***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
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
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.
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
Next up will be to swap the chinese 6n3 and 6n1 valves for better quality ones. Plenty of reading ahead methinks!
Dave
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!
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:10W×2(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.
Wait what ?
>Maximum output:10W×2(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.
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
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
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: http://www.diyaudio.com/forums/tubes-valves/163459-trying-make-sense-sweet-peach.html
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!
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: http://www.diyaudio.com/forums/tubes-valves/163459-trying-make-sense-sweet-peach.html
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!
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
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:
http://www.diyaudio.com/forums/tubes-valves/163459-trying-make-sense-sweet-peach-17.html#post2273390
You can't just reconnect the output tube in pentode mode, the bias changes dramatically (and for the better!) and the output impedance drops.
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.
It seems to me you have an almost insurmountable mis-match of 6W of power driving speakers rated at 86 Db. This rating at 86 Db is just about as low as it gets! Hooking up virtually any other set of speakers at higher ratings will bring the 'Peach' out in the open....breathing well. Your just plain strangling your poor amp! I suppose it would be OK for really close-in listening but with 6W with some large , perhaps horn driven speakers....they will rock your world! 98 to 100+ Db ratings will really open your eyes to the potential of low-power tube amps.
_____________________________________________________Rick.........
_____________________________________________________Rick.........
Hi Rick
You have to use what you have 🙂
What kind of budget are you looking at for speakers with that kind of rating (90db+)? Most of the speakers available seem to be in the region of 86-88db, or am I looking in the wrong places?
Dave
We have not yet established that there is 6W (or even 1W) coming from the amp yet though!
I run mine through 87dB/Watt speakers and despite playing very loud I don't have audible clipping yet, even back in triode mode.
If you connect up a oscilloscope to the speaker terminals and give us a reading of the maximum peak voltage achieved at clipping we can see if it's operating at full power. Try with the switch at 4ohm and 8ohm, and look for clipping (look for asymmetry too).
I have doubts about some of the drive in the amp to actually clip the output tube - I ended up using an SRPP stage to drive my GU50 in pentode mode before I could be 100% happy that the drive to the output tube exceeded the drivers capability by a comfortable margin.
Driving a triode tube always gives the you Vg1 > 0V problem (class A2 I think it's called) which I can't say the stock Peach circuit really does at all.
I run mine through 87dB/Watt speakers and despite playing very loud I don't have audible clipping yet, even back in triode mode.
If you connect up a oscilloscope to the speaker terminals and give us a reading of the maximum peak voltage achieved at clipping we can see if it's operating at full power. Try with the switch at 4ohm and 8ohm, and look for clipping (look for asymmetry too).
I have doubts about some of the drive in the amp to actually clip the output tube - I ended up using an SRPP stage to drive my GU50 in pentode mode before I could be 100% happy that the drive to the output tube exceeded the drivers capability by a comfortable margin.
Driving a triode tube always gives the you Vg1 > 0V problem (class A2 I think it's called) which I can't say the stock Peach circuit really does at all.
Phew! If this is aimed at me that is way beyond my skill\tool set 😀.
Can I do similar with a multi-meter? If so, I can give that a try if you like (if you tell me how to set-up - volume level, music type etc).
Happy to change the caps, as I'm OK with soldering etc, and will be doing that soon if the improvements are as good as you say.
I don't think I get clipping - all I get is distortion past approx half way round the volume control. I haven't gone to full volume yet as not sure if that would cause a problem. I will re-iterate that I get reasonable volume from the amp and speakers - not earth shattering by any means but plenty loud enough for normal listening.
Dave
Once you reach the threshold of clipping there are good reasons for not turning it up any further, all you will succeed in doing is sending progressively squarer waveforms mostly to your tweeters which will reward you for the abuse by probably burning up. Even if this does not happen it is not going to get significantly louder (3dB at hard clip) and it will sound terrible - there is also potential for damage to the output transformer, in extreme cases flyback induced voltages in the primary during cutoff of the output tube can destroy it..
Hope you get the point... Lots of reasons not to turn it up to "11".. 😀
A multimeter will give us a ballpark figure I guess, set it to AC and the lowest voltage (about 10V usually).
Then play some modern pop through it - start off quietly and turn it up until you just start to hear the distortion, and back off until the distortion is just gone. Then tell us the voltage, and your speaker impedance.
As noted do not run it too much with distortion.
The position of the control is irrelevant, the gain of recording varies as much as half the gain of the amp anyway - just position the control by ear.
A distortion above a particular volume is usually clipping, you'd need to borrow (or buy - look on eBay - scopes are cheap now!) an oscilloscope to see for sure. If the distortion doesn't sound tooo bad it may be clipping on one rail before the other (assymetrical clipping) - quite likely in a chinese single-ended amp TBH.
You may find you need to bias the output tubes properly as well - ask for recommendations for biasing EL34s (your tube type I think), I'd guess 30mA is about right but check here!
Try reading this thread its old but you might learn some useful information..
http://www.diyaudio.com/forums/tubes-valves/179200-any-thoughts-circuit.html
Regards
M. Gregg
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That's a great amp you made, how did you manage to get Edcor transformers in the UK? That's an issue that has puzzled me for ages!
The Peach has an inductor for the PSU already which is neat.
As it is it's fairly nice once you replace the coupling capacitors.
The weaknesses are the 6N3 input tubes (of which only half gets used) and the driver tube circuit design. I used a Mullard ECC82 in there (re-wired heater) that sounded good, the ECC82 is an ideal tube for the voltages and currents at that point, but not as linear as some.
For a redesign you have much scope but many compromises. For me the factors I needed were:
1) Pentode mode - full power and easy to drive
2) No feedback over the OPT
These two fundamental requirements led to the design I posted up. The reason for taking the OPT out of the feedback loop are:
a) It adds phase shift and non-linearity
b) At frequency extremes the loss is so high NFB fails anyway
c) It will work as designed anyway with a low impedance drive
so this leads to needing a low impedance output from an easy to drive pentode, something usually associated with a mosfet 😉
So I used a very tight feedback loop between the output tube and the driver tube, the whole thing being driven by an SRPP with 6N2P (high gain ECC83 equivalents) tubes.
As noted above perhaps a better design would be to load the SRPP (to reduce distortion to optimal design levels - SRPP works best into one load resistance) and then to mix that output with the output tube anode like the Schade feedback design. As it is I have a 22uF feedback capacitor - not ideal but it is bypassed, and it gives the driver feedback (not just the output tube) - thus lowering the impedance driving the OPT.
People think SRPP stages are a trendy fad, but having worked with them I view them differently. I view them as resistor free (the top tube sinks that heat), capable of driving difficult loads with huge voltage swing, and tweakable as required to very low distortions (by resistor loading). It was also the only topology that really opened out the dynamics of my SE, perhaps because of that potential to drive a big voltage swing.
I'm sure people listening to my Peach would swear it could not be a single ended amp, the terrific bass, dynamic power is larger than you'd think possible. Of course the total smoothness in the silky midrange may give it away. Anyone near Cambridge England PM me if you fancy a listen!
I just sent to Edcor over the internet and paid the shipping (Paypal)..took about two and a half weeks..They transfer to standard UK mail when they arrive and you loose the tracking (think they have got lost) if you wait you get a letter from the post office.. I was only using GXSE +power Tx so the weight was lower..I guess if you only had the Op Tx's you could get the CXSE for the same kind of shipping..
Regards
M. Gregg
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