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Old 29th March 2008, 02:26 PM   #1
JayH3 is offline JayH3  United States
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Default Please recommend me an amplifier design.

I plan on building myself a tube amp. I was going to copy a Jolida design but it was suggested I try to find something better.
I have plenty of experience wiring, but not so much in tube design.
What I am looking for:
Preferably an integrated amp with a preamp section.
A decent amount of power to drive my Paradigms (est 89~90) until I build a more efficient set of speakers.
Alot of the music I listen to has low bass so I am looking for a design with clear, tight bass.
No exotic parts. I want to be able to find easily find any tubes or transformers, etc for the initial build of if I need replacements.
Modern circuits like CCS.

The reason I dont want a kit is because eventually I would probably want to upgrade parts like capacitors and would rather just build it with the right parts the first time around.

I would also like an amp that sounds great both at low and high volumes. From what I read it sounds like toroidal opt's are good for that, but they seem to be very expensive. Would it be worth it to go that route?

Budget: I would like to keep it $700 or less, but will pay a little more if it will undoubtebly give much better sound quality.

Thanks for all the help.
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Old 29th March 2008, 05:26 PM   #2
kmaier is offline kmaier  United States
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Sorry, but I'm not sure you realize what you're asking for. A tube amplifier capable of delivering 80-90 watts output is not going to be cheap to build. A single pair of 6550 outputs do have a operational spec that approaches 100 watts, but don't expect them to last long... and I'm referring to "real" 6550 tubes from the 50's and 60's, not the copies currently available. That means a quad per channel for reliable operation.... and two quad sets will set you back around $275, plus input and driver tubes.

Also realize that your power supply will need to deliver a minimum of 300ma current for a single amplfier channel at a solid 500+volts to even come close and the output iron itself will need to be quite large to handle low frequencies at that power level. You may be able to buy Hammond iron cheaply, but their largest power tranny only delivers 465ma, and I would not recommend their larger power units due to massive magnetic fields and the problems associated with layout.

Regards, KM
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Old 29th March 2008, 06:56 PM   #3
JayH3 is offline JayH3  United States
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Quote:
Originally posted by kmaier
Sorry, but I'm not sure you realize what you're asking for. A tube amplifier capable of delivering 80-90 watts output is not going to be cheap to build. ...



Regards, KM
Im not sure sure if you mean 90 watts total or wpc, but I am only looking for about 40 wpc.

From what I have seen 40 wpc from a push pull design shouldnt be too difficult to attain. I see alot of those amps ussually have EL84, KT88, or 6550's.
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Old 29th March 2008, 07:02 PM   #4
John L is offline John L  United States
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I agree with the wattage part. If you can't acheive what you want with 20-30 watts of tube output, you are in love with overkill. My P-P receivers are between 25 and 30 watts, and they are more than capable of driving most anyone out of the house. Coupled to my Wharfedale Airedales, they would drive the neighbors crazy.

I'm not sure which Push-Pull amp you would be looking for, but I would suggest you start simple, like I am about to do. Go to Uncle George's Tube Lab.com , and check out his wonderful Single-Ended amps. I am going to build his Simple S-E Amplifier.

What is so great about his project is that he is the only one I know of, who has fully explained his theory and completely documented the step by step process with wonderful pictures. Reading his work is a joy to behold. He is far from pretty, but his projects are stunning.

As for the preamp part, that is also part of the project. But keep in mind that Single-ended amps are very inefficient, and his will put out about 7 watts each channel. But for the money you save, you can always pick up a nice Fostex, or go all the way with a Silver Iris and make it sing to high heavens.

Anyway, go visit his marvelous site and just let yourself get lost in it. YOu will be amazed at his knowledge and care.
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Old 29th March 2008, 07:13 PM   #5
JayH3 is offline JayH3  United States
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Quote:
Originally posted by John L
I agree with the wattage part. If you can't acheive what you want with 20-30 watts of tube output, you are in love with overkill. My P-P receivers are between 25 and 30 watts, and they are more than capable of driving most anyone out of the house. Coupled to my Wharfedale Airedales, they would drive the neighbors crazy.

I'm not sure which Push-Pull amp you would be looking for, but I would suggest you start simple, like I am about to do. Go to Uncle George's Tube Lab.com , and check out his wonderful Single-Ended amps. I am going to build his Simple S-E Amplifier.

What is so great about his project is that he is the only one I know of, who has fully explained his theory and completely documented the step by step process with wonderful pictures. Reading his work is a joy to behold. He is far from pretty, but his projects are stunning.

As for the preamp part, that is also part of the project. But keep in mind that Single-ended amps are very inefficient, and his will put out about 7 watts each channel. But for the money you save, you can always pick up a nice Fostex, or go all the way with a Silver Iris and make it sing to high heavens.

Anyway, go visit his marvelous site and just let yourself get lost in it. YOu will be amazed at his knowledge and care.

Thanks for the reply. Ill check out the website you suggested.

The reason I am looking for about 40wpc is my Paradigms, which I will probably be using for a while until I move, only have an efficiency of 89db. So with better speakers I am sure 40wpc would be overkill. I realize 40wpc should only be 3db louder per channel than a 20 wpc amp.

With a 20 wpc amp and inefficient speakers will I still be able to crank it to a nearly uncomfortable level with a little headroom?
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Old 29th March 2008, 07:14 PM   #6
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I have a set of Paradigm 7seMkIII. They are in a basement about 15' wide by 35' long.
Click the image to open in full size.

I've built a clone of the Dynaco ST35 (push-pull EL84, about 15 watts per side).
Click the image to open in full size. Click the image to open in full size.

I feel it can drive my Paradigm's plenty loud. Maybe if I played lots of orchestral music or bass heavy pipe organ stuff, I might need more - but I don't think the Paradigm's would tolerate it very well. Of course, you didn't specify which model of Paradigm you own - they make a fairly wide range. Maybe yours can handle more power.

The ST35 clone can cost you as little as $300 or so if you are really good at scrounging for parts. You might spend upwards of twice that if you take the easy route and just buy everything new. I'm sure there are plenty of good choices for amplifier design out there. I'm sure you'll probably get a couple recommendations to look around here for the El Cheapo and Baby Huey designs, too.
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Old 29th March 2008, 07:23 PM   #7
JayH3 is offline JayH3  United States
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Quote:
Originally posted by Ty_Bower


I've built a clone of the Dynaco ST35 (push-pull EL84, about 15 watts per side).


I feel it can drive my Paradigm's plenty loud. Maybe if I played lots of orchestral music or bass heavy pipe organ stuff, I might need more - but I don't think the Paradigm's would tolerate it very well. Of course, you didn't specify which model of Paradigm you own - they make a fairly wide range. Maybe yours can handle more power.

The ST35 clone can cost you as little as $300 or so if you are really good at scrounging for parts. You might spend upwards of twice that if you take the easy route and just buy everything new. I'm sure there are plenty of good choices for amplifier design out there. I'm sure you'll probably get a couple recommendations to look around here for the El Cheapo and Baby Huey designs, too. [/B]

I was thinking about a Dynaco design, but in my thread when I was thinking of copying a Jolida design someone said it was a 1957 design and I would be better off finding something more modern so I figured the Dynaco would be the same way.

Do you feel that your Dynaco clone can compete with more modern designs?

My Paradigms are Phantoms which are not as nice as yours but they will serve me for a little while longer. I beleive they can handle 100 watts each.
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Old 29th March 2008, 07:36 PM   #8
John L is offline John L  United States
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If P-P is what you want, and you are looking at the Dynaco ST-70, then the one to look at is Roy Mottram's Tubes 4 HiFi .com . He has the best reputation, that I know of, for taking care of his customers, and he has revamped the old design to make it better and last longer.

If I was going to build a P-P amp, this would be it. Also, if you look around the site, you can also find a PAT4 reconfiguration kit, where you can remove the solid state innards and replace them with tubes. Neat!

but I already have quite a few vintage tube receivers and a couple of integrated amps, so I am more interested in George's SET projects, since I am totally without any of those, and want to see for myself.
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Old 29th March 2008, 07:47 PM   #9
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JayH3,

Paul Joppa provides us with a useful rule of thumb. Joppa's Rule says that for a "typical" listening space, an amp speaker combo should be capable of producing 102 dB. SPL peaks, at a 1 M. distance. For 89 dB. efficient speakers, Joppa's Rule requires a bit more than 15 WPC. After factoring in speaker manufacturer misinformation in claimed performace, 30 or so WPC seem about right.

Speaker manufacturers will specify efficiency for 2.83 V. of drive. They also will specify a nominal impedance. When using a tube amp, the impedance curve of speakers matters a LOT. Allowance must be made for dips in impedance curve and the fact that 2.83 V. of drive is 1 W. into 8 Ohms, but it's 2 W. into 4 Ohms.

Ty Bower mentioned "El Cheapo". If you use 7591 O/P tubes, you can get the necessary 30 WPC from that style of circuitry. Since "El Cheapo" has a volume control, your desire for an "integrated" amp will be fulfilled. What sort of signal source(s) do you use?

Even using some "fancy" parts, like PEC hot molded Carbon controls, will not consume the budgeted $700.
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Old 29th March 2008, 07:57 PM   #10
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90w per channel is unnecessary with your speakers, unless you have a very large listening room. 40w seems a sensible target and you can get that much from a pair of 6550s or KT88s in ultralinear PP.

You could manage 40w also with EL34s, but only in pentode mode. 300Bs are also a possibility but the design would be more challenging and the cost would be too high for your budget. I think 6550s in UL PP seem your best choice.

Naturally, you will need an adequate power transformer but the key to the qualities you're asking for is to buy very good OP transformers. I don't believe Hammond falls into that category (others may dispute this) but there are suitable makes available without going to the expense and potential problems of toroids. Lundahl is one that springs to mind.

There are many amp designs that can be used, according to how adventurous you want to be. My own preference would be for an all-balanced design, using a 6SL7 LTP splitter for input, with a (pentode or PNP cascode) CCS in the tail. 6SU7, if you can get them, have the same characteristics as 6SL7 but are better matched.

The second stage would be a 6SN7 differential amplifier. Coupling between the first two stages would be via a step network, rather than using DC coupling. A step network would help to keep the voltages more workable, minimize the effect of any DC imbalance of the LTP and provide stability at low frequencies for the application of NFB.

Next would be a pair of MOSET source follower drivers, direct coupled to the OP tubes and using fixed bias on the gates. This arrangement would avoid altogether any danger of blocking distortion if the OP tubes are overdriven, such as can happen on transients. If you don't like the idea of SS devices, you could use a second 6SN7 as a cathode follower, but then you'd be using up more space and more heater power and it wouldn't sound any better.

For negative feedback, I would use cross-coupled balanced loops from the OP tube plates to the LTP plates, together with a global loop from the OPT secondary to the earthed grid of the LTP input stage. The thing is to use no more NFB that your speakers require for tight bass.

If you fancy the 'authority' of a pentode-mode OP stage, then you might be better off using 6SL7 (or 6SU7) for both the first and second stages, to give more gain so you can apply more NFB to give adequate damping.
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