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Wayne's BA 2018 linestage
Wayne's BA 2018 linestage
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Old 13th September 2020, 08:18 PM   #1701
MEPER is offline MEPER  Denmark
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I have built this line stage using the large output transistors and higher bias. I have also reduced the gain to about x2 as I don't need much gain. I have not yet tested the circuit. I expect to drive it using -+24V PSU or so. My music source is a steamer which outputs about 2Vpp is my guess. I have a crazy idea in mind regarding the volume pot. I want to put it at the output and use a low impedance pot like 220R or so......or maybe even 100R. If stage can drive a headphone it can also drive a 100R pot?
A 220R/100R pot should be able to drive most cables and also most power amp input stages....like M2X etc.?
I want to try to do it this way to have better signal to noise ratio.....better to attenuate a large signal than attenuate a small signal and then amplify it?
I need to ensure that the full input to linestage from my source does not drive linestage into clipping and also that linestage has good performance at the relative high input level?
Could this work well (I guess the same could apply for Whammy but I only use it as preamp)?
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Old 15th September 2020, 01:44 AM   #1702
airborne11b is offline airborne11b  United States
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Quote:
Originally Posted by MEPER View Post
I have built this line stage using the large output transistors and higher bias. I have also reduced the gain to about x2 as I don't need much gain. I have not yet tested the circuit. I expect to drive it using -+24V PSU or so. My music source is a steamer which outputs about 2Vpp is my guess. I have a crazy idea in mind regarding the volume pot. I want to put it at the output and use a low impedance pot like 220R or so......or maybe even 100R. If stage can drive a headphone it can also drive a 100R pot?
A 220R/100R pot should be able to drive most cables and also most power amp input stages....like M2X etc.?
I want to try to do it this way to have better signal to noise ratio.....better to attenuate a large signal than attenuate a small signal and then amplify it?
I need to ensure that the full input to linestage from my source does not drive linestage into clipping and also that linestage has good performance at the relative high input level?
Could this work well (I guess the same could apply for Whammy but I only use it as preamp)?
Don't ask me for an equation but a pot on the backside of the preamp will combine with the output impedance of the circuit. I don't think this configuration will help at all with S/N. Without doing any math, I would guess you would get about 20 dB of attenuation at the speaker which isn't much it would be very loud at full attenuation. It may be possible to use an autoformer on the backside but it would need to be custom wound for your application.
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Old 15th September 2020, 08:57 PM   #1703
Gaz2613 is offline Gaz2613  United Kingdom
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New toy courtesy of Andrew at SparkoS Labs. Will be submitting a write up on my site in the coming weeks. This PSU is configured for (+/-) 18V which is perfect for another Linestage build.

It is designed to take the monolithic 78xx and 79xx regulators and this one comes with the SparkoS ultra low noise discrete regulators which should make this one quiet power supply.
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Last edited by Gaz2613; 15th September 2020 at 09:08 PM.
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Old 16th September 2020, 12:36 AM   #1704
6L6 is offline 6L6  United States
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Wayne's BA 2018 linestage
Oohhh!! That’s neat.

Andrew is local to me, not more than a 30min drive, I really should look him up and see what neat things he has!
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Old 16th September 2020, 12:44 AM   #1705
airborne11b is offline airborne11b  United States
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Quote:
Originally Posted by Gaz2613 View Post
New toy courtesy of Andrew at SparkoS Labs. Will be submitting a write up on my site in the coming weeks. This PSU is configured for (+/-) 18V which is perfect for another Linestage build.

It is designed to take the monolithic 78xx and 79xx regulators and this one comes with the SparkoS ultra low noise discrete regulators which should make this one quiet power supply.
Excellent write up. Looks like an promising line level power supply option!
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Old 16th September 2020, 02:45 AM   #1706
RickRay is offline RickRay  United States
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I need someone with more theory knowledge to help answer a question. I changed R16 from 27k to 90k to increase the gain of line stage. That part works perfectly. Do I need to change the value of C1 from 10pF to approx. 3pF to maintain the same bandwidth or leave it alone?

I really need to figure out how to use a simulator, I know.
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Old 16th September 2020, 01:05 PM   #1707
6L6 is offline 6L6  United States
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Wayne's BA 2018 linestage
Don’t change the cap.
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Old 16th September 2020, 02:31 PM   #1708
RickRay is offline RickRay  United States
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Originally Posted by 6L6 View Post
Donít change the cap.
Thanks 6L6!
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Old 16th September 2020, 11:02 PM   #1709
avdesignguru is offline avdesignguru  United States
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Default BA2018 evaluation as a headphone amp

I finally got around to converting my BA2018 to large outputs, including the recommended R11, R12, R23 and C1 changes. I also added a switching headphone jack. The result certainly has plenty of drive, and pretty good sound quality, better than most of my other headphone amplifiers. It has about the same clarity and tonal balance as my Whammy when it is fitted with a good monolithic opamp such as the OPA1656ID. That was a surprise, given the discreet front end in the BA2018. That leads me to surmise that the sound of the BA circuit is the sum of its stages. The Whammy with a Burson V6 Classic installed does outperform the BA2018 in terms of detail, openness, and especially overall smoothness and listenabilty on a variety of headphone types.

Maybe it's just my particular power amp inputs but the switching HP jack creates a extremely loud and nasty momentary buzz in the loudspeakers while plugging in the headphones with the amplifier on. Yes, it's easy enough to power down the amp but it does seem to partially defeat the purpose of a switching jack. Referring to Mark Johnson's Noir HPA circuit, I even tried adding some 100 ohm resistors in series with the pre out signal and some 220K load resistors from center pin to shell on the pre-out RCA jacks but it didn't help. I don't see an alternative to powering down the amp other than adding some other switching scheme to short the power amp inputs when they are not in use and prior to HP plug insertion. Shorting the inputs would be necessary since there is low level hum and buzz from the power amp connection cabling when it is not connected to the rest of the internal BA2018 circuitry. Dead silent when connected.
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Old 17th September 2020, 01:26 AM   #1710
wirewiggler is offline wirewiggler  United States
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You could use a selector switch, i plan on building mine with the high outputs to drive headphones as well. I ordered a Glass audio 3 pos selector switch and found i already had one maybe it is fate Amp1-Amp2-Headphones.
Bill
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