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Old 10th December 2002, 06:57 AM   #1
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Default Tube preamp similar to Foreplay

Hi, guys.

Since I started building my own audio gears (not very long ago), I have been interested in tube stuffs. Everybody says that tubes sound different from solid-state ones. So, I decided to try it out.

First, I looked at tube power amps which have massive (and expensive) output transformers. Well... My budget is tight, and buying those output transformers is not going to happen in a near future. Then, I checked some tube/mosfet hybrid amps on the internet (and of course diyAudio.com), and found that it's not as common as typical tube power amps. Maybe it's difficult to make one, or maybe it doesn't sound good. I don't know. So, I posted a question on this forum, but didn't get what I wanted. I wanted a reliable hybrid amp.

Anyway... While I was checking this and that over the internet, what caught my eyes was a simple tube preamp called Foreplay. Though its schematic is not available to public because of the copyright things, it seems to be pretty simple, which means that it's easy to build for tube newbies like me. What I'm thinking now is to make a simple tube preamp like Foreplay and hook it up to the solid state power amps like gainclone. I have made gainclone and was pleased with the sound. I saw many posts on the Bottlehead forum saying that Foreplay is a high quality preamp and that it works pretty well with solid-state amps. So, it's very possible that it could be my first tube project.

One last thing I would like to ask experts like you before ordering Foreplay is whether there's no preamp similar to Foreplay. I mean, simple, OK-quality (hopefully high quality), not expensive, and compatible to solid-state power amps. When I was reading the posts on the Bottlehead forum, I felt there could be some kind of myth about Foreplay. I respect the people's thoughts and feelings on Foreplay, but I felt it anyway.

So, I would like to get some information on (1) your thoughts on Foreplay and (2) any alternative diy project similar to Foreplay. Any comment would be greatly appreciated. Thank you so much.
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Old 10th December 2002, 08:37 AM   #2
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Default Re: Tube preamp similar to Foreplay

The Foreplay is an 12AU7 common cathode followed by a 12AU7 cathode follower. The 1st mod is to add a CCS to the follower.

Have you been thru the simple tube line-stage threads here. There are a couple.

Another possibility is Rosenblitz's grounded grid line-stage. His book (a good read in its own right) Audio Reality has all the details.

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Old 10th December 2002, 12:29 PM   #3
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I also am new to tubes after spending most of my life under the influence of solid state. Granted the "Foreplay" is a budget kit that can be put together for a reasonable sum and deliver desireable performance. There is a complete preamp design that is spelled out in one of the tube forum posts and I think its the complete tube preamp.

With respect to your "Gainclone" what is it? What type of amplifier? Is it fully complimentary? What is the input impedance?

I am under the belief that not every SS amplifier will sound good with a tube preamp, not all solid state amplifiers sound good period. I'll be blunt here... If your "gainclone" isn't fully complimentry in circuit design I wouldn't bother making anything for it because it could very well be a waste of your time and talent. I listened to about 8 different SS poweramps that I own and used my YS audio's tube preamp as a source receiver. The only pleasing results I received were from fully complimentary designed SS amps like SAE or GAS. The Quasy complimentary designed amplifiers lacked the full detail that was present with a fully complimentary design. Different tube circuits sound/perform different and so do SS circuits.

Personally I am gathering parts to put together the complete 6SN7 preamp and power supply as posted in the forum here. I believe this preamp will deliver good performance and quality for a price less than the "foreplay."

With respect to hybrid amps/circuits... I for one am a purest as I believe that a SS design should be 100% soild state and contain Zero fets/mosfets. My belief is the same for tube circuits, I believe they should remain free of mosfet influence. That is just my opinion here and I'm sure others have different opinions.


Joe
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Old 10th December 2002, 12:47 PM   #4
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Jazz2250

I found your "Gainclone" after doing a search. Its based on a power op amp design. If this amp is properly made and the op amp is heat sinked properly it will put out about 12-15 watts. It is basically the same circuit that Peavey uses in its commercial UMA/UM series amplifier. To be blunt... it won't take any abuse of any kind before going up in a puff of smoke.

Joe
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Old 10th December 2002, 01:16 PM   #5
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Default Why not just buy the Foreplay?

That way you get all the parts complete in a kit (sourcing parts takes me a heck of a lot longer than the building), support from the Bottlehead forum, resale value on the unit (self builds have nine) and it's not even particularly expensive.

Cheers
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Old 10th December 2002, 01:24 PM   #6
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Question Full Complementary Design

Quote:
Originally posted by burnedfingers
I listened to about 8 different SS poweramps that I own and used my YS audio's tube preamp as a source receiver. The only pleasing results I received were from fully complimentary designed SS amps like SAE or GAS.

Joe
Hi Joe, I find your post interesting and that part is in the quote.
I own a Ampzilla II (full complementary circuitry) Before that I owned a SAEMkIVDM.
Here on this forum I have seen a lot of poweramp circuits. Most outputstages are complementary but most inputstages are not. I am on the brink of designing my own poweramp. What exactly do you feel is the reason that a full complementary circuit is better, sonically? Any reason you don't like JFET's?
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Old 10th December 2002, 11:14 PM   #7
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The Ampzilla and most SAE's are fully complimentary from the input stage(quad diff input) thru to the output stage.

I guess I don't like fets because when used in the output stage they sound tubby, when used in the diff input they sound overly bright and not natural.

Feel free to email and discuss.


To others.... sorry I got off the beaten path here.


Jazz2250

Brett has made a very good point here with the fact that the Bottlehead kits do contain all parts necessary to build the piece without having to source parts.
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