Hi Valery,
Success, it is finally playing. One channel is noticeably louder so I must have missed one of the resistor changes somewhere. I have to sit down again and go over everything. It sounds nice but I can't tell if there is much difference yet because of the imbalance. Fools my ear when doing an A/B comparison. Thanks for all your help.
Blessings, Terry
Success, it is finally playing. One channel is noticeably louder so I must have missed one of the resistor changes somewhere. I have to sit down again and go over everything. It sounds nice but I can't tell if there is much difference yet because of the imbalance. Fools my ear when doing an A/B comparison. Thanks for all your help.
Blessings, Terry
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Noticed your message too late - was going to recommend checking the feedback network (that's the only thing setting the gain here), but then noticed in the other thread you have solved it yourself
I have the boards set up per the schematic in post #246 After going over the boards I discovered that I had 100k in R13 instead of 47k in one of the boards. I'm not sure how that happened but as soon as I put the 47k in it works perfectly. I have had it playing for hours now and no issues. I modified my speaker protection circuit to have a 25 second delay so the hybrid has time to settle. 25 seconds feels like a long time.
Hi Valery,
I have a question about the MOSFET OPS. I want to discuss it here if that is OK. you didn't mention it but it looks like you have removed the base stoppers for the outputs. Is that correct? It also looks like you added zeners from the output to the base of each side but you don't give a value.
Thanks, Terry
I have a question about the MOSFET OPS. I want to discuss it here if that is OK. you didn't mention it but it looks like you have removed the base stoppers for the outputs. Is that correct? It also looks like you added zeners from the output to the base of each side but you don't give a value.
Thanks, Terry
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Hi Terry, thanks for observations - I actually forgot to put the values, here is the updated picture.
Cheers,
Valery
Attachments
Hybrid front-end - updated PCB
Hi All,
Those of you who have got initial version of the PCBs, can still use them with minor changes described earlier in the thread. However, if somebody is just planning to order - her is an updated PCB with all additional components in place, including optional ones.
Zip file contains gerbers, drilling map and PCAD ASCII interchange file (with .pcb extension) - some PCB workshops accept this all-in-one format.
Cheers,
Valery
Hi All,
Those of you who have got initial version of the PCBs, can still use them with minor changes described earlier in the thread. However, if somebody is just planning to order - her is an updated PCB with all additional components in place, including optional ones.
Zip file contains gerbers, drilling map and PCAD ASCII interchange file (with .pcb extension) - some PCB workshops accept this all-in-one format.
Cheers,
Valery
Attachments
I knew this would happen hence my question here.
No matter, mine works fine and I won't be building another. I've been listening to it all morning. Really nice!
Thanks Terry. Actually, this newer version incorporates only the minor "tweaks", including those developed while working on your build. Points, mentioned at the place where your link directs, are more "serious" - those are still for the future
I also audition it now - like its "transparency" with certain "warmth". Tube at the input proved to be a good choice - low noise, highly linear device.
Cheers,
Valery
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I have one board that won't quite cancel the offset, even with the pot installed. If I turn the pot it will initially go past zero but then back to +20mV. That is acceptable but jus weird that it keeps returning to 20mV. I'll try swapping in a different tube and see if it goes away. Kind of cool IPS. This one may make it into a case. Not too crazy about the startup function. I may have to pursue your solution. For a test this morning I tried turning everything on at once. It didn't like it very much. It did finally settle before the speaker protection kicked in but just barely. Looks like the warmer does need to be turned on first.
Blessings, Terry
Blessings, Terry
Yes, pre-warming is very recommended. Otherwise the tube is completely not operational in the beginning and thus the global NFB (important thing!) is not working either, leaving the circuit "unbalanced", with most of stability-ensuring measures also being off. Only when the tube warms up, the current starts flowing through it and the whole front-end begins balancing itself from an extreme, "touching the rail", initial position. Starting-up at this point, when it's already warm, is much better - faster, safer settling with all HF compensation in place.
In fact, you need one more delay and one more relay. When you just power-on, the tube warming transformer goes on right away and stays on. After this first delay runs out, this first relay powers on all the rest, and the second delay (the one you already have) just keeps the speakers off, letting the circuit to fully settle zero DC at the output.
Cheers,
Valery
Hi Ranchu,
I purchased my tubes locally, maybe Terry can come up with some good options for international ordering. Many suppliers offer matched tubes - this is definitely a better option. Matching has to be performed not between two tubes, but between two triodes within each tube.
Cheers,
Valery
Don't follow me, I bought used tubes that were advertised as matched. There were two numbers written on each box. The two numbers were different but matched the two numbers on the "matched" tube that was strapped to it. I actually bought 4 tubes. I forgot to try swapping in another tube before I dismantled the setup this morning. I only had 25mV offset on one channel. the other I could dial to zero with the added 50ohm pot. I've had quite a few amps that had that much. Doesn't bother me.
Blessings, Terry
Blessings, Terry
Something like this - Matched sections
These guys in the US - The Tube Store - have got Matched Sections Service and they sell 12AU7 (ECC-82) tubes
These guys in the US - The Tube Store - have got Matched Sections Service and they sell 12AU7 (ECC-82) tubes
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I used The Tube Store and they are actually in Canada as, far as I can tell. The order was shipped from Stony Creek, Ontario and the invoice has the address in Hamilton, Ontario. I could have physically gone there.
My tubes are new and matched. Hopefully I will have some time to get the boards stuffed soon.
My tubes are new and matched. Hopefully I will have some time to get the boards stuffed soon.
Jason, you're right - they are actually in Canada... just thought they are in the US at a first glance as all prices were in USD by default )
They offer an impressive selection
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