Cool, thanks Tom. I’ve designed a selection / volume control board with two buffers - one can be connected to one of six inputs, three balanced and three SE. The logic that controls the input selection also controls a relay that switches buffer between balanced and SE modes. I’ve also included a brief mute period when changing selections to counter anything generated when switching mode.
For info the SE output of the buffer is then run through a relay based volume control and then to the second buffer to provide both SE and balanced outputs.
Perfect. Sounds like a fun project.
BTW: Douglas Self has an excellent chapter in his Small Signal Audio book about quiet signal switching and muting. If you haven't already, I suggest flipping through that.
Tom
BTW: Douglas Self has an excellent chapter in his Small Signal Audio book about quiet signal switching and muting. If you haven't already, I suggest flipping through that.
Tom
Last edited:
What a way to find out my source wasn't happy driving a 10k potentiometer!
Just finished my new preamp. Universal buffer - 10k potentiometer - That driver.
Crazy bass power extravaganza!
I am totally happy with this one, didn't think this would happen at all.
Just finished my new preamp. Universal buffer - 10k potentiometer - That driver.
Crazy bass power extravaganza!
I am totally happy with this one, didn't think this would happen at all.
Still sounds great after work!
The case used to be a dlink switch. I have a lot of those cases around since I gut them for the PCB which we use in our multi link gateway device.The front plate was found in a pile of ruble at work. It was predrilled which you might see. Pictures of the innards will follow.
The case used to be a dlink switch. I have a lot of those cases around since I gut them for the PCB which we use in our multi link gateway device.The front plate was found in a pile of ruble at work. It was predrilled which you might see. Pictures of the innards will follow.
Attachments
Nice toroid transformer.
I'm not sure I like the control approach for the pot and sector switch; what was your aesthetic concept for them?
😊 Thank you!
The concept was, Corona home office without straight edge and much other than files and a power drill.
The concept was, Corona home office without straight edge and much other than files and a power drill.
One of the things you might consider when using an 'over-sized' transformer is to add some 'dummy-load' to increase the current consumption - I know it sounds a bit weird but sometimes this helps the whole power supply and active system to function better - it's simple to add a 'soaker resistor' (of the appropriate power rating) to check this out for yourself - it's one of the reasons why shunt regs work so well with light loads.
Thank you, I will try that before I swap out the psu for a Silent switcher which currently resides in my other preamp (Tom's That driver sans Universal buffer)!
I really don't like the thought of killing my previous creation, that case and construction is the best I can manage at this point. I'll post pics after work.
There is a That driver board in there along with a rk27 motor potentiometer and remote control pcb. And a silent switcher. If I could fit the universal buffer in there tas well, I would. A couple of extra inputs would also be nice.. I don't know. Two preamps I can't put to use.
Attachments
I am very happy with this compact build. Perhaps it would be better to stack the universal buffer on top of the That driver board using angles and standoffs.
I could put a second pair of phono inputs on the back and use a toggle switch for source selection.. I can't decide right now it seems.
To qualify my previous statement of great bass, the difference can only be heard when playing vinyl. My network player sounds the same with or without universal buffer. Works as it should, one could say. I suspected that my phono preamp could not drive the 10k potentiometer. That's fixed now.
I could put a second pair of phono inputs on the back and use a toggle switch for source selection.. I can't decide right now it seems.
To qualify my previous statement of great bass, the difference can only be heard when playing vinyl. My network player sounds the same with or without universal buffer. Works as it should, one could say. I suspected that my phono preamp could not drive the 10k potentiometer. That's fixed now.
Forgot the picture. The pics look like they do because of me posting with a cellphone
Attachments
Last edited:
Hey Tom,
I know you recommend a load of around 10K but what’s the lowest impedance the buffer will comfortably drive?
I know you recommend a load of around 10K but what’s the lowest impedance the buffer will comfortably drive?
I know it seems to drive the Purifi modules quite fine. And they have something like 4K input impedance.
The Universal Buffer can comfortably drive a 600 Ω load. I'm sure it'll drive heavier loads as well, but maybe not comfortably. Do note that the THD rises with heavier load, so I recommend loads of 1-2 kΩ or higher for the best performance.
I recommend a 10 kΩ volume pot (or 5 kΩ if you can find one). That's probably where the 10 kΩ number comes from. That recommendation is based on an optimization for lower noise. I'd go with a 2 kΩ pot if I could find one. The lowest resistance ALPS RK271 is 5 kΩ and it's special order from ALPS. That's what I use in my HPA-1.
Tom
For those planning to use the Universal Buffer as part of a high-end preamp, I now offer this low-noise power supply: Preamp Power Supply – Neurochrome
I have started a separate thread for the Preamp Power Supply: https://www.diyaudio.com/forums/ven...reamp-power-supply-12-650-ma.html#post6259992
The power supply is currently on intro sale at $139. The sale will end, and the price increase to $159, once I receive the first batch of supplies from my assembly house.
Tom
I have started a separate thread for the Preamp Power Supply: https://www.diyaudio.com/forums/ven...reamp-power-supply-12-650-ma.html#post6259992
The power supply is currently on intro sale at $139. The sale will end, and the price increase to $159, once I receive the first batch of supplies from my assembly house.
Tom
Attachments
My UB Board arrived today! Very fast, even with the cheapest shipping option!!!
As I already know, that you like questions about <b>Gain</b>, here's one more:
I'd like to connect a little switch, to change the Gain, eg. from non to 6db so from open to 1k Ohm. What I want to know here:
- is there a preferred type, non inductive, wirewound....
- should the resistor R8/R24 for the Gain be close to the location on the board
(- or is it safe to run a cable to the switch and back)
- can one hot plug this resistor
Thanks, greetings,
Jan
As I already know, that you like questions about <b>Gain</b>, here's one more:
I'd like to connect a little switch, to change the Gain, eg. from non to 6db so from open to 1k Ohm. What I want to know here:
- is there a preferred type, non inductive, wirewound....
- should the resistor R8/R24 for the Gain be close to the location on the board
(- or is it safe to run a cable to the switch and back)
- can one hot plug this resistor
Thanks, greetings,
Jan
A regular metal film type is preferred.
You can run a cable to a switch. Keep it short and don't run it past transformers or rectifiers.
You can flip the switch with the power on, if that's what you mean.
Pardon my belated response. I actually don't mind questions. What I do mind is when someone flies in out of nowhere, takes a public dump on everything I've accomplished, bosses me around, and leaves. That's what you saw earlier in this thread.
I have the parts necessary for the THD vs gain measurements. I'm currently working to improve my THD measurement capabilities so I can measure the difference, assuming there is a difference. I can certainly spend my time generating a THD+N vs gain plot on my current setup, but I guarantee you that it will simply show the THD+N floor of my setup. That's not very exciting. So I would rather improve my setup and post valid data once and for all. I don't enjoy doing the same work twice. It's probably a good two days of work once I get the setup running. If it was a "push a button and wait five seconds" task, I would have done it already.
Tom
Last edited: