I need a little help deciding what values of resistance I should use for the buffering transformers, and volume/balance pot for a passive preamp.
It will be driving a 12 foot long interconnect to a modern SS amp.
My dac and phonostage have standard outputs.
What would you'all recommend?
It will be driving a 12 foot long interconnect to a modern SS amp.
My dac and phonostage have standard outputs.
What would you'all recommend?
To put buffering transformers, and volume/balance pot in the power amplifier and make it an integrated amplifier. Put sources near the amplifier too. Gone are 103 3/16 nose lengths of cable and 4 connectors.
With such a cable length one should use active buffering which seems counterproductive with the desire to go passive.
With such a cable length one should use active buffering which seems counterproductive with the desire to go passive.
Last edited:
I bet your DAC and Phonostage can EASILY drive any 12 foot decent cable.
Do not destroy that perfect signal path with a clunky lonely pot in a metal box, plus the unneeded added connectors, surface contact, etc.
Do not destroy that perfect signal path with a clunky lonely pot in a metal box, plus the unneeded added connectors, surface contact, etc.
A decent attenuator integrated into the amplifier will work much better, as mentioned.
You need a low impedance source to drive a long cable. All my circuits have line level outputs are 47 ohm, set by a resistor.
I have a dac that has a 400 ohm output impedance and it works fine driving a 2 foot cable. Even a 10K pot will have what, over 2K output at some settings I think. With a long enough cable, you will actually hear the tonal balance change with the attenuator setting.
You need a low impedance source to drive a long cable. All my circuits have line level outputs are 47 ohm, set by a resistor.
I have a dac that has a 400 ohm output impedance and it works fine driving a 2 foot cable. Even a 10K pot will have what, over 2K output at some settings I think. With a long enough cable, you will actually hear the tonal balance change with the attenuator setting.
What solid state amp are we talking about here?
What is that amp's input impedance? Is that known?
What is that amp's input impedance? Is that known?
OK. So the deal is that I am trying to place a seperate amp between my speakers for a shorter speaker cable run, as well as being the only place I can put it.
The amp will sit behind my desk making it difficult to reach.
I want to use a completely neutral and transparent preamp. A passive is the only way I know to achieve this other than a more expensive clone of a Pass B1.
The amp will either be a clone of a Pass Aleph 30 (most likely), or a clone of an FM 711.
The amp will sit behind my desk making it difficult to reach.
I want to use a completely neutral and transparent preamp. A passive is the only way I know to achieve this other than a more expensive clone of a Pass B1.
The amp will either be a clone of a Pass Aleph 30 (most likely), or a clone of an FM 711.
What constitutes "neutral and transparent"?
No harmonic distortion or intermodulation distortion, no added noise, and completely flat frequency response through the audio frequency range?
Or is it something different from that?
A well-chosen op-amp configured as a unity gain buffer or perhaps with 6dB (2x) gain can both operate with no audible THD, IMD or noise, and also drive whatever kind of cable run you need. It would also provide a high impedance (light) load on any good potentiometer you want to use for a volume control.
Pass B1 is a simple nJFET source follower with nJFET active load. It's a simple unity gain buffer with a 25k ohm volume pot in front of it. The B1 buffer has high input impedance, low output impedance, can sink enough current into its load to drive long cable runs, and provides no voltage gain. You could make a buffer with tubes too (cathode follower with active load).
A single dual-op-amp like LM4562 would do the job better, cheaper, and easier, with lower distortion and noise to boot (LM4562 is unity gain stable). But I do understand there's more to getting the sound you like than simply obtaining the lowest possible distortion and noise. (Or is there? I don't know.)
--
Last edited:
I don't like the sound of naked opamps (class ab, tons of feedback).
To me, transparent means no added brightness or fatigue, with a grainless holographic presentation.
Did you'all recall my mention of transformers for buffering (before the volume pot high impedance, after, low impedance). Will this not work?
I actually prefer my components to be on the warm and sweet side. I just haven't figured out how to make a tube pre (such as a Marantz 7) work for my situation.
To me, transparent means no added brightness or fatigue, with a grainless holographic presentation.
Did you'all recall my mention of transformers for buffering (before the volume pot high impedance, after, low impedance). Will this not work?
I actually prefer my components to be on the warm and sweet side. I just haven't figured out how to make a tube pre (such as a Marantz 7) work for my situation.
As mentioned previously, a triode (tube) cathode follower would do the job you're asking for.
For less money, the Pass B1 could be put together using less expensive JFETs and it wouldn't suffer much in the performance department. Remember, there's no voltage gain. Basically, the B1 is a cathode follower made with nJFETs. That's it. Why not just build one? It doesn't look difficult, and Pass Labs DIY is selling the PCB with matched LSK170s for $40. Give it a simple +19VDC laptop power supply and it could work with that. Or build a simple linear DC supply.
A Marantz 7 would not be the right tool for the job. It was designed to work into vintage tube amplifiers like the Marantz 8b, which had much higher input impedance (usually >100k ohms, sometimes much higher than that). It also has a fair amount of gain, which probably would just add noise to your setup.
artosalo and I have discussed some low gain tube line preamps over the years. They're lurking in old threads here on diyAudio.
For less money, the Pass B1 could be put together using less expensive JFETs and it wouldn't suffer much in the performance department. Remember, there's no voltage gain. Basically, the B1 is a cathode follower made with nJFETs. That's it. Why not just build one? It doesn't look difficult, and Pass Labs DIY is selling the PCB with matched LSK170s for $40. Give it a simple +19VDC laptop power supply and it could work with that. Or build a simple linear DC supply.
A Marantz 7 would not be the right tool for the job. It was designed to work into vintage tube amplifiers like the Marantz 8b, which had much higher input impedance (usually >100k ohms, sometimes much higher than that). It also has a fair amount of gain, which probably would just add noise to your setup.
artosalo and I have discussed some low gain tube line preamps over the years. They're lurking in old threads here on diyAudio.
Last edited:
Read the description of this one.
https://m.aliexpress.us/item/325680...lgo_pvid=f1ac1cb2-819e-4e0e-bec2-259b9b321f32
https://m.aliexpress.us/item/325680...lgo_pvid=f1ac1cb2-819e-4e0e-bec2-259b9b321f32
You know... That's excellent advice. Just give it a try. It won't hurt anything. It might be good enough.
OK. I am going with the Pass Aleph 30 clone, and thinking about integrating the volume and balance control + a possible loudness eq circuit if I don't go with the seperate equalizer that I will need to purchase for my tube headphone amp.
I will also be using a seperate input selector unit.
I have been looking for a volume pot with integrated balance control, but can only find pots with silver contacts (yuck!).
I will also be using a seperate input selector unit.
I have been looking for a volume pot with integrated balance control, but can only find pots with silver contacts (yuck!).
What impedance value would the volume and balance pot need to be if I integrated it into the amp?
For the volume pot 10k would be fine, if your sources can all drive a 10k load.
With a long cable, use a low capacitance cable like expanded polyethylene.
The balance control could be a mono 10k linear pot with its wiper grounded,
and connected between the volume pot wipers. For a more narrow range of balance adjustment
add a resistor between the balance control and each wiper.
Attachments
Last edited:
What about the balance pot?
I use Cardas Hexlink Golden 5C clones (from Aliexpress).
They sound as good as I have heard from a single-ended copper interconnect.
I couldn't tell you what its specs are.