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Old 17th May 2005, 11:36 AM   #1
Cassiel is offline Cassiel  Libya
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Default Unhappy with the LIlliput design

First of all, to be fair, i didn't use Megahertz transformers, i did use a Hammond 125 ESE with the 2,5k secondary tap connected to my 8 Ohms, 97db/m, speaker.

Results were dissapointing, not that it sounds bad but frankly, my ecl86 SE sounds a lot better using the 125 ESE as well.
The operating point of the input tube, a NOS GE 6dj8, was changed as it didn't have enough gain as it was. Replaced the 1K bias resistor for a 330 ohms. Sound is kind of dark or "fat" i'm not very good with audio adjectives but it doesn't have the "live" sound of my ecl86 SE.
Would using the Megahertz transformer be a total change? For it must get a LOT better to make me happy. Maybe this tube it's not of my liking. Before spending 200 euros in those transformers i want to know it's going to sound better than my ecl86-125Ese cheapo amp.
Is really the 6AS7 better sonically than a ecl86? I'm beginning to doubt this.

Any ideas?

Also , can i use the 6AS7 as a rectifier in case i just forget about this amp?

Thanks.
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Old 17th May 2005, 12:05 PM   #2
plovati is offline plovati  Italy
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Default is the tube that makes the sound?

No, it is the curcuit.
That means first of all schematic, working point, components quality. The tube itself makes very little in this whole picture.

Lilliput is reputed to be good sounding budget amplifier. Hammond's 125 series OPT are not HI-Fi rated, as the same manufactor specify. Also changing the working point of the driver alters the tonal balance because I guess that the original design use a certain amount of harmonic cancellation.

The input sensitivity is 2.7V rms that should be enough with direct CD input and 97dB efficient speaker.

A try with better output transformer in my opinion should be done before to blame this project.
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Old 19th May 2005, 04:57 PM   #3
Cassiel is offline Cassiel  Libya
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The sound got better but stilll...the problem is i use a low level output source(less than 1volt). Also my transformer only allows for 80 mil DC bias and i guess is on the limit thus not sounding very good or as good as it did with 35m DC bias. At low volumes sounds ok but the problem is i like music LOUD.
I will make a pre and report results....thinking about the aikido by John Broskie and see if the amp really sings with a 2v input.

Haven't got a cd player as i fried mine in a stupid mod i tried.
Thanks for the reply.

Cheers,


aLVARO
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Old 19th May 2005, 10:15 PM   #4
plovati is offline plovati  Italy
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Default Parafeed or BIRSEP

Yea, the transformer reach its limits and you got saturation.You can try simply to add a inductore and use the 125ESE as parafeed, avoiding DC current troubles. See RDH4 to proper dimension inductance and coupling cap.
To have more power and sensitivity, on the same magazine that published Lilliput, a reader proposed a PSE version , called Birsep, with two section of 6080 paralleled and a cascaded Ecc88 driver.
The response curve and distortion are good and power is 6W.
Seek on Costruire Hi Fi (CHF) on some volume of this Years I think.
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Old 26th May 2005, 10:36 AM   #5
Cassiel is offline Cassiel  Libya
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Quote:
Yea, the transformer reach its limits and you got saturation.You can try simply to add a inductore and use the 125ESE as parafeed, avoiding DC current troubles.
Thought about that but what kind of choke should i look for? RDH4?, a book i guess, haven't got it but i will try to get it.

Quote:
To have more power and sensitivity, on the same magazine that published Lilliput, a reader proposed a PSE version , called Birsep, with two section of 6080 paralleled and a cascaded Ecc88 driver.
Thanks for the tip, sounds what i need. Will try that if i find it.

You've been very helpful Plovati, thanks again.

Cheers,
álvaro.
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Old 26th May 2005, 07:35 PM   #6
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Quote:
Originally posted by stalker
Thought about that but what kind of choke should i look for?
Due to the relatively high cost of parafeed chokes, we got some of the IXYS CCS chips to see how that works....

http://pmillett.addr.com/current_source.htm

dave
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Old 27th May 2005, 08:40 AM   #7
plovati is offline plovati  Italy
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Quote:
Originally posted by stalker
[B]

Thought about that but what kind of choke should i look for? RDH4?, a book i guess, haven't got it but i will try to get it.
Simple is here:
http://213.156.45.208/primo/Radiotron.asp
read first the index and dowload the chapter You want because are large PDF files.

Quote:
Thanks for the tip, sounds what i need. Will try that if i find it.
Send me a private message, I can send You the schematic of this variant.

Bye,
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Old 31st May 2005, 11:05 AM   #8
Cassiel is offline Cassiel  Libya
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Quote:
Due to the relatively high cost of parafeed chokes, we got some of the IXYS CCS chips to see how that works....
Ummm, interesting article but i think i'd just rather spend the money in a choke. I like the old style best... Anyway good experiment and great web page. Thanks for the link.

Plovati, i have downloaded all the chapters and will read it.


.
Quote:
Send me a private message, I can send You the schematic of this variant

Thanks because i couldn't find it in the net. I am sending you an email.

Cheers,

EDIT: i don't have access to your email address.
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Old 22nd August 2005, 09:32 AM   #9
Cassiel is offline Cassiel  Libya
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Hi, just wanted to say thanks to Plovati for providing me a schematic for the 6as7. Sounds great, i was unfair with the lilliput, i just needed more volts and a good driver stage.
You were right Plovati, it's the circuit not the valve. But what madness to get a good sound, for example if i leave both cathodes of the 6dj8 unbypassed the tone is not there anymore, great sound depends on such a little thing?

Well after 3 months of trying i finally have a great amp, i was about to give the 6as7 up. Thanks again Plovati. My next step would be to buy the Megahertz transformers. If it sounds great with the 2,5k tap from the Hammond 125 ESE, guess it would sound superb with those OT's.

Ciao,

Álvaro
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Old 22nd August 2005, 10:10 AM   #10
plovati is offline plovati  Italy
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Nice to know You're satisfied.
About yours question on tone with or without bypass cap, I need to understand if You've realized the original Lilliput (one section of 6DJ8 and 6AS7, 2,5kohm load) or the Birsep (two section parallelled, 1kohm load). The last is due to Sergio Birello and was published on italian magazine CHF with also the winding details of output transformer.

6AS7 is a choice of many smart designer that does not care about appearance, with the two section paralleled is a sort of super cheap 300B. But this tube require a current plenty driver and a harmonic cancellation, so choice of operating point and components (bypass cap for example) is essential to have a good tone.

Also a good power supply makes the difference. Power supply transformer must be realized by competent people. Pay attention to upgrade to too expensive components, this schematic may not worth the cost. 6AS7 with some other driver and power supply may instead have beneficial from some top quality parts, but in this case my advice is to buy a used Kiom AD1 amplifier from Luca Chiomenti.
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