[Orson Garnsey]

All,

An image of my Bugle:



Tribulations:

Note the in-line caps. These are here because I smoked the others and this is all I could find at RatShack; had to keep spinning!   I smoked them experimenting with 15v wall-warts as power supplies. I should have known the Bugle cannot handle 1100ma per side.  

Trials:

I've tried several different opamp combos. First, the specified OPA2134s. These sound great. Next, I sourced three Brown Dog adapters, mounted DIP sockets in them, and stuffed 'em with OPA627s. This is the combo I like best so far. However, it did seem to cause a problem. I changed the circuit gain from 50db to 63.5db to support a Denon DL-103. Played a few records, sounded good, and then a loud, high-pitched squeal emanated from my right channel. I changed the opamps to dual-package OPA2604s and played a few with no issues. The 2604s are good, but I liked the 627s better. The Bugle as you see it has OPA637s installed, which sound like the 627s. No squealing yet.

I am powering the Bugle with 12V SLA batteries.

Anyone reading this who is considering building a Bugle; just do it! Great fun and not that difficult to complete. Sounds fantastic too.

Those interested in how I sourced the pricey opamps should send me an email.

[hagtech]

Just like rolling tubes!  I think you might get a best combination by mixing parts.  Suggest OPA2134 in first two stages and then 2604 for output.  Or something like that.  First stage is most important for noise and cartridge matching/interaction.  You don't want a bipolar type here.  Output stage needs to be powerful.

The squeal is an RF oscillation.  It screws up everything, even in the lower registers.  You'll get dc bias offset and all kinds of issues.  The circuit board was not designed to handle the faster opamps.  But by adding localized supply decoupling, it might be good enough.  Maybe, there are still nasties caused by the sockets and added trace lengths to the feedback resistor, plus added capacitance on the inverting node.  Only a very fast scope will tell.

So try this, 0.1uF capacitors mounted to the adapters.  Or solder right to the opamps pins.  Run both supplies to ground.  That's two caps per stage.  Value is not critical, 0.01uF is fine, but caps need to be low impedance type such as ceramic or poly films.  The same type as used on the main circuit board will work fine.

jh

[Orson Garnsey]

So try this, 0.1uF capacitors mounted to the adapters. Or solder right to the opamps pins. Run both supplies to ground. That's two caps per stage. Value is not critical, 0.01uF is fine, but caps need to be low impedance type such as ceramic or poly films. The same type as used on the main circuit board will work fine.

Thanks, Jim. I'll figure that out and try it. It's funny to note that I was worried about buying a few extra resistors when I started my build... Now I am swapping opamps around like preamp tubes.

I am having fun.

[Orson Garnsey]

Just like rolling tubes!  I think you might get a best combination by mixing parts.  Suggest OPA2134 in first two stages and then 2604 for output.  Or something like that.  First stage is most important for noise and cartridge matching/interaction.  You don't want a bipolar type here.  Output stage needs to be powerful.

VERY good suggestion! Running this combo has proven to be best so far. Soundstaging improved and it's quieter. I expect that running something other than a 2134 in the first stage altered impedance. Now my analog system is besting my DAC in most cases.

I am going to leave the 2134 in the first stage and mix / match in the other two stages.

Hmmm.. I may need a development Bugle and a production Bugle

[Karlk]

Any thoughts on using AD825 opamps ?

[Yoda]

hagtech wrote:
Just like rolling tubes! I think you might get a best combination by mixing parts. Suggest OPA2134 in first two stages and then 2604 for output. Or something like that. First stage is most important for noise and cartridge matching/interaction. You don't want a bipolar type here. Output stage needs to be powerful.

What opamps would be good to try in the line stage section of the Oboe?

Matt

[PatOMalley]

hagtech wrote:
Just like rolling tubes! I think you might get a best combination by mixing parts. Suggest OPA2134 in first two stages and then 2604 for output. Or something like that. First stage is most important for noise and cartridge matching/interaction. You don't want a bipolar type here. Output stage needs to be powerful.

I thought both these opamps were bipolar.
I bought three 2604 thinking the earlier advice meant to use this opamp in all positions.
Then I bought two 2134 for the first two positions.
  To be clear: You are saying that there is less noise using 2134 @ U1, U2, and 2604 @ U3?

What to do with these left over opamps? ... i see one of those portable tin can headphone amps in my future.  

[Yoda]

"Shubert Impromptus op 90 & 142 / Alfred Brendel on VOX mastered in stereo by Van Gelder! "-

P'OMalley

Brendel is one of my favorite pianists.  Haven't heard that one though!