The Neurochrome 1ET400A/NC500 Input Buffer was reviewed by Positive Feedback: https://positive-feedback.com/audio-discourse/neurochrome-purifi-1et400a-hypex-nc500-input-buffer/ They seem to like it. 🙂
Tom
Tom
Hey tom,
Question have you ever considered taking the input buffer from your darn good 300b amp and pairing it with your LM3886 Done Right? I know you no longer do tube amps, but there are several amps in the market that have been well received that use class D with some sort of tube buffer. Amps like the billi amp or vtv with their custom input buffers.
I don’t know if that would be even possible, but it seems like a fun project.
Anything is possible and it would be a fun project. The main challenge with tube circuits is the power supply. You'd need a power transformer that can provide a few hundred volt for the tube section and ±30 V for the LM3886 ... or you would have to run the tube section on ~60 V (so from V+ to V-). Maybe one can find a tube that'll run well on such low voltage. If not, you're looking at having a custom transformer made or somehow generating a few hundred volt from ±30 V.
All of this is a solvable problem. I'm sure Toroidy in Poland would be happy to help with the transformer. I can handle the rest. The big question is then whether people would be willing to fork over big bucks for a custom transformer. Another big question is how I would position it relative to my other products. I've positioned myself as a provider of high-performance circuits, which, to me, means low distortion, low IMD, low noise, etc. A tube circuit whose purpose is to add distortion would stand out like a sore thumb.
Then again, maybe there are other avenues where such a circuit could be made available as a fun weekend project.
Tom
All of this is a solvable problem. I'm sure Toroidy in Poland would be happy to help with the transformer. I can handle the rest. The big question is then whether people would be willing to fork over big bucks for a custom transformer. Another big question is how I would position it relative to my other products. I've positioned myself as a provider of high-performance circuits, which, to me, means low distortion, low IMD, low noise, etc. A tube circuit whose purpose is to add distortion would stand out like a sore thumb.
Then again, maybe there are other avenues where such a circuit could be made available as a fun weekend project.
Tom
I think my question was more of a curiosity. I feel like the dishwasher making recipe recommendations to the chef.
I am just curious on how VTV or the bill amp have something like that in their designs.
it looks like the VTV amp adds Vacuum Tube Buffer using 6922 vacuum tube to the 1ET400A modules. https://vtvamplifier.com/product/vt...et400a-amplifier-with-vtv-vacuum-tube-buffer/
The billi amp is an integrated amp I think that is using ice power modules with a ECC99 tube pre-amp. https://heaven11audio.com/billie-amp-stereo-intergrated-amplifier/
Both of these have received some praise by some Youtube reviewers.
Separately, I have seen that the Fosi Audio V3 has received a lot of attention, in particular the fact that you can swap the OPAMP to change the sound signature. that one is TPA3255 design not a 3886.
I am not a business person to say how your product fits within your product line up.
I think of your 686 as a Porsche 911. Sophisticated, error correction tech “dream car” type of product. Certainly the 911 and its performance gives them great marketing copy, so that Porsche can then sell millions of grocery pushers SUV’s.
The LM done right is the solid line up starter. Its the fun Toyota 86, a small rear wheel drive sports car with good stock performance. However, it can be an excellent canvas for trial, experimentation, and modification.
I guess in the end its always possible that you can build a LM3886 power amp, and put whatever you want as a pre-amp.
Thanks again for the reply Tom, I appreciate your response.
PS: I just very recently got into the hobby and I stand neither in the Single Ended Triode or nothing, or the if it doesn't have .000000000000001 THD, I don't want it camp. Most of my current listening is thru a budget AVR and a AIYIMA T9.
Jose
The 6922, ECC99, ECC88, and 6SN7 would be tubes I'd look at. There are several topologies that would make for good buffers: SRPP, anode follower, etc. It looks like VTV powers the tube buffer from the ±65 V supply for the Class D amp. That gives them 130 V to work with which is enough for many tubes.
Adding a tube buffer to the LM3886DR would require a different power supply for reasons I outlined above unless a tube circuit that can run on ±30 V can be designed.
I'm not in the "if it's not 0.0000000000001% THD I'm not interested" category either. The reason I push for low THD is that it brings with it improvements on a wide range of other parameters too. I love pushing the performance to the limit. That's how I have fun. If I found tube design to be fun and a better fit for my business I'd do more of it.
Tom
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Thanks for the wisdom! I saw your email that you are going to be attending the Burning amp. Are you presenting?
Hi Tom,
I would like to add a volume control to my Input Buffer + Purifi 1ET400A feeding it with an unbalanced (RCA) signal.
I was thinking about the ALPS RK27 Stereo Motorized Potentiometer Smooth Cylindrical Shaft XXX kOhm.
I'm wondering if you would recommend the 10k, 50k or 100k version for your Input Buffer.
I appreciate any advice from you.
Thanks!
I would like to add a volume control to my Input Buffer + Purifi 1ET400A feeding it with an unbalanced (RCA) signal.
I was thinking about the ALPS RK27 Stereo Motorized Potentiometer Smooth Cylindrical Shaft XXX kOhm.
I'm wondering if you would recommend the 10k, 50k or 100k version for your Input Buffer.
I appreciate any advice from you.
Thanks!
Tom, when Purifi input buffer will be in stock again?
In case pcb boards will get any changes...would be possible to change op amp socket from SOIC to DIP (Sparkos 😎)?
thx
In case pcb boards will get any changes...would be possible to change op amp socket from SOIC to DIP (Sparkos 😎)?
thx
The next batch is currently in production. I expect to have more available by January 17. I made no changes to the circuit.
Note that some discrete opamps are only conditionally stable at gains above unity. This means that if you use them in a circuit with gain, such as the Purifi/Hypex Buffer you'll get pretty crappy transient response. I forget if Sparkos is one of those but it's easy to check. If the slope of the AVOL curve is -40 dB/dec the amp is conditionally stable at gains other than unity gain.
Tom
Note that some discrete opamps are only conditionally stable at gains above unity. This means that if you use them in a circuit with gain, such as the Purifi/Hypex Buffer you'll get pretty crappy transient response. I forget if Sparkos is one of those but it's easy to check. If the slope of the AVOL curve is -40 dB/dec the amp is conditionally stable at gains other than unity gain.
Tom
VTV puts a 14-pin connector on the 10-pin ribbon cable for some obscure reason. You'll have to add two 10-pin connectors. That's pretty easy. You just feed the cable through and press down on the clamping piece. Just make sure all the wires line up with the corresponding forks in the connector.
I think you may have to rewire the XLR connectors, but that's pretty easy as well.
Then just drill the four holes for mounting the board.
Tom
I think you may have to rewire the XLR connectors, but that's pretty easy as well.
Then just drill the four holes for mounting the board.
Tom
Hi Tom!
I'm making final checks before connecting my speakers to the buffer.
I provide a 432Hz signal with ~ 1VRMS to the buffer input using RCA input and measure the output signal.
The DC is ~20mV and AC is ~ 80mV no matter what volume level I set.
Today I checked my SMPS voltage and it's as expected, including the AUX voltage.
Could you please check if my wires connection is correct?
Also, what pins can I measure voltage to check if my buffer/amplifier is not damaged?
Thanks!
I'm making final checks before connecting my speakers to the buffer.
I provide a 432Hz signal with ~ 1VRMS to the buffer input using RCA input and measure the output signal.
The DC is ~20mV and AC is ~ 80mV no matter what volume level I set.
Today I checked my SMPS voltage and it's as expected, including the AUX voltage.
Could you please check if my wires connection is correct?
Also, what pins can I measure voltage to check if my buffer/amplifier is not damaged?
Thanks!
You should be able to find the AUX voltage here:
You should also have +12 V at U1, pin 8 and -12 V at U1 pin 4.
The input is connected correctly, assuming you have the RCA center connected to pin 2 of the input connector. I obviously can't tell how you have the rest connected.
Tom
You should also have +12 V at U1, pin 8 and -12 V at U1 pin 4.
The input is connected correctly, assuming you have the RCA center connected to pin 2 of the input connector. I obviously can't tell how you have the rest connected.
Tom
I had a splitter for the J10 to feed both channels from the same SMPS.
I removed this splitter and connected one channel directly.
AUX voltage on jumpers became 12V and -12V
When I increase volume on my iPad phone connector voltage on the speaker connectors is 1.2VAC.
Could I burn my Purifi module based on your experience? 🙂
Probably not. The modules are pretty rugged and also have some built-in protections against over/under-voltage and that sort of stuff. In fact, a customer of mine accidentally reversed the polarity of the ±65 V power supply. The amp modules survived but the power supply didn't.
I'd examine that splitter and see what went wrong with it. I do offer an SMPS Splitter to make life a bit easier for you.
Tom
I'd examine that splitter and see what went wrong with it. I do offer an SMPS Splitter to make life a bit easier for you.
Tom