Good VFM? The PANDA headphone amp. I'll say so!

[toad]

Cheers Mike, Hopefully that will be enough info for me. As much as I like my T585 my Arcam has the edge on it for music playback. Apparenty Jimmy Hughes, one of the reviewers of HiFi Choice and Hif-Fi+ uses the DV135 as his primary CD player.

It certainly produces a nice sound

Ian

[PinkFloyd]

I've had my T585 on standby since I bought it and have pretty much used it every day Ian, it really has filled out nicely over the past few months. A lot more relaxed sounding now and the bass has definitely improved a lot. Not bad for £199

[toad]

Don't get me wrong Mike, I think the T585 is excellent for the cash and as it's supposed to be better than my Arcam for video, it makes sense for it to be in my AV setup rather than my HP setup, not that I have a good enough TV to tell the difference yet LOL. TBH it was dirt cheap at £199 and represents fantastic value and it's pretty musical too.

Are you still using it as your main CDP?

[tripmaster]

Hi

I am trying to weigh up which headphone amp to buy. I will probably only use it as intended, but it may be nice to run it as a preamp for my Pass F5 Class A amp. Has anyone used a Panda as a pre?

I'm also considering the Cavalli Kumisa III

Thanks

Richard

[Koolind]

My panda have now been soldered and fired up. No kabooms or smoke !
I have adjusted the DC over the 1k5 resistors to 1.45v at both channels and checked the DC offset at the output.
Now for the big moment; Feeding it with some input and connecting a pair of headphones to it! To my big dissapointment there is only silence
What would be my first move ?
One thing that i noticed was that there wasnt at any point any DC offset to adjust; It was just 0.0-0.3. Presumeably this is simply because there isnt any signal to the output?

[leo]

Did you measure for DC offset after the 2R2 output resistors before the relay? maybe it was high enough to trip it so your not getting anything after the relay going to the output socket .

Edit, should be 10R not 2R2

[leo]

Nov 2, 2010 13:16:56 GMT tripmaster said:

Hi

I am trying to weigh up which headphone amp to buy. I will probably only use it as intended, but it may be nice to run it as a preamp for my Pass F5 Class A amp. Has anyone used a Panda as a pre?

I'm also considering the Cavalli Kumisa III

Thanks

Richard

Not heard a Panda yet but do have a CKIII (somewhere ) I'll be sure to compare them if I get one before you

[Deleted]

Koolind,

It doesn't work because most likely the DC offset on one or both channels is bigger then +/- 0.7 volt which makes the relay fall off as a safety feature.

You need to adjust the DC offset as per my reply Reply #765 on top of page 52 of this thread.
Then it'll probably work.

Make sure your measuring tip does not toch the groundplane !!!
Make sure you only touch the wire of the resistors OR solder a wire on it where you can attach the test leads on.

[Koolind]

I meassured at the actual output as in the little guide by Mike.
You are suggesting to meassure between the two blue resistors marked 2.2 and ground ?

[leo]

Try at the join between the emitter resistors 10R's with red probe and ground with black probe

[Deleted]

No as per my instructions in reply #765.
Mike's method ONLY works when the DC offset is already close to it's intended value.
It is probably not and therefore the relay is not making contact and thus the output cannot be adjusted at the output connection but can only be measured befrore the relay.
The only 2 easy points are the 2 10 Ohm resistors or the 2 51k resistors next to the relay.

the 2.2 resistors are in the power supply lines.
Do not measure there.
Another good point to put your test lead is the middle of the 2 10 Ohm resistors that are hiding between the back of the cooling fins and big capacitors.
Make sure you ONLY touch the leads of 1 of the 2 resistors at the point where they are close together (in the middle as it were)

[leo]

Sorry, Edited post it should have said 10R (emitter resistors) not 2R2

[Deleted]

If the DC is higher then a certain voltage there won't be a click nor a second click.
It will be clickless.

[PinkFloyd]

Frans,

I have built three now and they all fire up first time with the offset being about 30mV - 120mV before trimming.... maybe I have just been lucky!

Yes, my measuring points are assuming the relay hasn't cut out I must change the instructions to Fran's instructions for the "initial" fire up measurement.... once the DC is in an acceptable "zone" then it is good to fine tune it at the measurement points I suggest (ie: at the output / headphone socket)

Mike.

[Koolind]

Nov 2, 2010 21:09:55 GMT @solderdude said:

Koolind,

It doesn't work because most likely the DC offset on one or both channels is bigger then +/- 0.7 volt which makes the relay fall off as a safety feature.

You need to adjust the DC offset as per my reply Reply #765 on top of page 52 of this thread.
Then it'll probably work.

Make sure your measuring tip does not toch the groundplane !!!
Make sure you only touch the wire of the resistors OR solder a wire on it where you can attach the test leads on.

Ahh yes.. Now i realize why you said that the method suggested by Mike wasnt always ideal.. Thank you very much.. My panda is now roaring like a beast !

[Koolind]

Nov 2, 2010 21:26:00 GMT PinkFloyd said:

Frans,

I have built three now and they all fire up first time with the offset being about 30mV - 120mV before trimming.... maybe I have just been lucky!


Mike.

My DC offset was way off; more than 800mV i think - Would this suggest that there is some bad components or bad solderings somewhere?

[Deleted]

O.K.

The same thing happened with Mick's second built and Claus's build.

Mike have you been matching K246's before putting them in ?
This might explain why your builds fire up immediatly.

The pots are standard in their middle position when you receive them.
If you have matched the input FET's the middle setting is where it is supposed to be and will be close to perfect from the start.
When they are not matched the pots might need a lot of turns (25 turn pots) to reach the 0V DC setting.

[PinkFloyd]

Nov 2, 2010 21:26:01 GMT Koolind said:

Nov 2, 2010 21:09:55 GMT @solderdude said:

Koolind,

It doesn't work because most likely the DC offset on one or both channels is bigger then +/- 0.7 volt which makes the relay fall off as a safety feature.

You need to adjust the DC offset as per my reply Reply #765 on top of page 52 of this thread.
Then it'll probably work.

Make sure your measuring tip does not toch the groundplane !!!
Make sure you only touch the wire of the resistors OR solder a wire on it where you can attach the test leads on.

Ahh yes.. Now i realize why you said that the method suggested by Mike wasnt always ideal.. Thank you very much.. My panda is now roaring like a beast !

And....... "now" you can use my method to fine tune it

[Deleted]

yes.... after it has warmed up for some time with the lid on..

[leo]

At least they had the sense to implement DC offset protection . Shame there wasn't an led indicator for showing high DC offset
Anyway glad to hear its now working, time to run in and enjoy the tunes

[Koolind]

Nov 2, 2010 21:40:55 GMT leo said:

At least they had the sense to implement DC offset protection . Shame there wasn't an led indicator for showing high DC offset
Anyway glad to hear its now working, time to run in and enjoy the tunes

Well.. That would be a bit overkill i think. I suppose that you would rather just meassure from the 51K resistors instead avoiding the issue.

[Koolind]

I am suprised to see that it actually produce a decent amount of heat. The heatsinks are getting too hot to touch for more than a couple of seconds. When its put in a closed cabinet i suspect that it will get quite hot?

The sound however, seems really nice with lots of impact and power. Nice!

[PinkFloyd]

Nov 2, 2010 21:35:06 GMT @solderdude said:

O.K.

The same thing happened with Mick's second built and Claus's build.

Mike have you been matching K246's before putting them in ?
This might explain why your builds fire up immediatly.

The pots are standard in their middle position when you receive them.
If you have matched the input FET's the middle setting is where it is supposed to be and will be close to perfect from the start.
When they are not matched the pots might need a lot of turns (25 turn pots) to reach the 0V DC setting.

Hi Frans,

The kits are supplied with "ten" 2SK246 (you only need 6) so I have been pairing them up as close as poss with a very basic HFE test on a multimeter.... I have since got a better matching tool .... so they're not "matched" in the absolute sense.... I just choose 6 out of the ten that are closest to each other in HFE readings.

Panda three is a different kettle of fish though, I bought quite a lot of Toshiba 2SK246 (from the same batch) and have matched 6 that are pretty much identical to each other.... very time consuming and you will need (literally) a hundred to get a few "perfectly" matched 2SK246..... IMO, it is a waste of money as you can "trim" the offset down to acceptable levels with a cheap 200R trimpot but for the really anal enthusiast who has the time AND money AND test equipment to go through a batch of 100 transistors and select 6 perfect ones.... well, it may seem a good idea to him.

Personally, I think the 10 you get with the kit will get you as close as you need to get the amp up and running and the rest can be dealt with by the 200R trimpots. If we start introducing the concept of matching transistors and the equipment required to match them "correctly" then BANG goes what this thread is all about..... WORLD class sound for pennies.

I have no objections to anyone starting a "maxed out" Panda thread where every possible aspect of the design is picked to the bone and every possible scenario for making it sound "better" is explored.

I, for one, won't be partaking in such a thread though as I believe the Panda to be the best head amp I have ever heard and am HAPPY with the sonics it is amplifying into my ears.

I'm the opposite to Frans, I believe that components DO sound different, they all have a unique sonic signature..... the Panda "as is" has one of the nicest signatures I have EVER heard so I'm in no hurry to change that and certainly in no hurry to bastardise the design with my "own" signature.

Credit due to the designer of this amp.... it's pretty much IDEAL for my listening preferences and I am so happy with the sonic presentation.

I have "wrongly" started to mess about with Panda three.... bypassing electrolytics etc. and have promised to take Panda four to "new dimensions".... what?!! I am talking bollocks.... who am I (or anybody) to be so up their own arse that they can claim to "better" the design of another yet be unable to come up with a design of their own?!!

I couldn't design an amp like this if my life depended on it. I can "tweak" and I "play about" but I don't have the smarts to design one of these from the ground up and I really respect the guys that can.

I think I've finally found the amp (for me) and am so happy with the sounds it makes... I don't want to (or have no need to) change it.

[leo]

Have to agree regarding components , capacitors especially the audiograde ones add quite a bit of signature, a signature you soon get to know well enough

I'd be one wanting to try various alternatives in any amp I see which is filled with audiograde caps, to me those FG's are just like Marmite As already mentioned the design is pretty well sorted, just be worth trying a few alternative ingredients

[PinkFloyd]

to me those FG's are just like Marmite

You either love it or you hate it.