Sweet Peach EL34b Amp - Distortion? - diyAudio
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Old 6th January 2012, 03:45 PM   #1
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Default Sweet Peach EL34b Amp - Distortion?

***Newbie alert ***

Hi all

I have just bought a Sweet Peach EL34b amp, from Ebay, as I couldn't resist the price.

Obviously nothing has bedded in yet but the initial sound is OK apart from one thing: should I be getting distortion from about half-way on the volume?

I have tried with an Ipod in the MP3 connector, Ipod via dock into the line-in and a CD player. All exhibit the same issue - the distortion starts at approx half way.

As this is my first 'proper' valve amp I am not sure if this is right or whether it has arrived faulty.

Thanks in advance

Dave
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Old 6th January 2012, 04:14 PM   #2
kevinkr is offline kevinkr  United States
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It's normal if you have reached the rated output power of the amplifier, the position of the volume control is arbitrary for the point at which this happens, and depends on overall gain structure and the input voltage from your source. A hot (high output) source will result in distortion at lower settings of the volume control than a lower output source, output power in both instances should be just about identical.
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Old 6th January 2012, 04:23 PM   #3
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Thanks Kevin - I can breathe a little easier now

Next up will be to swap the chinese 6n3 and 6n1 valves for better quality ones. Plenty of reading ahead methinks!

Dave
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Old 6th January 2012, 04:24 PM   #4
DF96 is offline DF96  England
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They claim 10W at 1%. Mullard say 11W at 10% for the EL34 in single-ended mode. Maybe Chinese valves have to be measured using Chinese watts?
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Old 6th January 2012, 04:41 PM   #5
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Quote:
Originally Posted by DF96 View Post
They claim 10W at 1%. Mullard say 11W at 10% for the EL34 in single-ended mode. Maybe Chinese valves have to be measured using Chinese watts?
Or PMPO watts, which, according to Morgan Jones, means Purely Mythical Output Power?

Best regards!
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Old 6th January 2012, 05:11 PM   #6
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The company who made this amplifier has website with its specs: Hefei XiangSheng Electronic Co.,Ltd - Products - Vacuum Tube Amplifier - Sweet Peach Series Single ended Tube Amplifier - Sweet Peach-EL34B Single Ended Tube Amplifier

Wait what ?
>Maximum output:10W2(8Ω Triode connection mode)

10W out of a trioded EL34 ? Rather hell would freeze over.

I have no schematic, but around 6W sounds realistic.

You have to decide if that is enough for you. New tubes won't change anything except lost money for some overpriced 6n...p-EV tubes.
Maybe it is possible to wire the EL34 as pentodes and come close to the 10W ? I don't know, but maybe others are familiar with that amplifier.
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Old 7th January 2012, 08:22 AM   #7
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Thanks for the replies - I think I am going to be on a big learning curve here!

As to the volume level - it is actually more than sufficient for the room it is in driving small 86db speakers. I am not one for brain frying volume levels anyway

The sound is a little muddy at the moment (compared to the amp it replaced - a hybrid piece of digital junk that started me on the journey (sav-400a for those interested) but I am hoping that, as the tubes burn in, that will get better.

The replacement valves (Russian nos) come in at just on $10 shipped so worth a shot for that.

Prepare for more questions as I try to come up to speed

Dave
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Old 7th January 2012, 12:32 PM   #8
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Hi,

Congrats on the Sweet Peach! They actually have very high potential with some DIY so you are in the right place!

If it's your first time with tubes read the safety thread from front to back.

Then read this thread: Trying to make sense of the Sweet Peach

The first thing you will need to change are all of the coupling capacitors as they make it sound dull and muffled. I never appreciated what effect capacitors could have on sound until I replaced mine - it's night and day.

Post a photo and I'll point them out, but mine were fake WIMA ones in red. There are also two (electros IIRC) hidden on the input board near the volume pot, you can just short those out with a wire. The main effect on sound is changing the four red ones on the boards though, use 0.1 Polypropylene at 400V or greater (I used 1kV). Look at my photos on that thread I posted up and you will see.

ETA: I get more power from mine because it now runs in Pentode mode, but anyway read the other thread first!
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Old 7th January 2012, 07:57 PM   #9
Bone is offline Bone  United Kingdom
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Just ordered one of these to play with.
Globulator how did you connect the outputs in pentode mode. Did you use any resistors in the screen grid circuit or did you just connect them direct to B+?

Tony
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Old 7th January 2012, 08:26 PM   #10
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Quote:
Originally Posted by Bone View Post
Just ordered one of these to play with.
Globulator how did you connect the outputs in pentode mode. Did you use any resistors in the screen grid circuit or did you just connect them direct to B+?

Tony
Hi and congrats, I have the GU50 version but the principle is the same. It's a re-design though:

Trying to make sense of the Sweet Peach

You can't just reconnect the output tube in pentode mode, the bias changes dramatically (and for the better!) and the output impedance drops.

Click the image to open in full size.

My new circuit uses pentode mode for power and gain, and has high linearity without loop feedback going across the output transformer. This is achieved by having a very low impedance drive from the output stage. A good alternate would also be Schade feedback here.
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