[gavinbirss]

Hello,

The kit looked good so I did some googling on it and found the following : http://www.siteswithstyle.com/VoltSe...Push_Pull.html

Enjoy ...

 

[gavinbirss]

Dam looks like my text search did not reveal that I Woody already posted this link.

Sorry.

Gavin

 

[bg4533]

I just got my amp put together. I have mixed opinions of it so far, but it might have some problems too. Compared to my Denon AVR1200 the highs seem a bit rolled and bass is not as impactful. Compared to my Pimeta and HD650s well...it sucks. The midrange on the amp seems very nice though.

My first problem is that with the volume all the way up or all the way down I get a bit of radio playing through the speakers.

Problem 2 is a bit of hiss through the amp. Mainly through the tweeters. With a set of old speakers it isn't much, but with my Mission M73s it is significant.

Also, is it normal for a bit of the music to play through the tubes?

I have some MUR860s here, can I replace the rectifier with them?

Eventually I want to take out the volume control and use a PPA as a preamp. I am placing an order with Mouser and will order some Vishay RN60s to replace most of the resistors with.

 

[ilikemonkeys]

I get no radio playing from mine, and I live next to a tower. I get radio in my electric razor. THe bass is not impactful, but I have noticed did get much much better over time. The modifications I made offered a dramatic improvement in static, although i really never heard much to begin with.

Good luck. I love this little amp. Its really all I ever use anymore. Its just so easy to play with.

BILL

 

[Wodgy]

Quote:

Originally Posted by bg4533 I just got my amp put together. I have mixed opinions of it so far, but it might have some problems too. Compared to my Denon AVR1200 the highs seem a bit rolled and bass is not as impactful. Compared to my Pimeta and HD650s well...it sucks. The midrange on the amp seems very nice though.

It is definitely a different sound. I personally don't really like the PIMETA with many headphones, though it is a very nice combo with the Senns, because of the slightly aggressive presentation. This tube amp has more of a laid back presentation, but with an organic midrange. I agree with you on the bass impact comment, though to some extent that is relative. I would rate it on par with one of the digiamps that are now popular, but not as good as a NAD C370.

Quote:

My first problem is that with the volume all the way up or all the way down I get a bit of radio playing through the speakers.

I didn't notice this on mine, but try replacing the stock 100k potentiometer with a 10k pot, e.g. one of the low cost Panasonics. Lower impedance pots are less prone to interference.

Quote:

Also, is it normal for a bit of the music to play through the tubes?

If you're hearing music emanating from the amp, it's coming from the output transformers. All tube power amps do this, though it should be very quiet.

Quote:

Eventually I want to take out the volume control and use a PPA as a preamp. I am placing an order with Mouser and will order some Vishay RN60s to replace most of the resistors with.

The preamp idea will work well. My amp is in storage right now, so I can't check, but if there are carbon or carbon film resistors I wouldn't replace them with metal film types. It could change the voicing of the amp and remove some of the warmth. That might be what you're looking for though.

 

[aerius]

Latest update. Scored some polypropylene film & foil capacitors on ebay and replaced the Wima caps I had before. Marginal improvement if any, treble might be a tiny bit clearer but it's hard to tell.

Then seeing how getting rid of the small 22uf electrolytic capacitor in the power supply helped with noise, I thought to myself, what if I got rid of all the electrolytics and replaced them with film caps? Problem, I had to find some large film caps. So I went to check out the local surplus stores and found these things called motor run capacitors, and I did some research on them and found out they were actually large film caps. Bingo! I bought a few of them and stuck them into the power supply.

Result? Whoa, well, I got a lot more than I expected. Besides getting rid of almost every last bit of noise, the amp is now noticeably faster and more detailed, especially in the bass & lower midrange. Piano & electric bass notes which used to blend together are now distinct & separate, and I'm hearing details & textures in the bass which I've never heard before. I'd say the difference is almost as big as going from the Senn 600 to the 650 on a PPA, Gilmore Lite, or the previous version of my tube amp.

Note. These capacitors are huge, each of them is size of a beercan and I'm using 4 of them. They have to be mounted off the board.

 

[bhd812]

how easy and safe is this kit for a beginner?

I am good at soding but I have never built a amp before

 

[Syzygies]

Quote:

Originally Posted by bhd812 how easy and safe is this kit for a beginner? I am good at soding but I have never built a amp before

From their web page:

1. This project deals with lethal 115V line voltage and higher voltages

Build a PIMETA. You'll love it. When you no longer need to ask the above question, you're ready to work with such voltages. It's more than conceptually understanding what to do; this hobby keeps you up till dawn sometimes, which is when people make mistakes.

I met someone recently (he noticed my amp on a plane) who works on vintage tube guitar amps. He talks about it like he was keeping a wild cat at home. Like, go to India and practice eating with one hand, before even thinking of handling such voltages. He doesn't work on his amps tired.

 

[Wodgy]

This is as safe as kits get for a beginner. It's much safer than an equivalent kit from Bottlehead.

Don't bother with a PIMETA; it just doesn't sound anywhere near as good. I've built both.

 

[bhd812]

I ordered one..hehe you headfi people

I was going to order a jolida 102 today but I am in my cheap mood, well I will let you know it turns out.

 

[strogg]

Quote:

Originally Posted by aerius Then seeing how getting rid of the small 22uf electrolytic capacitor in the power supply helped with noise, I thought to myself, what if I got rid of all the electrolytics and replaced them with film caps? Problem, I had to find some large film caps. So I went to check out the local surplus stores and found these things called motor run capacitors, and I did some research on them and found out they were actually large film caps. Bingo! I bought a few of them and stuck them into the power supply. Result? Whoa, well, I got a lot more than I expected. Besides getting rid of almost every last bit of noise, the amp is now noticeably faster and more detailed, especially in the bass & lower midrange. Piano & electric bass notes which used to blend together are now distinct & separate, and I'm hearing details & textures in the bass which I've never heard before. I'd say the difference is almost as big as going from the Senn 600 to the 650 on a PPA, Gilmore Lite, or the previous version of my tube amp.

what values did you get? any more details on this you can shed?

anyway, an update for me!!:

first, i replaced the tubes with ge tubes from ebay. well, they made a noticeable change. change to the good, i don't know. but i think i hear more detail (which is head-fi speak for it probably didn't do anythign).

next
i replaced all the resistors with vishay's (except for 4 koa spears since mouser didn't have vishay's with that particular value). i also replaced the 4 film caps with wima polyfilm. i then added the cap across the hv line and the 6 snubber caps for the filament line (both suggested by the siteswithstyle site). i also put a uf4007 on the dc+ line right after the bridge rectifier (i was too cheap to replace the whole bridge).

anyway, the sound was... much much much different afterwards. it lost the warm fuzzy feeling. i now have an amp that sounds much more forward, much more detailed. the mids are starting to lack a little, but the highs are strong and hard without any noise. the lows are... different. i'm not sure if it's better or not, but it's just different for now. The biggest difference i hear, though, is the soundstage. the soundstage for my k501's completely changed. with almost every source/amp i've tried the k501's on, i always hear the sound coming from behind me, like at the back of my head. now, it's froming from almost in FRONT. the vocals, though, come from front and up, like from my forehead. i don't know why, but it does. it's really weird. i believe the component upgrade has to be the absolute best $20 i've ever spent on this amp.

so the following is the list of mods i personally did:
pentode->triode
replace resistors with vishay dale mil grade
remove c1 and c4
replaced film caps with wima polyfilms
add a 5 ohm across both output signals (required, really)
doubled electrolytic cap values and put .33uf caps across those
put a .01uf monolithic cap across hv
put 6 1uf caps across the filament line
replace volume pot with stepped attenuator (with vishay dale rn60d's)
replaced tubes with ge tubes
shielded output and power transformers
put ultrafast uf4007 diode on dc+
emi filter on power line (i don't know if that does anything at all)

 

[aerius]

Quote:

Originally Posted by strogg what values did you get? any more details on this you can shed?

Kinda hard to describe since my power supply doesn't look anything like the stock one. The power supply is completely off-board, though it does connect into the board where the electrolytic capacitors used to go.

It's basically as pictured in the rough sketch I did above, it's been 5 years since I've taken an electronics course so I hope I drew everything right. The power comes off the rectifier and goes in from the left. The point marked (1) is where it connects into where the 220uF cap used to go, (2) is where it connects to where the 100uF cap was, and (3) is the connection for where the 22uF cap was in the original. The 2.2k resistor is already part of the board so you don't need to worry about that. The 2H choke between (1) & (2) replaces the 470 ohm resistor (R18) on the original. As I mentioned, they're all 240V(AC) motor run polypropylene film capacitors, and they are huge.

One of these days I need to sit down and write out everything I've done to my kit.

 

[strogg]

Quote:

Originally Posted by aerius One of these days I need to sit down and write out everything I've done to my kit.

that'll probably take you a couple months

but yeah, although the schematic could improve, i understand exactly what you're saying (somehow!). thanks

ps: if i do what you do, this is what my power supply would look like:

just to make things clearer. tell me if i goofed somewhere

 

[dsavitsk]

Quote:

Originally Posted by Wodgy This is as safe as kits get for a beginner. It's much safer than an equivalent kit from Bottlehead. Don't bother with a PIMETA; it just doesn't sound anywhere near as good. I've built both.

But read this first http://www.diyaudio.com/forums/showt...threadid=30172

 

[aerius]

New & improved drawing of my current power supply and how it connects into the amp.

The 30uF cap is a direct replacement of the 22uF one, the circled 2H choke replaces the 470 ohm resistor (R18), and the 75uF cap to the right of the circled choke replaces the 100uF cap in the original. Hope that makes things a bit clearer.