Not yet. It is one of a few linestages that I will be evaluating with my upcoming MOFO build. I am finishing up a Class D build at the moment (Orchard Audio BOSC) and the MOFO is next on the building block.
Best,
Anand.
I have used several of the Chinese ladder pots, sound pretty good for 20 bucks or so.
They are a bit "clunky" feeling turning through the steps.
I find that using a larger knob, (approximately 2 inches) gives more leverage, which makes the pots feel much smoother in operation.
Lately, I have used the Alps blue pots from Parts Express with good results, and affordable pricing.
Russellc
@Jwjarch - he modified the boards to have 10X gain. Should have more than enough voltage to drive anything.
I have 96dB sensitive speakers too. This amp is more experimental and not for high SPL listening at all. I do have a Sony VFET here (closed loop gain of 16dB; 15 watts/8 ohms, 20 watts/4 ohms) and I am achieving 80-85dB SPL at the listening position which is 12 feet away in a room that is 16 feet wide, 26 feet deep and 10.5 feet tall.
I think I was getting close to 29.7VPP on +/- 18V supplies on the BA2018 (set for 10X or 20dB gain) with KSC2690/KSA1220 outputs on a scope (1Mohm input impedance). This should be at least 10 watts with a MOFO that has its own +24V supply.
The best thing to do is to test the whole enchilada when done due to impedance differences on the load side of the BA2018 (I think MOFO input impedance is 200K ohms, not 1 Mohm) and also with an 8 ohm load on the output of the MOFO.
Thanks for your real world experience. I’ll post here with measurement photos when I get mine.
Sharing is caring ;-)
Best,
Anand.
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jwjarch,
Yes indeed. My dac puts out 4.5V RMS which is 12.7VPP. If I were to use only my dac directly into a MOFO, I would get about 2 watts max! Which is fine for very casual listening ;-)
With 12.7VPP, this easily will drive the BA2018 (as I have configured) well into clipping since it only needs 2.97VPP (~ 1.05V RMS) to clip.
So there’s loads of headroom all around. My dac will be loafing and for everything but a 100dB jam session (@the MLP), the MOFO should be fine, so I am good. I forgot to mention that my low end (roughly < 100Hz) is augmented by a quad distributed sub system.
If this MOFO experiment works out I am going to try to build a balanced version with (2) BA2018 and (2) MOFO boards per monoblock. I’ll drill the heatsinks out so that they accept F4 boards as well. We’ll see how much power I’ll get then, although my biggest 8 ohm load resistor I have for testing is only 100watts!
Best,
Anand.
Yes indeed. My dac puts out 4.5V RMS which is 12.7VPP. If I were to use only my dac directly into a MOFO, I would get about 2 watts max! Which is fine for very casual listening ;-)
With 12.7VPP, this easily will drive the BA2018 (as I have configured) well into clipping since it only needs 2.97VPP (~ 1.05V RMS) to clip.
So there’s loads of headroom all around. My dac will be loafing and for everything but a 100dB jam session (@the MLP), the MOFO should be fine, so I am good. I forgot to mention that my low end (roughly < 100Hz) is augmented by a quad distributed sub system.
If this MOFO experiment works out I am going to try to build a balanced version with (2) BA2018 and (2) MOFO boards per monoblock. I’ll drill the heatsinks out so that they accept F4 boards as well. We’ll see how much power I’ll get then, although my biggest 8 ohm load resistor I have for testing is only 100watts!
Best,
Anand.
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couldn't find the right place to ask this question...but is there an alternative to using two board sets to make a balanced in/balanced out line stage. Has anybody done that and have any advice on doing it? I did scan the thread and I found someone else had asked the same question but couldn't find an answer. Two boards isn't a problem because they are compact and I can use a 4-gang ALPS pot or two stereo ones
So on a related note... The linestage requires a 'volume' knob, with the general choice being either a dual-gang pot or a dual-gang stepped attenuator.
The advantage of the stepped attenuator (along with generally better sound quality) is that the resistance is perfectly balanced on both channels (rarely achieved with a dual-gang pot).
Disadvantage is cost.
Missing from this discussion: the "balance" knob. I'm a novice; I'm used to seeing a balance knob on most pre-amps, but don't know the world of high-end audio as well.
So here is what I am thinking:
Instead of one volume knob and one balance knob, why not two volume knobs (one per channel)?
They could both be pots, and this setup means the user could make sure volume was perfectly balanced on both channels.
What are my novice eyes overlooking in what appears to (novice) me as a brilliant solution?
The advantage of the stepped attenuator (along with generally better sound quality) is that the resistance is perfectly balanced on both channels (rarely achieved with a dual-gang pot).
Disadvantage is cost.
Missing from this discussion: the "balance" knob. I'm a novice; I'm used to seeing a balance knob on most pre-amps, but don't know the world of high-end audio as well.
So here is what I am thinking:
Instead of one volume knob and one balance knob, why not two volume knobs (one per channel)?
They could both be pots, and this setup means the user could make sure volume was perfectly balanced on both channels.
What are my novice eyes overlooking in what appears to (novice) me as a brilliant solution?
I have seen some amps that have this, but it sounds like a huge pain in the *** to me.
With a balance knob you can proportionally even out the channels based on your hearing, speaker placement, room interaction, etc. Then once that is set, you can just turn the volume knob without any other steps.
With two volume knobs, you do this balancing act every time you change volume.
1) Stand up, turn the knobs.
2) Sit down. Try to tell if the balance is centered. If not, go back to step one. Maybe multiple times. And maybe by the time you get it right the song is close to over.
I'd much prefer a set and forget balance knob personally! Or upgrade the attenuator if it is a problem (but I've never seen any reason to go beyond a 20€ Alps).
Being a Novice (in a chatty mood) myself, I'd say that you only miss the little details:
If you'd have to adjust the volume totally independently (one volume-knob per channel), you'll rarely be spot on.
To get that comfy-feeling back, I'd suggest you find a way to connect them (like, use a hollow shaft and have the two knobs on one axis, and either make sure you can easily and precisely turn both at once, or mechanically sort of connect the two knobs through friction...
Handling two pots at once doubles the force needed to turn the knob, so you'd be adviced to find a good and very easy-going knob... (or you get mechanic, and use a 1:2 gear, halving the force, doubling the way needed)
Two knobs works very well. Nowhere near as bad as some make it out to be.
If you want balance control, look at this attenuator design of John Broskie's - center coarse and L/R fine, with 12-position switches, not his usual 6.
Attn-1: 100-Decrements Stepped Attenuator
The idea of coarse adjustment/fine adjustment is a bit strange if you haven't used it, I have one, it actually works brilliantly.
Nowhere near as bad as some make it out to be. If you want balance control, look at this attenuator design of John Broskie's - center coarse and L/R fine, with 12-position switches, not his usual 6.
Attn-1: 100-Decrements Stepped Attenuator
The idea of coarse adjustment/fine adjustment is a bit strange if you haven't used it, I have one, it actually works brilliantly.
Thanks everybody for the suggestions...I have used double volume knobs in the past, I once owned a Croft tube pre amp / amp which had two volume controls and Glenn Croft the designer was such a purist/minimalist that there were no markings on the knobs so you had to set everything by ear ( until you put dots on the knobs) It does deal with the absence of a balance control, which I have not seen for many years. The Broskie attenuator seems like an intelligent solution....you set the main volume with the centre knob and tune it with the outer ones , right? 6L6 is right, its not a major PITA to use two controls and it has the advantage of dealing with the uncertainty about whether the sound is properly balanced with a single pot. Many an hour have I spent wondering whether one channel is louder than the other
I used the wiring scheme for a balanced B1 feeding the + signal to one channel and the - signal to the other on the same board, with corresponding outputs going to an output XLR socket. Is there anything I need to do to connect those inputs to the Wayne LS board as it already allows for balanced input to each channel ?
I presume I can run both boards off the same TubeCAD PSU?
Soldering the SMDs wasnt too scary but I was left wondering if those were OK as I soldered in all the other components. Really like the use of terminal blocks on the board, great for tinkering !!
I used the wiring scheme for a balanced B1 feeding the + signal to one channel and the - signal to the other on the same board, with corresponding outputs going to an output XLR socket. Is there anything I need to do to connect those inputs to the Wayne LS board as it already allows for balanced input to each channel ?
I presume I can run both boards off the same TubeCAD PSU?
Soldering the SMDs wasnt too scary but I was left wondering if those were OK as I soldered in all the other components. Really like the use of terminal blocks on the board, great for tinkering !!