Tube Preamp

dcarlson

Ok, so I'm now looking for a tube pre. The Bottlehead Foreplay kit seems to be what I'm leaning towards.

http://www.bottlehead.com/et/adobespc/foreplay/foreplay_line_stage_kit.htm

Anyone have any other suggestions, on the cheap?

madmax

I can't imagine a cheaper more reasonable thing to buy. I have no experience with it though.
madmax

gmorris

At the very least it has a funny name.

dcarlson

Yeah, a quote from the website.

As soon as we finished designing the original S.E.X. (Single Ended eXperimenter's) amp kit, we knew we needed a line stage preamp to go before it. What else could you call this kit but Foreplay?

I'm pretty sure Wardsweb built one.

tonyv1

Just remember that the Foreplay inverts phase. Many tube preamps do this (CJ are known for this feature). Swapping leads at the speakers is the easiest way to correct it. Good luck with assembling the kit.

Shizelbs

I've read a lot of good things about the stuff that comes from those bottlehead folks. You may be able to find a good deal more reviews/opinions at www4.head-fi.org/forums/. Let us/me know what you think if you go down this road.

dcarlson

Originally posted by tonyv1
Just remember that the Foreplay inverts phase. Many tube preamps do this (CJ are known for this feature). Swapping leads at the speakers is the easiest way to correct it. Good luck with assembling the kit.

Is there any reason why they would do this?

tonyv1

Must be a compromise in the design of the preamp. They could have added another stage to reinvert the signal, but that adds cost. My Anthem tube preamp doesn't invert phase.

madmax

Originally posted by tonyv1
Must be a compromise in the design of the preamp. They could have added another stage to reinvert the signal, but that adds cost.

My Audio Illusions inverts the phase as well. Cost is really no issue there. They say that running through another stage to change the phase back adds noise which is obvious. If you put the two ideas together it makes sense that you get a little added noise and an added cost. It is part of the purist way of thinking. Why add any noise when you could just as easily swap the speaker wires and have absolute phase. Sure is a hassle with speakers like the SDA's but other than that it makes great sense.

madmax

dcarlson

I should do fine with a kit like that, right? At least for a first tube pre?

organ

I'm planning to build one as well. There are upgrades available for it also. I will start with the basic kit and then add the upgrades.

You can improve the sound of your ST-70. If you're in a soldering frenzy, try this. I'm interested to hear if you get the same results as me.

Start wiggling the wires going to your 7199 circuit board on the ST-70. Some will snap off because of the hot/cold cycles over the years. Strip that wire and solder it back on. You need to remove the old solder using a vacuum gun. I also removed the 7199 tube sockets and re-soldered it. I can say that there's a small improvement in sound since I did that. The problem is that the solder joints begin to soften up and become resistive over time and areas where there's a lot of heat are affected. You can do the same to the 6 caps on the driver board as well so you don't get the same problem I had which killed my output tubes. Remember to discharge the caps before working on the board.

If you try this, let me know what kind of results you get.

Maurice

dcarlson

I was thinking of going for the full kit on the Foreplay. I'd rather get it all done at once.

Today, I unplugged the dynaco to change the power cord, I'll take a look at the joints at the same time.

nemos2

Sorry, not to hijack the thread, but where in the system does this go? I am a little confused. Lets say that you have a CD player with L & R outputs, and a standard denon AVR, and then a seperate amp...where in this mess does the tube preamp go? What is the potential gain if the signal ends up going to the SS amp afterwards anyway?

Ian

dcarlson

You'd take the receiver out and put the preamp in it's place. Every component in the chain adds it's own sonic signature and the tube pre would most likely smooth things out.

*Edit*

Oh, and don't worry about the Hijack, I'm guilty of doing the same on a few occasions.

nemos2

could you place the tube preamp inbetween the CD player and the reciever?

if not can you split the signal leaving the CD player and go to both the tube preamp and the reciever?

gatemplin

The receiver has its own preamp so you have to bypass that by using the pre amp inputs, if it has them. It would go cd player to pre amp to power amp.

Tour2ma

nemos2,
Many Denons have Pre-Amp outputs, but no amp inputs, i.e., they do not employ external jumpers.

What you could do is steal a couple channels in the 755 for amping a tube pre and reassign their former HT duties to the Denon. However, you would also be looking at some speaker lead swaps as well, unless you can dedicate a pair to 2 ch duty...

dc,
You might consider a Dynaco PAS 3.... $200 to $250 US on the bay. Pretty well regarded and if you don't like it, you can get your money back on resale.

dcarlson

Nemos, I have my denon's R/L preouts going into my integrated amp and the integrated powers my speakers much like the situation discussed. I select the Aux in on the integrated (which is where I have the Denon going into) then set the integrated's volume level at 12:00 to bypass the internal amp. This allows me to use the Denon as I normally would for movies.

Tour, I've thought about the Pas-3. The only problem is the age and parts because I'd probably end up slightly modifying it anyway, inputs, yada... Thanks for the suggestion.

I kinda like the idea of the kit to give me a better idea of what's going on inside. The Foreplay seems pretty well regarded as well.

dcarlson

Well, I just finished ordering the full kit Foreplay. Should be 4-6 six weeks for delivery.

madmax

Keep us informed! Sounds like a fun project and from what I've read you will be very happy with the results.
madmax

organ

Sweet. The tube bug is really hitting you hard eh?:) Have you decided on the finish for the wooden base and colour for the metal plate? It's probably a good idea to do the finish and colour before putting it together.

Forgot to ask you this before. So did you go for standard or IEC connection on the ST-70? Did you re-solder the old wires and 7199 tube sockets yet?

I forgot to mention this on my previous post but not sre if it was the caps, wires or sockets that I re-soldered but the noise from the amp went down at least 50%. Now I have to put my ears up to the drivers to hear any buzz or hiss.

I re-soldred the connections for the rectifier socket a few days ago. No improvement there. What kind of solder are you using? I'm using silver solder from rat shack.

Maurice

dcarlson

It funny you mention it. The upgradeitis is hitting me hard for a couple of reasons. My fantasy hockey pool ended which lead me to come back here more often than I was during the hockey season and of course seeing the Dynaco in a classified and getting it.

I went with a new on/off switch and a standard connection for now, I had an extension cord lying around that I thought would be at least a bit of an improvement over the stock one, but no, now it sounds horrible (I don't know if there'd be a burn in on it). The problem with the IEC inlet is the space behind the power tranny is too tight to fit one in, I'll have to cut a hole beside the binding posts to fit one in there.

I checked all of the solder connections and they all seem very solid. The Ratshacks here suck, I can't find silver solder and I couldn't find a single pair of RCA inputs. I've tried to avoid soldering as much as possible until I get some silver solder which I'll have to order online along with some other supplies. Probably from partsexpress. I'll also make some calls around town to see what's available.

What's cool about the Foreplay is the amount of help available from owners who put up websites. Should be fun for sure.

organ

I hope the power cord needs to burn in. If the sound doesn't change, you can always re-install the stock power cord if you like the sound on that more.

You're right, there's not much space between the chassis and power tranny.

Another way to get good solder is to visit an electronic store if you have some nearby. They'll also carry resistrs, caps, diodes, etc so you can replace some on the amp.

There's a lot of Foreplay owners out there that want to help new builders. You can also find a lot of them in tube audio forums.

I'm going to an electronic shop today to pick up four 1/2w 100 ohms resistors to get my ST-70 to run in triode operation. 10min mod that require the removal of one cable from each power tube socket and soldering a resistor on each socket.

They also sell tubes. I saw 5AR4, EL-34 and all the famous signal tubes listed on their website. I'll have to have a look at them.

Power output will decrease to about 10w/ch but your suppose to get smoother and more liquid sound. Worth a try because it takes another 10 mins to get it back into pentode if you don't like triode.

If I have time, I'll do it toniht after work and let you know how it sounds.

Maurice