Help! Weak Bass!

TubeHead Johnny · 1st April 2007, 01:56 PM

Hi Folks!

Last September, I built an amplifier with EL34 tubes in Ultra Linear mode and fixed bias. It sounded really good until recently I changed the phase splitter from cathodyne to a long tailed pair, (because it would distort at higher volumes) and now the bass response is quite hollow. I checked and double checked my wiring and found nothing wrong. I fiddled with the size of the "tail" resistor from 22K to 10K to 6.8K and still weak bass. I then changed the inverter again from long tail pair to a floating paraphase and still weak bass.

There's 490V on the plates using a 250 mA PT, the the tubes are biased around 33 mA each. Is there's a solution?

Thank you,

Johnny

SY · 1st April 2007, 07:28 PM

Have you measured the frequency response and distortion?

TubeHead Johnny · 1st April 2007, 07:35 PM

As far as test equipment goes, I don't have much. (My meter doesn't even measure true RMS) I would like to get a good scope someday, but for now I have is my ears and I don't like what I hear. Any ideas?

~~~Johnny~~~

SY · 1st April 2007, 07:44 PM

Yes, get a scope and meter. ;-) Seriously, you wouldn't try working on a car without having a set of wrenches and a timing light, so you really need to have the right tools. Without them, you'll be going round in circles; with them, you'll have the problem nailed down in minutes.

ray_moth · 2nd April 2007, 08:23 AM

Perhaps if we could see a schematic, we might be able to comment on possible problems. From what you say, there is no obvious reason why your bass response should be 'hollow' - BTW, I'm not sure what you mean by that.

TubeHead Johnny · 2nd April 2007, 01:59 PM

When I say, "Hollow", I mean the speakers sound like they're out of phase, but like I said, I checked EVERYTHING. I'll post a schematic shortly.

~~~Johnny~~~

bigwill · 2nd April 2007, 02:19 PM

Better damping factor causing less perceived bass?

TubeHead Johnny · 2nd April 2007, 03:22 PM

Perhaps. Is there a way to get lower bass response out of a tube amp without using EQ or tone controls?

bigwill · 2nd April 2007, 03:28 PM

Less NFB might work (lower damping factor)

TubeHead Johnny · 2nd April 2007, 04:43 PM

The only NFB I used was already incorporated into the ultra-linear design. Do you think I would get better results if I change it to pentode operation?

~John~

1st April 2007, 01:56 PM	#1
TubeHead Johnny diyAudio Member Join Date: Jan 2005 Location: The Electric City, Schenectady, NY.	Help! Weak Bass! Hi Folks! Last September, I built an amplifier with EL34 tubes in Ultra Linear mode and fixed bias. It sounded really good until recently I changed the phase splitter from cathodyne to a long tailed pair, (because it would distort at higher volumes) and now the bass response is quite hollow. I checked and double checked my wiring and found nothing wrong. I fiddled with the size of the "tail" resistor from 22K to 10K to 6.8K and still weak bass. I then changed the inverter again from long tail pair to a floating paraphase and still weak bass. There's 490V on the plates using a 250 mA PT, the the tubes are biased around 33 mA each. Is there's a solution? Thank you, Johnny

1st April 2007, 07:28 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Have you measured the frequency response and distortion? __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

1st April 2007, 07:35 PM	#3
TubeHead Johnny diyAudio Member Join Date: Jan 2005 Location: The Electric City, Schenectady, NY.	Help! Weak Bass! As far as test equipment goes, I don't have much. (My meter doesn't even measure true RMS) I would like to get a good scope someday, but for now I have is my ears and I don't like what I hear. Any ideas? ~~~Johnny~~~

1st April 2007, 07:44 PM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Yes, get a scope and meter. ;-) Seriously, you wouldn't try working on a car without having a set of wrenches and a timing light, so you really need to have the right tools. Without them, you'll be going round in circles; with them, you'll have the problem nailed down in minutes. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

2nd April 2007, 08:23 AM	#5
ray_moth diyAudio Moderator Emeritus Join Date: Jan 2004 Location: Jakarta	Perhaps if we could see a schematic, we might be able to comment on possible problems. From what you say, there is no obvious reason why your bass response should be 'hollow' - BTW, I'm not sure what you mean by that.

2nd April 2007, 01:59 PM	#6
TubeHead Johnny diyAudio Member Join Date: Jan 2005 Location: The Electric City, Schenectady, NY.	When I say, "Hollow", I mean the speakers sound like they're out of phase, but like I said, I checked EVERYTHING. I'll post a schematic shortly. ~~~Johnny~~~

2nd April 2007, 02:19 PM	#7
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	Better damping factor causing less perceived bass?

2nd April 2007, 03:22 PM	#8
TubeHead Johnny diyAudio Member Join Date: Jan 2005 Location: The Electric City, Schenectady, NY.	Perhaps. Is there a way to get lower bass response out of a tube amp without using EQ or tone controls?

2nd April 2007, 03:28 PM	#9
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	Less NFB might work (lower damping factor)

2nd April 2007, 04:43 PM	#10
TubeHead Johnny diyAudio Member Join Date: Jan 2005 Location: The Electric City, Schenectady, NY.	The only NFB I used was already incorporated into the ultra-linear design. Do you think I would get better results if I change it to pentode operation? ~John~

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
AN Std 8 + SI Super T-Amp = Weak Bass?	matt_garman	Full Range	19	3rd November 2009 04:07 PM
Acoustat 1+1 weak output	danielm	Planars & Exotics	20	7th February 2007 08:21 PM
why am I getting weak sub output?	pasomark	Subwoofers	18	21st December 2005 04:58 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read