Look at these beauties

[Firebottle]

Getting exited now, just had these in the post, other bits on order:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/P1030829.jpg

:stalks: Alan

[loo]

Nice one Alan,
Seems like a good choice for the task ahead:cool:
Cheers
Paul

[Firebottle]

A sneak preview of the all new OTL:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/P1030863.jpg

:yay: Alan

[rubber duck]

6550s/KT88s? C'mon, spill the beans!

[Firebottle]

Not until I find out how much output I can get................:)

There's nothing under the chassis........yet.

:popcorn: Phew, found some at the back of the cupboard.

[Audio Al]

A sneak preview of the all new OTL:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/P1030863.jpg

:yay: Alan

WOW :wow: on looks its a winner already :eek:

Looking forward to the report on how it works :D

Love the OUTLAW name as well , COOL ;)

[loo]

Hi Alan,
looking good ,
although are those power tubes :eyebrows: not quiet close together ,
looking forward to reading your thoughts on sound .
cheers
Paul
P.s sadly she gave up the fight and passed away:(
hence my lack of correspondence

[Jimbo]

Hu Alan,

what make are the small tubes, are they ECC83,s?

[Firebottle]

Hi James,
They are ECC189 tubes, I think the make is RTC, I haven't got it in front of me at the moment :scratch:

:cool: (Banana Bread Beer) Alan

[Firebottle]

Well I thought I'd tackle the build and testing in a logical manner and make a test board first. It will also double up as a rig to match the valves.

I powered it up this afternoon and wang my wellies, sharpen my pencil and pour a beer, it gives a LOT of output :yay:
As with all high power OTLs it also gives a lot of heat from the big four.

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/P1040006.jpg

With just one output valve fitted I achieved 10W rms into 8 ohms.
With two output valves fitted I achieved 26W rms into 8 ohms; This will be the basis for a 26W per channel stereo poweramp.

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/P1040007.jpg

Wait for it...........

...with four output valves fitted I achieved 60W rms into 8 ohms; this will be the basis for a 60W monoblock :eek:

A bit more fettling and of course a listening test to come, but by crickey I'm pleased with that.

A good time for a :cool: Alan

PS I did a very quick power bandwidth test and it was only starting to drop at 80KHz.

[Jimbo]

Yo Alan, 26W is probably all I need:)

Looking forward to hearing that magical OTL sound!

cheers:cool:

[loo]

Dr firebottle ,
my God man have you taken leave of your senses, 60 watts a channel you've created a Monster :lol:
private jokes aside well done Alan :cool: I cant thankyou enough for going ahead with this ,
this is my most eagerly awaited Amplifier for a very long time I cant wait to hear it :eek:
Alan you know you are welcome to pop over with it anytime to compare against some other heaty meaty monsters
that includes letting you sleep over I will even feed you :eyebrows:
What a star you are king of OTL's:youtheman:
cheers
Paul

[Jimbo]

Alan,

are the monoblocks 30 watts each or 60?:eek:

[Firebottle]

Jimbo,

The monoblocks will be 60W for each!
There is a provision though, this will be a program material rating, not a continuous rating as in a sine wave test tone. A continuous tone would exceed the dissipation rating for the output valve anodes.

So for normal music 60W peaks can be output without clipping.

Cheers,
Alan

[Firebottle]

Don't know about the 'king of OTLs' but I've been fettling the circuit today.

Had to change a couple of component values a little to suit the valves better, but it's a superbly stable circuit. The output offset only varies by a few millivolts.

I've looked at all the supply rails to make sure there is no hum, but when I monitored the output there was a little hum present; Turned out when I disconnected the signal generator it disappeared :)

The sig genny was a battery operated model until I added a mains pack, looks like I added a bit of hum as well.

Listening test tomorrow.........

Alan

[Jimbo]

I will be tuning in tomorrow to read your results:)

[Gordon Steadman]

Don't know about the 'king of OTLs' but I've been fettling the circuit today.

Had to change a couple of component values a little to suit the valves better, but it's a superbly stable circuit. The output offset only varies by a few millivolts.

I've looked at all the supply rails to make sure there is no hum, but when I monitored the output there was a little hum present; Turned out when I disconnected the signal generator it disappeared :)

The sig genny was a battery operated model until I added a mains pack, looks like I added a bit of hum as well.

Listening test tomorrow.........

Alan

Some of us might even know what the hell you are talking about:doh:

[awkwardbydesign]

Some of us might even know what the hell you are talking about:doh:
Does that mean that without output transformers, DC can appear at the output, like a transistor amp?
See, I'm concentrating. I may be totally wrong, but I AM concentrating!

[Firebottle]

Richard you are absolutely correct. This OTL circuit, unlike many others, has dc feedback so has great stability.

I'm really pleased with it, it's technically well satisfying as well as the promised audio performance.
I'd like to think it is a 'best practice' design, plus a couple of tweaks for better balance and valve longevity.

Cheers,
Alan

[Jimbo]

Does that mean that without output transformers, DC can appear at the output, like a transistor amp?
See, I'm concentrating. I may be totally wrong, but I AM concentrating!

Having no output transformer should give the amp a magical totally transparent mid range. :cool:

[Jimbo]

Alan are these based on a Futterman design ?

[Firebottle]

Never mind the totally transparent mid range, the whole bandwidth should be transparent.
I did a quick test with full power square wave output and it was virtually perfect.

The design is different from a Futterman design. The input and driver stages are long tailed pairs with the associated ripple rejection and even harmonic distortion cancellation. The output stage uses a novel combination of local feedback and current drive to achieve good symmetry.

:cool: Alan

[awkwardbydesign]

Having no output transformer should give the amp a magical totally transparent mid range. :cool:
You mean like an SET amp WITH output transformer?:lol:

[Jimbo]

Never mind the totally transparent mid range, the whole bandwidth should be transparent.
I did a quick test with full power square wave output and it was virtually perfect.

The design is different from a Futterman design. The input and driver stages are long tailed pairs with the associated ripple rejection and even harmonic distortion cancellation. The output stage uses a novel combination of local feedback and current drive to achieve good symmetry.

:cool: Alan

Long tailed pairs, I think, draw current from the supply in constant DC do they not, so the supply is excluded from the signal path, therefore reducing its effect on sound quality?

Is this topography designed to protect loudspeakers in case of a fault by naturally limiting current? Or do you need to use protection circuits?

[loo]

Never mind the totally transparent mid range, the whole bandwidth should be transparent.
I did a quick test with full power square wave output and it was virtually perfect.

The design is different from a Futterman design. The input and driver stages are long tailed pairs with the associated ripple rejection and even harmonic distortion cancellation. The output stage uses a novel combination of local feedback and current drive to achieve good symmetry.

:cool: Alan

Hi Alan,
Ltp is that similar to the differential circuit used by you know who ?
And if so does that mean this amp can be used with a balanced
Input?
From what you've leaked I get the feeling this amp could be the
Absolute dogs danglees
Can't wait for your thoughts post listening testing
Cheers
Paul

[Firebottle]

Long tailed pairs, I think, draw current from the supply in constant DC do they not, so the supply is excluded from the signal path, therefore reducing its effect on sound quality?

Is this topography designed to protect loudspeakers in case of a fault by naturally limiting current? Or do you need to use protection circuits?

You are correct on the first point but the answer to the second is no. There is some protection built in, and I am going to include an additional board that gives a start up delay before connecting the speakers, plus disconnection in the event of brownouts or driver stage failure.

Paul,
'Ltp is that similar to the differential circuit used by you know who ?' No it's a different circuit technique.
'And if so does that mean this amp can be used with a balanced Input?' No, single ended only.

Still tinkering but checked the output level at different speaker load resistances. Large load resistor shown here:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/P1040012.jpg

With 2 output valves (as per stereo amp):
Into 4 ohms, which is usually a difficult load for an OTL - 15W
Into 15 ohms - 40W

:cool: Alan

[Jimbo]

Well I thought I'd tackle the build and testing in a logical manner and make a test board first. It will also double up as a rig to match the valves.

I powered it up this afternoon and wang my wellies, sharpen my pencil and pour a beer, it gives a LOT of output :yay:
As with all high power OTLs it also gives a lot of heat from the big four.

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/P1040006.jpg

With just one output valve fitted I achieved 10W rms into 8 ohms.
With two output valves fitted I achieved 26W rms into 8 ohms; This will be the basis for a 26W per channel stereo poweramp.

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/P1040007.jpg

Wait for it...........

...with four output valves fitted I achieved 60W rms into 8 ohms; this will be the basis for a 60W monoblock :eek:

A bit more fettling and of course a listening test to come, but by crickey I'm pleased with that.

A good time for a :cool: Alan

PS I did a very quick power bandwidth test and it was only starting to drop at 80KHz.

Did you crank up the bias on the output valves to get those 60 watts?

[Firebottle]

No - standard bias level, in fact it doesn't need much standing current to overcome cross over distortion.

Some interesting developments with the listening test, but not what I really wanted :doh:
It's fine at low level but at high volumes there is asymmetric distortion. It turns out the original circuit has a flaw, it's of course down to the unavailability of PNP type valves, the bugbear of OTL ams.
The local feedback works well for the common cathode half of the output stage but dynamically unbalances the driver stage, hence the asymmetric distortion.

It is not noticeable with a sine wave but certainly is with music. I'm working on a cure at the moment.

:cool: Alan

[Gazjam]

Are those KT88 output valves Alan?
What bias setting did you use?

Looks great btw.

[Jimbo]

No - standard bias level, in fact it doesn't need much standing current to overcome cross over distortion.

Some interesting developments with the listening test, but not what I really wanted :doh:
It's fine at low level but at high volumes there is asymmetric distortion. It turns out the original circuit has a flaw, it's of course down to the unavailability of PNP type valves, the bugbear of OTL ams.
The local feedback works well for the common cathode half of the output stage but dynamically unbalances the driver stage, hence the asymmetric distortion.

It is not noticeable with a sine wave but certainly is with music. I'm working on a cure at the moment.

:cool: Alan

I think thats why its difficult to make good sounding OTL amps. PNP type transistors are easy to get but then they are not valves :)

[Gordon Steadman]

I must have a look in the small print of my contract. There has to be a clause somewhere about upgrades if designs are updated:lol:

I expect I'll be told that originals are worth loads and their intrinsic value would be harmed if modified:rolleyes:

[Firebottle]

Well absolutely Gordon (contract - what contract? :eyebrows:).

Gazjam, they are not KT88, they are xxxx - it's a secret ;) I'll probably set them at 60 to 75mA per valve when finalised.

Anyway, I've cracked it. Sounds amazing, only in mono of course from the test board :yay:

Might be a little while before the stereo version is ready for test as I have some other things to build :) Got to plan the under chassis layout anyway.........

:cool: Alan

[Firebottle]

I brought the rig down from the workshop for a proper listening test.
Rigged it up from the vinyl front end and connected the ESL57s in parallel on the output. It seems weird just listening in mono (L+R) but sounding very good.

Here is the rig up the corner in place of the usual OTL:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/P1040013.jpg

Just to prove it was vinyl:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/P1040014.jpg

You can tell a lot about an amp from the square wave performance, here is the OuTLaw full power square wave output:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/P1040010.jpg

To check the stability before I connected it to the ESLs I used an 8 ohm load with 2.2uF in parallel, to mimic an electrostatic.
Here is the full power square wave output again:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/P1040011.jpg

All in all an excellent result, I think I know what the OuTLaw name now stands for: Output TransformerLess audio wonder :eyebrows:

:cool: Alan

[Firebottle]

Well it is finally finished and on test in the lounge at the moment. At first impression it really seems to have a grip on the music, the bottom end is stunning.
It's got slam and depth and clarity and ............ well it sounds rather good.

It wasn't without a little hiccup, when first switched on there was a hum but only on one channel. It turned out the offending channel was oscillating, I used alternative valves to the original circuit (as is my usual way) and I had to fit grid stoppers to the first stage.

On test on the workbench:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/Firebottle%20OuTLaw/P1040149.jpg

For the electronic voyeurs amongst you (ooh errh) here is the internal shot:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/Firebottle%20OuTLaw/P1040151.jpg

Here's one for Marco as I know he loves his 'grab handles', there's no accounting for taste :lol:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/Firebottle%20OuTLaw/P1040152.jpg

Here is the rear view, giving an impression of the size of the toroidal transformer:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/Firebottle%20OuTLaw/P1040153.jpg

Got to have one or two of the attraction of valve goodness, by gum these big valve chuck out some heat:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/Firebottle%20OuTLaw/P1040154.jpg

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/Firebottle%20OuTLaw/P1040156.jpg

I'm not 100% happy with the design so there may be a couple more tweaks to come, but excellent so far,

Cheers, Alan

[Jimbo]

Well it is finally finished and on test in the lounge at the moment. At first impression it really seems to have a grip on the music, the bottom end is stunning.
It's got slam and depth and clarity and ............ well it sounds rather good.

It wasn't without a little hiccup, when first switched on there was a hum but only on one channel. It turned out the offending channel was oscillating, I used alternative valves to the original circuit (as is my usual way) and I had to fit grid stoppers to the first stage.

On test on the workbench:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/Firebottle%20OuTLaw/P1040149.jpg

For the electronic voyeurs amongst you (ooh errh) here is the internal shot:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/Firebottle%20OuTLaw/P1040151.jpg

Here's one for Marco as I know he loves his 'grab handles', there's no accounting for taste :lol:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/Firebottle%20OuTLaw/P1040152.jpg

Here is the rear view, giving an impression of the size of the toroidal transformer:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/Firebottle%20OuTLaw/P1040153.jpg

Got to have one or two of the attraction of valve goodness, by gum these big valve chuck out some heat:

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/Firebottle%20OuTLaw/P1040154.jpg

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Valve%20amp/Firebottle%20OuTLaw/P1040156.jpg

I'm not 100% happy with the design so there may be a couple more tweaks to come, but excellent so far,

Cheers, Alan

Wow Alan that really looks the business! Can't wait to hear the beast!

[struth]

Marvelous work Alan...me is jealous.............think I'll have to save my pennies up.

[Marco]

Looks fantastic, Alan! I'd love to hear it some day - perhaps next time I pop over to France? :)

Aren't you worried, though, about all the horrible (life-threatening) X-rays, and associated harmful radiation, generated by those nasty valves? :D

S'ok, if you don't know what I'm talking about, just ignore me!

Marco.

[Gordon Steadman]

It will have to go some to sound better than the existing OTL. Glad to hear its on the way.

Would love to hear all those watts through the Teufels:eyebrows:

[Firebottle]

.......... about all the horrible (life-threatening) X-rays, and associated harmful radiation, generated by those nasty valves? :D

Marco.

I thought you might like the look of it ;)
No harmful radiation with this beast, OTLs are usually at the lower end of the supply voltage scale, unlike SETs with big valves and Kilovolts on them :eek:

[anthonyTD]

Looking good Alan,
And nice to see you have paid considerable attention to overcoming some of the more important issues involved with conventional OTL circuit design! :)
Anthony,TD...

[sq225917]

Looks ace

[anthonyTD]

And i think i recognise those output valves :eyebrows: i have a regulated power supply full of them! ;)
A...

[Firebottle]

Yes 2nd cousin to your valves, they do get rather hot don't they?

For interest what conclusions are you drawing about overcoming the 'important issues' of OTL design.
I know yours is a practised eye, to say the least :respect:, but you only have the photographs (oooh ehrr),

Cheers, Alan

[anthonyTD]

Hi Alan,
The fact that you seem to have addressed the three main issues that bother me about OTL's, one, distortion characteristics, second, being able to keep the valves inside of they'r maximum design disapation, while still allowing them to produce a decent amount of power when needed, and last but not least, output protection, ie; DC detection circuitry and monitoring of the output, which IMHO is critical' with OTL designs, and of the utmost importance as far as speaker protection, of course this applies equally to bipolar solid state designs too.:)

Yes 2nd cousin to your valves, they do get rather hot don't they?

For interest what conclusions are you drawing about overcoming the 'important issues' of OTL design.
I know yours is a practised eye, to say the least :respect:, but you only have the photographs (oooh ehrr),

Cheers, Alan

[Firebottle]

You certainly know your onions Anthony.
I've always found it difficult to understand why anyone would design a valve amp to run the valves past their normal rating :scratch:

[anthonyTD]

:)

I've always found it difficult to understand why anyone would design a valve amp to run the valves past their normal rating :scratch: