Motown Direct Amplifier-inspired Preamp?
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Further tests:
The 20 pf feedback cap and the 5.6K resistor takes care of the sq wave ringing so the 4.7K grid stopper on stage two makes no difference if it is installed or not so i yanked it out.
A bad solder joint on stage two grid resistor was not the problem causing the ringing,
The transformer primary has no effect on the scope shots for sq wave and phase shift
This was verified by doing before and after scope shots with the wire connected to the output cap or not.
Frequency response test - sine wave
at the lowest gain setting, 50% roll off occurs at 330KC KC
at the highest gain setting on the pot the roll off point is at 54KC
The 20 pf feedback cap and the 5.6K resistor takes care of the sq wave ringing so the 4.7K grid stopper on stage two makes no difference if it is installed or not so i yanked it out.
A bad solder joint on stage two grid resistor was not the problem causing the ringing,
The transformer primary has no effect on the scope shots for sq wave and phase shift
This was verified by doing before and after scope shots with the wire connected to the output cap or not.
Frequency response test - sine wave
at the lowest gain setting, 50% roll off occurs at 330KC KC
at the highest gain setting on the pot the roll off point is at 54KC
MidnightArrakis
Well-known member
There is nothing wrong with your computer monitor.
Do not attempt to adjust the picture.
We are controlling transmission.
We will control the horizontal.
We will control the vertical.
We can roll the image; make it flutter.
We can change the focus to a soft blur or sharpen it to crystal clarity.
For the next hour, sit quietly and we will control all that you see and hear.
We repeat: there is nothing wrong with your computer monitor.
You are about to participate in a great adventure.
You are about to experience the awe and mystery
which reaches from the inner mind to "The Outer Limits".
/
Do not attempt to adjust the picture.
We are controlling transmission.
We will control the horizontal.
We will control the vertical.
We can roll the image; make it flutter.
We can change the focus to a soft blur or sharpen it to crystal clarity.
For the next hour, sit quietly and we will control all that you see and hear.
We repeat: there is nothing wrong with your computer monitor.
You are about to participate in a great adventure.
You are about to experience the awe and mystery
which reaches from the inner mind to "The Outer Limits".
/
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Don't, worry, I am about to bolt the base plate on and call this thing good now that we have come full circle back to the original schematic,
Dave you have a good simulator, which one are you using?
FYI: open loop gain was measured at 278 before the transformer.
Somewhere down the line I might wind a SE transformer and try a class A output stage just for kicks.
Dave you have a good simulator, which one are you using?
FYI: open loop gain was measured at 278 before the transformer.
Somewhere down the line I might wind a SE transformer and try a class A output stage just for kicks.
Disco Volante
Well-known member
Kudos for all-analog computing to DaveP!
Help me understand: what is the purpose of R10? those two valve halves are paralelled, right?
Great project guys;-)
Help me understand: what is the purpose of R10? those two valve halves are paralelled, right?
Great project guys;-)
Well done @DaveP and @CJ !
Great job the two of you & very inspiring project.
Quick question: Is there an easy/ier to source replacement for V2 - 6BX7 GT ?
All the "equivalents" I found so far were mainly RCA USA, Tung-Sol (6BL7GT, 6DN7, 6BX7).
Not so common around here.
Thank you all for this thread.
M
Have a read of this, particularly PRR's comments
https://www.diyaudio.com/community/threads/vertical-deflection-tubes-for-audio-output.60346/
best
DaveP
This thread has just about run its course until CJ shows us the finished article.
I have started a new thread to reverse engineer the Collins 26C tube compressor here:-
https://groupdiy.com/threads/collins-26c-analysis.89027/#post-1173607
best
DaveP
I have started a new thread to reverse engineer the Collins 26C tube compressor here:-
https://groupdiy.com/threads/collins-26c-analysis.89027/#post-1173607
best
DaveP
MidnightArrakis
Well-known member
>> I'm just wondering.....since the XLR connector is "Pin-2 = High/Hot" and "Pin-3 = Low/Cold" and the TRS connector is wired as being "Tip = High/Hot" and "Ring = Low/Cold".....wouldn't that mean that the connections as shown in the schematic below for the TRS connector need to be reversed? Or.....what am I missing here?
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In a related thought, the following idea was presented in the Bo Hansen 325-DI schematic. With the proper output transformer one could easily support a balanced line, balanced mic level and a variable unbalanced 1/4” output for a monitor amplifier.
If using a single secondary output transformer one could still follow this same idea if only a line, mic or instrument amp level output was desired.
If using a single secondary output transformer one could still follow this same idea if only a line, mic or instrument amp level output was desired.
If you know what you are plugging the DI box into, then you could configure the output accordingly. I will be going into a Mackie 16 CH board for live shows so I am going to use line level TRS jacks with a ground lift.
And a couple of 1/4" mono "Thru" jack's on the front so the guitar players can go straight into their amp. These guitar players can get paranoid about going into a DI first, so I am going to have to explain to them how their signal will not be altered in any way (don't tell them about the 1 meg input resistor to ground).
I like the options map2112 has drawn, you could possibly use the mic and line XLR's on the same secondary winding as the xfmr will probably need a load resistor to dampen any ringing. Maybe use a switch for the pad so you only have to install one XLR.
And a couple of 1/4" mono "Thru" jack's on the front so the guitar players can go straight into their amp. These guitar players can get paranoid about going into a DI first, so I am going to have to explain to them how their signal will not be altered in any way (don't tell them about the 1 meg input resistor to ground).
I like the options map2112 has drawn, you could possibly use the mic and line XLR's on the same secondary winding as the xfmr will probably need a load resistor to dampen any ringing. Maybe use a switch for the pad so you only have to install one XLR.
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