HELP PLEASE! Choice of first power amp project.

[brianco]

Being a total beginner in unaided DIY I find that having read hundreds of pages on these forums that VERY little information/opinion is offered regarding the sound quality of published designs.
As I want to build a power amp which sounds as near as possible sweet as opposed to sterile, fast, accurate and which will drive Impulse H2 horns (about95Db) I will be very grateful if a music (mainly classical) will point me in the right direction.
I play mainly LPs on a highly modded Technics SP10Mk11, a Zeta arm carries an original Audionote Io cartridge , a very simple amplification system which has to do as my prototype Be Yamamura amplifiers have broken down. Be seems to have dissappeared again. (ANDREW T - I now live in Kelso!!!)
I can solder, build circuits but I know NO theory that you would notice. Any suggestions / help very much appreciated re. choice of circuit.
Regards to all,
Brianco

[TomWaits]

Originally posted by brianco
Being a total beginner in unaided DIY I find that having read hundreds of pages on these forums that VERY little information/opinion is offered regarding the sound quality of published designs.
As I want to build a power amp which sounds as near as possible sweet as opposed to sterile, fast, accurate and which will drive Impulse H2 horns (about95Db) I will be very grateful if a music (mainly classical) will point me in the right direction....Regards to all,
Brianco

Dude, you're in the wrong place. Head on over to the Tube area.

Cheers,

Shawn.

[moamps]

Welcome to the forums!
Re sweet-sounding power amps for your horns, my vote would go to something like F2 from Pass Labs. Pass amps are as sweet as you can get with a sand amp. And if you really have a sweet ear, you may wish to consider a tube amp project like Shawn suggested. Whatever you choose, it should be a Class A amplifier. 10W or so should suffice, IMO.
If it's not too much of a bother, I'd appreciate it if you could write a line or two on those Technics mods you've made.

Regards,
Milan

[anatech]

Hi Brianco,
As Milan said, Welcome to the forums!

I will suggest a rather broader range of amplifiers. Many sound very good, and bad with each technology. So now it really comes down to what you are comfortable building, and how loud you like it. The only time I peak my amps are when I'm playing classical music, rock not nearly as often.

The Symasym is a really nice sounding 50 watt solid state "kit", and board layouts are available. You can also buy some kits proper, including PCB's and parts.

On the tube front, you may want to look at a P-P 6BQ5 setup (10 ~ 14 watts). Most sound really nice. I you wish more power, then I'd suggest an ultralinear 6L6GC or EL-34 / 6CA7 type. Those can get up to 50 watts and 450 VDC supplies. Yes, you can go further.

So, can you give us a clue as to what you are comfortable with and how loud you are likely to turn it up. Be honest because it's only yourself you would be fooling.

-Chris

[brianco]

Originally posted by moamps

If it's not too much of a bother, I'd appreciate it if you could write a line or two on those Technics mods you've made.

Regards,
Milan [/B]

Thank you all for your welcome & advice.

Regarding the SP10, it is an ex-BBC TT, so has the big PS unit, in which there is some spare room. Virtually all electronics have been removed from the TT into the PS enclosure. They are joined by an umbilical cord. The deck is in an obsidian plinth (The Technics heavier one) from which the spongy supports have been replaced with large blocks of of pure fine structure carbon. Underneath is a Yamamura "sliding" equipment base. The Zeta is mounted on a carbon armboard, but it is soon to be replaced with a homemade dual-pivot ceramic and carbon 12" arm. The cartridge is the very earliest Audionote Io and has been rebuilt by Kondo about 4/5 years ago and is still working well. All wiring is with Be Yamamura early types & prototypes. It works well. I have a carbon 12"o/d disc (x1.25" deep) which I hope to have machined asa replacement platter.

Hope this gives you a clue. I have no Pics as all my cameras are film cameras.

Best wishes,
Brianco.

[AndrewT]

Hi Brianco,
when you move to Heriot, you will know you have arrived.

[brianco]

Hi AndrewT,

Heriot - if you were within 10 miles - is the ONLY place one COULD arrive, take any other direction one wouldbe leaving...! And I thought I had led a remote existance when I lived in rural Ireland.

Thanks for your note - hope we can meet up sometime. I have to behave myself for a while until some big man allows me to eMail anyone - when I am out of quarantine I will send you my tel. no.

Kindest regards,

Brianco

[FastEddy]

I am getting too old to solder tiny parts onto circuit boards, so I chose the modular approach ... and stripped down an existing (broken) amp to save a little on chasing around for all the parts ...

So, here is what I did: http://3dotaudio.com/ampics.html

Setup driving a pair of 86db planar speakers : http://www.magnepan.com/model_MMG

This setup sure sound good IMOP.

[john_ellis]

Hi Brianco

Someone recently asked about Bailey designs from the 1960's. One of his circuits I built could be good, as a starting point. This circuit appeared to receive little attention as a power amplifier. It was a "DC laboratory amplifier" published in Electronic Engineering.

Today, the specification may be a little pedestrian (typical distortion 0.01%) but it certainly has a good sound quality. In the published circuit, a differential input stage fed a single-VAS and a complementary driver/output pair. In other words, quite basic.

The key to the sound quality I think lies in the use of phase-lead compensation. This is where a feedback capacitor is taken from the VAS collector to the feedback point rather than the base of the VAS. This has the effect of reducing transient distortion rather than exacerbating it. John Linsley Hood used this approach, as I believe has Nelson Pass.

However, to get the best results I have found that a 220 pF compensation capacitor is about optimum as this also provides loading to avoid high frequency oscillation ( a subtle effect).

But to achieve a useful bandwidth of say 200 kHz the feedback resistor has to be in the order of 1.5k rather than the usual 10 k used in many diff-input circuits. This unbalances the differential pair if 10k is used on the input side. I have added a separate bias transistor to offset the DC bias so that this is no longer an issue. The solution is not elegant, but the sound quality is comparable to tube amps.

None of the original transistors I think are now available. The 40361/40362 devices could be replaced by BD139-BD140's and these in fact are very good devices, with typical gains on todays production devices (from ST and ON semi for exampe) are about 100, and in fact the lower spec. appears to have been increased from when these were first introduced.

The output devices were 2N3716/2N3792. I have built amps using 2N3055/MJ2955 pairs running happily from +/-35V power rails. The current production 2N3055/MJ2955 devices are epi and have fT's of around 5 MHz on those I have measured. Breakdown voltages have been over 80V, which I think may be due to the original RCA-2N3055 spec having BVcbo of 100V, which still has to be met.

Many people think that the 2N3055/MJ2955 are no longer the best, but they are on at least their 3rd major production revision, I think, and while the original 1 MHz RCA device was used in many amps, that really isn't hifi (as well as not being available anyway).

The biggest source of distortion seems to be from the gain non-linearity of the output devices, but even so 0.01% or thereabouts it quite respectable.

If you are interested, I will try to draw a circuit over the next few days.

Cheers
John

[Nordic]

Is MJ3055 same as TIP3055?

Want to try a schematic using the last... but only have the first in my box.