The Boogie Board

Discussion Forum for Mesa Boogie Products
It is currently Sat Aug 29, 2015 10:29 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 36 posts ]  Go to page Previous  1, 2, 3
Author Message
PostPosted: Wed Jan 13, 2010 3:49 pm 
Offline
Mark II

Joined: Wed Aug 10, 2005 6:56 pm
Posts: 66
Location: Parrish, FL
I just came across this old post again and found out through some troubleshooting that the issue was not at all related to the pre amp tube but instead with the speaker A/B selector toggle switch located on the rear of RK head on Ch. 3. I must have bumped it by accident. It caused the exact same issue described by the original poster. It sucks because I went out and purchased new pre amp and power tubes only to discover that the original 6L6 tubes in the RK I heads are no longer sold as Mesa replacement tubes. The newer 6L6s don't have the same bottom end as the older tubes. Hate them!


Top
 Profile  
 
PostPosted: Thu Jul 07, 2011 9:32 am 
Offline
Mark III

Joined: Tue Jun 22, 2010 9:20 am
Posts: 250

_________________
ESP Eclipse II w/EMG JH Set
Squier Bullet w/SD SH-2n/SH-6
Mini Rectifier
2x12 Horizontal Cab
Line UX6 w/ Overloud 2


Top
 Profile  
 
PostPosted: Mon Mar 05, 2012 7:11 pm 
Offline
Mark III
User avatar

Joined: Wed Feb 10, 2010 12:07 pm
Posts: 329
Location: Marysville, California, USA
I am thankful for this post as the V4 in my Heartbreaker fits this discussion.

Dennis

_________________
Mark III no mark w Randy's initials & some IIc+ parts
50 Caliber (6BQ5) 4xEL84
Heartbreaker
Fender 75
Acoustic 165

1970 LPGT
1981 The Strat
1983 GZ-300
1983 (Elite Neck)/2001 FrankenStrat
1990 Firebird
more guitars, so little characters


Top
 Profile  
 
PostPosted: Wed Jan 14, 2015 10:31 am 
Offline
Donating Member

Joined: Sun Jul 06, 2008 9:48 am
Posts: 620
Location: Central Texas
Sorry to revive an old thread, but I have a question about the cathode follower thing.

Mesa says V3 & V5 are the cathode followers in the Roadster. I checked the manual to see tube functions, and V3A is the channel 3 & 4's 4th gain stage, and V3B is channel 3 & 4's the 5th gain stage.

V3A & V3B cannot be a cathode follower and a gain stage, so what gives? Is the cathode follower only active in channels 1 & 2?

Thanks for anybody who can clarify for me.

_________________
2015 Gibson Les Paul Studio & 2008 American Fender Stratocaster
Mesa Studio Pre & Randall RM4
Audio Monk custom tube power amp
Mesa Boogie 2X12 Royal Atlantic cab & 1X12 Thiele
various pedals


Top
 Profile  
 
PostPosted: Wed Jan 14, 2015 7:45 pm 
Offline
Mark III
User avatar

Joined: Wed Sep 08, 2010 4:12 pm
Posts: 497
Location: Petaluma, California
Below is a quote from Randall Aiken ( Aiken Amplification ) that may help.
_______________

Q: Are cathode followers gain stages?
A: Yes. However, the problem is that people associate "gain stages" with, well...gain. The cathode follower has a maximum theoretical gain of unity, and typically a gain of around 0.5 to 0.7 or so. To us engineering types, a gain of less than unity is still called a gain (that is, unless it's called a loss or an attenuation, in which case the attenuation is the reciprocal of the gain), so a stage with a gain of unity still has a gain - a gain of 1. The cathode follower *is* an amplifier stage, but not a voltage amplifier in the typical sense. It is used as a "buffer" amplifier, which means it has a high input impedance and a low output impedance. This means it does not appreciably load the previous stage it is connected to, and the very low output impedance allows it to drive low impedance loads without much signal voltage loss. For example, if the previous stage had an output impedance of 100K, and you tried to connect a stage with a 10K input impedance to it, you would only get 9% of your original signal when you connected the second stage, because of the voltage divider formed by the 100K output impedance and the 10K input impedance. If you insert a cathode follower with a 1K output impedance and a 1Meg input impedance, the 10K stage can be driven with 90% of the original signal, because there is now effectively a 1K:10K voltage divider instead of a 100K:10K voltage divider. The cathode follower is basically an active "impedance transformer", in this sense. The reason the cathode follower is used in driving a tone stack is not only because the tone control network impedance is relatively low in comparison to the output impedance of the previous stage, so it would cause a loss of gain, but more importantly, the tone stack is a filter network that is designed to ideally be driven from a zero source impedance to achieve it's proper frequency response. The cathode follower provides a very low source impedance that allows the tone stack to work as designed. If the tone stack is driven from too large a source impedance, not only will there be a loss of gain, but there will be a different frequency response to the network, typically quite a few dB loss of the highs. The cathode follower prevents this loss, allowing the tone stack to retain more of it's theoretical frequency response.

_________________
MESA/Boogie - Product Specialist/Customer Service - http://www.mesaboogie.com/support/index.html


Top
 Profile  
 
PostPosted: Thu Jan 15, 2015 1:56 pm 
Offline
Donating Member

Joined: Sun Jul 06, 2008 9:48 am
Posts: 620
Location: Central Texas
Authorized Boogie,

Thank you for the information. So if I'm understanding things correctly, the 5th gain stage of the Roadster's 3rd & 4th channels is actually a cathode follower?

_________________
2015 Gibson Les Paul Studio & 2008 American Fender Stratocaster
Mesa Studio Pre & Randall RM4
Audio Monk custom tube power amp
Mesa Boogie 2X12 Royal Atlantic cab & 1X12 Thiele
various pedals


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 36 posts ]  Go to page Previous  1, 2, 3

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Google [Bot] and 2 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

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group