Hi all , I noticed that the presence control in the DR504 doesn't work fine , it act from hour 5 to 6 only. any suggestion for improve it?
Thanks
S.
DR504 presence control
Moderators: pompeiisneaks, Colossal
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tubelectron
- Posts: 128
- Joined: Sun Dec 04, 2011 10:33 am
- Location: France
Re: DR504 presence control
Sergio,
A long time ago, I had a SA112 Custom Hiwatt 50. Here's an old scanned picture of it :
[img:800:738]http://img15.hostingpics.net/pics/52906 ... om1979.jpg[/img]
The circuit of the SA112 is the same as the DR504, if I recall well. I never had issues of progressivity in the Presence control, as far as I remember...
Maybe you should check/clean/replace the Presence pot ? Or maybe there is a bad contact somewhere in the Presence circuit ?
A+!
A long time ago, I had a SA112 Custom Hiwatt 50. Here's an old scanned picture of it :
[img:800:738]http://img15.hostingpics.net/pics/52906 ... om1979.jpg[/img]
The circuit of the SA112 is the same as the DR504, if I recall well. I never had issues of progressivity in the Presence control, as far as I remember...
Maybe you should check/clean/replace the Presence pot ? Or maybe there is a bad contact somewhere in the Presence circuit ?
A+!
If it works, don't fix it...
www.guilhemamplification.jimdo.com
www.guilhemamplification.jimdo.com
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Stevem
- Posts: 4595
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: DR504 presence control
As with most of those controls they kind of have more range as the amp is played louder since they tap signal off of the speaker output side of the OT.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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gingertube
- Posts: 530
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- Location: Adelaide, South Oz
Re: DR504 presence control
Be aware that the HiWatt presence circuit is unique in the amp world.
Most amps presence work by progressively cutting feedback at high frequencies thus allowing brighter and brighter tone as the control is turned up toward 10 (more feedback cut).
The HiWatt Presence does not work this way. It is a flat response at centre setting with highs cut as turned down and highs boosted as turned up. That is, it works like a "TILT" tone control.
So what you are describing seems to be correct operation.
If it is not working at all then check the actual pot for an open circuit wiper connection.
For reference here is a trace I did quite a few years back.
http://bmamps.com/Schematics/hiwatt/hiwatt_sa412.pdf
Cheers,
Ian
Most amps presence work by progressively cutting feedback at high frequencies thus allowing brighter and brighter tone as the control is turned up toward 10 (more feedback cut).
The HiWatt Presence does not work this way. It is a flat response at centre setting with highs cut as turned down and highs boosted as turned up. That is, it works like a "TILT" tone control.
So what you are describing seems to be correct operation.
If it is not working at all then check the actual pot for an open circuit wiper connection.
For reference here is a trace I did quite a few years back.
http://bmamps.com/Schematics/hiwatt/hiwatt_sa412.pdf
Cheers,
Ian
Re: DR504 presence control
The Presence pot here is 100K LIN. Last one I worked on said, 100K LIN but measured 190K. It was the stock English pot. I replaced it with a CTS version that was spot on measurement-wise and it did change things for the better but, again, the top of the range was the most dramatic.
Measure your pot maybe. It is a very unusual design, I agree.
Measure your pot maybe. It is a very unusual design, I agree.
Most people stall out when fixing a mistake that they've made. Why?
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Stevem
- Posts: 4595
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: DR504 presence control
What?
When you pump more feedback voltage back into the amp the frequency range increases at the low and top range and the gain drops, the opposite effect takes place with less feedback voltage.
When you pump more feedback voltage back into the amp the frequency range increases at the low and top range and the gain drops, the opposite effect takes place with less feedback voltage.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: DR504 presence control
That schematic is correct and may well be the most readable and comprehensive schematic out there. Thank you, gingertube, brilliant work. 
This would be great as a sticky, can this be done?
Stevem, who is your comment directed to?
This would be great as a sticky, can this be done?
Stevem, who is your comment directed to?
Most people stall out when fixing a mistake that they've made. Why?