Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Hybrid line Level Valve and MosFet
Hybrid line Level Valve and MosFet
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 7th June 2019, 01:41 AM   #1
J.Schmaedecke is offline J.Schmaedecke  Brazil
diyAudio Member
 
J.Schmaedecke's Avatar
 
Join Date: Jun 2006
Default Hybrid line Level Valve and MosFet

I started with a CCDA amp line, and I did not like the sound.
So, I modified slightly from the CCDA and got the result I expected.
The frequency response at -1dB is from 5Hz to 250kHz.
The valve I used is the E88CC PentaLabs. I used the QA400 for distortion measurements.
Attached Images
File Type: jpg HybridLine.jpg (65.1 KB, 325 views)
File Type: jpg HybridLineTHD.jpg (118.3 KB, 322 views)
File Type: jpg HybridLineIMD.jpg (133.3 KB, 301 views)

Last edited by J.Schmaedecke; 7th June 2019 at 02:35 AM.
  Reply With Quote
Old 7th June 2019, 11:50 AM   #2
Mark Tillotson is offline Mark Tillotson
diyAudio Member
 
Join Date: May 2018
Location: Cambridge UK
R1 and R2 will worsen the noise performance - there are better ways to reduce the gain.
  Reply With Quote
Old 7th June 2019, 01:25 PM   #3
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Location: Waterloo, ON or Herefordshire UK
Hybrid line Level Valve and MosFet
no gate stopper needed for the FET ?

To lower the gain, if desired, I would increase the un-bypassed cathode resistor values
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

Last edited by Bigun; 7th June 2019 at 01:27 PM.
  Reply With Quote
Old 7th June 2019, 06:00 PM   #4
J.Schmaedecke is offline J.Schmaedecke  Brazil
diyAudio Member
 
J.Schmaedecke's Avatar
 
Join Date: Jun 2006
Mark and Bigun thank you for your comments. The high gain in this type of circuit is a problem. But it is necessary to maintain the performance. The increase in noise due to resistors R1 and R2 is not relevant. The signal-to-noise ratio is -74dB only by powering the cathode in AC mode as you can see in the spectrum. I'm going to redo the source in regulated DC mode and I'll show you the result.
Bigun, I will try to use the source of the heater to create a negative source to power the cathode and thus increase the cathode resistance without modifying the polarization. But if this increases the distortion of third and high harmonics, I will not use it. The gate resistor is not required in this circuit. The polarization of the Mosfet is in class A not entering the region susceptible to the oscillations as in class AB or key mode. But if this worries you, a 47 Ohm resistor is enough.
  Reply With Quote
Old 8th June 2019, 07:09 PM   #5
J.Schmaedecke is offline J.Schmaedecke  Brazil
diyAudio Member
 
J.Schmaedecke's Avatar
 
Join Date: Jun 2006
The image below shows 10kHz square wave with no tendency to oscillation.
With -7.5V at the cathode it was possible to use the 1.2k ohms resistor reducing the gain to 10dBV. Nice option.
I will post the schematic, and the QA400 images another time.
Attached Images
File Type: jpg 20190607_220748.jpg (831.5 KB, 211 views)
  Reply With Quote
Old 9th June 2019, 03:22 AM   #6
J.Schmaedecke is offline J.Schmaedecke  Brazil
diyAudio Member
 
J.Schmaedecke's Avatar
 
Join Date: Jun 2006
Quote:
Originally Posted by J.Schmaedecke View Post
...gain to 10dBV...
gain to 10dBs.
  Reply With Quote
Old 13th June 2019, 10:58 PM   #7
dudaindc is offline dudaindc  United States
diyAudio Member
 
dudaindc's Avatar
 
Join Date: Sep 2005
Location: Metro Washington DC
Nice one - I am definitely following this thread.
__________________
"All measurements are wrong! Thus, measurement is the art of handling errors."
  Reply With Quote
Old 16th June 2019, 09:30 PM   #8
J.Schmaedecke is offline J.Schmaedecke  Brazil
diyAudio Member
 
J.Schmaedecke's Avatar
 
Join Date: Jun 2006
This is the schematic of the low gain version with increase of the cathode resistor without loss of quality.
Attached Files
File Type: pdf HybridLineAmp.pdf (66.4 KB, 47 views)
  Reply With Quote
Old 17th June 2019, 03:48 AM   #9
J.Schmaedecke is offline J.Schmaedecke  Brazil
diyAudio Member
 
J.Schmaedecke's Avatar
 
Join Date: Jun 2006
THD and IMD
Attached Images
File Type: png PreHibridoLowGainTHD.png (45.9 KB, 97 views)
File Type: png PreHibridoLowGainIMD.png (49.0 KB, 21 views)
  Reply With Quote
Old 17th June 2019, 12:49 PM   #10
Ken Newton is offline Ken Newton  United States
diyAudio Member
 
Ken Newton's Avatar
 
Join Date: Apr 2003
Location: Eastern Pennsylvania
Quote:
Originally Posted by J.Schmaedecke View Post
I started with a CCDA amp line, and I did not like the sound.
So, I modified slightly from the CCDA and got the result I expected.
The frequency response at -1dB is from 5Hz to 250kHz.
The valve I used is the E88CC PentaLabs. I used the QA400 for distortion measurements.
Just curious to know:

1) What was the level of the 2nd harmonic in the CCDA stage?

2) How would you subjectively characterize the difference in sonics between the two stages, what didn't you like about the CCDA that sounds better to you with the hybrid stage?

Last edited by Ken Newton; 17th June 2019 at 12:54 PM.
  Reply With Quote

Reply


Hybrid line Level Valve and MosFetHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Speaker to Line Level Conversion From a Valve Amp For Adding Colour To mixes moley Tubes / Valves 25 30th January 2018 12:44 AM
Hybrid Valve/MOSFET Amplifier KatieandDad Solid State 9 25th August 2013 04:34 PM
Borbely low-voltage hybrid Tube-MOSFET opamp as a line amp... jazzpeter65 Solid State 27 26th March 2012 11:50 PM
Help with hybrid mosfet valve amp samvel65 Tubes / Valves 57 27th January 2010 11:35 PM


New To Site? Need Help?

All times are GMT. The time now is 04:16 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki