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An inexpensive audio transformer with DIY projects

#163
*** IMAGE REMOVED - UPDATED IMAGE LATER IN THREAD***

All of the resistor numbers above R16 have been re-sequenced because of the removal of R17 and R20 from the other schematics.
This should be exactly what you want.

-Frank
 
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#165
boomertech said:
All of the resistor numbers above R16 have been re-sequenced because of the removal of R17 and R20 from the other schematics.
This should be exactly what you want.

-Frank
Click to expand...

yeah I noticed that. as mentioned earlier I replaced R18 & R19 (on the newest schematic) with jumpers and I like it better that way since it has a little more dirt without them, so I ersonally would omit those.

BTW, I just tested the new output level control and it works like a charm(!), but you have lugs 1 & 3 reversed from what they should be on VR2 since lug 1 should go to ground.
i'm running TRTA freq response tests right now.
 
#166
here's the results of the frequency response test. there is some slight low end loss (-3db at 50hz) but it's really hard to tell when you're actually playing through it.
and this test was done with replacing C1 with a 1uf cap (and it looked nearly identical with the stock 100n cap).

TransboostFreqChart.jpg
 
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#167
johnk_10 said:
yeah I noticed that. as mentioned earlier I replaced R18 & R19 (on the newest schematic) with jumpers and I like it better that way since it has a little more dirt without them, so I ersonally would omit those.

BTW, I just tested the new output level control and it works like a charm(!), but you have lugs 1 & 3 reversed from what they should be on VR2 since lug 1 should go to ground.
i'm running TRTA freq response tests right now.
Click to expand...

I must have corrected the VR2 rotation arrow error after you took the first version.

That low freq roll-off must be from the R17/R18 (new schematic) resistors with the inductance of the tranny. I will use your resistor ratios R17/R18 and R24 and come up with values that will improve the low freq response.

If you are looking for more crunch, I would suggest keep the R18/R19 (new schem) 1K's and install hard clipping across the TY250 primary with a switch for more of that RAT crunch.

I will work something up and post it in a few.

-Frank
 
#168
boomertech said:
I must have corrected the VR2 rotation arrow error after you took the first version.

That low freq roll-off must be from the R17/R18 (new schematic) resistors with the inductance of the tranny. I will use your resistor ratios R17/R18 and R24 and come up with values that will improve the low freq response.

If you are looking for more crunch, I would suggest keep the R18/R19 (new schem) 1K's and install hard clipping across the TY250 primary with a switch for more of that RAT crunch.

I will work something up and post it in a few.

-Frank
Click to expand...

well, it might be my imagination, but I went back and forth with and without (actually jumpered) the R18/R19's and I though that the clipping sounded a bit more natural and less fizzy without them so I left them out on mine.
 
#170
johnk_10 said:
well, it might be my imagination, but I went back and forth with and without (actually jumpered) the R18/R19's and I though that the clipping sounded a bit more natural and less fizzy without them so I left them out on mine.
Click to expand...

The only reason I suggested to keep the 1K's was because they provide a gentle roundness to the clipping. If you like them at zero ohms, then that's your preference and there are no rules to dirt boxes.;)

Here are the suggestions for the resistors on the primary coil. They allow approximately the same current thru the coil as your 1K's and 2K2. I also tacked on a hard clipping circuit across the primary to give it more crunch.

*** IMAGE REMOVED - UPDATED IMAGE LATER IN THREAD***

-Frank
 
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#174
johnk_10 said:
the 220R's brought back some low end, but the LED clippers aren't working. they just cut the output to practically zero, even with the output level dimed.
Click to expand...

johnk_10 said:
it still works & sounds great with a JRC4558.
Click to expand...

With the new resistors, the 4558 is seeing a much heavier load. You can see from the data sheet that it really doesn't like loads under 1K... the output drops like a rock.

rc4558-6.jpg
 
#176
johnk_10 said:
well, without the leds it sounds great.
Click to expand...

I ran simulations on the tranny with the 1K's and 2k2 with a stiff generator and the response looks good down to 31Hz. I'm wondering if the 4558 was causing some of the low end roll-off. Can you go back to the 1K's and 2K2 with the 2134 and check T-RTA again?

-Frank
 
#178
BTW, just did the RTA test with the 3 220R's on the TX's primary and the freq response is the same as before.
I also tried 470Rs, 100Rs & 1K's and the freq response is always the same.
only the output level changes. (it has progressively more output with lower values at R17/R18.
I also tried it with an OPA2134 for U2 and the freq response remains unchanged.
 

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