unbolt one and tilt/rotate it as much as you can without extending the wires, and see if the hum changes in that channel.
If that is the problem, I'm afraid the only solution is to move them further apart.
On the ground jumper: if your source uses a 2-wire AC cord and there is no other "real" ground connection in the system, things do work better with that jumper in place. This is caused by the EMI filter in the source, which sends a bunch of AC line current into the signal "ground".
Pete
Not sure if I already answered you via email on this... in any case, changing from 8k to 5k won't make a big gain difference... the higher Z secondaries will make a bigger difference (I was using 8k:8). I think you'd be fine using 5k:32, that'll be about 4dB more gain than 8k:8.
Pete
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