Search found 122 matches

by Yazoo55
10 Mar 2024, 21:14
Forum: Modern Stompbox Effects (1975 - ...)
Topic: Wah Wah pedal switching
Replies: 3
Views: 507

Re: Wah Wah pedal switching

Thanks to you both. I was considering removing the footswitch and using a loop box to switch it in and out.
by Yazoo55
27 Feb 2024, 21:08
Forum: Modern Stompbox Effects (1975 - ...)
Topic: Wah Wah pedal switching
Replies: 3
Views: 507

Wah Wah pedal switching

The thing I really don't like with Wah Wah pedals is the on/off switch under the treadle, the way you can't avoid contact with it when you are working the treadle. I remember seeing a Wah Wah pedal with a slightly different design where the switch is under the treadle but there is a hole immediately...
by Yazoo55
24 Feb 2024, 19:15
Forum: Amplifiers
Topic: Mend-It Mark's cap discharger [schematic]
Replies: 3
Views: 14218

Re: Mend-It Mark's cap discharger [schematic]

He really knows his stuff. In a tape deck repair he actually rewound the motor. There is not much seems to stump him, taking on very complicated gear right across the spectrum. He repaired a chorus pedal with a faulty Reticon chip and was not amused when the chips he had all turned out to be fake. H...
by Yazoo55
18 Jan 2024, 20:53
Forum: Pedal Debugging & Troubleshooting Support
Topic: Rat - high pitched squeal
Replies: 4
Views: 686

Re: Rat - high pitched squeal

Try increasing the value of C12, 30pf. I recently repaired a Rat clone which had the same problem. I ended up using around 100pf and this solved the problem.
by Yazoo55
30 Dec 2023, 21:05
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

I’ve finally (almost) finished. Over Christmas I put an 8 ohm speaker I already had into a diy cabinet made out of an old melamine cupboard door. I’ve set this up with another speaker so I can sit in the middle and I am very pleased with the sound. It doesn’t need any extra pedals or even reverb and...
by Yazoo55
19 Dec 2023, 23:44
Forum: Amplifiers
Topic: Voltage Doubler for tube preamp
Replies: 10
Views: 3453

Re: Voltage Doubler for tube preamp

I have used back-to-back transformers a few times in the UK, using transformers with 12V secondaries to power the heaters in series. The problem is that with 240V, you end up with less than 200V under load for the HT supply, not enough for something like a Fender Champ. This is where a voltage doubl...
by Yazoo55
16 Dec 2023, 13:40
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

Sorry it didn’t work out for you. I can only guess that they selected specific MN3207s to work in the existing circuit. I don’t understand why they didn’t put in a bias adjuster. I must have spent nearly 2 weeks on that when I breadboarded it before I gave up and grafted in a different chorus design...
by Yazoo55
12 Dec 2023, 20:44
Forum: Amplifiers
Topic: Voltage Doubler for tube preamp
Replies: 10
Views: 3453

Re: Voltage Doubler for tube preamp

I also saw the Uncle Doug video and used the doubler in a Fender Champ build. It worked fine.
by Yazoo55
08 Dec 2023, 21:13
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

I have got it up and running now. I replaced the TDA2030s and both channels are working with chorus on one channel and the straight signal on the other. I changed the capacitor values C22 and C46 which connect to the 1K5 resistors on pin 2 of the TDA2030s to 22uf (from 4.7uf on the schematic). This ...
by Yazoo55
06 Dec 2023, 19:07
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

I connected the board up to the full transformer, a 2 x 15V toroidal and the voltage was too high, about +20v/-20V. I think I’ve cooked the TDA2030s in the process. I have changed over to a 2 x 10v transformer I already had and the voltages are lower, still too high for the MN3207. To sort this out,...
by Yazoo55
01 Dec 2023, 15:28
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

I have assembled the main board without the power chips for the moment. I tested it without the BBD chips to make sure the voltages were OK and I’m glad I did. I used a 12V bipolar power supply I had and while the other chips are getting about 9.3 volts, the sockets for the MN3207 and MN3102 are mea...
by Yazoo55
11 Nov 2023, 13:27
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

Would you like the Kicad files sent to you?
by Yazoo55
03 Nov 2023, 20:54
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

Excellent, this really helps.
by Yazoo55
03 Nov 2023, 11:08
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

Thanks. Are there any other pictures for the rest of the potentiometers? It would be good to confirm them as well. I’ve looked at the schematics for the JC-120, trying to make a comparison, and they are very different.
by Yazoo55
02 Nov 2023, 18:32
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

I’ve updating my Kicad schematic with the new chorus. I’ll start laying out the pcb next. Looking at the photos you provided, I noticed the distortion potentiometer, like the volume potentiometer, is marked “104B” which must mean 100k linear. The schematic gives the distortion pot as 25kA. You said ...
by Yazoo55
29 Oct 2023, 12:29
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

Thanks, I’ll change that resistor value. I’ve ordered in some TDA2030s which are supposed to be good substitutes for the upc1238s so the power amp is the next stage to try out.
by Yazoo55
28 Oct 2023, 13:17
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

OK, I’ve breadboarded the preamplifier section - it just about did my nut in, but it’s worth it when it finally works. I had real problems with the chorus and I spent literally days getting it working. I couldn’t get the original LFO to play nice with the MN3207 and in desperation I grafted the chor...
by Yazoo55
26 Oct 2023, 09:18
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

Thanks!
by Yazoo55
25 Oct 2023, 23:52
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

I’m making progress. I’ve breadboarded from the input up to “A” of the preamp. This has thrown up more queries though, R6 on IC 1 section 1 is listed as 68 ohms but the feedback resistor R8 is 68K. If I have got this right, this would give an amplification of 1000! I’m wondering whether R6 should be...
by Yazoo55
19 Oct 2023, 23:35
Forum: Amplifiers
Topic: Roland Jazz Chorus JC-20
Replies: 38
Views: 9595

Re: Roland Jazz Chorus JC-20

I’ve decided to try breadboarding the chorus section from C52 to point B. I’ll get back to you when I’ve done this.