K-16ls + ton pcb (just finished pics) - Page 2 - diyAudio
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Old 13th March 2011, 10:46 PM   #11
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Join Date: Apr 2004
Location: Monroe Township, NJ
No doubt, part of the distortion you hear is the cheap O/P trafos that shipped with the kit inability to function well at the frequency extremes. You may even be experiencing nasty O/P trafo core saturation associated with a deep bass NFB error correction signal.

However, clipping (regardless of volume control setting) is always "on the table". What's the claimed sensitivity of the speakers you're using? What does the impedance curve of the speakers look like? Speakers with dips in their impedance curves, particularly in the deep bass, tend to be poor mates for tubed power amps.
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Old 13th March 2011, 10:54 PM   #12
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Very nice! Congratulations. These kits seems to play very well, for the price. I have one k-502, but i can't get a very good sound with it. It plays good midranges, but bass is very weak im my system... So i'm planning to adapt the tone control k-tl to it.
Could you post the schematic here? I'm think will help many people, since is very hard to find the schematic on the net .
Many thanks!
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Old 13th March 2011, 11:07 PM   #13
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Click the image to open in full size.i would love to help with the schematic used camera phone, i will see if i can do it at work with scanner.

as for the speakers, i bought them for £35 with blown tweeters (since fixed) they are effectively dj speakers but i modded the tweeters for more topend and i made some resonance tubes to go in the bass port to enhance 60hz and below.

i doubt there are any spec sheets for them but since im no audiophile they sound fine to me, but its like we are talking about 2 different kits the opts measure 8cm in height and the bass is thunderous (i know this sound rediculous given the kit price but if only you could hear it) it just runs out of puff a little too early, but i think im getting my 16 watts worth its loud enough to annoy the neighbours, the guy i bought the speakers from told me that due to the losses in the cables at venues they have to be efficient he quoted me 96-98db sensitivity, but i do know that all the other speakers i tried on it sound much quiter.

tbh with the tone control i usually leave it set flat unless im listening to music from my ipod which doesnt have good gain.

Click the image to open in full size.

Last edited by mpleasant; 13th March 2011 at 11:28 PM.
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Old 14th March 2011, 02:19 AM   #14
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Some points about the main amp schematic: C2 and C5 can be changed to 68 nF., which will be an effective block to infrasonic noise (F3 becomes approx. 23 Hz.); changing O/P trafos will require changing C2 and C6, which are present for phase compensation of the GNFB loop; and each channel's O/P tubes share an unbypassed cathode bias resistor (R12 and R25). Those unbypassed resistors introduce degeneration, AKA local current NFB, which raises the O/P impedance. That raised O/P impedance complicates the end to end impedance requirement of the O/P trafos. Somebody better with numbers than me will have to provide you with a good value for any replacements that may get wound. 4 KOhms would be fine, IF those resistors were bypassed. I don't know if 6.6 KOhms will be "tall" enough.
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Old 14th March 2011, 09:03 PM   #15
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i guess you must have built many amps to know what goes where just like that!, im fairly new to valves but i do get the idea.

i think this kit will stay as is and i will collect some parts untill i have enough to build a new design then this time it will be custom, exactly how i want it and all the advice im recieving will be put to good use.

since i doubt everyone into valves is rich does anyone have any good suggestions on good places to salvage parts ie old tv's and expecially places where transformers can be found, i was wondering if a shaver isolation transformer could be used as they are 110.110 - 110.110 so i could use the two 110 for 240vac in and the output for +- 220vdc or + 440vdc.

also given the above mentioned schematic is effectively the 8w kit with 2 extra valves in parallel on each channel if i removed the 4 extra valves would i just get 8w or would it damage the amp?
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Old 16th March 2011, 07:27 PM   #16
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God bless you, mr. Mpleasant!
The schematics are perfect, there's no need to use a scanner. It will help me a lot, now i know where to adapt in the circuit of my amp.
I think the main problem with my amp is the speakers i'm using, only 88 dB (two 8" woofer by HiVi)... but i'm sure the tone control will solve it.
Once again, many thanks!
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Old 16th March 2011, 11:39 PM   #17
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Farnell often have 12 and 15v transformers on sale - I got some 50va ones recently for 3 euros each. They are good for heater supplies if you rectify to dc......

isolation transformers from industrial equipment is a good sourcesource too....
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Old 11th June 2011, 05:09 PM   #18
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Join Date: Jun 2011
Hi, I'm new to all of this tube amp building. I'm going to start building a 16LS kit. I've noticed that much better transformers are available for it. Could some one tell me which ones I should get. I'm sorry if this has been posted somewhere else, but I couldn't find any specifics.

Thanks
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Old 11th June 2011, 05:36 PM   #19
parb is offline parb  United States
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this was the first tubekit that i built. I built this over christmas a few years ago. I really enjoyed building it. I did a few upgrades of the caps which solves some low frequency hum and thought for the money it was a great experience. I am not sure i will do anything with the iron as i think this is mainly an amp useful for my office or similar...

been working on my build of the dx amp over the last few months. work is keeping me busy though...

I have been looking and thinking about my next project. The one i am most interested in is the moskido project. I may have to design a pcb for it (which i've never done before, but that seems like fun).

anyway, i am happy you are getting as much enjoyment out of your amp project as i had from my k16 kit!
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