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1073 transformer history?
Old 6th August 2019
  #61
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Quote:
Originally Posted by -JJ- View Post
I'm confused about your mod. The note from fish said R27 should be 10k and they were suggesting you reduce that value to 5k by either replacing it or soldering on a 2nd 10k resistor to the same terminals (two 10k resistors in parallel = 5k). But you're saying the original R27 was 22k and you've swapped that out with a 47k resistor. That should have reduced your gain instead of increasing it, no?

So fivefish response was wrong, when I did what he mentioned in the comment it decreased the volume, so later he said to replace that resistor to greater value.
Old 6th August 2019
  #62
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Quote:
Originally Posted by cesar delly View Post
So fivefish response was wrong, when I did what he mentioned in the comment it decreased the volume, so later he said to replace that resistor to greater value.
Hi

R27 is a 10K feedback resistor as standard so increasing its value will increase the gain.

Your decision is whether the new circuit with the wrong transformer and much boosted gain to make up for the transformer signal drop sounds better than the bog standard circuit with the correct type transformer and normal gain.

You want to thoroughly test it at the highest gain you can achieve with an appropriate microphone to see if it sounds better... my gut feel is it won't.

Why? Because you didn't do the JML mod and just fitting that transformer where the prior one was you will throw away 6dB when the prior transformer boosted 6dB.... 12dB difference. It will also be a mite mismatched impedance wise.

As the input level to the amplifier is 12dB lower you have to boost the amp another 12dB... in the process of raising this level,it will also bring up the noise floor by the same amount.

There's no such thing as a free lunch, etc.

Old 7th August 2019
  #63
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I can’t believe how freely accessible Mr Tanner is. We’re so lucky to have him here!
Old 10th August 2019
  #64
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Quote:
Originally Posted by Geoff_T View Post
Hi

R27 is a 10K feedback resistor as standard so increasing its value will increase the gain.

Your decision is whether the new circuit with the wrong transformer and much boosted gain to make up for the transformer signal drop sounds better than the bog standard circuit with the correct type transformer and normal gain.

You want to thoroughly test it at the highest gain you can achieve with an appropriate microphone to see if it sounds better... my gut feel is it won't.

Why? Because you didn't do the JML mod and just fitting that transformer where the prior one was you will throw away 6dB when the prior transformer boosted 6dB.... 12dB difference. It will also be a mite mismatched impedance wise.

As the input level to the amplifier is 12dB lower you have to boost the amp another 12dB... in the process of raising this level,it will also bring up the noise floor by the same amount.

There's no such thing as a free lunch, etc.




Thanks again for all your help!
Have you ever added a hi pass filter to a 1272? If so can you give me information on how to achieve this? Is there any kits available you can refer me? Thank you for your time!
Old 10th August 2019
  #65
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Quote:
Originally Posted by cesar delly View Post
Thanks again for all your help!
Have you ever added a hi pass filter to a 1272? If so can you give me information on how to achieve this? Is there any kits available you can refer me? Thank you for your time!
Hi

Actually, I have never modified a 1272 as the only contact I have had with them is either to make them (as spares department at Neve), repair them, or adjust their gain in a console.

The "use a 1272 as a pre" thing is only about 25 years with Brent Averill being an early producer of such things.

You could make a crude high pass filter by switching the value of a coupling capacitor for a much smaller value....
Old 10th August 2019
  #66
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Quote:
Originally Posted by Geoff_T View Post
Hi

Actually, I have never modified a 1272 as the only contact I have had with them is either to make them (as spares department at Neve), repair them, or adjust their gain in a console.

The "use a 1272 as a pre" thing is only about 25 years with Brent Averill being an early producer of such things.

You could make a crude high pass filter by switching the value of a coupling capacitor for a much smaller value....
Witch. Capacitor would that be? I have the actual Brent Averill mic ore 1272 racked. Idk if that helps
Old 10th August 2019
  #67
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Quote:
Originally Posted by cesar delly View Post
Witch. Capacitor would that be? I have the actual Brent Averill mic ore 1272 racked. Idk if that helps
Hi

I mentioned crude because that's what my suggeston was... the ringed capacitors are input decoupling especially C8 on the pre stage...

Being a tantalum electrolytic its response will go right down to 20Hz with minimal loss... but you could add a capacitor in series with the input on pin U and make it a very small value that you could experiment with and use a switch that either inserted that value or connected the input straight to pin U.

As it's experimentation and I've given a huge clue on how to do it (never having done or had the need to myself) just start with a handful of small capacitors and see which value sounds best...

NB When capacitors are connected in series, the total capacitance is less than any one of the series capacitors' individual capacitances. So the capacitor you add will make a major difference to the low frequency signals.
Attached Thumbnails
1073 transformer history?-b283.jpg  

Last edited by Geoff_T; 10th August 2019 at 08:42 PM..
Old 10th August 2019
  #68
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Quote:
Originally Posted by Geoff_T View Post
Hi

I mentioned crude because that's what my suggeston was... the ringed capacitors are input decoupling especially C8 on the pre stage...

Being a tantalum electrolytic its response will go right down to 20Hz with minimal loss... but you could add a capacitor in series with the input on pin U and make it a very small value that you could experiment with and use a switch that either inserted that value or connected the input straight to pin U.

As it's experimentation and I've given a huge clue on how to do it (never having done or had the need to myself) just start with a handful of small capacitors and see which value sounds best...

NB When capacitors are connected in series, the total capacitance is less than any one of the series capacitors' individual capacitances. So the capacitor you add will make a major difference to the low frequency signals.
Thanks you for the detailed information, last question and sorry for being a beginner at this, how would I ad a 3 way switch?
Attached Thumbnails
1073 transformer history?-e5a2221b-8708-4d30-9df9-a00d78a6b815.jpg  
Old 11th August 2019
  #69
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Quote:
Originally Posted by cesar delly View Post
Thanks you for the detailed information, last question and sorry for being a beginner at this, how would I ad a 3 way switch?
Hi

You don't touch the 283 pcb.... you put your capacitor in series with the input pin U.

Take the wire off pin U....a three way switch has three open contacts and a wiper.

The wiper connects to pin U on the B283 connector.

The wire that went to pin U goes to position 1 of your switch... that's filter off.

Solder one leg of two capacitors to switch positions 2 and 3.

Connect the two other legs of those capacitors to pin 1.

That's how to do it.... you need to work out how you would do it.
Old 11th August 2019
  #70
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Sorry I’m confused to what is “U”
Old 12th August 2019
  #71
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Quote:
Originally Posted by cesar delly View Post
Sorry I’m confused to what is “U”
Hi

It's the second from last pin on the connector the B283AV is plugged into.

Please read through my emails again.

Old 12th August 2019
  #72
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Quote:
Originally Posted by Geoff_T View Post
Hi

It's the second from last pin on the connector the B283AV is plugged into.

Please read through my emails again.

Oh I see it on the schematic pic. Thank you! My bad for asking all this questions. I appreciate the information.
Old 13th August 2019
  #73
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Quote:
Originally Posted by Geoff_T View Post
Hi

It's the second from last pin on the connector the B283AV is plugged into.

Please read through my emails again.

Will this switch work or do I need a 6 pin switch? Thanks again for your time! ??
Old 13th August 2019
  #74
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Here’s the switch
Attached Thumbnails
1073 transformer history?-55541b7a-8d63-400d-a33e-aa84296a9bb4.jpg  
Old 13th August 2019
  #75
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Quote:
Originally Posted by cesar delly View Post
Here’s the switch
That's a two way switch so use one capacitor. As before, wiper (center pin) to pin U.

Wire that went to U to one of the other pins... and wire a cap of your choice across the outer two pins.

If that switch has three positions, the middle position is no connection.
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