DOA - Discrete Op Amps

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Use the RTA feature in REW to get nice FFT curves averaged and windowed anyway you like.

Here’s an example:
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I have to take a look at it as most of my inital tests are in the fft viewer.
My target is a specific harmonic ratio, not the lowest total.

I need to shop for a new sound card.

On my plots, the blue trace you can see the Ur22 floor. It is looped back externally as control data.
 
Still moving along, here is the general idea in Brent Butler's expired patent. I only modified/added a few things to accommodate the dual op-amp dip 8 and eliminate the diodes. So far works inverting, non-inverting and unity gain. The pentode comments are interesting and will explore later.
 

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From Russia, arrived today. Can't wait to hear them.
The US types are available in large quantity but still want to have more sources.
The thumb drive is for size compare. I have not tested the OTK 6s7b before.

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Almost a week listening. I put the original tl072 back in, sounds crappy, put in a 5532 sounds better but no where as sweet like the minature tubes.

Tone circuit chosen because its more demanding on opamp-tube output.

confirms the fft profile in previous post 16 . a copy is here. blue is loopback control fron analyzer and magenta tube-op-amp output.

Note: this thread started out in Lounge and was moved but its really a lounge subject i think. just pure WAG crazy testing and what ifs.

Adios amigos, steaming off to Tobago.

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Back in town now.
Have been asked for more details on circuit so here is. No time right now to CAD.
Note - the adapter has no capacitors on board. Its all left to the mother socket to add.
Many possible configurations, the BJT opamps are stable. the substrate jfet op-amps are hit-mis.
I'm going to purchase a discrete jfet op-amp and cut the trace , insert tube and re-test.
A small compensation cap ie 10-pf probably could be used on adapter but have not explored.
Cons: have not totally solved the power up - heater issue. So on dh100 I let the heaters run before turning preamp on.
CCS for the 5744 tube is 4.5ma E-452 from Mouser. A much lower current would be appropriate for 12ax7. You should start with 12AU7 or 6sN7 etc.

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Rev 1.0

No need to worry!

I have made the schematic for it. I hope I did not missed anything.

JFetter, please be so kind to check the image I attached, so there won't be any problems. I correct everything wrong to keep the quality consistent.
Also: Using a 555 relay timer circuit on the heater supply could be the answer to delayed turn on of op amp
I would also need help in calculating/getting to know how many mA the CCS should provide for each tube types.

Thanks for your help!
 

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ok , I have to do a midscale operating point list for the recommended tubes.
But I know from actual testing that the circuit works fine using either mid, extreme hi or low end of Anode current. Only the PPout max is effected.

I'll try to use the CCS parts stocked by Digi-key and Mouser.
I tested a discrete version of the CC with three parallel J174 and works fine but is too bulky for space available. The CCS diode is very compact.


Also note: The tube is not operating as 'starved' using the CCS.

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Okay! Looking forward to the operating points!

Also I would like to warn everyone that I included the 5532 as a recommended tube! Silly me, I was tired last night. I'm going to correct it today. Sorry about that.

This is a simple circuit that can be built up by anyone and your drawing really helps.

Also, micro tubes were designed to be soldered into a circuit.
So you can keep things really compact by using them.
 
Ordered four types of CC. I think that will cover the full range of receiving tubes.

E-701 0.7ma
E-152 1.5ma
E-272 2.7ma
E-452 4.5ma

So I'll match them to the most common tubes. The criteria being lowest THD and highest PP output. A compromise somewhere in the center.

They are $2.10 each in tens from Mouser.

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Yes I have the CC parts, board is not here but don't really need it.
I can test in circuit on the Hafler preamp.

I did an update on my test bench this week, looked for better analyzer card.
Ended up getting a UR22mkII and low end Win 10 computer. Got it all going today.

The new UR22mk2 is a big improvement. More bandwith and more good headroom.


Also going to use up my inventory of 5532 SOIC (with cert of origin) parts by using some pcb adapters.

Should have all proto next week.
 
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