mrarroyo
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Post by mrarroyo on Aug 9, 2012 10:11:50 GMT
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Post by Deleted on Aug 9, 2012 18:10:05 GMT
Unusual find Miguel. They don't state approx. battery charge time anywhere though. Almost worth buying out of curiosoty alone
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mrarroyo
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Post by mrarroyo on Aug 11, 2012 10:12:23 GMT
I am following up on eBay, I am currently the high bidder at $1.25 plus $16.95 for S&H. We will see if I get it, willing to go as high as $40 USD total.
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Post by PinkFloyd on Aug 11, 2012 10:41:31 GMT
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Post by Deleted on Aug 11, 2012 11:25:59 GMT
I am following up on eBay, I am currently the high bidder at $1.25 plus $16.95 for S&H. We will see if I get it, willing to go as high as $40 USD total. I'm glad you said that, I was watching the same one ;D I'll wait for the next one then....
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mrarroyo
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Post by mrarroyo on Aug 12, 2012 10:59:34 GMT
I did not win that bid but picked it up from the site posted by Mike. I hope to roll in some op-amps in lieu of the NE5532. So do you all think that the 4562 a pair of 797 or the OPA111 I got from Mike would work here?
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Post by Deleted on Aug 12, 2012 12:38:17 GMT
Miguel, Don't know whether it is relevant but the metal can versions of the OPA111 are the best op-amp (to my ears) in my Beresford Caimanised 7520 DAC and my battery powered portable C-Moy HP amp. In both applications I hear distinct improvement from the metal can variety over the square 'plastic' version of the OPA111. FWIW there has been a guy on eBay, HK based IIRC, selling them in pairs mounted on a 2 into 1 adapter but I can't see them ATM. Dave.
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Post by dalethorn on Aug 13, 2012 4:04:30 GMT
Am I imagining this? Palm-sized vacuum tube preamps? I suppose they have a good source for the tiny tubes?
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mrarroyo
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Post by mrarroyo on Aug 13, 2012 10:22:11 GMT
Dave, I bought a pair of metal OPA111 from Mike a while back. Dale one of the first users of the 6111 in a portable configuration was from Millet via TTVJ.
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Post by Deleted on Aug 13, 2012 11:37:27 GMT
Miguel, And have you compared the metal canned OPA111s against any others and if so, what did you think? I'd be interested in your opinion, either way. Just in case you are not enthralled with them I might be interested in taking them off your hands if they came with a 2 into 1 adapter. Don't want to trouble Mike ATM . TIA, Dave.
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mrarroyo
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Post by mrarroyo on Aug 14, 2012 9:47:09 GMT
I have not had an amp that could take them Dave, so they have sat in the box all this time. If I do not like them I will let you know.
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layums
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Post by layums on Aug 29, 2012 15:32:57 GMT
just tripped over this thread, does this thing sound any good?
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joethearachnid
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Post by joethearachnid on Aug 29, 2012 19:30:49 GMT
I'm also interested. A portable tube amp for £40 delivered sounds almost too good to be true.
-JoetheArachnid
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mrarroyo
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Post by mrarroyo on Aug 30, 2012 9:37:51 GMT
The amp shipped from China on 8/12 via regular mail, I am still waiting for it.
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Post by Deleted on Aug 30, 2012 10:30:02 GMT
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mrarroyo
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Post by mrarroyo on Aug 31, 2012 9:56:31 GMT
Thanks for the info, I am going away on holiday for 10 days so I hope it is waiting for me when I return.
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mrarroyo
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Post by mrarroyo on Sept 9, 2012 20:36:59 GMT
The amp arrived while we were away on a 10 day long vacation. I picked it up last night and upon first turn on it was horrible! Plus …
1. It gets quite warm bordering on hot, I would not carry this in a pocket since I would be afraid of getting burnt. 2. The volume pot is very noisy when raising or lowering the volume. Once you set it up it is fine. 3. The battery makes a physical noise so I took the amp apart and used some putty to quite it up. 4. I used the same putty to dampen the tube. Contrary to the Millet TTVJ portable tube amp the tube does not make noises when the amp is bumped. 5. The newer amps like the one I got has a socket to allow rolling of op-amps. 6. It takes about 3 hours to charge and the amp will run about 3 hours on a charge.
The unit has run for about 4 hours and the sound is a lot better. The top end is not very extended when compared with an iBasso D4 and the bass is a bit loose. At about $62 it is ok as a conversation piece and unless it improves a lot (doubt it) it is a paper weight. Perhaps an LM4562 will improve its sound.
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Post by Deleted on Sept 9, 2012 23:06:00 GMT
That was my main concern, short charge life on a portable making it pretty useless. Add the other problems Miguel has reported and it really is a non-starter
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Post by Deleted on Sept 10, 2012 0:32:50 GMT
I'm also interested. A portable tube amp for £40 delivered sounds almost too good to be true. -JoetheArachnid It appears Joe is quite right . . . A shame though . . .
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Post by dicky on Sept 10, 2012 9:00:14 GMT
Hi Miguel, what value is the 2W resistor(s)? I have one of these units and it came with 22 ohms. It seems if this value is reduced (11 ohms) it affects the tube voltage and somehow improves sound. The one shown in your picture has 2 resistors in parallel - perhaps yours doesn't? I changed the pot in mine and I'm actually quite happy with it. Regards, Dicky
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mrarroyo
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Post by mrarroyo on Sept 10, 2012 10:06:53 GMT
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Post by dicky on Sept 10, 2012 11:06:52 GMT
Miguel, mine was the same. I replaced the 22 ohm 2W resistor with 11 ohm and it sounds a whole lot better. The interference dissappeared and the bass was way better.
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mrarroyo
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Post by mrarroyo on Sept 10, 2012 22:04:50 GMT
Which is the 22 ohm resistor?
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joethearachnid
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Post by joethearachnid on Sept 10, 2012 23:05:53 GMT
I would hazard a guess at the biggest resistor at the far volpot side of the board. I'm too lazy to actually check the stripes. Dicky, what does that resistor actually do? It'll be interesting if it improves the sound enough to make the amp worthwhile.
-JoetheArachnid
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Post by Deleted on Sept 11, 2012 5:02:30 GMT
Which is the 22 ohm resistor? Miguel don't worry about it. The resistor in your amp is 10 Ohm already. In the original (the picture on ebay) they used two 22 Ohm in parallel giving 11 Ohm. The resistor is in series with the heater and some other resistors to supply the heater with 6V from a higher (12V or 9V ?) battery pack. Given the values I fiugure the battery pack would be 9V unless some other resistors also get hot, in which case 12V could be used. The amplifier is a simple C'Moy (6 Ohm output resistance) with a tubefollower in front of it. I take it it uses the 6BF7 (which is a 300mA tube at 6V) meaning it will draw 3W ! just for the heater where the amplifier part itself simply draws a few mW (I am guessing 9V battery). Heat can be improved by using a switchmode regulator for the heater. It will drop to 2W increasing battery life with 50% and lower heat output. Also the opamp has NO local decoupling caps at all. Certainly when opamp swapping and using fast opamps you are asking for oscillations. A LOT can be improved in the design but I guess we all have gotten used to that idea by now with cheap Chinese designs.
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