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Old 25th December 2008, 02:44 AM   #1
ljk11 is offline ljk11  Trinidad and Tobago
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Default any Welborne Labs Ultrapath owners ?

Anybody here built the Welborne Labs Ultrapath preamp kit ?
I just built it, sounds good however there seems to be way too much gain and the dip switch thingy on the stepped attenuatorfor adjusting gain increments doesnt seem to be working.

I tried putting a resistor on the output but it appears to lose some of the low end.

Any suggestions for reducing the gain ?
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Old 25th December 2008, 08:12 PM   #2
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A resistor on the output is probably not a good idea. However, a resistor divider on the input of the next stage might be a good option. You could also add a resistor divider to the input of the preamp.
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Old 26th December 2008, 01:24 AM   #3
ljk11 is offline ljk11  Trinidad and Tobago
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this might seem like a stupid question
but what is the difference between putting the divider on the output of the preamp as opposed to put it on the input of the amp ?
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Old 26th December 2008, 02:30 AM   #4
ljk11 is offline ljk11  Trinidad and Tobago
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any suggestion on what values resistors for divider I could put ?

Welborne labs says the Ultrapath is <600 ohms output impedance

I am using a 3886 gainclone from chipamp.com, not sure what the input impedance is of that.

thx
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Old 26th December 2008, 06:45 AM   #5
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Quote:
Originally posted by ljk11
what is the difference between putting the divider on the output of the preamp as opposed to put it on the input of the amp ?
It's the same as putting a pot at the output of the source as opposed to the input of the line stage. With very short cables, very little. With long cables, it could be an issue.

How about reducing gain in the source, or in the GC? Check the datasheet to see how low the gain can be set while remaining stable. Otherwise, increase R1 a bit.
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Old 26th December 2008, 06:50 PM   #6
ljk11 is offline ljk11  Trinidad and Tobago
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well I can live with it for the while but rather not.

One other thing is powering it off/on causes bad thumps/crackles in the amp, probably because of the relays used in the remote control attenuator/battery switching circuit.

I've email Welborne but no reply so far.
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Old 26th December 2008, 08:32 PM   #7
Osprey is offline Osprey  United States
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It might be interesting to know which amp you are driving with the preamp. Can the amp be reduced by one stage to make use of the gain in the preamp? I think it is always a bad idea to build up gain only to reduce it in a following stage. What is the point in that?

I think it is better to start at the grids of the output tubes and work forward towards the input. Use as few stages as possible to get the gain you need to drive the output tubes to full power taking into account any feedback that reduces the gain.
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Old 27th December 2008, 03:06 AM   #8
ljk11 is offline ljk11  Trinidad and Tobago
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its a chipamp.com 3886 gainclone

it appears to be difficult to find other people who have built the Welborne Ultrapath battery powered preamp
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Old 27th December 2008, 10:12 AM   #9
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I would be surprised if you received response form Ron - he has gained a pretty solid reputation for not being solid. More than a few customers have been left without product and technical support. I hope your experiences are more positive.

Cheers
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Old 27th December 2008, 12:32 PM   #10
ljk11 is offline ljk11  Trinidad and Tobago
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yeah, I purchased it a few months ago, I didnt know there were issues with service, however I got it and it was missing some parts,

he actually fedexed the parts 2day right away
he also sent a wrong part and he fedexed that again 2day
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