Buffer.

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pre65
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#1 Buffer.

Post by pre65 »

With the MoFo amps, my Audionote copy pre works well, but the passive pre (with chip volume control) does not have enough drive, so I got thinking about a buffer of some sort.

All the cheapo Ebay kits are preamp/buffers with volume control, which I don't need, or want.

So, I have choices.(not necessarily in order)

1) find a circuit and make something.

2) Buy one secondhand.

3) Borrow one to see it a buffer does what I want.

Any suggestions or recommendations ?
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Nick
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#2 Re: Buffer.

Post by Nick »

A "buffer" suggests unity gain, so you need something with gain.
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#3 Re: Buffer.

Post by pre65 »

Nick wrote: Wed Jul 15, 2020 2:21 pm A "buffer" suggests unity gain, so you need something with gain.
OK, so what is the norm to give a passive pre "drive capability" ?

What is the difference between a buffer with gain, and a pre amp ?
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#4 Re: Buffer.

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OK, so what is the norm to give a passive pre "drive capability" ?
Not sure what the norm is, but I guess a buffer. Depends what you mean by "drive capability" that’s not a well defined term. I guess you mean "more drive capacity"
What is the difference between a buffer with gain, and a pre amp ?
Basically nothing. Though strictly speaking if a buffer is a unity voltage gain device with current gain. So "buffer with gain" is confusing,

I think given that your amplifier has slightly less than unity voltage gain as a source follower, if you need more volume from a given source you need more voltage gain.

Names and words can be problematic, There are precise ways of describing things for a reason.
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#5 Re: Buffer.

Post by Ray P »

Phil, If you check out the MoFo thread on DIY Audio you'll see a common theme of people using voltage gain stages in front of their MoFos.
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#6 Re: Buffer.

Post by ed »

Phil,
with the greatest respect..if you asked those questions on another diy audio forum I can guess that you would be howled out for asking other people to do all the work for you....

at the same time it's acknowledged that there is no such thing as a stupid question as all answers to all questions will be informative to some readers.....

moving on...to get a flavour of the sound of my mofo I put a fairly hi-class opamp in front with a gain of 3. Thats about as easy a test as you could do and it would give you a feel for whether you want to put some real effort into a better gain stage.

As Ray has pointed out, there are a number of well regarded hi-gain front ends on diyaudio.
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#7 Re: Buffer.

Post by Ray P »

Phil, somewhere I saw on the MoFo thread (on DIY Audio) reference to the input voltage required to drive the MoFo (I think based on the original build) - if you can find that you'll be able to deduce how much gain you required after your source. I know that for my own situuation I have the figure of 20dB gain lodged in my memory banks.

Alternatively, you could just go empirical and buy a cheap pre-amp off ebay to start with (though most of the listings don't seem to mention gain!), for example (can't vouch for the quality though);

https://www.ebay.co.uk/itm/OPA2604-Serv ... 1438.l2649

For something a little more refined as a starting point, I seriously considered using one of these in front of a MoFo (10x gain = 20dB)

https://jimsaudio.com/tube-stereo-pream ... assembled/

but then I realised I had many of the parts needed for a 4P1L gain stage using the Bartola Siberian (G4) schematic (19dB gain)
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#8 Re: Buffer.

Post by Nick »

Or just use the preamp he already has.
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#9 Re: Buffer.

Post by Ray P »

Nick wrote: Thu Jul 16, 2020 9:48 am Or just use the preamp he already has.
Given the topic, I assumed he didn't have one?
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#10 Re: Buffer.

Post by steve s »

Reading through what your saying Phil, does your passive pre sound better than your audio note copy through the mofo?
Just not enough gain
I would guess the sound of the mofo is easily diluted with pre amp/driver stage choice
I evaluated mine initially with no pre, just using the output from the cd/dac. That told me what the mofo stage sounded like, . the overall sound of amplifier stage can easily be changed by what is used with
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#11 Re: Buffer.

Post by Nick »

Ray P wrote: Thu Jul 16, 2020 9:50 am
Nick wrote: Thu Jul 16, 2020 9:48 am Or just use the preamp he already has.
Given the topic, I assumed he didn't have one?
From first post "With the MoFo amps, my Audionote copy pre works well"
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#12 Re: Buffer.

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#13 Re: Buffer.

Post by pre65 »

Sorry if I've confused anyone.

The MoFo's and my Audionote (copy) pre are simply a match made in heaven. :D

But, as I have other pre's it would be nice if they were capable of driving the MoFo's as well, so the buffer idea is still active (pun).

I also have a World Designs Pre3, and I'll try that tomorrow and see if it still misbehaves itself. If it performs I must make an effort to get the fault sorted.
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#14 Re: Buffer.

Post by Paul Barker »

Phil you must be losing youre ability to follow a logical path or youve got time to waste on stupid plans.
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#15 Re: Buffer.

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Paul Barker wrote: Thu Jul 16, 2020 8:42 pm Phil you must be losing your ability to follow a logical path or you've got time to waste on stupid plans.
Maybe Paul, maybe I should pass on buffers and put some effort into making the MoFos more presentable, OR make a proper start on rejuvenating the 833a (GU48) project which I would like to finish before Mr G Reaper comes my way. :lol:
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