DIY Audio Projects Forum
 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

It is currently 27 Jan 2020, 03:45

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 675 posts ]  Go to page Previous  1 ... 64, 65, 66, 67, 68
Author Message
PostPosted: 03 Jan 2020, 21:42 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4066
Location: Arizona, USA
Hi, You need the 1M resistor or at least something over say 100K. It allows the charge on the output capacitor a path to ground if there is a bolcking one in the power amp. The preamp can easily drive any SS amp that has over about a 2K ohm input. Optimum is over 10K. The output you indicated is the max it can deliver, using the volume control you can get anything you want . Typically you would adjust it for 1-2 volts to drive most power amps. My power amps need about 2.5 volts for full output.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 03 Jan 2020, 22:52 
Offline

Joined: 23 Feb 2017, 02:02
Posts: 584
You can meansure the voltage approximatley with multimeter on ac mode, then put a test tone at 100HZ and observe the output voltage in RMS


Top
 Profile  
 
PostPosted: 07 Jan 2020, 09:50 
Offline

Joined: 24 Oct 2010, 07:05
Posts: 298
Maybe I'm going to repeat all the answers before my post, but I should clarify several things.
First of all about the stated 20V maximum output: the value is for estimating the overload capacity, not for normal usage. Having the gain of 7 Forewatt should get 20/7=2.9V input to output 20V. I can't say this input voltage level is impossible to get, especially from modern devices, but far before this point you will overload the power amplifier. So the volume control is your help in mitigating the problem.


Top
 Profile  
 
PostPosted: 07 Jan 2020, 10:05 
Offline

Joined: 24 Oct 2010, 07:05
Posts: 298
About the resistor on the output. As you can see the left side of the output capacitor is connected to the voltage near 100V. If the right side is not connected to anything (like when you omit the 1M resistor) any path to the ground (the input side of connected power amplifier will serve the duty) will charge the capacitor and the first pulse of the charging current will pose the 100V voltage to the path. The left-side 100V is not appears instantly, so if the path in the right side has a resistor the voltage on the charging path will also rise gradually. But if the input of the power amplifier has a blocking capacitor the initial voltage will divide between the output capacitor of the Forewatt and the blocking capacitor. The input capacitor maybe not rated for such voltage at all.
Answering to the question: I doubt that buzzing is related to the 1M resistor. Most probably there is a ground issue.


Top
 Profile  
 
PostPosted: 07 Jan 2020, 12:35 
Offline
User avatar

Joined: 08 Jul 2019, 06:05
Posts: 8
Location: Ottawa, ON, Canada
Thank you Bruce and Poty for both answers. Very helpful. I definitely have one or more ground issues I need to resolve...

Best regards,

D


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 675 posts ]  Go to page Previous  1 ... 64, 65, 66, 67, 68

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 16 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
DIY Tube Projects :: DIY Tube Amp Kits :: DIY Speaker Projects :: DIY Solid State Projects :: DIY IC / Op-amp Projects :: DIY Phono Projects :: DIY Cable Projects :: Hi-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy