The Heavy Cross - ideas about a transconductance phase-splitting amp - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, 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 1st February 2014, 04:34 PM   #1
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Default The Heavy Cross - ideas about a transconductance phase-splitting amp

Hi,

when fiddling and simming around with global-feedback-free transconductance and current conveyor structures, I tried to sketch a circuit that could be used as a SE-to-balanced converter, or as fully differential preamp.
I came up with the circuit to the very left.
When redrawing and tidying up the sketches the circuit to the 2nd left evolved, which is identical apart from the improved current mirrors.
Basically I drew 1 input instead of 2 and Q2 and the parts in its collector branch changed places with the parts from Q1´s emitter branch.
Seeing the sketch to the right I knew I had seen something similar somewhere before.
Anyway, I gave it the name Heavy Cross due to the crosswise interconnection of the current mirrors, and besides for me its the very best song from Gossip.

This circuit simmed very well already, the output offset voltages differed slightly, which is due to the NPN and PNP-branch not beeing true complementary.
The asymmetry also showed in different THD-values, although on a very low niveau.

Then I added a second, mostly identical circuit to see if this could symmetrize things and to provide for a second inverting input.
See 2nd attachment.
The only difference beeing interchanged outputs of the two branches.
The 2 output-pairs are connected together, which is possible since we are working in the current domain.
The inv input of the second circuit may then be connected to gnd, or fed with a inverted input signal.
So we can convert SE-to-balanced or work in fully differential mode.
In any case will the output offsets and THD now be equal.
The idle currents are defined mainly by the value of the Res and(!) the supply voltages.
Fortunately this doesn´t spoil the PSRR, so the requirements regarding the power supplies remain feasable.

jauu
Calvin

ps. well I finally remembered ... the Paradise Phono uses a very similar topology

Last edited by Calvin; 1st February 2014 at 04:42 PM.
  Reply With Quote
Old 2nd February 2014, 05:40 PM   #2
RCruz is offline RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
Following
__________________
RC
  Reply With Quote
Old 3rd February 2014, 09:53 AM   #3
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

here´s the schematic for a totally paradiseish phase splitter.
I must stress that at the time the schematic is just brainworks and Sims.
It still needs real world testing.
Anyway, comparing it to the schematic of the Paradise Rev.3 and You´ll notice the similarities.
Paradise | HeavyCross
Input stage NPN:
Q1,30,31,32 | Q1,1b
Input stage PNP:
Q2,25,26,29 | Q2,2b
NPN Emitter Current Mirror:
Q4,5,13,14 | Q5,6,51,61,5h
PNP Emitter Current mirror:
Q11,12,15,16 | Q9,10,91,101,9h
NPN Collector Current Mirror:
Q3,10,17,18,22 | Q3,4,31,41,3h
PNP Collector Current Mirror:
Q6,7,8,9,24 | Q7,8,71,81,7h
NPN Emitter Resistors:
R2,21,22,23 | Re1
PNP Emitter Resistors:
R24,25,26,28 | Re2

Differences mainly occur in the Collector branches of the Current mirrors and the CM-topology.

The Paradise has a CCS loading the Emitter-side-CMs (Q49,50,51,52, R5,30,36).
This CCS defines the idle currents of the whole circuit.
The CMs beeing of cascoded type.
The Collector-side-CMs are loaded by the RIAA network.
The CMs here beeing of improved Wilson w. helper type.
The HeavyCross´s CMs are all of the improved Wilson w. helper type to achieve maximum symmetry.
The loads are the identical Ri and Ri2 for both branches.
The idle currents are defined by RE1 and Re2 and the level of the supply voltages.

Due to differences between the NPN and PNP transistors the Outputs will settle at different Offsets and exhibit slightly different THD.
To keep Offsets small NPNs and PNPs should be matched as should be the input Pairs Q1,1b,2,2b.
There are two ways to cancel the Offsets.
1) Trimming Re2.
As the Offsets are of similar level but opposite polarity it might suffice to trim only Re2. The Offsets should become 0V if the currents through Re1 and Re2 equal in value.
2) Trimming R8 and R10.
This trims the idle currents of the PNP-CMs.
The Paradise Offset is trimmed in that the idle currents through the Emitter-CMs of NPN and PNP branch are varied and as such they also affect the idle currents through the Collector-CMs, hence the output offset.

A minor difference occurs in the Input stage.
The paradise uses multiple paralleled transistors to achieve the required low-noise characteristic.
The HeavyCross makes use of either just a single complementary pair (Q1,Q2) or optionally of a Complementary-Feedback-Pair (CFP, Q1,1b,R11 and Q2,2b,R12).
With the former the input impedance settles at app. 300k.
If that proves to be a bit low --remember that the Zin directly affects the RIAA equalizer and that therefore the 100k input resistor of the Calvin Buffer had to be omitted with-- the CFP may be used raising the Zin to roundabout 14Megs.

So there are certain differences due to the different application, but I think the basic topological similarities are noticeable.

Interestingly didn´t the more elaborated CMs improve the THD-figures against the basic two transistor CM.
So if anybody starts testing, he might want to start start with the simple leftmost schematic of #1 and parts and values from #3.

It it were to be used with the Paradise the HeavyCross would be inserted at the output of the RIAA-Equalizer Network.
Its two outputs were connected to two Buffers, say the Calvins.
The output of the Calvin-Buffer connected to the V(out) output of the HeavyCross would be connected to the DC-servo input.
Trimming the HeavyCross´s output Offsets should be done either before putting it into the Paradise or in that the input of the HeavyCross is grounded and the outputs trimmed to 0V.

jauu
Calvin

ps. Joachim I forgot to ask for Your permission or approvement of this add-on.
Is it ok, or shall I shutup and p***off?

Last edited by Calvin; 3rd February 2014 at 10:07 AM.
  Reply With Quote
Old 3rd February 2014, 10:27 PM   #4
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
I did not know that the Paradise is a " Style ". I was always waiting what comes after " Post Modern ".
  Reply With Quote
Old 5th February 2014, 11:24 AM   #5
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

so, do You approve or do You disapprove?

jauu
Calvin
  Reply With Quote
Old 5th February 2014, 12:23 PM   #6
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
You can do what you like. The Paradise circuit is in the open domain.
I think your circuit can come very handy.
I am also thinking about the oposite : a balanced to unbalanced converter.
  Reply With Quote
Old 5th February 2014, 12:25 PM   #7
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
You forgot a resistor parallel to C1.
  Reply With Quote
Old 5th February 2014, 06:34 PM   #8
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

You´re right if its used standalone.
Then I´d add a bandwidth-limiting filter with DC-bias path.
But for the Parasise its correct as the preceeding RIAA network serves as DC-path and a additional R would alter the RIAA-response.
R1,C1 serve her just as soft-filter against HF entering the circuit.

So here´s something for show and tell

jauu
Calvin
Attached Images
File Type: gif HeavyCross - Paradise Phase-Splitter.gif (37.4 KB, 125 views)

Last edited by Calvin; 5th February 2014 at 06:54 PM.
  Reply With Quote
Old 22nd April 2014, 12:34 PM   #9
diyAudio Member
 
Join Date: Jul 2010
Location: Dresden, Germany
Did anyone try out this? I would be interested in the results.
I just cannot try it on my own as i am far away from a soldering station...

Cheers,
Walter
  Reply With Quote
Old 23rd April 2014, 06:08 AM   #10
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

doesn´t seem so.
Though the working principle is very simple, the whole circuit probabely looks too complex to be trusted
Also, as is, it´d be just at the beginning of its development.
Subassemblies like a dc-servo may be added as well as variants with current inputs to be used as I/V converter, or MC-prepre.

jauu
Calvin
  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
phase splitting transformers Empee Tubes / Valves 16 27th January 2008 06:39 PM
More Phase Splitting Questions Sherman Tubes / Valves 17 29th June 2007 02:52 PM


New To Site? Need Help?

All times are GMT. The time now is 12:29 AM.


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