Problem related to Push-Pull or EL34?


I have compared my EL84 amp with an EL34 amp and what strikes me is that the EL34 amp is boomy. I know that my room has a problem in the bass region and it’s like the E34 amp makes this worse. So why is that? Both are Push-Pull, but my EL84 amp has got the original capacitors replaced to “ultrafast” capacitors. So this makes me wonder if there is any truth in what I've heard: 

  1. ...the Push-Pull design in itself increases the bass and makes the sound a little boomy.

  2. can counteract this by replacing capacitors to “ultrafast” capacitors.

  3. ...EL34 tubes by design emphasis bass frequencies.

This makes me very frustrated because I really like this EL34 amp (LM EL34IA) except for this bass problem. The amp is in my budget range and I need the 40W it gives (which means Push-Pull).

Any thoughts?

 Push-Pull design in itself does not increase the bass and make the sound a little boomy.

EL34 tubes by design do not emphasize bass frequencies.

The choice of capacitors is significant in the sonics and performance of an amp. But so is the design and implementation.
Very simply put, Push-pull design has more power and less distortion than a single-ended amp. A PP amp can also operate in either Class A or A/B, so this affects the sound produced.

In your case, it could be the tubes installed. Input tubes, especially gain, and the output tubes can emphasize bass or any other area of the frequency spectrum. Your EL34 amp may need output tubes which are more linear. 
   Another consideration is power. Is this amp powerful enough to drive the speakers. You need enough current to push the bass drivers.
And then there's the room. Bass frequencies may need absorbion, there may be standing waves creating more bass in your music.

In my limited experience, all things being equal, e.g., power rating, cables, speakers, etc., the tube amps with higher output impedance/low damping factor tend to have a more boomy bass response. You can try a different output tap, 4 ohm vs. 8 ohm, and see if that makes a positive difference.
Good idea on trying a different output impedance. Also true about damping factor.
I expect some expects will weigh in about this.

Tube amps with output impedances greater than 1 ohm will not have a flat response into a speaker's varying impedance. They will act as tone controls! So, choose your tube amp/speakers with this consideration in mind!
Tube amps with output impedances greater than 1 ohm will not have a flat response into a speaker's varying impedance. They will act as tone controls! So, choose your tube amp/speakers with this consideration in mind!
While this is off topic, the actual situation is more complex than described above. This is because all amps make distortion, and the ear interprets distortion as tonality *unless the amp is clipping*. Apparently the brain has tipping points, where its processing of the sound changes from one portion of the brain to another- in the case of distortion, the brain can actually favor tonality caused by distortion over actual frequency response errors (or lack thereof). For this reason, an amplifier with a higher output impedance can often come off as more neutral than an amplifier with a lower output impedance, even though the latter is more 'flat'.
In the case of the OP, I think trying different taps is a good idea, and it may also be a good idea to try a different speaker cable. Tube amps have generally higher output impedances and so appear more sensitive to cables. For this reason its always a good idea to keep the speaker cables as short as possible. 
The obvious question is, what speaker is the amp hooked up to? All amp/speaker combinations are "systems", the sound of each dependent on the other. Why is it assumed it is the amp that is boomy, rather than the result of the amp/speaker interaction?

When comparing these two tube amplifiers everything else is the same except for the amplifiers. I have just switched between the amplifiers. I have tried both the 8 ohms tap and the 4 ohms tap.

I’m grateful for your posts but I wonder how I will know when the "damping factor" of a tube amp is problematic and how do I know what the "damping factor" of this amplifier is?

roberjerman wrote:

"Tube amps with output impedances greater than 1 ohm will not have a flat response into a speaker’s varying impedance. They will act as tone controls! So, choose your tube amp/speakers with this consideration in mind!"
This may be right, but how do I, an ordinary music lover, not a technician, know what to look for? What should I look for in specs for the tube amp and the speakers?

The LM34IA has 40W and my old EL84 amp (without boomines) has 35W so it can’t be due to lack of power. Speaker sensitivity is 89dB (Tannoy Eaton Legacy).

I have heard another possible explanation why I get this boomines. The LM34IA is slow and the capacitors should be replaced with "ultrafast capacitors". This maybe why I don’t have boomy sound from my old EL84 amp (Tube Technology Unisis Signature) which has "ultrafast capacitors".

So as I see it there are only two things that can cause this problem; the tubes (solution: try another brand with tighter bass) and/or the capacitors (solution: replace the capacitor to faster).
Maybe also this "damping factor" that I don’t understand what to do/look for to exclude.

Or am I totally lost in my conclusions?

I’m not an EE, but I’ve never heard of a case where troubleshooting starts with changing out the caps.
If a tube amp/speaker sounds slow and boomy it could be the rectification of the amp.

I would not worry about damping factor.
It could be as simple as the tubes. Maybe you are hearing bass bloat.
What power tubes are installed?

The Tannoy Eaton Legacy seems like an easy load to drive, but room placement is important and will affect results.


Yes, I'm gonna change the tubes, but I really wanna know the brand of the stock tubes before I do that. They are just labeled "Line Magnetic". If this dosen't do the trick I will have the capacitors replaced.

Yes, the speakers are easy to drive, and as I wrote, with my old EL84 amp there's no problem with boomines. Or, to be honest, there's a faint hint of boomines. And yes, I know there's a problem somewhere around 46-50Hz.

I have no idea what I have no idea what constitutes an "ultra-fast capacitor" but it's unlikely caps are the issue as stated by others above. Also you don't actually need to understand damping factor, just the different output taps and use the one that sounds better. lowrider gives you good advice on trying better tubes likely the LM branded tubes are a cost effective option from China, better tubes are out there.

Curious about your Tube Technology Unisis Signature amp, I used to own the Tube Technology Fusion CD64 cd player and absolutely loved it. Sadly it died but based on that listen your "old" amp may in fact be a better amp that the LM amp you're considering.

Last thing did you try moving the speakers around to compensate for that boominess?
Yes, maybe my old TT is a better. But I have had problems with it or maybe I have had bad luck with the two last quads EL84 tubes. I’ve had trouble with elaking tubes and the bias not being stable and I’m not even sure if I have the right information of how to adjust the bias. A friend of mine said I should adjust the tubes to120mV. I don’t know if it’s to high or not and I can’t find any information anywhere.
TT once sold a meter for the bias adjustment and when that meter showed 3.0 the bias was spot on. But 3.0 what? How do I translate that to mV?
So, the reason for a new amp is that I’m tried of all this hassle.
@simna I can understand your frustration but have you tried reaching out to Tube Technology?


Yes, but the company doesn't excist anymore. I've heard that the guy who owned TT has left England for US (and are now working for Manley I think).

Oh ok I saw their website was still up but hard to tell if they were still in business. Are you in the US or elsewhere? If you are in the US, or even not, perhaps try reaching out to Zia Faruqui through Manley? I corresponded with him once years back about getting my CD player fixed but ultimately balked at sending it back to him in England.


I'm in Sweden. You mean he answered your mail? I would love to have the schematics over the Unisis Signature and have someone figure out how to bias it without the special bias meter TT made. Or even better he could tell me how many mV the tubes should have.

Do you know how to get in touch with him? Mail address?

@simna Yes he answered my email this was some time ago maybe about 4-5 years ago. I have since changed my email and don’t have the correspondence any longer but it was the Tube Technology contact email; so I don’t know if it’s still active but worth a try.

Also I was just reading the owners manual of your amp online and this statement jumped out at me:

If your dealer cannot offer this re-tubing service it is possible to fit a replacement tube andadjust the bias yourself with the aid of a custom TT Bias Meter available from anauthorised Tube Technology dealer.

Does an everyday bias meter work on the amp or do you need this custom unit? Are you able to bias at all?


Actually to bias is not the big problem. There's a 8-pin connector on one side of the amp where this special TT Bias Meter is supposed to be connected. I have figured out which pin goes to which tube and then I use a multimeter to measure the tubes mV. But I don't know if 120mV is too much or too little. And then I have another problem. If I adjust the tubes one day to 120mV, next day some of the them measures 122 - 128mV.  The guy who bought these tubes for me (russian no-name) says that it's OK for a tube to change from one day to the other within 10%. But I don't know if this is true.

The measurement of tube voltage will change every day and at different times during the day. It’s caused by the fluctuation of line voltage coming into the dwelling and the mains.

The measurements you stated are acceptable.

@lowrider is correct those measurements are totally fine and if you think your amp sounds better than LM I would say keep it and be happy.
Pleased that OP has tangentially, but nonetheless, highlighted how good E-84's can sound. One of my favorite output tubes that "doesn't get the press it deserves". And, yes, it does have nice rich bass that often warrants a "double take".
EL-34's offer a lighter style, more "finesse" like a Lafite Wine... it seems to me. -Though I know the circuit is at least as important.
See if you can't listen to an EL-84 amp sometime.
Listen to a Manley Stingray and that will give you a good impression of a well designed EL84 amp. I have one, love it. I also have their EL34 monoblocks and they sound wonderful too.