Bravo / Indeed Headphone amplifiers

[clausdk]

if it turns out to be the PSU I'll eat my hat and send you a 5amp PSU


We want pictures

[Deleted]

WOULD YOU!! That would be GREAT, Mike.

In fear of repeating myself, YOU OR INDEED ANYONE ELSE, that has received parts from me, owes me nothing, i enjoy what i do on this forum, and if it makes other members happy that`s a bonus, i appreciate that Electronics is your living Mike, therefore i feel payment is in order, this is one of my hobbies, and trust me on this, if i didnt want to do what i do, i bl""dy well wouldn`t.

[PinkFloyd]

Feb 4, 2010 23:00:54 GMT @clausdk said:

if it turns out to be the PSU I'll eat my hat and send you a 5amp PSU


We want pictures

I can do you a pic of "George" eating a "cat" but, unfortunately, have none of me eating a hat ;D



I will buy a hat and gladly "eat it" if it turns out that Gomez's PSU is the culprit

[PinkFloyd]

Feb 4, 2010 23:12:12 GMT @heliharris said:

WOULD YOU!! That would be GREAT, Mike.

In fear of repeating myself, YOU OR INDEED ANYONE ELSE, that has received parts from me, owes me nothing, i enjoy what i do on this forum, and if it makes other members happy that`s a bonus, i appreciate that Electronics is your living Mike, therefore i feel payment is in order, this is one of my hobbies, and trust me on this, if i didnt want to do what i do, i bl""dy well wouldn`t.

PM me your details and shut the **** up

[gomez]

"
NO..... it will NOT be heading back to HK.... I'd like to think that Henry will ship a new EH valve over to you to save on shipping costs.... IMO, from what you describe, it's the valve NOT the PSU...... if it turns out to be the PSU I'll eat my hat and send you a 5amp PSU "

You just gotta love this place & the people in it. Such a rare find.

[Deleted]

Feb 4, 2010 23:00:54 GMT @clausdk said:

if it turns out to be the PSU I'll eat my hat and send you a 5amp PSU


We want pictures

Is the PSU a SMPS ?

[PinkFloyd]

Feb 4, 2010 23:22:41 GMT @sandyk said:

Feb 4, 2010 23:00:54 GMT @clausdk said:

if it turns out to be the PSU I'll eat my hat and send you a 5amp PSU


We want pictures

Is the PSU a SMPS ?

Yes.

[Deleted]

Feb 4, 2010 19:59:10 GMT @heliharris said:

Ian,

There is no hum at all on mine, i have turned everything off and on that`s around it, and no hum.

I have been listening to it for an hour now,( been playing to itself all afternoon) all types of music, the Bass is simply stunning, its sooooo musical, its HIGHLY recommended by me, £63 what a bargain.

Mick, it was the power supply. Changed it this morning and the low level stuff disappeared. The noise floor just wasn't quite 'black.'

Quiet as a mouse now. I've got dark black.

I prefer the 6h23n in comparison to the one that came with it, but I'm nervous now of the biasing!!

I can see this starting me off on a bottle search .......

Since changing the supply, the amp sounds more 'focussed' and sharp. Maybe it's starting to 'burn' itself in more but it has really settled for some reason. I'm getting less interference today. (Saturday) Maybe everyone around here has switched off. Who knows.

Listening to Vaughan Williams 4th Symphony on it and it really copes well with the complexity of the mix. Even on the verge of 'raspiness' on the brass in the first movement. (That could be the recording though). There also seems to be more space around the sound.

It makes me wonder how much of it's sound is being held back by the supply. (or altered) I felt a bit underwhelmed at first and thought I was being a bit 'snobbish' since I have better in the house to compare with, but after some running time, it seems to be improving and I'm starting to really bond with it.

Along with that lush sound, there is a nice 'bite' to the sound in orchestral stuff. (It suddenly seemed to appear which is a bit strange)

I'm also going to put a better power supply on it eventually. (Definitely 2 amp) It works nicely with the K701 and drives it with absolute ease too.

The sliding issue is a pain. It needs feet to keep it still. I was thinking of taking some rubber gromits off my congas and sticking them on top of the nuts at the bottom. Trouble is, it's nuts aren't big enough. (A common problem for many) ;D

Ian

[PinkFloyd]

Ian,

Mine is pretty silent too, I am using the "indeed" 2amp PSU. When I have time I will knock up a 24V Pinkie and see if it makes any difference.

Don't worry too much about the biasing.... listen to a few valves and, when you find one that you like THEN bias it (as per instructions)...... if you think you will ever go back to the EH valves then mark the position of the trimpots (before the bias) so you know where you were

I've been a bit sidetracked with the WAD HD-83 amp but will be getting back to these cracking little amps shortly

[leo]

If the bias is off too much you may get some nasties like distortion, sharpness etc, a bit out isn't too bad but if it quite a bit out

Just need a cheap multimeter and small screwdriver for the trimmer, dead easy

[Deleted]

Feb 6, 2010 17:58:06 GMT leo said:

If the bias is off too much you may get some nasties like distortion, sharpness etc, a bit out isn't too bad but if it quite a bit out

Just need a cheap multimeter and small screwdriver for the trimmer, dead easy

The sound has settled a lot. It's very good.

I checked the plates in the dark to see if there were any signs of the voltage being too high. Difficult because it's lit up, but they look OK so at least if the voltage is low, then no harm.

I think it's ok though.

Ian

[Deleted]

Ian first off don`t worry to much about the feet, that will be sorted asap, if you get my drift"".

Pleased you have sorted your "hummm" problem, lucky you could lay your hands on another PSU.

I am over the moon with mine, but have yet to try a different valve, so an "Ear orgasm" as Mike puts it might well be on the cards when i do. Biasing I would have to get detailed instructions( "lay man type, idiot proof") from Mike before i attempt that!!.

Be great if Mike could do a" LITTLE PINKIE" for it , works wonders on my XCAN-V3, so have no doubts about it enhancing the Bravo.

I have found that it needs to be hot ( at least an hours run time) before it gives off its best, and when it does, its sooooo musical, pretty much as you describe, i would agree with, the Bass is astonishing, and the clarity and detail brilliant, for such a low cost Amp.

It really Makes the 681`s sing, made for each other , i would say.

Regards Mick.

[Deleted]

Actually Mick, I've been listening all day. It's an astonishing listen for that kind of money.

It's the first chance I've had to do an extended detailed listen on a hot tube without the raised noise floor.

The thing is, the power supply was also affecting (I think) the top. It wasn't as crystal as it is now. It seems to have really cleaned up its act, so if that's the result of putting a better supply on then it works big time.

I tend to look for all the problems rather than think something is good because it's new. (or potential problems)

I did have a Little Dot II+ some time back which I really quite liked and it blew up on me big time!!! Scared me with regards to valves (Although I have other valve stuff).

I had an ultra expensive set up (speakers) installed for test in my house with this gi-normous valve amp. I was scared stupid because of the cost of it (and nearly bought it because it was stunning) and a bloody valve popped. (£24,000)

I was so embarrassed when I phoned the dealer. He laughed it off with C'ext la vie so I was pretty relieved, but it really made me slightly nervous of valve gear.

Anyway, this little device is fan bloody tastic. It's staying.

Ian

[PinkFloyd]

Just checked the bias on the Bravo amp and it was pretty way out measuring 12.1V Right channel and 13.2 left channel They obviously don't precision bias at the factory (probably too time consuming to do each one and they just set the trimpots to midway)

Soooo..... had a quick look at the circuit and changed the bias to the recommended 16.5V both channels.

I thought this amp sounded good before adjusting the bias but now it sounds REALLY good!

Adjusting the bias is SIMPLE folks, don't be put off, here's how to do it.... I have made the instructions as simple as possible:

There are two yellow trimpots (LTP and RTP) for tuning the DC bias voltage of each channel. After the valves have been running for a long period ( a few months) or after changing to a new valve the it will be necessary to re calibrate the bias.

For this operation you will need a small screwdriver and a multimeter set to the 20V DC range.



1. Power ON the amp with no audio signal input. Ensure that the Valve is fitted.

3. Wait at least 5 minutes for the amp to heat up.

4. Use the multi-meter to detect the DC voltage between the test point L220 on the PCB and GND. (ie: probe between L220 and GND)

5. If it needs adjusting turn the screw on the top of the LTP trimpot with a small screwdriver
(clockwise or anticlockwise) until the voltage is as close to +16.5V as possible.

6. Then, repeat step 4 and 5 for the other channel.

7. Leave the amp on for a further 30 minutes and re-check / adjust.

Job done!


Valve removed for illustration purposes only... always ensure valve is fitted when performing a re-bias.


Hope this helps

[Deleted]

I was saying to Ian ((toad) yesterday, i have thousands of pounds of Hi-Fi gear in my living room, but here i am in my study, as happy as a Monk in a Convent, listening to an iPod classic Sendstation port connector, Chord interconnect, Frans filter, Bravo( original valve) moded 681`s total cost around £300, TOTALLY immersed in the music. FANTASTIC, wife`s not happy though!!!!!!

[Deleted]

Hope this helps

That`s spot on Mike, even i can understand that

Thank you.

[PinkFloyd]

Seriously guys.... if yours are pretty well out (which my Bravo was) then please do set the bias to 16.5V per channel..... erm, you will be pretty pleased

Once you have done this there will be no stopping you

Mike.

[PinkFloyd]

By the way...... to pop the hood all you have to undo are the 4 nuts on the bottom of the amp..... it then comes apart.

[PinkFloyd]

With the amp now fully heated up (about 30 mins) I am now running at 16.17V per side and the SQ is absolutely stunning... full bodied, deep, dynamic and superbly detailed.... an absolutely corking buy for the money

[Deleted]

Thanks Mike. That's exactly what the makers should have sent out. Now it's really clear.

Ian

[PinkFloyd]

Feb 6, 2010 22:53:52 GMT @iancraig10 said:

Thanks Mike. That's exactly what the makers should have sent out. Now it's really clear.

Ian

If they biased them all correctly at the factory it would take them a good hour for the entire process Ian.... time is money as they say..... they obviously just set the trimpot to midway and send them out like that... will still sound half decent but not "optimum".... a cheap multimeter and a small screwdriver is all you require to set it up to optimum

[gomez]

Feb 6, 2010 22:44:52 GMT PinkFloyd said:

With the amp now fully heated up (about 30 mins) I am now running at 16.17V per side and the SQ is absolutely stunning... full bodied, deep, dynamic and superbly detailed.... an absolutely corking buy for the money

Excellent guide Mike I think I'll leave mine until them new valves your sending arrive not much point trimming my hisser but things are looking very very interesting for next week bit of rolling bit of trimming loads of listening I am so pleased I found this place & you Guys.

Paul.............

[PinkFloyd]

Feb 6, 2010 23:21:26 GMT gomez said:

Feb 6, 2010 22:44:52 GMT PinkFloyd said:

With the amp now fully heated up (about 30 mins) I am now running at 16.17V per side and the SQ is absolutely stunning... full bodied, deep, dynamic and superbly detailed.... an absolutely corking buy for the money

Excellent guide Mike I think I'll leave mine until them new valves your sending arrive not much point trimming my hisser but things are looking very very interesting for next week bit of rolling bit of trimming loads of listening I am so pleased I found this place & you Guys.

Paul.............

Try trimming them Gomez

[gomez]

Ok Mike will give it a go first thing in the morning.

[Deleted]

A question for the designer.

Would the rather low Anode current of approx. 0.4mA , as set by the Red LED (1.8V ?) and the 3Kohm emitter resistor, in conjunction with the >500pF to 700pF Input Capacitance of the FET ,lead to a small amount of premature HF rolloff ?

SandyK