hbadger:
Absolutely, but rather than my blathering on it might be helpful if you asked specific questions. Your follow-up post and your very recent join date suggest that you may be new to DIY audio; if so, there's a lot to learn and much context in which to store that information. You'll find that people are quite generous here at diyAudio.
I'm no expert and my BA2018 preamp was actually a rather simple project; I cheated in buying a pre-built system that handles attenuation and source selection (and includes a nifty display), mostly because I wanted to try out the MUSES attenuator (which is fantastic). My write-up on the Pass Pictures thread will provide some details that may be helpful to you and I'm happy to provide other information, including the .fpd files I created for the front and rear panels. My version of the BA2018 was not inexpensive to build but, as I noted in the write-up, I expect to use this as my main preamplifier for a very long time. You could build something quite good for a lot less.
Ask away.
Regards,
Scott
I am still learning, but was playing with some square waves through my BA2018. I read a 680 nS rise time. That equates to a 500 kHz bandwidth, am I way off?
The Risetime - Bandwidth equivalency relationship focuses upon the small signal risetime, far FAR away from slewing. Since Wayne's circuit has a JFET input stage, you'll need an input square wave that switches back and forth between -0.2V and +0.2V, or smaller.
Thanks, Scott, and you're right. I have a few years experience building Eurorack modules, but the world of amps is new, I'm still at the "staring at a box of parts and asking what have I got myself into" stage.
Your writeup on the build thread does answer some of my immediate questions-- the muse display is gorgeous--
Pictures of your diy Pass amplifier -- am I right that you have the PSUs in a different chassis, and then run power via the umbilical to the preamp?
And since you like dual mono, each board of the linestage gets its own power supply plus one for the lights. Could you (or someone else) answer why each channel would need its own PSU?
In euorrack, one power supply is typically shared across a number of modules (like 20 or so), each of which is playing a very separate havoc on the overall power demands of the system. You just put two 10uf caps on each module (one from positive to ground, one from negative to ground) to smooth power delivery to the the individual module. I'm naively expecting that a linestage isn't going to draw that much current (naively also thinking that the amp is the unit with the big current draw), so some smoothing caps should allow two channels to share one PSU without much issue.
hbadger:
If you wanted to keep things simple, a single power supply for a BA2018 would be fine. Quite a few power supplies have been discussed in this thread and any of them would be sufficient to power both channels on the BA2018 board. It just so happens, though, that the board will accommodate separate power supplies. And I like running separate supplies whenever I can. The engineers here may chime in, but my inelegant perspective is that if there's even a remote chance that a peak demand in one channel might starve the other of power, or if using just one power supply raises the possibility of noise affecting both audio channels, then I'd prefer to complicate things with a second power supply. That said, I believe your eurorack experience holds true in audio.
And yes, you are correct that I've built the BA2018 power supply in a separate chassis. A six foot (1.9M) umbilical connects the two enclosures.
If you're considering building a BA2018 as a preamp, are you also thinking about an amplifier to accompany it? If so, I'd urge you to focus on the various FirstWatt options on offer here at diyAudio. Nelson Pass's brilliance in circuit design is complimented by his generosity in allowing us to build his amplifiers, and you would have a very, very hard time finding a more suitable amp to pair with a BA2018.
Just my two cents.
Regards,
Scott
If you wanted to keep things simple, a single power supply for a BA2018 would be fine. Quite a few power supplies have been discussed in this thread and any of them would be sufficient to power both channels on the BA2018 board. It just so happens, though, that the board will accommodate separate power supplies. And I like running separate supplies whenever I can. The engineers here may chime in, but my inelegant perspective is that if there's even a remote chance that a peak demand in one channel might starve the other of power, or if using just one power supply raises the possibility of noise affecting both audio channels, then I'd prefer to complicate things with a second power supply. That said, I believe your eurorack experience holds true in audio.
And yes, you are correct that I've built the BA2018 power supply in a separate chassis. A six foot (1.9M) umbilical connects the two enclosures.
If you're considering building a BA2018 as a preamp, are you also thinking about an amplifier to accompany it? If so, I'd urge you to focus on the various FirstWatt options on offer here at diyAudio. Nelson Pass's brilliance in circuit design is complimented by his generosity in allowing us to build his amplifiers, and you would have a very, very hard time finding a more suitable amp to pair with a BA2018.
Just my two cents.
Regards,
Scott
I'll match your 2c with one of my own
but two power supplies raises the possibility of variance in the power supplied to both channels (unless the two supplies are *exactly* matched), and doubles the odds of getting a noisy power supply in the chain.
Of course it is personal preference, and I have far less experience than you 🙂
Yes, I bought the (Pass) Amp Camp kit and the BA2018 kit, figuring that would give me a good setup. And silly me, I haven't even gotten to the speakers yet... that might have to be a Christmas present.
I may want to build an F7 or some other Pass design in the future; thought it best to start with something easier and where I'll curse myself less over mistakes.
but two power supplies raises the possibility of variance in the power supplied to both channels (unless the two supplies are *exactly* matched), and doubles the odds of getting a noisy power supply in the chain.
Of course it is personal preference, and I have far less experience than you 🙂
Yes, I bought the (Pass) Amp Camp kit and the BA2018 kit, figuring that would give me a good setup. And silly me, I haven't even gotten to the speakers yet... that might have to be a Christmas present.
I may want to build an F7 or some other Pass design in the future; thought it best to start with something easier and where I'll curse myself less over mistakes.
hbadger:
It sounds like you're well on your way. The forums here are resources: if you have questions as you progress through your projects, ask for advice or help. You'll get plenty of feedback, some of it actually helpful.
Good luck!
Regards,
Scott
It sounds like you're well on your way. The forums here are resources: if you have questions as you progress through your projects, ask for advice or help. You'll get plenty of feedback, some of it actually helpful.
Good luck!
Regards,
Scott
Yeah, just some plywood you hammered together, the excellent fit and finish was pure luck.
What are you using for a volume pot? That thing looks like some crazy rotating barrel with individual resistors all over it; the electronic equivalent of steam-punk. Love it!
(also, I'm trying to decide what to use as a volume pot for mine, thus trawling for suggestions. Currently thinking of something from the ALPS RK271 series)
Do a search for "stepped attenuator" to find similar items. I'm going to use an Alps 20k log pot for mine, at least to begin with.
I built my BA2018 with 10X (20dB) of overall gain. KSC2690A (and counterpart) “beefy” outputs, +/- 18VDC bench supply, and with a 410mV PP input, 4.2V PP output, I did a BODE plot analysis and the unit measures flat from < 10Hz up to a -3dB point of 798khz. There was no load on the outputs other than that of the scope which is ~ 1Megaohm.
I can test it with a more realistic load (like 47k ohm), and lower voltages and repeat the analysis if there is interest.
Best,
Anand.
0.8 MHz bandwidth at a gain of 10X means a gain-bandwidth-product of . . . . . pretty darn good.
Hey, thanks, I didn't know stepped attenuators existed.
The Alps pot was my plan as well, but the folks at Goldpot (goldpt.com) think their stepped attenuators are better. All I know is they came up early in the google search results and their website looks authentic 90s' (i.e. they care more about sound design than javascript).
Anyone on the forum have a preference?
@ Anand - Thanks for the measurement. that's what i was trying to do but failing miserably, LOL My signal generator only produces positive square waves, need to upgrade. I was also using too high a signal level as Mark pointed out. I plan to step my boards up to 10X gain also. Have you had a chance to listen to it yet?
There are many highly regarded attenuators/potentiometers around.
Takman are said to be very good, all the attenuators in their varying typologies, and my preference is either
PEC KKA2531S28, 25k; digikey part #KKA2531S28-ND or Muses72320...
I first became aware of stepped attenuators in 1979 from an article in Audio Magazine. A series design, I built (and still use) it in my Leach preamp.
https://leachlegacy.ece.gatech.edu/papers/stepatten/stepatten.pdf
Since then I've seen lots of different designs from ladders to shunts and even a complicated 138-step model from HFNRR in 1991 that featured dual concentric switches.
While you can buy stepped attenuators you can also still roll your own and choose how it behaves from step to step and make it as good (precise) as you can afford. Take a look at the stepped attenuator page at Hi Fi Collective.
Stepped Attenuators | Hifi Collective
https://leachlegacy.ece.gatech.edu/papers/stepatten/stepatten.pdf
Since then I've seen lots of different designs from ladders to shunts and even a complicated 138-step model from HFNRR in 1991 that featured dual concentric switches.
While you can buy stepped attenuators you can also still roll your own and choose how it behaves from step to step and make it as good (precise) as you can afford. Take a look at the stepped attenuator page at Hi Fi Collective.
Stepped Attenuators | Hifi Collective
There are stepped attenuators on eBay that use SMD resistors to pack the attenuator into an extremely small volume. Include the acronym DACT in your search string.