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M2 inspired balanced output preamp idea
M2 inspired balanced output preamp idea
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Old 16th February 2019, 08:36 PM   #1
woofertester is online now woofertester  United States
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Default M2 inspired balanced output preamp idea

An Aleph30 is sitting on a shelf awaiting a balanced output preamp.

Also sitting on a shelf are the parts for an M2 and some of the pcbs in the attached pictures. The buffer PCBs were acquired from eBay. They have a ridiculously wide frequency bandwidth.

The idea is to have one buffer channel driving an M2 Edcor transformer and a pair of buffer channels buffering the balanced output of the Edcor transformer.

Today I set up an Edcor PC600-15k using a sig gen and a scope. Driving 1/2 of the 600 ohm input and measuring across the 15k winding there is a voltage gain of approximately 9.5 and a -3dB bandwidth of 18Hz to 25 KHz with the output unloaded and the input driven by a 50 ohm sig gen.

Interestingly, the voltage gain is nearly identical to a BA3 preamp that I am finishing for a long-time friend. The parts cost for the M2 inspired preamp will be much less than the parts cost for the BA3 preamp.

Any comments/questions/suggestions are welcomed. Execution of this idea will have to await finishing the BA3 preamp and acquiring or re-purposing some enclosures.
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Old 16th February 2019, 08:40 PM   #2
Zen Mod is offline Zen Mod  Serbia
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M2 inspired balanced output preamp idea
care to cover that story with some schmtc ?

can't grasp are you talking about autoformer or xformer arrangement

though , through some fun I had making Iron Pre and Iron Pumpkin , I have a strong feeling that you need buffer(s) just in front of iron , no need after
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Old 16th February 2019, 08:45 PM   #3
BeardyWan is offline BeardyWan
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watching closely..
I have been blundering about using this buffer in Spice (and largely unsuccessfully transcribing from virtual to real). Each board is a two channels and my intent was to use one channel to drive the autoformer and the second as a buffer to drive some current for a big 2Sk180 configured as a choke loaded source follower. A kluged buffered version of the SIT-3 Nelson posted. Its on hold pending more and understanding.
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Old 16th February 2019, 09:18 PM   #4
woofertester is online now woofertester  United States
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Quote:
Originally Posted by Zen Mod View Post
care to cover that story with some schmtc ?

can't grasp are you talking about autoformer or xformer arrangement

though , through some fun I had making Iron Pre and Iron Pumpkin , I have a strong feeling that you need buffer(s) just in front of iron , no need after
Not autoformer. The autoformer gives you gain of N + 1. For me, N by itself is good enough... and ... I want the input isolated from the output.

So.. it is very simply

unbalanced input => buffer pcb => Edcor => buffer pcb balanced => output

I agree that output buffer is not required. Output buffer is only required if there is a need to drive a low impedance load.

You could call this an unbalanced to balanced converter with voltage gain.

One note is that there will be zero negative feedback which will make this preamp Zen-ish.

You could do this idea with B1 buffers.
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Old 16th February 2019, 09:26 PM   #5
woofertester is online now woofertester  United States
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Quote:
Originally Posted by BeardyWan View Post
watching closely..
I have been blundering about using this buffer in Spice (and largely unsuccessfully transcribing from virtual to real). Each board is a two channels and my intent was to use one channel to drive the autoformer and the second as a buffer to drive some current for a big 2Sk180 configured as a choke loaded source follower. A kluged buffered version of the SIT-3 Nelson posted. Its on hold pending more and understanding.
These buffer PCBs work well. You could apply + / - 40V with no problem making them useful with an OPS power supply.

The cost of finished working PCBs is so low that it is silly to acquire all the parts and assemble yourself. Unless that is what you love to do.
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Old 16th February 2019, 09:47 PM   #6
Mark Johnson is offline Mark Johnson  United States
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M2 inspired balanced output preamp idea
Calculate the output impedance of the preamp. How much capacitance can it drive without damaging the HF response? How many feet of interconnect cable is that? What happens when you connect a solid state power amp whose input impedance is 10K ohms, at the far end of a 5 meter interconnect cable?
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Old 16th February 2019, 09:49 PM   #7
Zen Mod is offline Zen Mod  Serbia
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M2 inspired balanced output preamp idea
my recent musings :

What's wrong with the kiss,boy ?

that one hope to be soon in Store

also Iron Pumpkin(s) and other smaller vegetable animals

practically , idea is old as ..... xformer



plenty of buffer iterations around , same as plenty of possible Iron candidates

so , fun guarranteed
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Old 17th February 2019, 03:46 AM   #8
PKI is offline PKI  United States
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M2 inspired balanced output preamp idea
Quote:
Originally Posted by woofertester View Post
An Aleph30 is sitting on a shelf awaiting a balanced output preamp.



Also sitting on a shelf are the parts for an M2 and some of the pcbs in the attached pictures. The buffer PCBs were acquired from eBay. They have a ridiculously wide frequency bandwidth.



The idea is to have one buffer channel driving an M2 Edcor transformer and a pair of buffer channels buffering the balanced output of the Edcor transformer.



Today I set up an Edcor PC600-15k using a sig gen and a scope. Driving 1/2 of the 600 ohm input and measuring across the 15k winding there is a voltage gain of approximately 9.5 and a -3dB bandwidth of 18Hz to 25 KHz with the output unloaded and the input driven by a 50 ohm sig gen.



Interestingly, the voltage gain is nearly identical to a BA3 preamp that I am finishing for a long-time friend. The parts cost for the M2 inspired preamp will be much less than the parts cost for the BA3 preamp.



Any comments/questions/suggestions are welcomed. Execution of this idea will have to await finishing the BA3 preamp and acquiring or re-purposing some enclosures.


Would you mind sharing a link for those buffer boards on eBay?
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Old 17th February 2019, 03:50 AM   #9
woofertester is online now woofertester  United States
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Originally Posted by PKI View Post
Would you mind sharing a link for those buffer boards on eBay?
As requested

JFET input Cascoded Buffer Preamp Board use of Toshiba 2SK246/2SJ103, C2240/A970 699970145561 | eBay
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Old 17th February 2019, 04:03 AM   #10
PKI is offline PKI  United States
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M2 inspired balanced output preamp idea
thank you!
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