comfortINA - the comfortable phono preamp - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 2nd June 2013, 07:25 PM   #1
usul27 is offline usul27  Switzerland
diyAudio Member
 
usul27's Avatar
 
Join Date: Apr 2005
Location: -
Default comfortINA - the comfortable phono preamp

2 years ago I started a project for a phono preamp, that can be completely controlled remotely (incl. input resistance, capacitance and amplification) and can be used for all kinds of systems (LO-MC, HO-MC, MM). Unfortunately the project was on hold for a long time, but now it's time to to it finally.

The planned features:
- amplification, input capacitance and input resistance selectable during operation with remote control
- integrated volume control, no need for an external preamplifier
- based on platINA design, but with SMD ICs (that are still large enough to be soldered with a good soldering iron)
- 1-4 inputs
- optional digital output and USB output

If you're looking for the ultimate "comfort" RIAA stage - are there any features that you would like to see?

I do not plan to implement different equalization curves, because this will be a stereo preamp.
  Reply With Quote
Old 3rd June 2013, 05:52 AM   #2
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

Similar to the PlatInA, I'd offer assistance. I've some ideas about the input stage up to a fully differential circuit, orientating at the PlatINAs basic topology, but with uC controlled comfort.
Just one Q: do you intend to go commercial as with the PlatINA? Or will it be bare PCBs only?

jauu
Calvin
  Reply With Quote
Old 3rd June 2013, 02:49 PM   #3
usul27 is offline usul27  Switzerland
diyAudio Member
 
usul27's Avatar
 
Join Date: Apr 2005
Location: -
Hi Calvin,

it's always good to get help. I'm planning to use low-resistance analog switches (<2 Ohm) in the input stage to change the input capacitance and resistance. There will be also 2-3 analog switches to change the gain of the input stage (CN0146 from AD shows a similar setup).
Every input gets it's own input stage, switching takes place after the first stage amplification (if there is more than a single input).
I have to test some analog switches to find out which work best.


I do not plan to sell finished comfortINAs, but PCBs to interested people. That might change if there is a huge demand. Circuit diagrams will be available to everybody free of charge.
  Reply With Quote
Old 3rd June 2013, 02:50 PM   #4
usul27 is offline usul27  Switzerland
diyAudio Member
 
usul27's Avatar
 
Join Date: Apr 2005
Location: -
P.S. I'm not sure yet, if a 2-layer PCB will be enough. It could happen, that I have to use a 4 layer board.
  Reply With Quote
Old 5th June 2013, 10:05 AM   #5
usul27 is offline usul27  Switzerland
diyAudio Member
 
usul27's Avatar
 
Join Date: Apr 2005
Location: -
A first draft of the input
Click the image to open in full size.
  Reply With Quote
Old 7th June 2013, 06:22 AM   #6
usul27 is offline usul27  Switzerland
diyAudio Member
 
usul27's Avatar
 
Join Date: Apr 2005
Location: -
I've checked several options for the input gain stage. The original platINA design used DIP switches to select the amplification of this stage. Unfortunately for a high gain, an external resistance of down to 10 Ohm is needed. Switching this with analog switches with some tolerance, can result in gain variations between the two channels. Also ultra-low Ron analog switches from ADI are only available in TSSOP packages. That would require a 4 layer board (I'm still trying to get the circuit on a two layer board).

Therefore I will try another approach: I accept minor balance errors in the input stage and adjust them later. The error in the input stage should be <1dB, therefore correction should not be a problem.

This makes it possible to use higher resistance switches like the ADG451 that are available in SOIC packages (and even DIP, but I think I will go for SOIC).
  Reply With Quote
Old 7th June 2013, 08:19 AM   #7
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

I wouldn´t rule out the TSSOp and TQFN- Packages and also not a 4-layer board. Ok, the boards would have to be populated at least in part by a professional, but that shouldn´t be a prob in a group buy, even at lowest device number counts. And it certainly is no real cost problem.
It´d allow for improvements due to devices only manufactured in those SMD-casings.

Extremely low on-value and tightly tolerated analog switches would only be required for the gain setting resistor in a INA-stage. For the impedance setting switches one could well use low-ohmic switches around 10Ohm.
The first could be omitted with completely with a 2-chip chipset in TQFN-casings, thereby also eliminating zipper noise and other issues of a discrete solution.

jauu
Calvin
  Reply With Quote
Old 7th June 2013, 11:20 AM   #8
usul27 is offline usul27  Switzerland
diyAudio Member
 
usul27's Avatar
 
Join Date: Apr 2005
Location: -
Hi Calvin,

I haven't decided yet. I think, TSSOP is still an option. The main problem for me is prototyping will become much more expensive.

Another option for a pure MC stage might be the PG2505. Its 10k input impedance is a problem for MM, but not for MC. The 0.5dB gain variation would also not be a problem, because it would be corrected later.

I'm thinking about the concept to have a balanced MC input stage and a different unbalanced input stage.

Daniel
  Reply With Quote
Old 18th July 2013, 11:37 AM   #9
usul27 is offline usul27  Switzerland
diyAudio Member
 
usul27's Avatar
 
Join Date: Apr 2005
Location: -
Ok, I did some calculations now based on the ADG451. With a 0.1Ohm tolerance between different ICs, the final tolerance in the gain would be max. 0.05dB. With maximum tolerance of the ADG451 of 0.5Ohm, the channel tolerance would be 0.25dB. In the highest gain setting I will use two parallel switches.
I will test some of these ICs to see how big the tolerances are in reality.
  Reply With Quote
Old 24th July 2013, 07:41 AM   #10
usul27 is offline usul27  Switzerland
diyAudio Member
 
usul27's Avatar
 
Join Date: Apr 2005
Location: -
I noticed a small but important difference between the ADG451 and the newer (and smaller) ADG1411: The ADG1411 does not need an additional 5V power supply, which makes the circuit and also the PCB much simpler. Looks like I will go for the ADG1411.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Phono Preamp PCB wanted - Transcendental Sound Grounded Grid Phono Preamp nathanjh13 Analogue Source 0 14th June 2012 10:19 AM
About a phono preamp gaetan8888 Analogue Source 13 16th November 2009 04:51 AM
new phono stage or old preamp with phono? flohmann Analog Line Level 2 2nd October 2008 09:51 PM
Electret mic preamp - will phono preamp work? darthmullet Analogue Source 6 12th October 2007 07:32 AM
Phono preamp Original Burnedfingers Tubes / Valves 14 16th June 2006 01:14 PM


New To Site? Need Help?

All times are GMT. The time now is 07:50 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2