 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
66.91.168.87
In Reply to: RE: why not build an 'idealised design' PP EL84M amp? posted by Timbo in Oz on August 12, 2017 at 02:40:42
Hi Timbo, and thanks for the suggestion. I would like to stick with a preferably vintage or classic design. the amp is already supplied with a valve rectifier, as well as output transformers that look like they are designed for cathode biased output stage of about 12 watts per channel.
Follow Ups:
OT? Pentode? Ultralinear?
I purchased a physically damaged Eico HF-81 on Ebay a long time ago. Chassis was bent, no cover but iron all good. Been wanting to build a decent PP 6V6 or EL-84 amp using the iron.
The HF-81 was about the best sounding PP EL-84 amp of it's day so I'm guessing with the right iron you could pretty much copy the HF-81 or the power amp version which used the same iron and whose nomenclature I can no longer recall.
I don't remember. The amp operated in pentode mode, which i will also need to follow. The eico 81 has a 12au7 in front of the 12ax7 driver/splitter tube, and the au7 is for the tape monitor circuit. I wonder if including that tube would be too much gain if i also used it my amp? Does anyone have any experience with that? cheers.
And lots of NFB / gain killing.Noisy.
Esp. into EL84s where lots of gain in the driver is almost pointless. While low GM / 'grunt', is also not good.
IMO&E many classic PP EL84 power amps and integrateds can sound a lot nicer with the changes I've suggested.
It is, of course, your money, but why re-build an amp so that it will sound less good than it could?
I listen to classical music and vocal acoustic music, live, as often as possible.
Live acoustic classical and choral music is dynamically and tonally demanding.
Sensibly progressive gain structure in any system, and I do mean any system, (not just audio) is a good idea.
IMO&E the best way to get really good - excellent in fact - sound from a small PP EL84 (or EL84M) amp is to
i) get the gain structure right. A 12AX7 splitter driver violates that
ii) a nice big and stiff PSU, which requires soft recovery SS diodes.
The PSU could use i) brute force with BIG electrolytic caps and by passing OR ii) use a choke input filter into a largish film cap, then another choke, and so on with caps.
IME the large e-caps approach works just fine.
For me an amplifier has to do its job, which is getting out of the way of the music.
This is not hard to do.
Classic era PP valve amplifiers, even little PP EL84 items, have the capability of very high energy storage in their PSUs.
This always sounds better.
Refusing to go down this track - for 'vintage' sound reasons - is beyond my understanding.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 08/14/17 08/14/17
Many amps from the '50s and '60s used the 12AX7 (or equivalent) as a phase splitter ahead of the output tubes. It might not be the best choice for this use, but it does work.
--------------------------
Buy Chinese. Bury freedom.
My interest in audio has always, at bottom, been in simply recorded (minimal miking) acoustic music.And, its reproduction at home as well as I can afford, on a low budget.
(NB I don't hate pop/rock music, it's just not very important to me, and the classical music just IS. then, Blues and Jazz, and pop.)
I have learned a LOT about what works, and enough of how / why, and have achieved a very high musical ROI in return. I will keep learning.
When I swapped the LEAK St60 I'd been gifted, for the St20s, it was my intention to use them in OEM form.
But I soon found that was going to mean $$$$$$ for decent NOS GZ34s. And $$$$$ for NOS PSU caps.
Then I found a whole bunch of NOS 6CG7s, 6DJ8s and the amazing EL84M. And, then found out about SS SR diodes. And, CCSs for splitters. And how that all might work. WITH a really high storage PSU, too. ALL for far less money than a restoration, and far more dbw. (? real watts.)
One day soon I - might - come up with the funds to convert one of the LEAKS to CLCL... OR LCLC... using PP film caps, and compare it to SR SS diodes and BIG electro caps, just to check. Valve rectifiers will not be in the mix.
But, ...... I do keep putting it off! I wonder why? ;-)
Viz? I _ will- be investing in two line-level SE/bal traffos so as to run each LEAK 'strapped, balanced' - and safely - into the rebuilt QUAD 63s. Giving 40Watts RMS / into 2/4/8 ohms! I'm expecting 4 ohms to be best, given that they and the QUADs won't be doing much in the bass. 1st HP @150 Hz.
Music? I got into performing music at 9 years old in a cathedral choir and soon was able to hear 'us and the place' in simple stereo. A Permanent convert, if you will.
It was revelatory. Systems that go deep and loud really are necessary. Mid 30 Hz minimum? Search here.
Yes, I do use (and have made) such recordings of choirs plus organs et al instruments, to asssess judge what I've done to the gear, and the layout / room. (Surround IS better if it's done to give more 3d).
So, 'audio' isn't my hobby, learning about it became necessary to progress on listening to music at home.
LBNL and for me. SS can help a lot to get tubes doing audio to sound blameless, whenever the recording is blameless.
Still learning, but I am confident I won't go off using SS to help valves do their excellent work as audio amplifiers.
Nor will I stop sticking to established and audibly superior design principles.
I'll leave you with a question?
How many amplifiers have you built that are capable of matching rise and settling times into real-life loads?
It matters, IMO a lot more than a given topology ever can.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 08/14/17 08/14/17 08/14/17 08/14/17
I feel this arrangement helps give the Princeton and Princeton Reverb its unique tone. Compared to the Deluxe Reverb (with its long-tail pair PI).
Other things (like speaker sizes) and front end arrangement also effect the tone. I really like the PR, esp for practice.
8^)
Not an effects amp.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
My experience with cathodyne or Concertina PI guitar amps is they distort slower and earlier in the volume range, than the usual long-tail PI setups.
Makes for a different overdrive tone. Quite unique. I can tell a usual 12AX7 (7025) cathodyne PI amp just by playing the amp at various volume levels and listening to the response. It's that unique.
Cathodyne PI guitar amps were usually the low-end push-pull amps of the manufacturer's line. So other factors also apply. Like cheaper iron, speakers, and parts.
8^)
I have never heard that before.
"The eico 81 has a 12au7 in front of the 12ax7 driver/splitter tube, and the au7 is for the tape monitor circuit."
Buffering the recording O/Ps with cathode followers is a good thing. Loading down the low level mag. preamp section will result in info. loss.
"I wonder if including that tube would be too much gain if i also used it my amp?"
Excessive gain is a serious negative. Attenuating a signal only to boost in again has a very deleterious effect on S/N ratio. :> ((
As I stated previously, I'd like to see a photo of the chassis being worked on.
Eli D.
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
