Disappointing results from RH84 - Page 2 - 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 3rd March 2014, 06:56 AM   #11
diyAudio Member
 
jazbo8's Avatar
 
Join Date: Jan 2011
Location: In Transient
Quote:
Originally Posted by tomchr View Post
It shouldn't be a problem to bypass the cathode resistor on the driver with a cap. That's what I do in my Novar Spud.

~Tom
When using a triode as the driver for the RH amplifiers, the cathode is left un-bypassed to increase the driver's plate resistance, this is one of the design features specified by Mr. Kitic.
  Reply With Quote
Old 3rd March 2014, 10:17 PM   #12
2bamp is offline 2bamp  Canada
diyAudio Member
 
Join Date: Dec 2013
I thought that the intended use of the amp was with an mp3 player on the input. Oh well...

The voltages were measured through a Vector socket on top of the chassis. I will have to remeasure, as they don't quite add up. 340v is a bit strong on the power tubes, so I will have to add some sand.

I will try adding a small cathode bypass cap. If that doesn't do it, I will have to add another triode stage. I am sure a couple of 6C4 could fit in my chassis with a pot. A gain of 2 would likely be all I need. Hopefully it doesn't come to that.
  Reply With Quote
Old 3rd March 2014, 10:22 PM   #13
tomchr is offline tomchr  United States
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Greater Seattle Area
Quote:
Originally Posted by jazbo8 View Post
When using a triode as the driver for the RH amplifiers, the cathode is left un-bypassed to increase the driver's plate resistance, this is one of the design features specified by Mr. Kitic.
It's Schade Feedback. There's nothing magic about it... I can't comment on AK's design choices, only say that it works well either way.

~Tom
__________________
21st Century Maida Regulator, Universal Filament Regulator, Damn Good 300B, Novar Spud, and more...
Neurochrome : : Audio - http://www.neurochrome.com/audio - Engineering : : Done : : Right
  Reply With Quote
Old 3rd March 2014, 10:26 PM   #14
diyAudio Member
 
Sodacose's Avatar
 
Join Date: Feb 2006
Location: mke, wi
2bamp-

If you think it's definitely the mp3 player output, you could give this nifty little trick a shot:

Antique Radio Forums • View topic - Passive Amplifier for your iPod 2 radio jack

I've always wanted to try it, but I haven't really had a need (perhaps when I finish my RH84 build...)

Part in question:

RadioShack Audio Output Transformer : Transformers | RadioShack.com

$2.99 a pop.
__________________
I think my ear just popped a boner.
  Reply With Quote
Old 4th March 2014, 02:38 AM   #15
2bamp is offline 2bamp  Canada
diyAudio Member
 
Join Date: Dec 2013
Wow, great reading there. Looks like it is a matter of an impedance mismatch.

I am going to have to try a CD player as my source. I bet I have some suitable little transformers in my parts collection to make the matching unit. I will post up my results. Thanks for the idea.
  Reply With Quote
Old 4th March 2014, 03:14 AM   #16
diyAudio Member
 
Sodacose's Avatar
 
Join Date: Feb 2006
Location: mke, wi
Hopefully you were right about the lack of oomph from the driver. Would make sense that it's just not seeing enough V's from a headphone out. A 2V out from a CD player (or a mp3 player with that little transformer trick) might be all you need. Will be interested to hear results as I've just ordered some Transcendar iron for my build...
__________________
I think my ear just popped a boner.
  Reply With Quote
Old 4th March 2014, 03:57 AM   #17
diyAudio Member
 
jazbo8's Avatar
 
Join Date: Jan 2011
Location: In Transient
Quote:
Originally Posted by tomchr View Post
It's Schade Feedback. There's nothing magic about it... I can't comment on AK's design choices, only say that it works well either way.

~Tom
I know what you are saying, I was merely pointing out that it was a key design choice on the RH amplifiers - it was left out on purpose.
  Reply With Quote
Old 4th March 2014, 08:17 AM   #18
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
Quote:
Originally Posted by jazbo8 View Post
I know what you are saying, I was merely pointing out that it was a key design choice on the RH amplifiers - it was left out on purpose.
Indeed - its fairly important not to bypass the driver cathode.

Shoog
  Reply With Quote
Old 4th March 2014, 11:32 PM   #19
2bamp is offline 2bamp  Canada
diyAudio Member
 
Join Date: Dec 2013
I did some A/B testing with my consoles that use similar tubes. I can honestly say that I am happy with the RH84 as built. I just needed to listen more carefully.

It doesn't have quite as much power, but the sound quality much better. I won't bore you with "audiophile speak," but the frequency response and voicing are on a whole different level. The improved design built with NOS PIO caps instead of ceramic probably has a lot to do with it. My solution to the reduced power: move the amplifier to a smaller room.

For my next build, I am going to try making an integrated amp optimized for the lower line level of my digital sources. I am thinking of a single triode stage on the front end into a volume pot. I have lots of TV tubes, so perhaps a 6SN7, 6CG7 or a pair of 6C4.

Anybody done this already? I have scoured the interwebz, but haven't found any examples.
  Reply With Quote
Old 4th March 2014, 11:53 PM   #20
diyAudio Member
 
aardvarkash10's Avatar
 
Join Date: Mar 2007
Location: Auckland, NZ
i'd be more inclined to put a 1:2 or transformer in the input. Two advantages - it would come close to matching your digital input voltages to CD line voltage, so less messing for different sources, and it would provide separation of ground loops
__________________
"Folks, you can't prove truthiness with information. You prove truthiness with more truthiness. In a process known as truthinessiness." - Stephen Colbert, The Colbert Report
  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
Disappointing stadium sound Cal Weldon PA Systems 46 10th December 2011 11:07 PM
Disappointing CD's.... mpmarino Music 153 7th May 2009 03:23 PM
OPA549 disappointing la9 Chip Amps 19 21st February 2006 09:34 PM
Adire DPL12, very disappointing? Otter Subwoofers 30 6th February 2005 03:36 AM


New To Site? Need Help?

All times are GMT. The time now is 02:26 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