I thought this looked interesting!
High speed power amplifier w/spk protection Goldmund ! on eBay (end time 02-Mar-10 16:39:33 GMT)
High speed power amplifier w/spk protection Goldmund ! on eBay (end time 02-Mar-10 16:39:33 GMT)
Yup, I saw that and the kit looked to be fairly good value. The schematic will only be provided if you buy the kit, though - that leaves no way to evaluate or simulate it before buying.
I took a look at the Naim NAP-140 schematic (apparently used on the EBay clones as well). It seems to be similar on the input side to the Self Blameless, and on the output side to the Quasi. It simulates reasonably well, but the choice of the output and driver transistors is important - it appears to do better in the sim with old 'slow' output transistors like the 2n3773. Some mods also have significant impact on sonics. It's probably a tweaker's paradise, but not recommended for reproducible 'build and forget' projects.
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There's a lot of info on the pink fish forum regarding the naim clones, and it's all prety good, but like you say it's all about tweaking. I thought the goldmund clone was interesting just due to the amount of bits for the money. Iv'e emailed him to find out what the input voltage is, and what the out put was. I wouldn't want to spend a fortune on another power supply, especially not knowing if it is any good. How do you do these simulations, and what's your favourite amp? Barry
Just on a whim, I bought one of those Goldmund clone kits off EBay today - I have the remaining parts (output transistors, transformer, filter caps, etc.) to complete one prototype. The main attraction is that it's a single board unit, with the rectifier, filter caps and two channels all on one board - this helps reduce the cabinet wiring clutter a bit. It will probably take a couple of weeks to get here, and another month to completely assemble and test - let's see how it goes...
I use LTSpice for simulation. At the moment, the Quad current-dumping topology is my favourite discrete amp topology. BTW, there are Quad 405 bare PCBs as well as PCBs + inductors on EBay from seller 'tubeshunter'. I haven't tried it out, but it looks tempting. I can probably kludge my own current-dumping variant onto that Quad 405 board, but it appears to have only a TO-3 outline for the output transistors. Another issue is matching and alignment: In the Quad topology, low THD and good sonics are obtained only when the reactive bridge is precisely balanced, which requires some measurement/matching.
There are also bare PCBs for the JLH 1969 and 1996 Class-A circuits on EBay. However, Class A is too wasteful of power for continuous use in the tropics. Maybe a version with scaled-down rail voltages and something like 5W output might be worth looking at for a small bookshelf amp to drive 3" full-ranges.
Hi, Is that an Indian flag you have there? Funny you should mention Quad. My best amp i've had was a quad 303. I just sold a Naim nait 3 on ebay. I quite liked it but I needed the money to make my own. I am very interested to see what you think of the goldmund. I know the real ones sell for the price of a house in England! Do you know what transformer to use with that? I have a 160va 25-0-25 for the gainclone. Wondered if that was too small!. Iv'e been searching the web for anyone who has made the goldmund, but no luck. Regards Barry
Yup, I'm an Indian in Bangalore. Quick thinking on that Goldmund clone - it's a convenient board, if nothing else.
I received the schematics from the seller, and it is basically a cascoded FET-input LTP, driving Hitachi-topology VAS, driving a Self Type-II EF at the output. Almost the exact same thing has been attempted on numerous projects here at DIYAudio - in particular, several versions of Symasym use very similar topologies, sometimes with more elaborate cascoding in the VAS.
If the Goldmund clone sounds anything like Symasym, I don't think it will be a disappointment. The Hitachi-style VAS (and its sequels) are known to be both very detailed overall, as well as authoritative in bass. It's a capable circuit, hopefully the layout will do it justice. One can also upgrade the component selection if necessary.
A 25-0-25 160 VA transformer should be fine for both a gainclone and the Symasym/Goldmund. I plan to use a 24-0-24 250 VA EI-transformer that I have lying around.
If your in Bangalore and i'm in Cornwall I imagine there is quite a time difference. I wish my English was half as good as yours. Now you must not be too technical with me as I am a bit stupid when it comes to circuitry, but i'll do some googling and see if I can learn. I am looking forward to the kit coming. What output transistors would you reccommend. Barry
It's hard to beat the Toshiba 2sc5200/2sa1943 pair - they're fast, linear, rugged and inexpensive. There are probably some Sankens that have better specs, but Sankens are also counterfeited heavily. You best bet is probably the Toshiba or its Fairchild clone, the KSC5200/KSA1943 pair, sourced from a reputed distributor.
I only have access to 3 good dealers and none of them sell the Toshiba or the Fairchild. One, (farnell) does however sell Magnatec sc5200 and sa1943. Will these be OK. There are a lot of Toshiba on ebay, but they are probably all fake.
Iv'e bought a nice case from Hong Kong. It cost almost £80 but it is very nice. Pre-drilled with lettering and nice quality RCAs and knobs. I have to buy and sell on ebay to earn the money to make my own. I'm 61 and retired early so I have plenty of time but no cash. Same old story... I just sold a Naim Nait 3 and am about to sell a John Shearne (rare British amp, in case you don't know) and a Creek T43 tuner. Iv'e decided to go digital with the tuner as I seem to have poor reception for analogue. Barry
Iv'e bought a nice case from Hong Kong. It cost almost £80 but it is very nice. Pre-drilled with lettering and nice quality RCAs and knobs. I have to buy and sell on ebay to earn the money to make my own. I'm 61 and retired early so I have plenty of time but no cash. Same old story... I just sold a Naim Nait 3 and am about to sell a John Shearne (rare British amp, in case you don't know) and a Creek T43 tuner. Iv'e decided to go digital with the tuner as I seem to have poor reception for analogue. Barry
Thanks for sharing photos. Nice amp.
Good idea with the additional filter caps. I guess you had a reason for doing this?
The same chassis is on it's way to me, except that I ordered the 80mm AV-228 version.
Did you perform the mods proprosed by Linuxguru?
Which opamp did you use?
How does it sound?
Thanks
Jan
Good idea with the additional filter caps. I guess you had a reason for doing this?
The same chassis is on it's way to me, except that I ordered the 80mm AV-228 version.
Did you perform the mods proprosed by Linuxguru?
Which opamp did you use?
How does it sound?
Thanks
Jan
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