Search found 747 matches

by RhythMick
Sat Jul 31, 2021 8:44 am
Forum: Everyones Projects
Topic: Poundland 45
Replies: 160
Views: 34875

Re: Poundland 45

Fascinating. Glad you found it and well done for proving it with the cutout, and for posting it. We've found similar results but not followed through to prove it so thanks.

We've used material like Tufnol for non-conductive safety enclosures.
by RhythMick
Tue Jul 27, 2021 7:27 pm
Forum: Valves
Topic: D3a Triode Square Wave shows HF boost
Replies: 17
Views: 14190

Re: D3a Triode Square Wave shows HF boost

Nick wrote: Mon Jul 26, 2021 10:59 pm
RhythMick wrote: Mon Jul 26, 2021 9:32 pm Ok I see ... But there wasn't a blocking cap in the test circuit, either before or after the D3a.
How do you think the AC/DC input switch on the scope is done? I assumed you weren’t putting 150v or so into the scope input with it set to DC.
Doh
by RhythMick
Mon Jul 26, 2021 9:32 pm
Forum: Valves
Topic: D3a Triode Square Wave shows HF boost
Replies: 17
Views: 14190

Re: D3a Triode Square Wave shows HF boost

I think Mike (and me) meant the DC blocking capacitor stopping DC from showing a horizontal line instead of calibrating for input capacitance. If you used a 10kHz square, the flat top would not be so affected by the blocking cap. Ok I see ... But there wasn't a blocking cap in the test circuit, eit...
by RhythMick
Mon Jul 26, 2021 2:55 pm
Forum: Valves
Topic: D3a Triode Square Wave shows HF boost
Replies: 17
Views: 14190

Re: D3a Triode Square Wave shows HF boost

Mike H wrote: Sun Jul 25, 2021 10:05 pm I was going to say, looks to me like a classic case of a series capacitor with not large enough value.
I think the Picoscope doesn't have probe calibration while the Siglent does.
by RhythMick
Sun Jul 25, 2021 3:24 pm
Forum: Valves
Topic: D3a Triode Square Wave shows HF boost
Replies: 17
Views: 14190

Re: D3a Triode Square Wave shows HF boost

Nick wrote: Sun Jul 25, 2021 1:44 pm Much better. The remaining slope is probably the ac input protection. Try at 10khz

For the frequency sweep I meant an amplitude against frequency plot. Not an fft.
Ok thanks Nick I'll try and figure out how to do that.
by RhythMick
Sat Jul 24, 2021 12:02 pm
Forum: Valves
Topic: D3a Triode Square Wave shows HF boost
Replies: 17
Views: 14190

Re: D3a Triode Square Wave shows HF boost

Ok my previous post prompted me to hook up the Siglent.
PXL_20210724_105843192_compress15.jpg
PXL_20210724_105843192_compress15.jpg (249.51 KiB) Viewed 8313 times
Looks better. The square wave is still coming from the Picoscope.
by RhythMick
Sat Jul 24, 2021 11:50 am
Forum: Valves
Topic: D3a Triode Square Wave shows HF boost
Replies: 17
Views: 14190

Re: D3a Triode Square Wave shows HF boost

I would measure with a sine wave sweep to see if there is a HF boost that you need to worry about. Also, 100nv is 30dB more than it will normally see, do you see the same effect with 1mv input? Thanks Nick I'll report back tomorrow. I've reconstructed the test build so I can get directly to the pin...
by RhythMick
Sat Jul 24, 2021 11:41 am
Forum: Valves
Topic: D3a Triode Square Wave shows HF boost
Replies: 17
Views: 14190

Re: D3a Triode Square Wave shows HF boost

I thought a droop on the top of a square wave was LF rolloff not HF boost? I'm not seeing HF overshoot. Or am I missing something here? Many use the d3a as input and driver in a power amp so that could see a 1V input. 10K anode load and 1.5V bias should be fine for HT around 300V I'm not understand...
by RhythMick
Fri Jul 23, 2021 10:44 pm
Forum: Valves
Topic: D3a Triode Square Wave shows HF boost
Replies: 17
Views: 14190

Re: D3a Triode Square Wave shows HF boost

Nick wrote: Fri Jul 23, 2021 10:10 pm I would measure with a sine wave sweep to see if there is a HF boost that you need to worry about. Also, 100nv is 30dB more than it will normally see, do you see the same effect with 1mv input?
Thanks Nick I'll report back tomorrow.
by RhythMick
Fri Jul 23, 2021 9:19 pm
Forum: Valves
Topic: D3a Triode Square Wave shows HF boost
Replies: 17
Views: 14190

D3a Triode Square Wave shows HF boost

After spending way too much time and effort with work I finally got back to making progress on the phono. I'm starting with a real simple D3a Triode stage and want to get the output from that as clean as I can get it before I start experimenting with what comes after. I've set up the D3a as follows,...
by RhythMick
Wed Jul 21, 2021 8:48 am
Forum: Everyones Projects
Topic: Question re Izzy Wizzy phono stage
Replies: 18
Views: 6073

Re: Question re Izzy Wizzy phono stage

izzy wizzy wrote: Wed Jul 21, 2021 8:41 am Here it is. It's a bit of a mess but seems to work fine.

My LTSPICE is setup like the Tutorials on Intact Audio with the files by Stephie Bench so uses drop down tube models. I'm not sure this will work with LTSPICE using the regular models.

Make sure you have the latest version.
Many thanks
by RhythMick
Wed Jul 21, 2021 7:51 am
Forum: Everyones Projects
Topic: Question re Izzy Wizzy phono stage
Replies: 18
Views: 6073

Re: Question re Izzy Wizzy phono stage

izzy wizzy wrote: Tue Jul 20, 2021 11:00 pm Sure. You'll have to tell what exact circuit you want as I have so many variations even from the latest shown on my site.
Well the circuit I am looking at is your current phono from the website. D3a pentode DC coupled via single stage RIAA into 5687 LTP into LL1660.
by RhythMick
Tue Jul 20, 2021 2:00 pm
Forum: Everyones Projects
Topic: Question re Izzy Wizzy phono stage
Replies: 18
Views: 6073

Re: Question re Izzy Wizzy phono stage

izzy wizzy wrote: Sun Jul 04, 2021 12:50 pm If you need help with the sim to choose EQ values, happy to help. Will be interested to see what direction you take.
Actually do you have a file you could send me for your circuit? I have LTSpice and have done a couple of things but wouldn't know how to use the D3a or 5687 models...
by RhythMick
Sun Jul 18, 2021 9:23 pm
Forum: Everyones Projects
Topic: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
Replies: 1182
Views: 413491

Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Andrew wrote: Sun Jul 18, 2021 9:21 pm Good to see you chaps are still having fun with these :)
Absolutely. I think they are brilliant.
by RhythMick
Sun Jul 18, 2021 8:13 am
Forum: Everyones Projects
Topic: Passive RIAA - single Vs double stage
Replies: 4
Views: 1724

Re: Passive RIAA - single Vs double stage

Ok I going to build the PSU and a prototyping amp with the valves and RIAA on interchangable turret boards. HM-3 inputs one end, HT & GND and valve heater connections along one edge, outputs to LL1660 other end. One per channel. I should be able to prototype and swap in different amp modules to ...