help please - modify phono corrector - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 28th June 2014, 05:11 PM   #1
Vincin is offline Vincin  Viet Nam
diyAudio Member
 
Join Date: Aug 2006
Location: HCMC
Default help please - modify phono corrector

What do I change in the attached schematic to use the E80CC valve, instead of the 6072A.

Nothing wrong with the 6072a valve, the circuit sounds very good using this valve. I just have a bunch of NOS E80CC and want to put them to use.

thanks a million.
Attached Images
File Type: jpg image.jpg (40.5 KB, 123 views)
  Reply With Quote
Old 28th June 2014, 05:19 PM   #2
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Just recalculate most of the component values, to take account of the different valve characteristics (e.g. anode impedance, quiescent current). First, reverse engineer the circuit to determine exactly what the designer had in mind. Then redesign it for a different valve.

Alternatively, find a similar circuit already designed for 6072 or 12AY7.
  Reply With Quote
Old 28th June 2014, 05:29 PM   #3
Vincin is offline Vincin  Viet Nam
diyAudio Member
 
Join Date: Aug 2006
Location: HCMC
Sir, I wish I could do what you said: "reverse engineering". Then I would have the opportunity to enjoy this hobby 10 times more. The matter of fact is that I do not even understand how the first stage cascode circuit works.

all I know is the RC EQ networks need to be changed to compensate for the different valve.

so if you could spare 5 minutes to punch some numbers and advise me exactly what I need to do, I would appreciate that very much.
  Reply With Quote
Old 28th June 2014, 05:39 PM   #4
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Sorry, it would take a lot more than 5 minutes. Hours, at the very least.

If you can find a circuit designed for E80CC then use it. If not, it may be that E80CC is not a suitable valve for a phono preamp.
  Reply With Quote
Old 28th June 2014, 07:15 PM   #5
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
E80CC has a mu of 27 and a transconductance of 2700uhmos vs a mu of 40 and a transconductance of 1700 for the 12AY7A. The cascode section would give you more gain, the second stage significantly less.

You can adjust the value of R8 so that the plate current with the E80CC is approximately 1.2mA.

You can adjust R19 so that the plate current is approximately 1.3mA.

Finally you may need to adjust the value of R17 - this should be sufficient for decent RIAA conformance. Do you have any means of measuring the frequency response?

The gain in the first stage will be higher, the second lower. I'd just swap the tube and do some voltage measurements to see whether resistor values listed need to be changed.

I don't have models for this tube so I can't simulate this circuit, but it is quite similar to one of my more recent designs and should not be too difficult to tweak.

Are you building from scratch or converting a 12AY7 based pre-amplifier you already own? The reason I ask is if you are building I would suggest somewhat higher operating currents in each stage for better linearity, and better drive capability in the second stage.

Without good models or samples it is very difficult to advise what the specific values need to be, but with the exception of R17 none of the other values are critical. When I design a new phono stage I model it in spice, build a prototype and determine how close to my design goals the design comes and then modify it on the bench until it achieves something close to the targeted performance.

I have both quite a lot of test equipment and experience designing phono stages, making random tube changes without a clear expectation of performance goals and without the means of extensively testing the changes is not an ideal recipe for achieving good performance. If you are willing to invest the money for the required test gear and the time to learn it can be a worthwhile process.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 28th June 2014, 07:57 PM   #6
Ketje is online now Ketje  Belgium
diyAudio Member
 
Join Date: Dec 2012
Location: Flanders
Curious values has those resistors.According to the 6072 data from GE ,R8 results in a higher current and less voltage on the top plate.Still fuctionig but giving less headroom.
Putting in a E80CC (practicaly the same as a ECC40) make the resistors allmost right.
Beware , the E80CC draws much more heater current.
Second stage ,data says R19 not 1k2 but 1k8 and for a E80CC 3k9 to get the indicated current (voltage on R15.
Mona
  Reply With Quote
Old 29th June 2014, 10:35 AM   #7
Vincin is offline Vincin  Viet Nam
diyAudio Member
 
Join Date: Aug 2006
Location: HCMC
Kevin,

thanks. The circuit I posted is of Audio Note UK, same as in most of their phono preamp. I built their kit phono stage years ago.

I plugged the E80CC in there this morning, sound is ok. Up the second stage current by reducing the cathode resistor Rk from 1.2K to 820Ohm, and down anode resistor Ra from 10K to 68K, new Ia = 2.45ma, as you have suggested "higher operating" point, the sound is even better. The better drive and lower impedence must have helped a bit.

I guess this will do it. Im not that much of a golden ear who can pick out un-even frequency response so I will pass the steps to make it perfect.

One question remained though: that 270K resistor, how do I change this given the 1st stage lower driving impendence of the new valve (E80CC vs 6072/12AY7).

thank you very much
  Reply With Quote
Old 29th June 2014, 10:54 AM   #8
Ketje is online now Ketje  Belgium
diyAudio Member
 
Join Date: Dec 2012
Location: Flanders
The output impedance of a cascode circuit is very high,somewhat like a penthode,several 100-th Kohm.So the output is almost =R7. If you didn't change that the 270k is ok.
Mona
  Reply With Quote
Old 29th June 2014, 11:24 AM   #9
Vincin is offline Vincin  Viet Nam
diyAudio Member
 
Join Date: Aug 2006
Location: HCMC
great, no further change.

on a different technical aspect of the same phono circuit, I have a question on suitable output capacitor value. The phono output is driving a Silk TVC used as volume control at the input of an active linestage. Yes I have read that the valve phono stage is not suitable to drive TVC ie: high impendence, LC resonance & damping etc.. I wish I understand all that but I simply clueless.... I use the TVC because it sounds so much better than the resistor volume control type, and Im able to eliminate the ground loop at the input of the linestage.

Silk state on their website their TVC has more than 1000H primary inductance.

so in the ballpark estimate what output cap value for the phono stage should i use? my vinyl rig is tuned to a resonance frequency of 7-8hz I think.

at the moment I use 0.47uf, there is a bit bass reinforcement, which is quite nice actually.
  Reply With Quote
Old 29th June 2014, 04:29 PM   #10
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
You may want to try a range of values to suit the LF rise you want (or not) I would try a 1uF and see where that takes you. Much larger is probably not required..
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  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
Power Factor Corrector Inductors Mostech Power Supplies 0 8th February 2011 08:58 AM
Kulish Corrector applications GEirin Solid State 12 30th December 2007 07:52 PM
Phono preamp- how to modify to get deeper LF? MaciekP Tubes / Valves 4 15th March 2004 11:13 PM
help me modify my phono amp.(Please) sleepy Analogue Source 5 28th February 2003 01:01 PM


New To Site? Need Help?

All times are GMT. The time now is 10:12 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