[setamp]

I have noticed recently that my system sounds best when the battery powering my Dodd Tube Buffer is running low.  I have tested this several times with the same result.  When the battery is fully charged, my system sounds aggressive with upper-mids sounding forward and fatiguing.  As the battery drains, it becomes much more relaxed and the upper-mids recess.  The other day, I thought my battery was charged fully and was surprised at how organic and real my system sounded (more like when the battery is low).  Within minutes I noticed the left channel was weaker than the right and a few minutes later the battery died.  Once again it sounded great with a weak battery and it was not due to expectations as I thought it was fully charged.

Why would this happen and what is this telling me?  Could it be that my source is too hot for the gain of my amp?  I have ordered another battery to see if the one I own is faulty (it is not holding a charge as well as it used to).

My setup is an EE Minimax Dac Plus > Dodd Buffer (6h30dr) > AMB Beta 22 headphone amp with gain of 5 > Audeze LCD2 headphones.

Any thoughts?

[TrungT]

What charger do you have?

[setamp]

I have a CTEK charger.  I am at work and can't recall the model.  I always disconnect the CTEK when listening for under 3 hours.

[usp1]

This is quite curious indeed. SInce I always keep my ctek charger connected, I have always had a full battery. It might be interesting to try this out.

[jtwrace]

The best most inexpensive charger is this http://www.amazon.com/CTEK-800-Smart-Battery-Charger/dp/B002QUT8IC

Leave it connected all the time and be done with it.  Works great and trouble free.

[setamp]

I think I have this one:

http://www.amazon.com/Ctek-Battery-Charger-56158-56-158/dp/B000FQBWCY/ref=sr_1_1?s=automotive&ie=UTF8&qid=1338915625&sr=1-1

What I am trying to figure out is why it sounds better when the battery is low vs fully charged. 

[cheap-Jack]

Hi.

I have noticed recently that my system sounds best when the battery powering my Dodd Tube Buffer is running low.  Why would this happen and what is this telling me?

Nothing mysterious, my friend. This is phyiscs.

When battery runs low, the gain of the buffer drops, permitting higher swing of the music signals without RISKING overloading the active stage(s) of the buffer & its receiving power amp down the chain.

Subjectivey our ears detect more music & our brain interpretes better music.


Obvoulsy when battery runs low, you got to turn up the volume pot setting, right? Less resistance inside the volume pot signal path will have LESS sonic impact on the music signals. That's why you heard "it sounded great".

Again, this is physics. It also proves the buffer gets way too much gain for your system. NOT a good sign at all, IME.

Ever want to try to go WITHOUT the buffer amp? Just let yr phono-preamp connected direct to yr power amps? I bet you you will find the music is even more "relaxed" & more "organic"! I have done it so successfully since day one many years back.

FYI, I went thru this exercise already many years back. Gain is a muic killer, IME. I've now settled down very satified MUSICALLY withOUT any active linestage. For CD musics, never ever find gain not enough to drive my tube power amp.

Use your own ears to judge. Don't let whoevers' talks, even the amp vendors, to affect yr hearing finding.

c-J

[cheap-Jack]

Hi.

I have noticed recently that my system sounds best when the battery powering my Dodd Tube Buffer is running low.  I have tested this several times with the same result.  When the battery is fully charged, my system sounds aggressive with upper-mids sounding forward and fatiguing.
Any thoughts?

FYI, my 2 MM cartridge tube phono-preamps are heatd by an outboard 6V NiCd battery rechargeable by a digital mode power pack.

I always keep it fully charged before my music session.

One time somehow I did not charged up the heater cell enough & after few hours of listening, the gain of the phonostage drops bigtime & the music sound very weak - way too "relaxed". So I checked the heater voltage - dropped down to 4.5V !!!!!!

The sound goes back to normal when the heater cell is fully charged back up.

c-J

[setamp]

My system definitely sounds better with the buffer in place. 
I do suspect gain is the issue.  I will try reducing the gain on my amp.
Thanks

[usp1]

But the Dodd buffer does not have any gain, so why would taking it out of the chain affect gain.

[HAL]

In this case the Dodd Battery Buffer has no voltage gain, only current gain.  This would mean only the output impedance is changing as the battery voltage is dropping. 

What is likely happening is that the output impedance is increasing as the battery voltage is dropping.  At low battery voltage, you might be creating system synergy.

A thought would be to measure the battery voltage where you like the sound.  You could use a battery pack optimized for that voltage instead of the normal 12VDC AGM battery (~10.8V - 13.1V range).  The A123 style LiFePO4 batteries are nominally 3.3V @2.3Ah per cell and 3 in series are in the 8.4V to 10.8V range.  Depends on how many hours of operation you want as to how many you series and parallel.  These style of batteries need specific battery chargers for use. 

This will work best if you are using a 6V filament tube like the 7308, 6922, 6DJ8 and 6H30 styles as that is using the voltage regulator.

I would ask Gary if there are any drawbacks to the idea.

Just a thought.

[cheap-Jack]

Hi.

(1) In this case the Dodd Battery Buffer has no voltage gain, only current gain.  This would mean only the output impedance is changing as the battery voltage is dropping. 

(2) What is likely happening is that the output impedance is increasing as the battery voltage is dropping.  At low battery voltage, you might be creating system synergy.

(3) A thought would be to measure the battery voltage where you like the sound.  You could use a battery pack optimized for that voltage instead of the normal 12VDC AGM battery (~10.8V - 13.1V range).  The A123 style LiFePO4 batteries are nominally 3.3V @2.3Ah per cell and 3 in series are in the 8.4V to 10.8V range.  Depends on how many hours of operation you want as to how many you series and parallel.  These style of batteries need specific battery chargers for use. 

(4) This will work best if you are using a 6V filament tube like the 7308, 6922, 6DJ8 and 6H30 styles as that is using the voltage regulator.

So it is a ONE single stage "buffer" - technically a cathode follower which gives no voltage gain, but only current gain. That's quite an unusual design. I wish I can read the schematic so that I can pin point the problem.

(1)&(2)  The KEY function of a "buffer" or a cathode follower is an impedance reducer. So the O/P Z of the buffer can be calculated by the following formula:-
Z=1/gM ohms    (gM is the transconducance of the buffer tube).
Say 6922, its gM in its manual specified at 12mA/V.
So the O/P Z of the 6922 buffer will be 1/0.012=83.33R. (approximately).
Such low low O/P Z is good for long run interconnect to the power amp.

We can see this O/P Z formula does not show any direct relevance to any Z fluctuation due to its plate curent decrease as result of the battery voltage drop.

Even if there were any buffer O/P Z increase- supposingly, there should not be any effect to the power amp, tube or SS, with I/P Z many many times larger than the low low O/P Z of the buffer.

(3) Until we can get access to the Dodd buffer schematic, we don't know what Vp the buffer tube is operating at, so any suggestion to change the 12V battery supply voltage should be avoided.

(4) Unless setamp is a veteran DIYer, I don't recommend him to do any drastic
change in the orginal design of the buffer, including the heater voltage.

My BIG question is:- WHY Dodd did not incorporate this simple 1-stage buffer
into its phono-preamp in the first place?????

Any high school kid can build a catholde follower - "buffer", no sweats.

Marketing tactics or what? Famous vendors' last word - MONEY!

c-J

[HAL]

The filament voltage in the Dodd Battery buffer is switch selectable between 12VDC and 6VDC.  In 12VDC mode, it runs the filament on the battery directly and in 6V mode it runs off the regulator.   If he is using a 12A_7 style tube with a 12 volt filament, the filament voltage will change as the battery voltage changes.  If he uses a 6DJ8 family or 6H30, it runs off 6VDC regulator. Not knowing what tube is being used, all I can do is say how my kit is wired for the filament supply.

This does mean using 12V filament tubes, the filament supply will depend on the battery voltage.   

[cheap-Jack]

Hi.

Anyway we can get access to Dodd pre-amps & buffer schematics? Save us guessing?

In Dodd's site, I don't seem to read any technical stuffs about its products.
Sales pitch only for Joe Blow type consumers. Nothing for technical guys like me to read.

My curiosity lies on the "unique battery powered" design of the HV for the tube plate -  powered by 12V batteris or what not?

c-J

[setamp]

I am using a 6h30dr

[S Clark]

Hi.

Anyway we can get access to Dodd pre-amps & buffer schematics? Save us guessing?

In Dodd's site, I don't seem to read any technical stuffs about its products.
Sales pitch only for Joe Blow type consumers. Nothing for technical guys like me to read.

My curiosity lies on the "unique battery powered" design of the HV for the tube plate -  powered by 12V batteris or what not?

c-J

You're not the only one that would like to get their hand on it. No way  Gary or any small business owner  is going to release schematics on something as unique as a battery driven tube buffer, pre, or amp.  There just aren't that many guys that have figured out how to make it happen without running the battery down.

Scott

[2wo]

"My curiosity lies on the "unique battery powered" design of the HV for the tube plate -  powered by 12V batteris or what not?"

I think I figured it out and it is pretty trick ...John

[setamp]

The problem I was having seems to have been due to a bad battery.  I replaced the battery and the sound is great with a full charge.

[cheap-Jack]

Hi.

"My curiosity lies on the "unique battery powered" design of the HV for the tube plate -  powered by 12V batteris or what not?"

I think I figured it out and it is pretty trick ...John

What "trick" is it?

c-J

[cheap-Jack]

Hi.

You're not the only one that would like to get their hand on it. No way  Gary or any small business owner  is going to release schematics on something as unique as a battery driven tube buffer, pre, or amp.  There just aren't that many guys that have figured out how to make it happen without running the battery down.

Take it easy. I am NOT one of those who want to "get their hand on it" in order to copy whoever's brainchild.

FYI, I've design/built excellent sounding phonostage+passive linestages that have made many very expensive brandname stuffs SHY sonically as I have gone thru many auditions in top-notch audio studios to find out this fact.

First off, I never believe there is any real NEED in using any active linestage or line preamps for HOME audio, considering phono-preamp, CD playe all get enough gain to drive any power amps direct. So technically any
active line-amps or evn buffer amps are redundant.

So why so many audiophiles still go for active line-amps or buffer amps? More electronics can deliver better sound??????? Sorry, I totally DISagree.

Like it or not, it is markerteering!!! So many innnocent audio consumers so easily take in the wooing of the vendors' sales pitches.

I am curious to find out how 2x2x12V batteries can operate 6922 type HV tubes? Strictly on technicality ground. Nothing else.

c-J