[G E]

After a recent equipment change out I found myself without phono preamp capabilities.  After looking at options to buy new, buy used or build, I decided to build.  I love the smell of solder and flux in the morning.  And I chose the Bugle and its PS attachment.  Some day I may go for the Cornet 2.

Jim's turnaround of my order was incredibly fast and it is very much appreciated.

I read though this entire site and focused on the Bugle threads and I do have some questions:

1) I understand opamp rolling is possible and that the standard 2134s should populate U1 and U2 positions and U3 is the position for substitute opamps, correct?

2) When used with the power suppy module built to standard spec (+-15vdc), the voltages on the opamp supply pins should be +-15 vdc, correct?

3) I plan to substitute ad8620 for opamp at u3.  Supply voltages are limited to +-13 vdc for this chip.  assuming the stock regulators provide +- 15 vdc, can i simply substitute the voltage regulators with 79m12 / 78m12 and leave all other resistors, capacitor and transformer parts as listed in both the power supply and the bugle?

4) What blue  LED part # has everyone been using?

5) Are C7 and C10 on the Bugle card still needed when used with the power supply?

Thanks in advance for  your help!

Greg

[poty]

2) When used with the power suppy module built to standard spec (+-15vdc), the voltages on the opamp supply pins should be +-15 vdc, correct?

Correct.

3) ...can i simply substitute the voltage regulators with 79m12 / 78m12 and leave all other resistors, capacitor and transformer parts as listed in both the power supply and the bugle?

Yes, you can. Maybe for more stability and less heating you should increase serial resistors before regulators.

5) Are C7 and C10 on the Bugle card still needed when used with the power supply?

No, the capacitors could be omited. Together with battery holders.

[G E]

The last of my parts arruved from Digikey yesterday and I am on my way to Bugle and power  supply build!  Spent part of the day today fguring out chassis lay out - I scavenged an old satellite receiver box which allows 3.25 inches separation between PS board and Bugle card. 

I found some RCA phono jacks that have nylon insulators and did a trial installation and they do NOT ground out to chassis.  They came from Mouser where I sourced some other parts like LEDs, flux, solder wick, IC sockets, fuses(.062 amp) fuse holder and a few things that were somewhat cheaper at Mouser than Digikey.

I also found a substitute for the unobtanium P3103, .01 uf 50v Polypropylene cap:  Wima .01 uf 63v, 2.5% tolerance polypropylene, mouser # 505-fkp20.01/63/2.5   I suggest that others go up a voltage rating size so that the leads fit a little better.  These have short legs and it takes careful bending to make them fit the PC card.

Can't wait to start stuffing cards, it has been a couple years since my last project and I also want to be able to spin some records again!


ge

[G E]

I completed the power supply tonight - pretty much a stock build except I used 12 volt regulators instead of 15 volt.  I will be using the AD 8620 opamp in my Bugle and its max rails are +- 13vdc. 

My effective voltages out are -12.02 and +11.81, so pretty close.

One question I have - R4 and R7 run hot, too hot to keep a finger on them for more than a moment or two.  Is this normal?  Should I go to two watt resistors here?

Tomorrow I start the Bugle card!  Looking forward to it!

Greg

[poty]

My effective voltages out are -12.02 and +11.81, so pretty close.

0,2V difference? Nothing bad, but strange.

One question I have - R4 and R7 run hot, too hot to keep a finger on them for more than a moment or two.  Is this normal?  Should I go to two watt resistors here?

Check the resistors' value and wattage. Could you measure the voltage on them (it's AC!)?

[G E]

Oops!  I forgot to mention I am using Jim's suggested transformer alternate, 70034te which has 2x18 volt secondaries (full load) compared with original spec transformer with 2x15 volt secondaries, full load rating.

The resistors are the correct value. I checked all resistor values prior to the build. They are rated for 1 watt.

I'll measure some voltages tonight and see how they compare with the schematic. If they run high in front of the regulators which resistors need to be changed and how do I calculate new values?  Or am I better off ordering the original spec transformer?

Thanks in advance for the help!

Greg

[poty]

I don't think it could be a problem. Either the power rating is incorrect or something is wrong with the resistors or transformer. Have you checked the primaries' connection?

[G E]

Resistors were checked prior to installation and they are the correct value. The transformer is functioning within spec and all solder joints visually inspected using a lighted magnifying glass.  No issues there.

I am trying to confirm if hot to touch is within normal operating parameters for these 2 resistors.  Sometimes parts in circuits get hot even with heat sinks attached. 

I completed the power supply build last night and although it was late I wanted to fire it up to see if I got my +- 12 VDC. I did. Tonight I will check voltages at various points and compare with schematic. If all checks out, It follows that resistive values must be OK and perhaps I might want to increase wattage for "peace of mind". 

 

[Speedskater]

Wait a second! You are dropping the DC output voltage from 15V to 12V DC,  but you increased the transformer AC voltage from 15v to 18V AC. That doesn't compute.

[G E]

Wait a second! You are dropping the DC output voltage from 15V to 12V DC,  but you increased the transformer AC voltage from 15v to 18V AC. That doesn't compute.

I used digikey part #497-1475-5 for the negative voltage regulator and its analogous part for the positive voltage regulator. These are from their precision series delivering voltage within 2% of specified rating. For 12 volt devices this means anything between 11.76 and 12.24 is acceptable.  These regulators can accept an input voltage up to -35 vdc (or +35vdc).

I chose the 18 volt transformer because it was listed by Jim as an alternate to the 70023, it has more current capability and it was a bit cheaper.