Search found 84 matches

by r3xj0hn570n
Sun Oct 03, 2021 9:11 am
Forum: DIY
Topic: Building a DIY amp with NVA amplifier boards
Replies: 308
Views: 63890
Norfolk Island

Re: Building a DIY amp with NVA amplifier boards

Choke before caps for the output stage, tweaked to 43vdc. 50+ on the output drivers though. They should be fine...
by r3xj0hn570n
Sun Oct 03, 2021 7:41 am
Forum: DIY
Topic: Building a DIY amp with NVA amplifier boards
Replies: 308
Views: 63890
Norfolk Island

Re: Building a DIY amp with NVA amplifier boards

IMG_20211003_181901-04.jpeg
IMG_20211003_181901-04.jpeg (419.36 KiB) Viewed 225 times
Rainy sunday progress
by r3xj0hn570n
Tue Sep 28, 2021 8:21 am
Forum: DIY
Topic: Doc modding Marantz imperial 7
Replies: 1629
Views: 223878
Norfolk Island

Re: Doc modding Marantz imperial 7

So I have created a horn by pushing thesphere close to the flat bottom of the wooden cube enclosure ? I will have to research the asymmetric aspect, horns are not something I have bothered to learn about because I never thought I would ever be building one. Loudspeakers are horribly inefficient. Th...
by r3xj0hn570n
Mon Sep 27, 2021 10:03 pm
Forum: DIY
Topic: Doc modding Marantz imperial 7
Replies: 1629
Views: 223878
Norfolk Island

Re: Doc modding Marantz imperial 7

Thought of the day regarding loading... An unbaffled speaker in free space doesn't work very well due to cancellation, simply S + -S = 0. Typical loading like a sealed box mostly removes -S leaving just S, except below resonance etc etc. Resonant loading (port) inverts -S to be S at one particular f...
by r3xj0hn570n
Sun Sep 26, 2021 9:15 am
Forum: DIY
Topic: Building a DIY amp with NVA amplifier boards
Replies: 308
Views: 63890
Norfolk Island

Re: Building a DIY amp with NVA amplifier boards

Yep, GP140 & GP145 (pretty much the same as the TIPs). Also might try some 2sb1560 + 2sd2390s, these are purpose built darlington audio output transistors.
by r3xj0hn570n
Sat Sep 25, 2021 8:22 pm
Forum: DIY
Topic: Doc modding Marantz imperial 7
Replies: 1629
Views: 223878
Norfolk Island

Re: Doc modding Marantz imperial 7

I have found a suitable driver which has a published FR graph which is about as smooth as I am going to get. Starts to roll off naturally about 7 kHz so ideal. It's also a 5,25" which when modelled in winisd gives a suitable enclosure size. It is also 88d so 4dB more efficient than the cheap C...
by r3xj0hn570n
Sat Sep 25, 2021 8:16 pm
Forum: DIY
Topic: Doc modding Marantz imperial 7
Replies: 1629
Views: 223878
Norfolk Island

Re: Doc modding Marantz imperial 7

That produced the lowest amount of perceivable bass and as it gets further away the bass becomes more prominent but less detailed. I am a bit of a bass head which is why I like the bipolar opposing driver baffle step compensation but with this sphere at a certain distance from the driver the freque...
by r3xj0hn570n
Sat Sep 25, 2021 8:03 pm
Forum: DIY
Topic: Building a DIY amp with NVA amplifier boards
Replies: 308
Views: 63890
Norfolk Island

Re: Building a DIY amp with NVA amplifier boards

That transformer has a fair few windings by the look of it. Don't play too much and lose the magic. It was a class G amp, so the high voltage winding is a little on the high side. Knocking that back with a choke input for the output transistors. The drivers will see the full 54V from a different br...
by r3xj0hn570n
Fri Sep 24, 2021 11:10 pm
Forum: DIY
Topic: Building a DIY amp with NVA amplifier boards
Replies: 308
Views: 63890
Norfolk Island

Re: Building a DIY amp with NVA amplifier boards

I know it's not my thread, but i thought Stu and others might be interested in a slight diversion... delme.jpg These boards have been sitting in a box for the last 20 years. I think they were old then as they are much larger than the others. The enormous transformer is from a dead onyko AV amp, an o...